/*
 * Copyright 2024-2026 Revetware LLC.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.soklet.servlet.javax;

import com.soklet.MarshaledResponse;
import com.soklet.Request;
import com.soklet.Response;
import com.soklet.ResponseCookie;
import com.soklet.StatusCode;
import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;

import javax.annotation.concurrent.NotThreadSafe;
import javax.servlet.ServletContext;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.IDN;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.StandardCharsets;
import java.nio.charset.UnsupportedCharsetException;
import java.time.Duration;
import java.time.Instant;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.TreeMap;
import java.util.stream.Collectors;

import static java.lang.String.format;
import static java.util.Objects.requireNonNull;

/**
 * Soklet integration implementation of {@link HttpServletResponse}.
 *
 * @author <a href="https://www.revetkn.com">Mark Allen</a>
 */
@NotThreadSafe
public final class SokletHttpServletResponse implements HttpServletResponse {
        @NonNull
        private static final Integer DEFAULT_RESPONSE_BUFFER_SIZE_IN_BYTES;
        @NonNull
        private static final Charset DEFAULT_CHARSET;
        @NonNull
        private static final DateTimeFormatter DATE_TIME_FORMATTER;

        static {
                DEFAULT_RESPONSE_BUFFER_SIZE_IN_BYTES = 1_024;
                DEFAULT_CHARSET = StandardCharsets.ISO_8859_1; // Per Servlet spec
                DATE_TIME_FORMATTER = DateTimeFormatter.ofPattern("EEE, dd MMM yyyy HH:mm:ss zzz")
                                .withLocale(Locale.US)
                                .withZone(ZoneId.of("GMT"));
        }

        @NonNull
        private final String rawPath; // Raw path (no query), e.g. "/test/abc" or "*"
        @Nullable
        private final HttpServletRequest httpServletRequest;
        @NonNull
        private final ServletContext servletContext;
        @NonNull
        private final List<@NonNull Cookie> cookies;
        @NonNull
        private final Map<@NonNull String, @NonNull List<@NonNull String>> headers;
        @NonNull
        private ByteArrayOutputStream responseOutputStream;
        @NonNull
        private ResponseWriteMethod responseWriteMethod;
        @NonNull
        private Integer statusCode;
        @NonNull
        private Boolean responseCommitted;
        @NonNull
        private Boolean responseFinalized;
        @Nullable
        private Locale locale;
        @Nullable
        private String errorMessage;
        @Nullable
        private String redirectUrl;
        @Nullable
        private Charset charset;
        @Nullable
        private String contentType;
        @NonNull
        private Integer responseBufferSizeInBytes;
        @Nullable
        private SokletServletOutputStream servletOutputStream;
        @Nullable
        private SokletServletPrintWriter printWriter;

        @NonNull
        public static SokletHttpServletResponse fromRequest(@NonNull HttpServletRequest request) {
                requireNonNull(request);
                String rawPath = request.getRequestURI();
                if (rawPath == null || rawPath.isEmpty())
                        rawPath = "/";
                ServletContext servletContext = requireNonNull(request.getServletContext());
                return new SokletHttpServletResponse(request, rawPath, servletContext);
        }

        @NonNull
        public static SokletHttpServletResponse fromRequest(@NonNull Request request,
                                                                                                                                                                                                                        @NonNull ServletContext servletContext) {
                requireNonNull(request);
                requireNonNull(servletContext);
                HttpServletRequest httpServletRequest = SokletHttpServletRequest.withRequest(request)
                                .servletContext(servletContext)
                                .build();
                return fromRequest(httpServletRequest);
        }

        /**
         * Creates a response bound to Soklet's raw path construct.
         * <p>
         * This is the exact path component sent by the client, without URL decoding and without a query string
         * (for example, {@code "/a%20b/c"}). It corresponds to {@link Request#getRawPath()}.
         *
         * @param rawPath raw path component of the request (no query string)
         * @param servletContext servlet context for this response
         * @return a response bound to the raw request path
         */
        @NonNull
        public static SokletHttpServletResponse fromRawPath(@NonNull String rawPath,
                                                                                                                                                                                                                        @NonNull ServletContext servletContext) {
                requireNonNull(rawPath);
                requireNonNull(servletContext);
                return new SokletHttpServletResponse(null, rawPath, servletContext);
        }

        private SokletHttpServletResponse(@Nullable HttpServletRequest httpServletRequest,
                                                                                                                                                @NonNull String rawPath,
                                                                                                                                                @NonNull ServletContext servletContext) {
                requireNonNull(rawPath);
                requireNonNull(servletContext);

                this.httpServletRequest = httpServletRequest;
                this.rawPath = rawPath;
                this.servletContext = servletContext;
                this.statusCode = HttpServletResponse.SC_OK;
                this.responseWriteMethod = ResponseWriteMethod.UNSPECIFIED;
                this.responseBufferSizeInBytes = DEFAULT_RESPONSE_BUFFER_SIZE_IN_BYTES;
                this.responseOutputStream = new ByteArrayOutputStream(DEFAULT_RESPONSE_BUFFER_SIZE_IN_BYTES);
                this.cookies = new ArrayList<>();
                this.headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
                this.responseCommitted = false;
                this.responseFinalized = false;
        }

        @NonNull
        public Response toResponse() {
                MarshaledResponse marshaledResponse = toMarshaledResponse();

                return Response.withStatusCode(marshaledResponse.getStatusCode())
                                .body(getResponseOutputStream().toByteArray())
                                .headers(marshaledResponse.getHeaders())
                                .cookies(marshaledResponse.getCookies())
                                .build();
        }

        @NonNull
        public MarshaledResponse toMarshaledResponse() {
                byte[] body = getResponseOutputStream().toByteArray();

                Map<@NonNull String, @NonNull Set<@NonNull String>> headers = getHeaders().entrySet().stream()
                                .collect(Collectors.toMap(
                                                Map.Entry::getKey,
                                                entry -> new LinkedHashSet<>(entry.getValue()),
                                                (left, right) -> {
                                                        left.addAll(right);
                                                        return left;
                                                },
                                                LinkedHashMap::new
                                ));

                Set<@NonNull ResponseCookie> cookies = getCookies().stream()
                                .map(cookie -> {
                                        ResponseCookie.Builder builder = ResponseCookie.with(cookie.getName(), cookie.getValue())
                                                        .path(cookie.getPath())
                                                        .secure(cookie.getSecure())
                                                        .httpOnly(cookie.isHttpOnly())
                                                        .domain(cookie.getDomain());

                                        if (cookie.getMaxAge() >= 0)
                                                builder.maxAge(Duration.ofSeconds(cookie.getMaxAge()));

                                        return builder.build();
                                })
                                .collect(Collectors.toSet());

                return MarshaledResponse.withStatusCode(getStatus())
                                .body(body)
                                .headers(headers)
                                .cookies(cookies)
                                .build();
        }

        @NonNull
        private String getRawPath() {
                return this.rawPath;
        }

        @NonNull
        private Optional<HttpServletRequest> getHttpServletRequest() {
                return Optional.ofNullable(this.httpServletRequest);
        }

        @NonNull
        private ServletContext getServletContext() {
                return this.servletContext;
        }

        @NonNull
        private List<@NonNull Cookie> getCookies() {
                return this.cookies;
        }

        @NonNull
        private Map<@NonNull String, @NonNull List<@NonNull String>> getHeaders() {
                return this.headers;
        }

        @NonNull
        private List<@NonNull String> getSetCookieHeaderValues() {
                if (getCookies().isEmpty())
                        return List.of();

                List<@NonNull String> values = new ArrayList<>(getCookies().size());

                for (Cookie cookie : getCookies())
                        values.add(toSetCookieHeaderValue(cookie));

                return values;
        }

        @NonNull
        private String toSetCookieHeaderValue(@NonNull Cookie cookie) {
                requireNonNull(cookie);

                ResponseCookie.Builder builder = ResponseCookie.with(cookie.getName(), cookie.getValue())
                                .path(cookie.getPath())
                                .secure(cookie.getSecure())
                                .httpOnly(cookie.isHttpOnly())
                                .domain(cookie.getDomain());

                if (cookie.getMaxAge() >= 0)
                        builder.maxAge(Duration.ofSeconds(cookie.getMaxAge()));

                return builder.build().toSetCookieHeaderRepresentation();
        }

        private void putHeaderValue(@NonNull String name,
                                                                                                                        @NonNull String value,
                                                                                                                        boolean replace) {
                requireNonNull(name);
                requireNonNull(value);

                if (replace) {
                        List<@NonNull String> values = new ArrayList<>();
                        values.add(value);
                        getHeaders().put(name, values);
                } else {
                        getHeaders().computeIfAbsent(name, k -> new ArrayList<>()).add(value);
                }
        }

        @NonNull
        private Integer getStatusCode() {
                return this.statusCode;
        }

        private void setStatusCode(@NonNull Integer statusCode) {
                requireNonNull(statusCode);
                this.statusCode = statusCode;
        }

        @NonNull
        private Optional<String> getErrorMessage() {
                return Optional.ofNullable(this.errorMessage);
        }

        private void setErrorMessage(@Nullable String errorMessage) {
                this.errorMessage = errorMessage;
        }

        @NonNull
        private Optional<String> getRedirectUrl() {
                return Optional.ofNullable(this.redirectUrl);
        }

        private void setRedirectUrl(@Nullable String redirectUrl) {
                this.redirectUrl = redirectUrl;
        }

        @NonNull
        private Optional<Charset> getCharset() {
                return Optional.ofNullable(this.charset);
        }

        @Nullable
        private Charset getContextResponseCharset() {
                String encoding = getServletContext().getResponseCharacterEncoding();

                if (encoding == null || encoding.isBlank())
                        return null;

                try {
                        return Charset.forName(encoding);
                } catch (IllegalCharsetNameException | UnsupportedCharsetException e) {
                        return null;
                }
        }

        @NonNull
        private Charset getEffectiveCharset() {
                Charset explicit = this.charset;

                if (explicit != null)
                        return explicit;

                Charset context = getContextResponseCharset();
                return context == null ? DEFAULT_CHARSET : context;
        }

        private void setCharset(@Nullable Charset charset) {
                this.charset = charset;
        }

        @NonNull
        private Boolean getResponseCommitted() {
                return this.responseCommitted;
        }

        private void setResponseCommitted(@NonNull Boolean responseCommitted) {
                requireNonNull(responseCommitted);
                this.responseCommitted = responseCommitted;
        }

        @NonNull
        private Boolean getResponseFinalized() {
                return this.responseFinalized;
        }

        private void setResponseFinalized(@NonNull Boolean responseFinalized) {
                requireNonNull(responseFinalized);
                this.responseFinalized = responseFinalized;
        }

        private void writeDefaultErrorBody(int statusCode,
                                                                                                                                                 @Nullable String message) {
                if (getResponseOutputStream().size() > 0)
                        return;

                String payload = message;

                if (payload == null || payload.isBlank())
                        payload = StatusCode.fromStatusCode(statusCode)
                                        .map(StatusCode::getReasonPhrase)
                                        .orElse("Error");

                if (payload.isBlank())
                        return;

                Charset charset = getEffectiveCharset();
                byte[] bytes = payload.getBytes(charset);
                getResponseOutputStream().write(bytes, 0, bytes.length);

                String currentContentType = getContentType();

                if (currentContentType == null || currentContentType.isBlank())
                        setContentType("text/plain; charset=" + charset.name());
        }

        private void maybeCommitOnWrite() {
                if (!getResponseCommitted() && getResponseOutputStream().size() >= getResponseBufferSizeInBytes())
                        setResponseCommitted(true);
        }

        private void ensureResponseIsUncommitted() {
                if (getResponseCommitted())
                        throw new IllegalStateException("Response has already been committed.");
        }

        @NonNull
        private String dateHeaderRepresentation(@NonNull Long millisSinceEpoch) {
                requireNonNull(millisSinceEpoch);
                return DATE_TIME_FORMATTER.format(Instant.ofEpochMilli(millisSinceEpoch));
        }

        @NonNull
        private Optional<SokletServletOutputStream> getServletOutputStream() {
                return Optional.ofNullable(this.servletOutputStream);
        }

        private void setServletOutputStream(@Nullable SokletServletOutputStream servletOutputStream) {
                this.servletOutputStream = servletOutputStream;
        }

        @NonNull
        private Optional<SokletServletPrintWriter> getPrintWriter() {
                return Optional.ofNullable(this.printWriter);
        }

        public void setPrintWriter(@Nullable SokletServletPrintWriter printWriter) {
                this.printWriter = printWriter;
        }

        @NonNull
        private ByteArrayOutputStream getResponseOutputStream() {
                return this.responseOutputStream;
        }

        private void setResponseOutputStream(@NonNull ByteArrayOutputStream responseOutputStream) {
                requireNonNull(responseOutputStream);
                this.responseOutputStream = responseOutputStream;
        }

        @NonNull
        private Integer getResponseBufferSizeInBytes() {
                return this.responseBufferSizeInBytes;
        }

        private void setResponseBufferSizeInBytes(@NonNull Integer responseBufferSizeInBytes) {
                requireNonNull(responseBufferSizeInBytes);
                this.responseBufferSizeInBytes = responseBufferSizeInBytes;
        }

        @NonNull
        private ResponseWriteMethod getResponseWriteMethod() {
                return this.responseWriteMethod;
        }

        private void setResponseWriteMethod(@NonNull ResponseWriteMethod responseWriteMethod) {
                requireNonNull(responseWriteMethod);
                this.responseWriteMethod = responseWriteMethod;
        }

        private enum ResponseWriteMethod {
                UNSPECIFIED,
                SERVLET_OUTPUT_STREAM,
                PRINT_WRITER
        }

        // Implementation of HttpServletResponse methods below:

        @Override
        public void addCookie(@Nullable Cookie cookie) {
                if (isCommitted())
                        return;

                if (cookie != null)
                        getCookies().add(cookie);
        }

        @Override
        public boolean containsHeader(@Nullable String name) {
                if (name == null)
                        return false;

                if ("Set-Cookie".equalsIgnoreCase(name))
                        return !getCookies().isEmpty() || getHeaders().containsKey(name);

                return getHeaders().containsKey(name);
        }

        @Override
        @Nullable
        public String encodeURL(@Nullable String url) {
                return url;
        }

        @Override
        @Nullable
        public String encodeRedirectURL(@Nullable String url) {
                return url;
        }

        @Override
        @Deprecated
        public String encodeUrl(@Nullable String url) {
                return url;
        }

        @Override
        @Deprecated
        public String encodeRedirectUrl(@Nullable String url) {
                return url;
        }

        @Override
        public void sendError(int sc,
                                                                                                @Nullable String msg) throws IOException {
                ensureResponseIsUncommitted();
                resetBuffer();
                setStatus(sc);
                setErrorMessage(msg);
                writeDefaultErrorBody(sc, msg);
                setResponseCommitted(true);
        }

        @Override
        public void sendError(int sc) throws IOException {
                ensureResponseIsUncommitted();
                resetBuffer();
                setStatus(sc);
                setErrorMessage(null);
                writeDefaultErrorBody(sc, null);
                setResponseCommitted(true);
        }

        @NonNull
        private String getRedirectBaseUrl() {
                HttpServletRequest httpServletRequest = getHttpServletRequest().orElse(null);

                if (httpServletRequest == null)
                        return "http://localhost";

                String scheme = httpServletRequest.getScheme();
                if (scheme == null || scheme.isBlank())
                        scheme = "http";
                String host = httpServletRequest.getServerName();
                if (host == null || host.isBlank())
                        host = "localhost";
                host = normalizeHostForLocation(host);
                int port = httpServletRequest.getServerPort();
                boolean defaultPort = port <= 0 || ("https".equalsIgnoreCase(scheme) && port == 443) || ("http".equalsIgnoreCase(scheme) && port == 80);
                String authorityHost = host;

                if (host != null && host.indexOf(':') >= 0 && !host.startsWith("[") && !host.endsWith("]"))
                        authorityHost = "[" + host + "]";

                String authority = defaultPort ? authorityHost : format("%s:%d", authorityHost, port);
                validateAuthority(scheme, authority);
                return format("%s://%s", scheme, authority);
        }

        @Nullable
        private String getRawQuery() {
                HttpServletRequest httpServletRequest = getHttpServletRequest().orElse(null);

                if (httpServletRequest == null)
                        return null;

                String rawQuery = httpServletRequest.getQueryString();
                return rawQuery == null || rawQuery.isEmpty() ? null : rawQuery;
        }

        private static final class ParsedLocation {
                @Nullable
                private final String scheme;
                @Nullable
                private final String rawAuthority;
                @NonNull
                private final String rawPath;
                @Nullable
                private final String rawQuery;
                @Nullable
                private final String rawFragment;
                private final boolean opaque;

                private ParsedLocation(@Nullable String scheme,
                                                                                                         @Nullable String rawAuthority,
                                                                                                         @NonNull String rawPath,
                                                                                                         @Nullable String rawQuery,
                                                                                                         @Nullable String rawFragment,
                                                                                                         boolean opaque) {
                        this.scheme = scheme;
                        this.rawAuthority = rawAuthority;
                        this.rawPath = rawPath;
                        this.rawQuery = rawQuery;
                        this.rawFragment = rawFragment;
                        this.opaque = opaque;
                }
        }

        private static final class ParsedPath {
                @NonNull
                private final String rawPath;
                @Nullable
                private final String rawQuery;
                @Nullable
                private final String rawFragment;

                private ParsedPath(@NonNull String rawPath,
                                                                                         @Nullable String rawQuery,
                                                                                         @Nullable String rawFragment) {
                        this.rawPath = rawPath;
                        this.rawQuery = rawQuery;
                        this.rawFragment = rawFragment;
                }
        }

        @NonNull
        private ParsedPath parsePathAndSuffix(@NonNull String rawPath) {
                String path = rawPath;
                String rawQuery = null;
                String rawFragment = null;

                int hash = path.indexOf('#');
                if (hash >= 0) {
                        rawFragment = path.substring(hash + 1);
                        path = path.substring(0, hash);
                }

                int question = path.indexOf('?');
                if (question >= 0) {
                        rawQuery = path.substring(question + 1);
                        path = path.substring(0, question);
                }

                return new ParsedPath(path, rawQuery, rawFragment);
        }

        private boolean isAsciiAlpha(char c) {
                return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
        }

        private boolean isAsciiDigit(char c) {
                return c >= '0' && c <= '9';
        }

        private boolean isSchemeChar(char c) {
                return isAsciiAlpha(c) || isAsciiDigit(c) || c == '+' || c == '-' || c == '.';
        }

        private boolean isValidScheme(@NonNull String scheme) {
                if (scheme.isEmpty())
                        return false;

                if (!isAsciiAlpha(scheme.charAt(0)))
                        return false;

                for (int i = 1; i < scheme.length(); i++) {
                        if (!isSchemeChar(scheme.charAt(i)))
                                return false;
                }

                return true;
        }

        private boolean containsNonAscii(@NonNull String value) {
                for (int i = 0; i < value.length(); i++) {
                        if (value.charAt(i) > 0x7F)
                                return true;
                }

                return false;
        }

        @NonNull
        private String normalizeHostForLocation(@NonNull String host) {
                requireNonNull(host);
                String normalized = host.trim();

                if (normalized.isEmpty())
                        throw new IllegalArgumentException("Redirect host is invalid");

                if (normalized.startsWith("[") && normalized.endsWith("]"))
                        return normalized;

                if (normalized.indexOf(':') >= 0)
                        return normalized;

                if (containsNonAscii(normalized)) {
                        try {
                                normalized = IDN.toASCII(normalized);
                        } catch (IllegalArgumentException e) {
                                throw new IllegalArgumentException("Redirect host is invalid", e);
                        }
                }

                return normalized;
        }

        private int countColons(@NonNull String value) {
                int count = 0;

                for (int i = 0; i < value.length(); i++) {
                        if (value.charAt(i) == ':')
                                count++;
                }

                return count;
        }

        @Nullable
        private String normalizeAuthority(@NonNull String scheme,
                                                                                                                                                @Nullable String rawAuthority) {
                requireNonNull(scheme);

                if (rawAuthority == null || rawAuthority.isBlank())
                        return null;

                String authority = rawAuthority.trim();
                String userInfo = null;
                String hostPort = authority;
                int at = authority.lastIndexOf('@');

                if (at >= 0) {
                        userInfo = authority.substring(0, at);
                        hostPort = authority.substring(at + 1);
                }

                String normalizedHostPort;

                if (hostPort.startsWith("[")) {
                        int close = hostPort.indexOf(']');
                        if (close < 0)
                                throw new IllegalArgumentException("Redirect location is invalid");

                        normalizedHostPort = hostPort;
                } else {
                        int colonCount = countColons(hostPort);
                        String host = hostPort;
                        String port = null;

                        if (colonCount > 1) {
                                host = hostPort;
                        } else if (colonCount == 1) {
                                int colon = hostPort.lastIndexOf(':');

                                if (colon <= 0 || colon == hostPort.length() - 1)
                                        throw new IllegalArgumentException("Redirect location is invalid");

                                String portCandidate = hostPort.substring(colon + 1);
                                boolean allDigits = true;

                                for (int i = 0; i < portCandidate.length(); i++) {
                                        if (!isAsciiDigit(portCandidate.charAt(i))) {
                                                allDigits = false;
                                                break;
                                        }
                                }

                                if (!allDigits)
                                        throw new IllegalArgumentException("Redirect location is invalid");

                                host = hostPort.substring(0, colon);
                                port = portCandidate;
                        }

                        String normalizedHost = normalizeHostForLocation(host);

                        if (normalizedHost.indexOf(':') >= 0 && !normalizedHost.startsWith("["))
                                normalizedHost = "[" + normalizedHost + "]";

                        normalizedHostPort = port == null ? normalizedHost : normalizedHost + ":" + port;
                }

                String normalized = userInfo == null ? normalizedHostPort : userInfo + "@" + normalizedHostPort;
                validateAuthority(scheme, normalized);
                return normalized;
        }

        private void validateAuthority(@NonNull String scheme,
                                                                                                                                 @Nullable String authority) {
                requireNonNull(scheme);

                try {
                        new URI(scheme, authority, null, null, null);
                } catch (URISyntaxException e) {
                        throw new IllegalArgumentException("Redirect location is invalid", e);
                }
        }

        private boolean isUnreserved(char c) {
                return isAsciiAlpha(c) || isAsciiDigit(c) || c == '-' || c == '.' || c == '_' || c == '~';
        }

        private boolean isSubDelim(char c) {
                return c == '!' || c == '$' || c == '&' || c == '\'' || c == '(' || c == ')'
                                || c == '*' || c == '+' || c == ',' || c == ';' || c == '=';
        }

        private boolean isPchar(char c) {
                return isUnreserved(c) || isSubDelim(c) || c == ':' || c == '@';
        }

        private boolean isAllowedInPath(char c) {
                return isPchar(c) || c == '/';
        }

        private boolean isAllowedInQueryOrFragment(char c) {
                return isPchar(c) || c == '/' || c == '?';
        }

        private boolean isHexDigit(char c) {
                return (c >= '0' && c <= '9')
                                || (c >= 'A' && c <= 'F')
                                || (c >= 'a' && c <= 'f');
        }

        @NonNull
        private String encodePreservingEscapes(@NonNull String input,
                                                                                                                                                                 boolean allowQueryOrFragmentChars) {
                requireNonNull(input);

                StringBuilder out = new StringBuilder(input.length());
                int length = input.length();

                for (int i = 0; i < length; ) {
                        char c = input.charAt(i);

                        if (c == '%' && i + 2 < length
                                        && isHexDigit(input.charAt(i + 1)) && isHexDigit(input.charAt(i + 2))) {
                                out.append('%').append(input.charAt(i + 1)).append(input.charAt(i + 2));
                                i += 3;
                                continue;
                        }

                        boolean allowed = allowQueryOrFragmentChars ? isAllowedInQueryOrFragment(c) : isAllowedInPath(c);

                        if (allowed) {
                                out.append(c);
                                i++;
                                continue;
                        }

                        int codePoint = input.codePointAt(i);
                        byte[] bytes = new String(Character.toChars(codePoint)).getBytes(StandardCharsets.UTF_8);

                        for (byte b : bytes) {
                                out.append('%');
                                int v = b & 0xFF;
                                out.append(Character.toUpperCase(Character.forDigit((v >> 4) & 0xF, 16)));
                                out.append(Character.toUpperCase(Character.forDigit(v & 0xF, 16)));
                        }

                        i += Character.charCount(codePoint);
                }

                return out.toString();
        }

        private int firstDelimiterIndex(@NonNull String value) {
                int slash = value.indexOf('/');
                int question = value.indexOf('?');
                int hash = value.indexOf('#');
                int index = -1;

                if (slash >= 0)
                        index = slash;
                if (question >= 0 && (index == -1 || question < index))
                        index = question;
                if (hash >= 0 && (index == -1 || hash < index))
                        index = hash;

                return index;
        }

        @Nullable
        private ParsedLocation parseLocationFallback(@NonNull String location) {
                int colon = location.indexOf(':');
                if (colon <= 0)
                        return null;

                String scheme = location.substring(0, colon);
                if (!isValidScheme(scheme))
                        return null;

                String rest = location.substring(colon + 1);

                if (rest.startsWith("//")) {
                        String authorityAndPath = rest.substring(2);
                        int delimiterIndex = firstDelimiterIndex(authorityAndPath);
                        String rawAuthority = delimiterIndex == -1 ? authorityAndPath : authorityAndPath.substring(0, delimiterIndex);
                        String remainder = delimiterIndex == -1 ? "" : authorityAndPath.substring(delimiterIndex);
                        ParsedPath parsedPath = parsePathAndSuffix(remainder);
                        return new ParsedLocation(scheme, rawAuthority.isEmpty() ? null : rawAuthority,
                                        parsedPath.rawPath, parsedPath.rawQuery, parsedPath.rawFragment, false);
                }

                if (rest.startsWith("/")) {
                        ParsedPath parsedPath = parsePathAndSuffix(rest);
                        return new ParsedLocation(scheme, null, parsedPath.rawPath, parsedPath.rawQuery, parsedPath.rawFragment, false);
                }

                return new ParsedLocation(scheme, null, rest, null, null, true);
        }

        @NonNull
        private ParsedLocation parseLocation(@NonNull String location) {
                requireNonNull(location);

                try {
                        URI uri = URI.create(location);
                        String rawPath = uri.getRawPath() == null ? "" : uri.getRawPath();
                        return new ParsedLocation(uri.getScheme(), uri.getRawAuthority(), rawPath, uri.getRawQuery(), uri.getRawFragment(), uri.isOpaque());
                } catch (Exception ignored) {
                        ParsedLocation fallback = parseLocationFallback(location);
                        if (fallback != null)
                                return fallback;

                        ParsedPath parsedPath = parsePathAndSuffix(location);
                        return new ParsedLocation(null, null, parsedPath.rawPath, parsedPath.rawQuery, parsedPath.rawFragment, false);
                }
        }

        @NonNull
        private String normalizePath(@NonNull String path) {
                requireNonNull(path);

                if (path.isEmpty())
                        return path;

                String input = path;
                StringBuilder output = new StringBuilder();

                while (!input.isEmpty()) {
                        if (input.startsWith("../")) {
                                input = input.substring(3);
                        } else if (input.startsWith("./")) {
                                input = input.substring(2);
                        } else if (input.startsWith("/./")) {
                                input = input.substring(2);
                        } else if (input.equals("/.")) {
                                input = "/";
                        } else if (input.startsWith("/../")) {
                                input = input.substring(3);
                                removeLastSegment(output);
                        } else if (input.equals("/..")) {
                                input = "/";
                                removeLastSegment(output);
                        } else if (input.equals(".") || input.equals("..")) {
                                input = "";
                        } else {
                                int start = input.startsWith("/") ? 1 : 0;
                                int nextSlash = input.indexOf('/', start);

                                if (nextSlash == -1) {
                                        output.append(input);
                                        input = "";
                                } else {
                                        output.append(input, 0, nextSlash);
                                        input = input.substring(nextSlash);
                                }
                        }
                }

                return output.toString();
        }

        private void removeLastSegment(@NonNull StringBuilder output) {
                requireNonNull(output);

                int length = output.length();

                if (length == 0)
                        return;

                int end = length;

                if (end > 0 && output.charAt(end - 1) == '/')
                        end--;

                if (end <= 0) {
                        output.setLength(0);
                        return;
                }

                int lastSlash = output.lastIndexOf("/", end - 1);

                if (lastSlash >= 0)
                        output.delete(lastSlash, output.length());
                else
                        output.setLength(0);
        }

        @NonNull
        private String buildAbsoluteLocation(@NonNull String scheme,
                                                                                                                                                         @Nullable String rawAuthority,
                                                                                                                                                         @NonNull String rawPath,
                                                                                                                                                         @Nullable String rawQuery,
                                                                                                                                                         @Nullable String rawFragment) {
                requireNonNull(scheme);
                requireNonNull(rawPath);

                String encodedPath = encodePreservingEscapes(rawPath, false);
                String encodedQuery = rawQuery == null ? null : encodePreservingEscapes(rawQuery, true);
                String encodedFragment = rawFragment == null ? null : encodePreservingEscapes(rawFragment, true);

                StringBuilder out = new StringBuilder();
                out.append(scheme).append(':');

                if (rawAuthority != null) {
                        out.append("//").append(rawAuthority);
                }

                out.append(encodedPath);

                if (encodedQuery != null)
                        out.append('?').append(encodedQuery);

                if (encodedFragment != null)
                        out.append('#').append(encodedFragment);

                return out.toString();
        }

        @NonNull
        private String buildOpaqueLocation(@NonNull String location) {
                requireNonNull(location);

                try {
                        return URI.create(location).toASCIIString();
                } catch (Exception e) {
                        throw new IllegalArgumentException("Redirect location is invalid", e);
                }
        }

        @Override
        public void sendRedirect(@Nullable String location) throws IOException {
                ensureResponseIsUncommitted();

                if (location == null)
                        throw new IllegalArgumentException("Redirect location must not be null");

                setStatus(HttpServletResponse.SC_FOUND);
                resetBuffer();

                // This method can accept relative URLs; the servlet container must convert the relative URL to an absolute URL
                // before sending the response to the client. If the location is relative without a leading '/' the container
                // interprets it as relative to the current request URI. If the location is relative with a leading '/'
                // the container interprets it as relative to the servlet container root. If the location is relative with two
                // leading '/' the container interprets it as a network-path reference (see RFC 3986: Uniform Resource
                // Identifier (URI): Generic Syntax, section 4.2 "Relative Reference").
                String baseUrl = getRedirectBaseUrl();
                URI baseUri = URI.create(baseUrl);
                String scheme = baseUri.getScheme();
                String baseAuthority = baseUri.getRawAuthority();
                String finalLocation;
                ParsedLocation parsed = parseLocation(location);

                if (parsed.opaque) {
                        finalLocation = buildOpaqueLocation(location);
                } else if (location.startsWith("//")) {
                        // Network-path reference: keep host from location but inherit scheme
                        String normalizedAuthority = normalizeAuthority(scheme, parsed.rawAuthority);

                        if (normalizedAuthority == null || normalizedAuthority.isBlank())
                                throw new IllegalArgumentException("Redirect location is invalid");

                        String normalized = normalizePath(parsed.rawPath);
                        finalLocation = buildAbsoluteLocation(scheme, normalizedAuthority, normalized, parsed.rawQuery, parsed.rawFragment);
                } else if (parsed.scheme != null) {
                        // URL is already absolute
                        String normalizedAuthority = normalizeAuthority(parsed.scheme, parsed.rawAuthority);
                        finalLocation = buildAbsoluteLocation(parsed.scheme, normalizedAuthority, parsed.rawPath, parsed.rawQuery, parsed.rawFragment);
                } else if (location.startsWith("/")) {
                        // URL is relative with leading /
                        String normalized = normalizePath(parsed.rawPath);
                        finalLocation = buildAbsoluteLocation(scheme, baseAuthority, normalized, parsed.rawQuery, parsed.rawFragment);
                } else {
                        // URL is relative but does not have leading '/', resolve against the parent of the current path
                        String base = getRawPath();
                        String path = parsed.rawPath;
                        String query = parsed.rawQuery;

                        if (path.isEmpty() && query == null)
                                query = getRawQuery();

                        if (path.isEmpty()) {
                                String normalized = normalizePath(base);
                                finalLocation = buildAbsoluteLocation(scheme, baseAuthority, normalized, query, parsed.rawFragment);
                        } else {
                                int idx = base.lastIndexOf('/');
                                String parent = (idx <= 0) ? "/" : base.substring(0, idx);
                                String resolvedPath = parent.endsWith("/") ? parent + path : parent + "/" + path;
                                String normalized = normalizePath(resolvedPath);
                                finalLocation = buildAbsoluteLocation(scheme, baseAuthority, normalized, query, parsed.rawFragment);
                        }
                }

                setRedirectUrl(finalLocation);
                setHeader("Location", finalLocation);

                flushBuffer();
                setResponseCommitted(true);
        }

        @Override
        public void setDateHeader(@Nullable String name,
                                                                                                                long date) {
                if (isCommitted())
                        return;

                setHeader(name, dateHeaderRepresentation(date));
        }

        @Override
        public void addDateHeader(@Nullable String name,
                                                                                                                long date) {
                if (isCommitted())
                        return;

                addHeader(name, dateHeaderRepresentation(date));
        }

        @Override
        public void setHeader(@Nullable String name,
                                                                                                @Nullable String value) {
                if (isCommitted())
                        return;

                if (name != null && !name.isBlank() && value != null) {
                        if ("Content-Type".equalsIgnoreCase(name)) {
                                setContentType(value);
                                return;
                        }

                        putHeaderValue(name, value, true);
                }
        }

        @Override
        public void addHeader(@Nullable String name,
                                                                                                @Nullable String value) {
                if (isCommitted())
                        return;

                if (name != null && !name.isBlank() && value != null) {
                        if ("Content-Type".equalsIgnoreCase(name)) {
                                setContentType(value);
                                return;
                        }

                        putHeaderValue(name, value, false);
                }
        }

        @Override
        public void setIntHeader(@Nullable String name,
                                                                                                         int value) {
                setHeader(name, String.valueOf(value));
        }

        @Override
        public void addIntHeader(@Nullable String name,
                                                                                                         int value) {
                addHeader(name, String.valueOf(value));
        }

        @Override
        public void setStatus(int sc) {
                if (isCommitted())
                        return;

                this.statusCode = sc;
        }

        @Override
        @Deprecated
        public void setStatus(int sc,
                                                                                                @Nullable String sm) {
                if (isCommitted())
                        return;

                this.statusCode = sc;
                this.errorMessage = sm;
        }

        @Override
        public int getStatus() {
                return getStatusCode();
        }

        @Override
        @Nullable
        public String getHeader(@Nullable String name) {
                if (name == null)
                        return null;

                if ("Set-Cookie".equalsIgnoreCase(name)) {
                        List<@NonNull String> values = getHeaders().get(name);

                        if (values != null && !values.isEmpty())
                                return values.get(0);

                        List<@NonNull String> cookieValues = getSetCookieHeaderValues();
                        return cookieValues.isEmpty() ? null : cookieValues.get(0);
                }

                List<@NonNull String> values = getHeaders().get(name);
                return values == null || values.size() == 0 ? null : values.get(0);
        }

        @Override
        @NonNull
        public Collection<@NonNull String> getHeaders(@Nullable String name) {
                if (name == null)
                        return List.of();

                if ("Set-Cookie".equalsIgnoreCase(name)) {
                        List<@NonNull String> values = getHeaders().get(name);
                        List<@NonNull String> cookieValues = getSetCookieHeaderValues();

                        if ((values == null || values.isEmpty()) && cookieValues.isEmpty())
                                return List.of();

                        List<@NonNull String> combined = new ArrayList<>();

                        if (values != null)
                                combined.addAll(values);

                        combined.addAll(cookieValues);
                        return Collections.unmodifiableList(combined);
                }

                List<@NonNull String> values = getHeaders().get(name);
                return values == null ? List.of() : Collections.unmodifiableList(values);
        }

        @Override
        @NonNull
        public Collection<@NonNull String> getHeaderNames() {
                Set<@NonNull String> names = new java.util.TreeSet<>(String.CASE_INSENSITIVE_ORDER);
                names.addAll(getHeaders().keySet());

                if (!getCookies().isEmpty())
                        names.add("Set-Cookie");

                return Collections.unmodifiableSet(names);
        }

        @Override
        @NonNull
        public String getCharacterEncoding() {
                return getEffectiveCharset().name();
        }

        @Override
        @Nullable
        public String getContentType() {
                String headerValue = getHeader("Content-Type");
                return headerValue != null ? headerValue : this.contentType;
        }

        @Override
        @NonNull
        public ServletOutputStream getOutputStream() throws IOException {
                // Returns a ServletOutputStream suitable for writing binary data in the response.
                // The servlet container does not encode the binary data.
                // Calling flush() on the ServletOutputStream commits the response.
                // Either this method or getWriter() may be called to write the body, not both, except when reset() has been called.
                ResponseWriteMethod currentResponseWriteMethod = getResponseWriteMethod();

                if (currentResponseWriteMethod == ResponseWriteMethod.UNSPECIFIED) {
                        setResponseWriteMethod(ResponseWriteMethod.SERVLET_OUTPUT_STREAM);
                        this.servletOutputStream = SokletServletOutputStream.withOutputStream(getResponseOutputStream())
                                        .onWriteOccurred((ignored1, ignored2) -> maybeCommitOnWrite())
                                        .onWriteFinalized((ignored) -> {
                                                setResponseCommitted(true);
                                                setResponseFinalized(true);
                                        }).build();
                        return getServletOutputStream().get();
                } else if (currentResponseWriteMethod == ResponseWriteMethod.SERVLET_OUTPUT_STREAM) {
                        return getServletOutputStream().get();
                } else {
                        throw new IllegalStateException(format("Cannot use %s for writing response; already using %s",
                                        ServletOutputStream.class.getSimpleName(), PrintWriter.class.getSimpleName()));
                }
        }

        @NonNull
        private Boolean writerObtained() {
                return getResponseWriteMethod() == ResponseWriteMethod.PRINT_WRITER;
        }

        @NonNull
        private Optional<String> extractCharsetFromContentType(@Nullable String type) {
                if (type == null)
                        return Optional.empty();

                String[] parts = type.split(";");

                for (int i = 1; i < parts.length; i++) {
                        String p = parts[i].trim();
                        if (p.toLowerCase(Locale.ROOT).startsWith("charset=")) {
                                String cs = p.substring("charset=".length()).trim();

                                if (cs.startsWith("\"") && cs.endsWith("\"") && cs.length() >= 2)
                                        cs = cs.substring(1, cs.length() - 1);

                                return Optional.of(cs);
                        }
                }

                return Optional.empty();
        }

        // Helper: remove any charset=... from Content-Type (preserve other params)
        @NonNull
        private Optional<String> stripCharsetParam(@Nullable String type) {
                if (type == null)
                        return Optional.empty();

                String[] parts = type.split(";");
                String base = parts[0].trim();
                List<@NonNull String> kept = new ArrayList<>();

                for (int i = 1; i < parts.length; i++) {
                        String p = parts[i].trim();

                        if (!p.toLowerCase(Locale.ROOT).startsWith("charset=") && !p.isEmpty())
                                kept.add(p);
                }

                return Optional.ofNullable(kept.isEmpty() ? base : base + "; " + String.join("; ", kept));
        }

        // Helper: ensure Content-Type includes the given charset (replacing any existing one)
        @NonNull
        private Optional<String> withCharset(@Nullable String type,
                                                                                                                                                                 @NonNull String charsetName) {
                requireNonNull(charsetName);

                if (type == null)
                        return Optional.empty();

                String baseNoCs = stripCharsetParam(type).orElse("text/plain");
                return Optional.of(baseNoCs + "; charset=" + charsetName);
        }

        @Override
        public PrintWriter getWriter() throws IOException {
                // Returns a PrintWriter object that can send character text to the client.
                // The PrintWriter uses the character encoding returned by getCharacterEncoding().
                // If the response's character encoding has not been specified as described in getCharacterEncoding
                // (i.e., the method just returns the default value), getWriter updates it to the effective default.
                // Calling flush() on the PrintWriter commits the response.
                //
                // Either this method or getOutputStream() may be called to write the body, not both, except when reset() has been called.
                // Returns a PrintWriter that uses the character encoding returned by getCharacterEncoding().
                // If not specified yet, calling getWriter() fixes the encoding to the effective default.
                ResponseWriteMethod currentResponseWriteMethod = getResponseWriteMethod();

                if (currentResponseWriteMethod == ResponseWriteMethod.UNSPECIFIED) {
                        // Freeze encoding now
                        Charset enc = getEffectiveCharset();
                        setCharset(enc); // record the chosen encoding explicitly

                        // If a content type is already present and lacks charset, append the frozen charset to header
                        String currentContentType = getContentType();

                        if (currentContentType != null) {
                                Optional<String> csInHeader = extractCharsetFromContentType(currentContentType);
                                if (csInHeader.isEmpty() || !csInHeader.get().equalsIgnoreCase(enc.name())) {
                                        String updated = withCharset(currentContentType, enc.name()).orElse(null);

                                        if (updated != null) {
                                                this.contentType = updated;
                                                putHeaderValue("Content-Type", updated, true);
                                        } else {
                                                this.contentType = currentContentType;
                                                putHeaderValue("Content-Type", currentContentType, true);
                                        }
                                }
                        }

                        setResponseWriteMethod(ResponseWriteMethod.PRINT_WRITER);

                        this.printWriter =
                                        SokletServletPrintWriter.withWriter(
                                                                        new OutputStreamWriter(getResponseOutputStream(), enc))
                                                        .onWriteOccurred((ignored1, ignored2) -> maybeCommitOnWrite())
                                                        .onWriteFinalized((ignored) -> {
                                                                setResponseCommitted(true);
                                                                setResponseFinalized(true);
                                                        })
                                                        .build();

                        return getPrintWriter().get();
                } else if (currentResponseWriteMethod == ResponseWriteMethod.PRINT_WRITER) {
                        return getPrintWriter().get();
                } else {
                        throw new IllegalStateException(format("Cannot use %s for writing response; already using %s",
                                        PrintWriter.class.getSimpleName(), ServletOutputStream.class.getSimpleName()));
                }
        }

        @Override
        public void setCharacterEncoding(@Nullable String charset) {
                if (isCommitted())
                        return;

                // Spec: no effect after getWriter() or after commit
                if (writerObtained())
                        return;

                if (charset == null || charset.isBlank()) {
                        // Clear explicit charset; default will be chosen at writer time if needed
                        setCharset(null);

                        // If a Content-Type is set, remove its charset=... parameter
                        String currentContentType = getContentType();

                        if (currentContentType != null) {
                                String updated = stripCharsetParam(currentContentType).orElse(null);
                                this.contentType = updated;
                                if (updated == null || updated.isBlank()) {
                                        getHeaders().remove("Content-Type");
                                } else {
                                        putHeaderValue("Content-Type", updated, true);
                                }
                        }

                        return;
                }

                Charset cs;

                try {
                        cs = Charset.forName(charset);
                } catch (IllegalCharsetNameException | UnsupportedCharsetException e) {
                        return;
                }
                setCharset(cs);

                // If a Content-Type is set, reflect/replace the charset=... in the header
                String currentContentType = getContentType();

                if (currentContentType != null) {
                        String updated = withCharset(currentContentType, cs.name()).orElse(null);

                        if (updated != null) {
                                this.contentType = updated;
                                putHeaderValue("Content-Type", updated, true);
                        } else {
                                this.contentType = currentContentType;
                                putHeaderValue("Content-Type", currentContentType, true);
                        }
                }
        }

        @Override
        public void setContentLength(int len) {
                if (isCommitted())
                        return;

                setHeader("Content-Length", String.valueOf(len));
        }

        @Override
        public void setContentLengthLong(long len) {
                if (isCommitted())
                        return;

                setHeader("Content-Length", String.valueOf(len));
        }

        @Override
        public void setContentType(@Nullable String type) {
                // This method may be called repeatedly to change content type and character encoding.
                // This method has no effect if called after the response has been committed.
                // It does not set the response's character encoding if it is called after getWriter has been called
                // or after the response has been committed.
                if (isCommitted())
                        return;

                if (!writerObtained()) {
                        // Before writer: charset can still be established/overridden
                        this.contentType = type;

                        if (type == null || type.isBlank()) {
                                getHeaders().remove("Content-Type");
                                return;
                        }

                        // If caller specified charset=..., adopt it as the current explicit charset
                        Optional<String> cs = extractCharsetFromContentType(type);
                        if (cs.isPresent()) {
                                try {
                                        setCharset(Charset.forName(cs.get()));
                                } catch (IllegalCharsetNameException | UnsupportedCharsetException ignored) {
                                        // Ignore invalid charset token; leave current charset unchanged.
                                }
                                putHeaderValue("Content-Type", type, true);
                        } else {
                                // No charset in type. If an explicit charset already exists (via setCharacterEncoding),
                                // reflect it in the header; otherwise just set the type as-is.
                                if (getCharset().isPresent()) {
                                        String updated = withCharset(type, getCharset().get().name()).orElse(null);

                                        if (updated != null) {
                                                this.contentType = updated;
                                                putHeaderValue("Content-Type", updated, true);
                                        } else {
                                                putHeaderValue("Content-Type", type, true);
                                        }
                                } else {
                                        putHeaderValue("Content-Type", type, true);
                                }
                        }
                } else {
                        // After writer: charset is frozen. We can change the MIME type, but we must NOT change encoding.
                        // If caller supplies a charset, normalize the header back to the locked encoding.
                        this.contentType = type;

                        if (type == null || type.isBlank()) {
                                // Allowed: clear header; does not change actual encoding used by writer
                                getHeaders().remove("Content-Type");
                                return;
                        }

                        String locked = getCharacterEncoding(); // the frozen encoding name
                        String normalized = withCharset(type, locked).orElse(null);

                        if (normalized != null) {
                                this.contentType = normalized;
                                putHeaderValue("Content-Type", normalized, true);
                        } else {
                                this.contentType = type;
                                putHeaderValue("Content-Type", type, true);
                        }
                }
        }

        @Override
        public void setBufferSize(int size) {
                ensureResponseIsUncommitted();

                if (size <= 0)
                        throw new IllegalArgumentException("Buffer size must be greater than 0");

                // Per Servlet spec, setBufferSize must be called before any content is written
                if (getResponseOutputStream().size() > 0)
                        throw new IllegalStateException("setBufferSize must be called before any content is written");

                setResponseBufferSizeInBytes(size);

                if (!writerObtained() && getServletOutputStream().isEmpty())
                        setResponseOutputStream(new ByteArrayOutputStream(getResponseBufferSizeInBytes()));
        }

        @Override
        public int getBufferSize() {
                return getResponseBufferSizeInBytes();
        }

        @Override
        public void flushBuffer() throws IOException {
                if (!isCommitted())
                        setResponseCommitted(true);

                SokletServletPrintWriter currentWriter = getPrintWriter().orElse(null);
                SokletServletOutputStream currentOutputStream = getServletOutputStream().orElse(null);

                if (currentWriter != null) {
                        currentWriter.flush();
                } else if (currentOutputStream != null) {
                        currentOutputStream.flush();
                } else {
                        getResponseOutputStream().flush();
                }
        }

        @Override
        public void resetBuffer() {
                ensureResponseIsUncommitted();
                getResponseOutputStream().reset();
        }

        @Override
        public boolean isCommitted() {
                return getResponseCommitted();
        }

        @Override
        public void reset() {
                // Clears any data that exists in the buffer as well as the status code, headers.
                // The state of calling getWriter() or getOutputStream() is also cleared.
                // It is legal, for instance, to call getWriter(), reset() and then getOutputStream().
                // If getWriter() or getOutputStream() have been called before this method, then the corresponding returned
                // Writer or OutputStream will be staled and the behavior of using the stale object is undefined.
                // If the response has been committed, this method throws an IllegalStateException.

                ensureResponseIsUncommitted();

                setStatusCode(HttpServletResponse.SC_OK);
                setServletOutputStream(null);
                setPrintWriter(null);
                setResponseWriteMethod(ResponseWriteMethod.UNSPECIFIED);
                setResponseOutputStream(new ByteArrayOutputStream(getResponseBufferSizeInBytes()));
                getHeaders().clear();
                getCookies().clear();

                // Clear content-type/charset & locale to a pristine state
                this.contentType = null;
                setCharset(null);
                this.locale = null;
                this.errorMessage = null;
                this.redirectUrl = null;
        }

        @Override
        public void setLocale(@Nullable Locale locale) {
                if (isCommitted())
                        return;

                this.locale = locale;

                if (locale != null && !writerObtained() && getCharset().isEmpty()) {
                        Charset contextCharset = getContextResponseCharset();
                        Charset selectedCharset = contextCharset == null ? DEFAULT_CHARSET : contextCharset;
                        setCharacterEncoding(selectedCharset.name());
                }

                if (locale == null) {
                        getHeaders().remove("Content-Language");
                        return;
                }

                String tag = locale.toLanguageTag();

                if (tag.isBlank())
                        getHeaders().remove("Content-Language");
                else
                        putHeaderValue("Content-Language", tag, true);
        }

        @Override
        public Locale getLocale() {
                return this.locale == null ? Locale.getDefault() : this.locale;
        }
}