/*
    * ====================================================================
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  package org.apache.hc.client5.http.impl.cache;
  
  import java.net.URI;
  import java.net.URISyntaxException;
  import java.nio.charset.StandardCharsets;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Locale;
  import java.util.Spliterator;
  import java.util.Spliterators;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.function.Consumer;
  import java.util.stream.StreamSupport;
  
  import org.apache.hc.client5.http.cache.HttpCacheEntry;
  import org.apache.hc.core5.annotation.Contract;
  import org.apache.hc.core5.annotation.Internal;
  import org.apache.hc.core5.annotation.ThreadingBehavior;
  import org.apache.hc.core5.function.Resolver;
  import org.apache.hc.core5.http.Header;
  import org.apache.hc.core5.http.HeaderElement;
  import org.apache.hc.core5.http.HttpHeaders;
  import org.apache.hc.core5.http.HttpHost;
  import org.apache.hc.core5.http.HttpRequest;
  import org.apache.hc.core5.http.MessageHeaders;
  import org.apache.hc.core5.http.NameValuePair;
  import org.apache.hc.core5.http.URIScheme;
  import org.apache.hc.core5.http.message.BasicHeaderElementIterator;
  import org.apache.hc.core5.http.message.BasicHeaderValueFormatter;
  import org.apache.hc.core5.http.message.BasicNameValuePair;
  import org.apache.hc.core5.http.message.MessageSupport;
  import org.apache.hc.core5.net.PercentCodec;
  import org.apache.hc.core5.net.URIAuthority;
  import org.apache.hc.core5.net.URIBuilder;
  import org.apache.hc.core5.util.Args;
  import org.apache.hc.core5.util.CharArrayBuffer;
  import org.apache.hc.core5.util.TextUtils;
  
  /**
   * @since 4.1
   */
  @Contract(threading = ThreadingBehavior.STATELESS)
  public class CacheKeyGenerator implements Resolver<URI, String> {
  
      /**
       * Default instance of {@link CacheKeyGenerator}.
       */
      public static final CacheKeyGenerator INSTANCE = new CacheKeyGenerator();
  
      @Override
      public String resolve(final URI uri) {
          return generateKey(uri);
      }
  
      /**
       * Returns text representation of the request URI of the given {@link HttpRequest}.
       * This method will use {@link HttpRequest#getPath()}, {@link HttpRequest#getScheme()} and
       * {@link HttpRequest#getAuthority()} values when available or attributes of target
       * {@link HttpHost } in order to construct an absolute URI.
       * <p>
       * This method will not attempt to ensure validity of the resultant text representation.
       *
       * @param target target host
       * @param request the {@link HttpRequest}
       *
       * @return String the request URI
       */
      @Internal
      public static String getRequestUri(final HttpHost target, final HttpRequest request) {
          Args.notNull(target, "Target");
          Args.notNull(request, "HTTP request");
         final StringBuilder buf = new StringBuilder();
         final URIAuthority authority = request.getAuthority();
         if (authority != null) {
             final String scheme = request.getScheme();
             buf.append(scheme != null ? scheme : URIScheme.HTTP.id).append("://");
             buf.append(authority.getHostName());
             if (authority.getPort() >= 0) {
                 buf.append(":").append(authority.getPort());
             }
         } else {
             buf.append(target.getSchemeName()).append("://");
             buf.append(target.getHostName());
             if (target.getPort() >= 0) {
                 buf.append(":").append(target.getPort());
             }
         }
         final String path = request.getPath();
         if (path == null) {
             buf.append("/");
         } else {
             if (buf.length() > 0 && !path.startsWith("/")) {
                 buf.append("/");
             }
             buf.append(path);
         }
         return buf.toString();
     }
 
     /**
      * Returns normalized representation of the request URI optimized for use as a cache key.
      * This method ensures the resultant URI has an explicit port in the authority component,
      * and explicit path component and no fragment.
      */
     @Internal
     public static URI normalize(final URI requestUri) throws URISyntaxException {
         Args.notNull(requestUri, "URI");
         final URIBuilder builder = new URIBuilder(requestUri);
         if (builder.getHost() != null) {
             if (builder.getScheme() == null) {
                 builder.setScheme(URIScheme.HTTP.id);
             }
             if (builder.getPort() <= -1) {
                 if (URIScheme.HTTP.same(builder.getScheme())) {
                     builder.setPort(80);
                 } else if (URIScheme.HTTPS.same(builder.getScheme())) {
                     builder.setPort(443);
                 }
             }
         }
         builder.setFragment(null);
         return builder.optimize().build();
     }
 
     /**
      * Lenient URI parser that normalizes valid {@link URI}s and returns {@code null} for malformed URIs.
      */
     @Internal
     public static URI normalize(final String requestUri) {
         if (requestUri == null) {
             return null;
         }
         try {
             return CacheKeyGenerator.normalize(new URI(requestUri));
         } catch (final URISyntaxException ex) {
             return null;
         }
     }
 
     /**
      * Computes a key for the given request {@link URI} that can be used as
      * a unique identifier for cached resources. The URI is expected to
      * in an absolute form.
      *
      * @param requestUri request URI
      * @return cache key
      */
     public String generateKey(final URI requestUri) {
         try {
             final URI normalizeRequestUri = normalize(requestUri);
             return normalizeRequestUri.toASCIIString();
         } catch (final URISyntaxException ex) {
             return requestUri.toASCIIString();
         }
     }
 
     /**
      * Computes a root key for the given {@link HttpHost} and {@link HttpRequest}
      * that can be used as a unique identifier for cached resources.
      *
      * @param host The host for this request
      * @param request the {@link HttpRequest}
      * @return cache key
      */
     public String generateKey(final HttpHost host, final HttpRequest request) {
         final String s = getRequestUri(host, request);
         try {
             return generateKey(new URI(s));
         } catch (final URISyntaxException ex) {
             return s;
         }
     }
 
     /**
      * Returns all variant names contained in {@literal VARY} headers of the given message.
      *
      * @since 5.4
      */
     public static List<String> variantNames(final MessageHeaders message) {
         if (message == null) {
             return null;
         }
         final List<String> names = new ArrayList<>();
         for (final Iterator<Header> it = message.headerIterator(HttpHeaders.VARY); it.hasNext(); ) {
             final Header header = it.next();
             MessageSupport.parseTokens(header, names::add);
         }
         return names;
     }
 
     @Internal
     public static void normalizeElements(final MessageHeaders message, final String headerName, final Consumer<String> consumer) {
         // User-Agent as a special case due to its grammar
         if (headerName.equalsIgnoreCase(HttpHeaders.USER_AGENT)) {
             final Header header = message.getFirstHeader(headerName);
             if (header != null) {
                 consumer.accept(header.getValue().toLowerCase(Locale.ROOT));
             }
         } else {
             normalizeElements(message.headerIterator(headerName), consumer);
         }
     }
 
     @Internal
     public static void normalizeElements(final Iterator<Header> iterator, final Consumer<String> consumer) {
         final Iterator<HeaderElement> it = new BasicHeaderElementIterator(iterator);
         StreamSupport.stream(Spliterators.spliteratorUnknownSize(it, Spliterator.NONNULL), false)
                 .filter(e -> !TextUtils.isBlank(e.getName()))
                 .map(e -> {
                     if (e.getValue() == null && e.getParameterCount() == 0) {
                         return e.getName().toLowerCase(Locale.ROOT);
                     } else {
                         final CharArrayBuffer buf = new CharArrayBuffer(1024);
                         BasicHeaderValueFormatter.INSTANCE.formatNameValuePair(
                                 buf,
                                 new BasicNameValuePair(
                                     e.getName().toLowerCase(Locale.ROOT),
                                     !TextUtils.isBlank(e.getValue()) ? e.getValue() : null),
                                 false);
                         if (e.getParameterCount() > 0) {
                             for (final NameValuePair nvp : e.getParameters()) {
                                 if (!TextUtils.isBlank(nvp.getName())) {
                                     buf.append(';');
                                     BasicHeaderValueFormatter.INSTANCE.formatNameValuePair(
                                             buf,
                                             new BasicNameValuePair(
                                                     nvp.getName().toLowerCase(Locale.ROOT),
                                                     !TextUtils.isBlank(nvp.getValue()) ? nvp.getValue() : null),
                                             false);
                                 }
                             }
                         }
                         return buf.toString();
                     }
                 })
                 .sorted()
                 .distinct()
                 .forEach(consumer);
     }
 
     /**
      * Computes a "variant key" for the given request and the given variants.
      * @param request originating request
      * @param variantNames variant names
      * @return variant key
      *
      * @since 5.4
      */
     public String generateVariantKey(final HttpRequest request, final Collection<String> variantNames) {
         Args.notNull(variantNames, "Variant names");
         final StringBuilder buf = new StringBuilder("{");
         final AtomicBoolean firstHeader = new AtomicBoolean();
         variantNames.stream()
                 .map(h -> h.toLowerCase(Locale.ROOT))
                 .sorted()
                 .distinct()
                 .forEach(h -> {
                     if (!firstHeader.compareAndSet(false, true)) {
                         buf.append("&");
                     }
                     buf.append(PercentCodec.encode(h, StandardCharsets.UTF_8)).append("=");
                     final AtomicBoolean firstToken = new AtomicBoolean();
                     normalizeElements(request, h, t -> {
                         if (!firstToken.compareAndSet(false, true)) {
                             buf.append(",");
                         }
                         buf.append(PercentCodec.encode(t, StandardCharsets.UTF_8));
                     });
                 });
         buf.append("}");
         return buf.toString();
     }
 
     /**
      * Computes a "variant key" from the headers of the given request if the given
      * cache entry can have variants ({@code Vary} header is present).
      *
      * @param request originating request
      * @param entry cache entry
      * @return variant key if the given cache entry can have variants, {@code null} otherwise.
      */
     public String generateVariantKey(final HttpRequest request, final HttpCacheEntry entry) {
         if (entry.containsHeader(HttpHeaders.VARY)) {
             final List<String> variantNames = variantNames(entry);
             return generateVariantKey(request, variantNames);
         } else {
             return null;
         }
     }
 
     /**
      * Computes a key for the given {@link HttpHost} and {@link HttpRequest}
      * that can be used as a unique identifier for cached resources. if the request has a
      * {@literal VARY} header the identifier will also include variant key.
      *
      * @param host The host for this request
      * @param request the {@link HttpRequest}
      * @param entry the parent entry used to track the variants
      * @return cache key
      *
      * @deprecated Use {@link #generateKey(HttpHost, HttpRequest)} or {@link #generateVariantKey(HttpRequest, Collection)}
      */
     @Deprecated
     public String generateKey(final HttpHost host, final HttpRequest request, final HttpCacheEntry entry) {
         final String rootKey = generateKey(host, request);
         final List<String> variantNames = variantNames(entry);
         if (variantNames.isEmpty()) {
             return rootKey;
         } else {
             return generateVariantKey(request, variantNames) + rootKey;
         }
     }
 
 }