/*
    * Copyright 2017 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty5.handler.codec.http;
  
  import io.netty5.util.AsciiString;
  import io.netty5.util.internal.UnstableApi;
  
  import java.util.AbstractMap.SimpleImmutableEntry;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.NoSuchElementException;
  import java.util.Set;
  
  import static io.netty5.handler.codec.CharSequenceValueConverter.INSTANCE;
  import static io.netty5.handler.codec.http.DefaultHttpHeaders.HttpNameValidator;
  import static io.netty5.util.AsciiString.contentEquals;
  import static io.netty5.util.AsciiString.contentEqualsIgnoreCase;
  
  /**
   * A variant of {@link HttpHeaders} which only supports read-only methods.
   * <p>
   * Any array passed to this class may be used directly in the underlying data structures of this class. If these
   * arrays may be modified it is the caller's responsibility to supply this class with a copy of the array.
   * <p>
   * This may be a good alternative to {@link DefaultHttpHeaders} if your have a fixed set of headers which will not
   * change.
   */
  @UnstableApi
  public final class ReadOnlyHttpHeaders extends HttpHeaders {
      private final CharSequence[] nameValuePairs;
  
      /**
       * Create a new instance.
       * @param validateHeaders {@code true} to validate the contents of each header name.
       * @param nameValuePairs An array of the structure {@code [<name,value>,<name,value>,...]}.
       *                      A copy will <strong>NOT</strong> be made of this array. If the contents of this array
       *                      may be modified externally you are responsible for passing in a copy.
       */
      public ReadOnlyHttpHeaders(boolean validateHeaders, CharSequence... nameValuePairs) {
          if ((nameValuePairs.length & 1) != 0) {
              throw newInvalidArraySizeException();
          }
          if (validateHeaders) {
              validateHeaders(nameValuePairs);
          }
          this.nameValuePairs = nameValuePairs;
      }
  
      private static IllegalArgumentException newInvalidArraySizeException() {
          return new IllegalArgumentException("nameValuePairs must be arrays of [name, value] pairs");
      }
  
      private static void validateHeaders(CharSequence... keyValuePairs) {
          for (int i = 0; i < keyValuePairs.length; i += 2) {
              HttpNameValidator.validateName(keyValuePairs[i]);
          }
      }
  
      private CharSequence get0(CharSequence name) {
          final int nameHash = AsciiString.hashCode(name);
          for (int i = 0; i < nameValuePairs.length; i += 2) {
              CharSequence roName = nameValuePairs[i];
              if (AsciiString.hashCode(roName) == nameHash && contentEqualsIgnoreCase(roName, name)) {
                  // Suppress a warning out of bounds access since the constructor allows only pairs
                  return nameValuePairs[i + 1]; // lgtm[java/index-out-of-bounds]
              }
          }
          return null;
      }
  
      @Override
      public String get(String name) {
          CharSequence value = get0(name);
          return value == null ? null : value.toString();
      }
  
      @Override
      public Integer getInt(CharSequence name) {
          CharSequence value = get0(name);
          return value == null ? null : INSTANCE.convertToInt(value);
      }
  
     @Override
     public int getInt(CharSequence name, int defaultValue) {
         CharSequence value = get0(name);
         return value == null ? defaultValue : INSTANCE.convertToInt(value);
     }
 
     @Override
     public Short getShort(CharSequence name) {
         CharSequence value = get0(name);
         return value == null ? null : INSTANCE.convertToShort(value);
     }
 
     @Override
     public short getShort(CharSequence name, short defaultValue) {
         CharSequence value = get0(name);
         return value == null ? defaultValue : INSTANCE.convertToShort(value);
     }
 
     @Override
     public Long getTimeMillis(CharSequence name) {
         CharSequence value = get0(name);
         if (value == null) {
             return null;
         }
         try {
             return INSTANCE.convertToTimeMillis(value);
         } catch (RuntimeException e) {
             return null;
         }
     }
 
     @Override
     public long getTimeMillis(CharSequence name, long defaultValue) {
         CharSequence value = get0(name);
         if (value == null) {
             return defaultValue;
         }
         try {
             return INSTANCE.convertToTimeMillis(value);
         } catch (RuntimeException e) {
             return defaultValue;
         }
     }
 
     @Override
     public List<String> getAll(String name) {
         if (isEmpty()) {
             return Collections.emptyList();
         }
         final int nameHash = AsciiString.hashCode(name);
         List<String> values = new ArrayList<>(4);
         for (int i = 0; i < nameValuePairs.length; i += 2) {
             CharSequence roName = nameValuePairs[i];
             if (AsciiString.hashCode(roName) == nameHash && contentEqualsIgnoreCase(roName, name)) {
                 values.add(nameValuePairs[i + 1].toString()); // lgtm[java/index-out-of-bounds]
             }
         }
         return values;
     }
 
     @Override
     public List<Map.Entry<String, String>> entries() {
         if (isEmpty()) {
             return Collections.emptyList();
         }
         List<Map.Entry<String, String>> entries = new ArrayList<>(size());
         for (int i = 0; i < nameValuePairs.length; i += 2) {
             entries.add(new SimpleImmutableEntry<>(nameValuePairs[i].toString(),
                     nameValuePairs[i + 1].toString())); // lgtm[java/index-out-of-bounds]
         }
         return entries;
     }
 
     @Override
     public boolean contains(String name) {
         return get0(name) != null;
     }
 
     @Override
     public boolean contains(String name, String value, boolean ignoreCase) {
         return containsValue(name, value, ignoreCase);
     }
 
     @Override
     public boolean containsValue(CharSequence name, CharSequence value, boolean ignoreCase) {
         if (ignoreCase) {
             for (int i = 0; i < nameValuePairs.length; i += 2) {
                 if (contentEqualsIgnoreCase(nameValuePairs[i], name) &&
                         contentEqualsIgnoreCase(nameValuePairs[i + 1], value)) { // lgtm[java/index-out-of-bounds]
                     return true;
                 }
             }
         } else {
             for (int i = 0; i < nameValuePairs.length; i += 2) {
                 if (contentEqualsIgnoreCase(nameValuePairs[i], name) &&
                         contentEquals(nameValuePairs[i + 1], value)) { // lgtm[java/index-out-of-bounds]
                     return true;
                 }
             }
         }
         return false;
     }
 
     @Override
     public Iterator<String> valueStringIterator(CharSequence name) {
         return new ReadOnlyStringValueIterator(name);
     }
 
     @Override
     public Iterator<CharSequence> valueCharSequenceIterator(CharSequence name) {
         return new ReadOnlyValueIterator(name);
     }
 
     @Override
     public Iterator<Map.Entry<String, String>> iterator() {
         return new ReadOnlyStringIterator();
     }
 
     @Override
     public Iterator<Map.Entry<CharSequence, CharSequence>> iteratorCharSequence() {
         return new ReadOnlyIterator();
     }
 
     @Override
     public boolean isEmpty() {
         return nameValuePairs.length == 0;
     }
 
     @Override
     public int size() {
         return nameValuePairs.length >>> 1;
     }
 
     @Override
     public Set<String> names() {
         if (isEmpty()) {
             return Collections.emptySet();
         }
         Set<String> names = new LinkedHashSet<>(size());
         for (int i = 0; i < nameValuePairs.length; i += 2) {
             names.add(nameValuePairs[i].toString());
         }
         return names;
     }
 
     @Override
     public HttpHeaders add(String name, Object value) {
         throw new UnsupportedOperationException("read only");
     }
 
     @Override
     public HttpHeaders add(String name, Iterable<?> values) {
         throw new UnsupportedOperationException("read only");
     }
 
     @Override
     public HttpHeaders addInt(CharSequence name, int value) {
         throw new UnsupportedOperationException("read only");
     }
 
     @Override
     public HttpHeaders addShort(CharSequence name, short value) {
         throw new UnsupportedOperationException("read only");
     }
 
     @Override
     public HttpHeaders set(String name, Object value) {
         throw new UnsupportedOperationException("read only");
     }
 
     @Override
     public HttpHeaders set(String name, Iterable<?> values) {
         throw new UnsupportedOperationException("read only");
     }
 
     @Override
     public HttpHeaders setInt(CharSequence name, int value) {
         throw new UnsupportedOperationException("read only");
     }
 
     @Override
     public HttpHeaders setShort(CharSequence name, short value) {
         throw new UnsupportedOperationException("read only");
     }
 
     @Override
     public HttpHeaders remove(String name) {
         throw new UnsupportedOperationException("read only");
     }
 
     @Override
     public HttpHeaders clear() {
         throw new UnsupportedOperationException("read only");
     }
 
     private final class ReadOnlyIterator implements Map.Entry<CharSequence, CharSequence>,
             Iterator<Map.Entry<CharSequence, CharSequence>> {
         private CharSequence key;
         private CharSequence value;
         private int nextNameIndex;
 
         @Override
         public boolean hasNext() {
             return nextNameIndex != nameValuePairs.length;
         }
 
         @Override
         public Map.Entry<CharSequence, CharSequence> next() {
             if (!hasNext()) {
                 throw new NoSuchElementException();
             }
             key = nameValuePairs[nextNameIndex];
             value = nameValuePairs[nextNameIndex + 1];
             nextNameIndex += 2;
             return this;
         }
 
         @Override
         public void remove() {
             throw new UnsupportedOperationException("read only");
         }
 
         @Override
         public CharSequence getKey() {
             return key;
         }
 
         @Override
         public CharSequence getValue() {
             return value;
         }
 
         @Override
         public CharSequence setValue(CharSequence value) {
             throw new UnsupportedOperationException("read only");
         }
 
         @Override
         public String toString() {
             return key.toString() + '=' + value.toString();
         }
     }
 
     private final class ReadOnlyStringIterator implements Map.Entry<String, String>,
             Iterator<Map.Entry<String, String>> {
         private String key;
         private String value;
         private int nextNameIndex;
 
         @Override
         public boolean hasNext() {
             return nextNameIndex != nameValuePairs.length;
         }
 
         @Override
         public Map.Entry<String, String> next() {
             if (!hasNext()) {
                 throw new NoSuchElementException();
             }
             key = nameValuePairs[nextNameIndex].toString();
             value = nameValuePairs[nextNameIndex + 1].toString();
             nextNameIndex += 2;
             return this;
         }
 
         @Override
         public void remove() {
             throw new UnsupportedOperationException("read only");
         }
 
         @Override
         public String getKey() {
             return key;
         }
 
         @Override
         public String getValue() {
             return value;
         }
 
         @Override
         public String setValue(String value) {
             throw new UnsupportedOperationException("read only");
         }
 
         @Override
         public String toString() {
             return key + '=' + value;
         }
     }
 
     private final class ReadOnlyStringValueIterator implements Iterator<String> {
         private final CharSequence name;
         private final int nameHash;
         private int nextNameIndex;
 
         ReadOnlyStringValueIterator(CharSequence name) {
             this.name = name;
             nameHash = AsciiString.hashCode(name);
             nextNameIndex = findNextValue();
         }
 
         @Override
         public boolean hasNext() {
             return nextNameIndex != -1;
         }
 
         @Override
         public String next() {
             if (!hasNext()) {
                 throw new NoSuchElementException();
             }
             String value = nameValuePairs[nextNameIndex + 1].toString();
             nextNameIndex = findNextValue();
             return value;
         }
 
         @Override
         public void remove() {
             throw new UnsupportedOperationException("read only");
         }
 
         private int findNextValue() {
             for (int i = nextNameIndex; i < nameValuePairs.length; i += 2) {
                 final CharSequence roName = nameValuePairs[i];
                 if (nameHash == AsciiString.hashCode(roName) && contentEqualsIgnoreCase(name, roName)) {
                     return i;
                 }
             }
             return -1;
         }
     }
 
     private final class ReadOnlyValueIterator implements Iterator<CharSequence> {
         private final CharSequence name;
         private final int nameHash;
         private int nextNameIndex;
 
         ReadOnlyValueIterator(CharSequence name) {
             this.name = name;
             nameHash = AsciiString.hashCode(name);
             nextNameIndex = findNextValue();
         }
 
         @Override
         public boolean hasNext() {
             return nextNameIndex != -1;
         }
 
         @Override
         public CharSequence next() {
             if (!hasNext()) {
                 throw new NoSuchElementException();
             }
             CharSequence value = nameValuePairs[nextNameIndex + 1];
             nextNameIndex = findNextValue();
             return value;
         }
 
         @Override
         public void remove() {
             throw new UnsupportedOperationException("read only");
         }
 
         private int findNextValue() {
             for (int i = nextNameIndex; i < nameValuePairs.length; i += 2) {
                 final CharSequence roName = nameValuePairs[i];
                 if (nameHash == AsciiString.hashCode(roName) && contentEqualsIgnoreCase(name, roName)) {
                     return i;
                 }
             }
             return -1;
         }
     }
 }