/*
    * 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.
   */
  package org.eclipse.aether.util.graph.manager;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.HashMap;
  
  /**
   * Warning: this is a special map-like construct that suits only and should be used only in this package!
   * It has the following properties:
   * <ul>
   *     <li>memorizes once calculated hashCode</li>
   *     <li>once hashCode calculated, goes into "read only" mode (put method will fail)</li>
   *     <li>otherwise all the rest is same as for {@link HashMap}</li>
   * </ul>
   *
   * This class is not a generic map class; only those methods are "protected" that are in use in this very
   * package.
   *
   * @param <K>
   * @param <V>
   */
  public class MMap<K, V> {
      private static final MMap<?, ?> EMPTY_MAP = new MMap<>(new HashMap<>(0)).done();
  
      @SuppressWarnings("unchecked")
      public static <K, V> MMap<K, V> empty() {
          return (MMap<K, V>) MMap.EMPTY_MAP;
      }
  
      public static <K, V> MMap<K, V> copy(MMap<K, V> orig) {
          return new MMap<>(new HashMap<>(orig.delegate));
      }
  
      public static <K, V> MMap<K, Collection<V>> copyWithKey(K key, MMap<K, Collection<V>> orig) {
          HashMap<K, Collection<V>> delegateLocal = new HashMap<>(orig.delegate);
          delegateLocal.computeIfPresent(key, (k, v) -> new ArrayList<>(v));
          return new MMap<>(delegateLocal);
      }
  
      protected final HashMap<K, V> delegate;
  
      private MMap(HashMap<K, V> delegate) {
          this.delegate = delegate;
      }
  
      public boolean containsKey(K key) {
          return delegate.containsKey(key);
      }
  
      public V get(K key) {
          return delegate.get(key);
      }
  
      public V put(K key, V value) {
          return delegate.put(key, value);
      }
  
      public MMap<K, V> done() {
          return new DoneMMap<>(delegate);
      }
  
      @Override
      public int hashCode() {
          throw new IllegalStateException("MMap is not done yet");
      }
  
      @Override
      public boolean equals(Object o) {
          throw new IllegalStateException("MMap is not done yet");
      }
  
      private static class DoneMMap<K, V> extends MMap<K, V> {
          private final int hashCode;
  
          private DoneMMap(HashMap<K, V> delegate) {
              super(delegate);
              this.hashCode = delegate.hashCode();
          }
  
          @Override
          public V put(K key, V value) {
             throw new IllegalStateException("Done MMap is immutable");
         }
 
         @Override
         public MMap<K, V> done() {
             return this;
         }
 
         @Override
         public int hashCode() {
             return hashCode;
         }
 
         @Override
         public boolean equals(Object o) {
             if (!(o instanceof MMap)) {
                 return false;
             }
             MMap<?, ?> other = (MMap<?, ?>) o;
             return delegate.equals(other.delegate);
         }
     }
 }