/*
    * Copyright (C) 2012 The Guava Authors
    *
    * 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.google.common.reflect;
  
  import com.google.common.annotations.Beta;
  import com.google.common.collect.ForwardingMap;
  import com.google.common.collect.ImmutableMap;
  
  import java.util.Map;
  
  /**
   * A type-to-instance map backed by an {@link ImmutableMap}. See also {@link
   * MutableTypeToInstanceMap}.
   *
   * @author Ben Yu
   * @since 13.0
   */
  @Beta
  public final class ImmutableTypeToInstanceMap<B> extends ForwardingMap<TypeToken<? extends B>, B>
      implements TypeToInstanceMap<B> {
  
    /** Returns an empty type to instance map. */
    public static <B> ImmutableTypeToInstanceMap<B> of() {
      return new ImmutableTypeToInstanceMap<B>(ImmutableMap.<TypeToken<? extends B>, B>of());
    }
  
    /** Returns a new builder. */
    public static <B> Builder<B> builder() {
      return new Builder<B>();
    }
  
    /**
     * A builder for creating immutable type-to-instance maps. Example:
     * <pre>   {@code
     *
     *   static final ImmutableTypeToInstanceMap<Handler<?>> HANDLERS =
     *       ImmutableTypeToInstanceMap.<Handler<?>>builder()
     *           .put(new TypeToken<Handler<Foo>>() {}, new FooHandler())
     *           .put(new TypeToken<Handler<Bar>>() {}, new SubBarHandler())
     *           .build();}</pre>
     *
     * <p>After invoking {@link #build()} it is still possible to add more entries
     * and build again. Thus each map generated by this builder will be a superset
     * of any map generated before it.
     *
     * @since 13.0
     */
    @Beta
    public static final class Builder<B> {
      private final ImmutableMap.Builder<TypeToken<? extends B>, B> mapBuilder
          = ImmutableMap.builder();
  
      private Builder() {}
  
      /**
       * Associates {@code key} with {@code value} in the built map. Duplicate
       * keys are not allowed, and will cause {@link #build} to fail.
       */
      public <T extends B> Builder<B> put(Class<T> key, T value) {
        mapBuilder.put(TypeToken.of(key), value);
        return this;
      }
  
      /**
       * Associates {@code key} with {@code value} in the built map. Duplicate
       * keys are not allowed, and will cause {@link #build} to fail.
       */
      public <T extends B> Builder<B> put(TypeToken<T> key, T value) {
        mapBuilder.put(key.rejectTypeVariables(), value);
        return this;
      }
  
      /**
       * Returns a new immutable type-to-instance map containing the entries
       * provided to this builder.
       *
       * @throws IllegalArgumentException if duplicate keys were added
       */
      public ImmutableTypeToInstanceMap<B> build() {
        return new ImmutableTypeToInstanceMap<B>(mapBuilder.build());
      }
    }
  
    private final ImmutableMap<TypeToken<? extends B>, B> delegate;
  
   private ImmutableTypeToInstanceMap(ImmutableMap<TypeToken<? extends B>, B> delegate) {
     this.delegate = delegate;
   }
 
   @Override public <T extends B> T getInstance(TypeToken<T> type) {
     return trustedGet(type.rejectTypeVariables());
   }
 
   /**
    * Guaranteed to throw an exception and leave the map unmodified.
    *
    * @throws UnsupportedOperationException always
    */
   @Override public <T extends B> T putInstance(TypeToken<T> type, T value) {
     throw new UnsupportedOperationException();
   }
 
   @Override public <T extends B> T getInstance(Class<T> type) {
     return trustedGet(TypeToken.of(type));
   }
 
   /**
    * Guaranteed to throw an exception and leave the map unmodified.
    *
    * @throws UnsupportedOperationException always
    */
   @Override public <T extends B> T putInstance(Class<T> type, T value) {
     throw new UnsupportedOperationException();
   }
 
   @Override protected Map<TypeToken<? extends B>, B> delegate() {
     return delegate;
   }
 
   @SuppressWarnings("unchecked") // value could not get in if not a T
   private <T extends B> T trustedGet(TypeToken<T> type) {
     return (T) delegate.get(type);
   }
 }