/*
 * Copyright (c) 2012, the Dart project authors.
 * 
 * Licensed under the Eclipse Public License v1.0 (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.eclipse.org/legal/epl-v10.html
 * 
 * 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.dart.engine.internal.type;

import com.google.dart.engine.element.TypeParameterElement;
import com.google.dart.engine.internal.element.ElementPair;
import com.google.dart.engine.type.Type;
import com.google.dart.engine.type.TypeParameterType;
import com.google.dart.engine.utilities.general.ObjectUtilities;

import java.util.HashSet;
import java.util.Set;

/**
 * Instances of the class {@code TypeParameterTypeImpl} defines the behavior of objects representing
 * the type introduced by a type parameter.
 * 
 * @coverage dart.engine.type
 */
public class TypeParameterTypeImpl extends TypeImpl implements TypeParameterType {
  /**
   * An empty array of type parameter types.
   */
  public static final TypeParameterType[] EMPTY_ARRAY = new TypeParameterType[0];

  /**
   * Return an array containing the type parameter types defined by the given array of type
   * parameter elements.
   * 
   * @param typeParameters the type parameter elements defining the type parameter types to be
   *          returned
   * @return the type parameter types defined by the type parameter elements
   */
  public static TypeParameterType[] getTypes(TypeParameterElement[] typeParameters) {
    int count = typeParameters.length;
    if (count == 0) {
      return EMPTY_ARRAY;
    }
    TypeParameterType[] types = new TypeParameterType[count];
    for (int i = 0; i < count; i++) {
      types[i] = typeParameters[i].getType();
    }
    return types;
  }

  /**
   * Initialize a newly created type parameter type to be declared by the given element and to have
   * the given name.
   * 
   * @param element the element representing the declaration of the type parameter
   */
  public TypeParameterTypeImpl(TypeParameterElement element) {
    super(element, element.getName());
  }

  @Override
  public boolean equals(Object object) {
    return object instanceof TypeParameterTypeImpl
        && ObjectUtilities.equals(getElement(), ((TypeParameterTypeImpl) object).getElement());
  }

  @Override
  public TypeParameterElement getElement() {
    return (TypeParameterElement) super.getElement();
  }

  @Override
  public int hashCode() {
    return getElement().hashCode();
  }

  @Override
  public Type substitute(Type[] argumentTypes, Type[] parameterTypes) {
    int length = parameterTypes.length;
    for (int i = 0; i < length; i++) {
      if (parameterTypes[i].equals(this)) {
        return argumentTypes[i];
      }
    }
    return this;
  }

  @Override
  protected boolean internalEquals(Object object, Set<ElementPair> visitedElementPairs) {
    return equals(object);
  }

  @Override
  protected boolean internalIsMoreSpecificThan(Type s, boolean withDynamic,
      Set<TypePair> visitedTypePairs) {
    //
    // A type T is more specific than a type S, written T << S,  if one of the following conditions
    // is met:
    //
    // Reflexivity: T is S.
    //
    if (this.equals(s)) {
      return true;
    }

    // S is dynamic.
    //
    if (s.isDynamic()) {
      return true;
    }

    return isMoreSpecificThan(s, new HashSet<Type>(), withDynamic, visitedTypePairs);
  }

  @Override
  protected boolean internalIsSubtypeOf(Type type, Set<TypePair> visitedTypePairs) {
    return isMoreSpecificThan(type, true, new HashSet<TypePair>());
  }

  private boolean isMoreSpecificThan(Type s, Set<Type> visitedTypes, boolean withDynamic,
      Set<TypePair> visitedTypePairs) {
    //
    // T is a type parameter and S is the upper bound of T.
    //
    Type bound = getElement().getBound();
    if (s.equals(bound)) {
      return true;
    }

    //
    // T is a type parameter and S is Object.
    //
    if (s.isObject()) {
      return true;
    }

    // We need upper bound to continue.
    if (bound == null) {
      return false;
    }

    //
    // Transitivity: T << U and U << S.
    //
    if (bound instanceof TypeParameterTypeImpl) {
      TypeParameterTypeImpl boundTypeParameter = (TypeParameterTypeImpl) bound;
      // First check for infinite loops
      if (visitedTypes.contains(bound)) {
        return false;
      }
      visitedTypes.add(bound);
      // Then check upper bound.
      return boundTypeParameter.isMoreSpecificThan(s, visitedTypes, withDynamic, visitedTypePairs);
    }

    // Check interface type.
    return ((TypeImpl) bound).isMoreSpecificThan(s, withDynamic, visitedTypePairs);
  }
}