/*
 * Copyright 2017 The Closure Compiler 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.javascript.jscomp;

import static com.google.common.base.Preconditions.checkState;

import com.google.javascript.rhino.Node;
import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Memoize a scope creator.
 *
 * This allows you to make multiple passes, without worrying about
 * the expense of generating Scope objects over and over again.
 *
 * On the other hand, you also have to be more aware of what your passes
 * are doing. Scopes are memoized stupidly, so if the underlying tree
 * changes, the scope may be out of sync.
 */
class MemoizedScopeCreator implements ScopeCreator {

  private final Map<Node, AbstractScope<?, ?>> scopesByScopeRoot = new LinkedHashMap<>();
  private final ScopeCreator delegate;

  /**
   * @param delegate The real source of Scope objects.
   */
  MemoizedScopeCreator(ScopeCreator delegate) {
    this.delegate = delegate;
  }

  @Override
  public AbstractScope<?, ?> createScope(Node n, AbstractScope<?, ?> parent) {
    AbstractScope<?, ?> scope = scopesByScopeRoot.get(n);
    if (scope == null) {
      scope = delegate.createScope(n, parent);
      scopesByScopeRoot.put(n, scope);
    } else {
      checkState(parent == scope.getParent());
    }
    return scope;
  }
}
