/*
 * Copyright (C) 2006 Google Inc.
 *
 * 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.inject.internal;

import com.google.inject.internal.InjectorImpl.InjectorOptions;
import com.google.inject.spi.Dependency;
import java.util.IdentityHashMap;
import java.util.Map;

Internal context. Used to coordinate injections and support circular dependencies.
Author:
crazybob@google.com (Bob Lee)/**
 * Internal context. Used to coordinate injections and support circular dependencies.
 *
 * @author crazybob@google.com (Bob Lee)
 */
final class InternalContext implements AutoCloseable {

  private final InjectorOptions options;

  private final Map<Object, ConstructionContext<?>> constructionContexts =
      new IdentityHashMap<Object, ConstructionContext<?>>();

  
Keeps track of the type that is currently being requested for injection. /** Keeps track of the type that is currently being requested for injection. */
  private Dependency<?> dependency;

  
Keeps track of the hierarchy of types needed during injection.
This is a pairwise combination of dependencies and sources, with dependencies or keys on
even indices, and sources on odd indices. This structure is to avoid the memory overhead of
DependencyAndSource objects, which can add to several tens of megabytes in large applications.
/**
   * Keeps track of the hierarchy of types needed during injection.
   *
   * <p>This is a pairwise combination of dependencies and sources, with dependencies or keys on
   * even indices, and sources on odd indices. This structure is to avoid the memory overhead of
   * DependencyAndSource objects, which can add to several tens of megabytes in large applications.
   */
  private Object[] dependencyStack = new Object[16];

  private int dependencyStackSize = 0;


  
The number of times enter() has been called + 1 for initial construction. This value is decremented when exit() is called. /**
   * The number of times {@link #enter()} has been called + 1 for initial construction. This value
   * is decremented when {@link #exit()} is called.
   */
  private int enterCount;

  
A single element array to clear when the enterCount hits 0. 
This is the value stored in the InjectorImpl.localContext thread local. /**
   * A single element array to clear when the {@link #enterCount} hits {@code 0}.
   *
   * <p>This is the value stored in the {@code InjectorImpl.localContext} thread local.
   */
  private final Object[] toClear;

  InternalContext(InjectorOptions options, Object[] toClear) {
    this.options = options;
    this.toClear = toClear;
    this.enterCount = 1;
  }

  
Should only be called by InjectorImpl.enterContext(). /** Should only be called by InjectorImpl.enterContext(). */
  void enter() {
    enterCount++;
  }

  
Should be called any any method that received an instance via InjectorImpl.enterContext(). /** Should be called any any method that received an instance via InjectorImpl.enterContext(). */
  @Override
  public void close() {
    int newCount = --enterCount;
    if (newCount < 0) {
      throw new IllegalStateException("Called close() too many times");
    }
    if (newCount == 0) {
      toClear[0] = null;
    }
  }

  InjectorOptions getInjectorOptions() {
    return options;
  }

  @SuppressWarnings("unchecked")
  <T> ConstructionContext<T> getConstructionContext(Object key) {
    ConstructionContext<T> constructionContext =
        (ConstructionContext<T>) constructionContexts.get(key);
    if (constructionContext == null) {
      constructionContext = new ConstructionContext<>();
      constructionContexts.put(key, constructionContext);
    }
    return constructionContext;
  }

  Dependency<?> getDependency() {
    return dependency;
  }

  
Sets the new current dependency & adds it to the state. /** Sets the new current dependency & adds it to the state. */
  Dependency<?> pushDependency(Dependency<?> dependency, Object source) {
    Dependency<?> previous = this.dependency;
    this.dependency = dependency;
    doPushState(dependency, source);
    return previous;
  }


  
Pops the current state & sets the new dependency. /** Pops the current state & sets the new dependency. */
  void popStateAndSetDependency(Dependency<?> newDependency) {
    popState();
    this.dependency = newDependency;
  }


  
Adds to the state without setting the dependency. /** Adds to the state without setting the dependency. */
  void pushState(com.google.inject.Key<?> key, Object source) {
    doPushState(key, source);
  }


  private void doPushState(Object dependencyOrKey, Object source) {
    int localSize = dependencyStackSize;
    Object[] localStack = dependencyStack;
    if (localStack.length < localSize + 2) {
      localStack = dependencyStack =
        java.util.Arrays.copyOf(localStack, (localStack.length * 3) / 2 + 2);
    }
    localStack[localSize++] = dependencyOrKey;
    localStack[localSize++] = source;
    dependencyStackSize = localSize;
  }


  
Pops from the state without setting a dependency. /** Pops from the state without setting a dependency. */
  void popState() {
    // N.B. we don't null out the array entries.  It isn't necessary since all the objects in the
    // array (Key, Dependency, or Binding source objects) are all tied to the lifetime of the
    // injector, which is greater than the lifetime of this object.  So removing them from the array
    // doesn't matter.
    dependencyStackSize -= 2;
  }


  
Returns the current dependency chain (all the state stored in the dependencyStack). /** Returns the current dependency chain (all the state stored in the dependencyStack). */
  java.util.List<com.google.inject.spi.DependencyAndSource> getDependencyChain() {
    com.google.common.collect.ImmutableList.Builder<com.google.inject.spi.DependencyAndSource>
        builder = com.google.common.collect.ImmutableList.builder();
    for (int i = 0; i < dependencyStackSize; i += 2) {
      Object evenEntry = dependencyStack[i];
      Dependency<?> dependency;
      if (evenEntry instanceof com.google.inject.Key) {
        dependency = Dependency.get((com.google.inject.Key<?>) evenEntry);
      } else {
        dependency = (Dependency<?>) evenEntry;
      }
      builder.add(new com.google.inject.spi.DependencyAndSource(dependency, dependencyStack[i + 1]));
    }
    return builder.build();
  }

}