/**
 * Copyright 2010 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 org.waveprotocol.wave.client.paging;

import static junit.framework.Assert.assertFalse;
import static junit.framework.Assert.assertTrue;

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

/**
 * Validates the invariants of an active region with respect to a block
 * structure.
 *
 */
public final class ActiveRegionValidator {

  private final FakeBlock root;
  private final ActiveRegion target;

  private ActiveRegionValidator(FakeBlock root, ActiveRegion target) {
    this.root = root;
    this.target = target;
  }

  /**
   * Checks invariants of the active region. In particular, the ancestor chain
   * of all points inclusively between its start and end are paged in.
   */
  public static void validate(FakeBlock root, ActiveRegion target) {
    new ActiveRegionValidator(root, target).checkActiveRegion();
  }

  private void checkActiveRegion() {
    Set<FakeBlock> unchecked = new HashSet<FakeBlock>(root.collect());
    SimpleMoveablePoint active = SimpleMoveablePoint.at(target.getStart());

    checkPagedIn((FakeBlock) active.block, unchecked);
    while (!active.equals(target.getEnd())) {
      active.next();
      checkPagedIn((FakeBlock) active.block, unchecked);
    }

    // All remaining blocks should be unpaged.
    for (FakeBlock block : unchecked) {
      assertFalse(block.isPagedIn());
    }
  }

  private void checkPagedIn(FakeBlock block, Collection<FakeBlock> unchecked) {
    if (unchecked.contains(block)) {
      assertTrue(block.isPagedIn());
      unchecked.remove(block);

      checkPagedIn(block.getParent(), unchecked);
    }
  }
}