/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * 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.android.tools.build.apkzlib.zip;

import com.google.common.base.MoreObjects;
import com.google.common.base.Preconditions;
import com.google.common.primitives.Ints;
import java.util.Comparator;
import javax.annotation.Nullable;

/**
 * Represents an entry in the {@link FileUseMap}. Each entry contains an interval of bytes. The end
 * of the interval is exclusive.
 *
 * <p>Entries can either be free or used. Used entries <em>must</em> store an object. Free entries
 * do not store anything.
 *
 * <p>File map entries are used to keep track of which parts of a file map are used and not.
 *
 * @param <T> the type of data stored
 */
class FileUseMapEntry<T> {

  /** Comparator that compares entries by their start date. */
  public static final Comparator<FileUseMapEntry<?>> COMPARE_BY_START =
      (o1, o2) -> Ints.saturatedCast(o1.getStart() - o2.getStart());

  /** Comparator that compares entries by their size. */
  public static final Comparator<FileUseMapEntry<?>> COMPARE_BY_SIZE =
      (o1, o2) -> Ints.saturatedCast(o1.getSize() - o2.getSize());

  /** The first byte in the entry. */
  private final long start;

  /** The first byte no longer in the entry. */
  private final long end;

  /** The stored data. If {@code null} then this entry represents a free entry. */
  @Nullable private final T store;

  /**
   * Creates a new map entry.
   *
   * @param start the start of the entry
   * @param end the end of the entry (first byte no longer in the entry)
   * @param store the data to store in the entry or {@code null} if this is a free entry
   */
  private FileUseMapEntry(long start, long end, @Nullable T store) {
    Preconditions.checkArgument(start >= 0, "start < 0");
    Preconditions.checkArgument(end > start, "end <= start");

    this.start = start;
    this.end = end;
    this.store = store;
  }

  /**
   * Creates a new free entry.
   *
   * @param start the start of the entry
   * @param end the end of the entry (first byte no longer in the entry)
   * @return the entry
   */
  public static FileUseMapEntry<Object> makeFree(long start, long end) {
    return new FileUseMapEntry<>(start, end, null);
  }

  /**
   * Creates a new used entry.
   *
   * @param start the start of the entry
   * @param end the end of the entry (first byte no longer in the entry)
   * @param store the data to store in the entry
   * @param <T> the type of data to store in the entry
   * @return the entry
   */
  public static <T> FileUseMapEntry<T> makeUsed(long start, long end, T store) {
    Preconditions.checkNotNull(store, "store == null");
    return new FileUseMapEntry<>(start, end, store);
  }

  /**
   * Obtains the first byte in the entry.
   *
   * @return the first byte in the entry (if the same value as {@link #getEnd()} then the entry is
   *     empty and contains no data)
   */
  long getStart() {
    return start;
  }

  /**
   * Obtains the first byte no longer in the entry.
   *
   * @return the first byte no longer in the entry
   */
  long getEnd() {
    return end;
  }

  /**
   * Obtains the size of the entry.
   *
   * @return the number of bytes contained in the entry
   */
  long getSize() {
    return end - start;
  }

  /**
   * Determines if this is a free entry.
   *
   * @return is this entry free?
   */
  boolean isFree() {
    return store == null;
  }

  /**
   * Obtains the data stored in the entry.
   *
   * @return the data stored or {@code null} if this entry is a free entry
   */
  @Nullable
  T getStore() {
    return store;
  }

  @Override
  public String toString() {
    return MoreObjects.toStringHelper(this)
        .add("start", start)
        .add("end", end)
        .add("store", store)
        .toString();
  }
}