/*
 * Copyright (C) 2011 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.jack.dx.dex;

/**
 * Constants that show up in and are otherwise related to {@code .dex}
 * files, and helper methods for same.
 */
public final class DexFormat {
  private DexFormat() {}

  /**
   * API level to target in order to produce the most modern file
   * format
   */
  public static final int API_CURRENT = 14;

  /** API level to target in order to suppress extended opcode usage */
  public static final int API_NO_EXTENDED_OPCODES = 13;

  /**
   * file name of the primary {@code .dex} file inside an
   * application or library {@code .jar} file
   */
  public static final String DEX_IN_JAR_NAME = "classes.dex";

  /** common prefix for all dex file "magic numbers" */
  public static final String MAGIC_PREFIX = "dex\n";

  /** common suffix for all dex file "magic numbers" */
  public static final String MAGIC_SUFFIX = "\0";

  /** dex file version number for the current format variant */
  public static final String VERSION_CURRENT = "036";

  /** dex file version number for API level 13 and earlier */
  public static final String VERSION_FOR_API_13 = "035";

  /**
   * value used to indicate endianness of file contents
   */
  public static final int ENDIAN_TAG = 0x12345678;

  /**
   * Maximum addressable field or method index.
   * The largest addressable member is 0xffff, in the "instruction formats" spec as field@CCCC or
   * meth@CCCC.
   */
  public static final int MAX_MEMBER_IDX = 0xFFFF;

  /**
   * Maximum addressable type index.
   * The largest addressable type is 0xffff, in the "instruction formats" spec as type@CCCC.
   */
  public static final int MAX_TYPE_IDX = 0xFFFF;

  /**
   * Returns the API level corresponding to the given magic number,
   * or {@code -1} if the given array is not a well-formed dex file
   * magic number.
   */
  public static int magicToApi(byte[] magic) {
    if (magic.length != 8) {
      return -1;
    }

    if ((magic[0] != 'd') || (magic[1] != 'e') || (magic[2] != 'x') || (magic[3] != '\n')
        || (magic[7] != '\0')) {
      return -1;
    }

    String version = "" + ((char) magic[4]) + ((char) magic[5]) + ((char) magic[6]);

    if (version.equals(VERSION_CURRENT)) {
      return API_CURRENT;
    } else if (version.equals(VERSION_FOR_API_13)) {
      return 13;
    }

    return -1;
  }

  /**
   * Returns the magic number corresponding to the given target API level.
   */
  public static String apiToMagic(int targetApiLevel) {
    String version;

    if (targetApiLevel >= API_CURRENT) {
      version = VERSION_CURRENT;
    } else {
      version = VERSION_FOR_API_13;
    }

    return MAGIC_PREFIX + version + MAGIC_SUFFIX;
  }
}