// Copyright 2015 The Bazel Authors. All rights reserved.
//
// 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.devtools.build.zip;

import java.io.IOException;
import java.io.InputStream;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.zip.ZipException;

/** A utility class for reading and writing {@link ZipFileEntry}s from byte arrays. */
public class ZipUtil {

  /**
   * Midnight Jan 1st 1980. Uses the current time zone as the DOS format does not support time zones
   * and will always assume the current zone.
   */
  public static final long DOS_EPOCH =
      new GregorianCalendar(1980, Calendar.JANUARY, 1, 0, 0, 0).getTimeInMillis();

  /** 23:59:59 Dec 31st 2107. The maximum date representable in DOS format. */
  public static final long MAX_DOS_DATE =
      new GregorianCalendar(2107, Calendar.DECEMBER, 31, 23, 59, 59).getTimeInMillis();

  /* DOS format timestamp field offsets. */
  private static final int DOS_MINUTE_OFFSET = 5;
  private static final int DOS_HOUR_OFFSET = 11;
  private static final int DOS_DAY_OFFSET = 16;
  private static final int DOS_MONTH_OFFSET = 21;
  private static final int DOS_YEAR_OFFSET = 25;

  /** Converts a integral value to the corresponding little endian array. */
  private static byte[] integerToLittleEndian(byte[] buf, int offset, long value, int numBytes) {
    for (int i = 0; i < numBytes; i++) {
      buf[i + offset] = (byte) ((value & (0xffL << (i * 8))) >> (i * 8));
    }
    return buf;
  }

  /** Converts a short to the corresponding 2-byte little endian array. */
  static byte[] shortToLittleEndian(short value) {
    return integerToLittleEndian(new byte[2], 0, value, 2);
  }

  /** Writes a short to the buffer as a 2-byte little endian array starting at offset. */
  static byte[] shortToLittleEndian(byte[] buf, int offset, short value) {
    return integerToLittleEndian(buf, offset, value, 2);
  }

  /** Converts an int to the corresponding 4-byte little endian array. */
  static byte[] intToLittleEndian(int value) {
    return integerToLittleEndian(new byte[4], 0, value, 4);
  }

  /** Writes an int to the buffer as a 4-byte little endian array starting at offset. */
  static byte[] intToLittleEndian(byte[] buf, int offset, int value) {
    return integerToLittleEndian(buf, offset, value, 4);
  }

  /** Converts a long to the corresponding 8-byte little endian array. */
  static byte[] longToLittleEndian(long value) {
    return integerToLittleEndian(new byte[8], 0, value, 8);
  }

  /** Writes a long to the buffer as a 8-byte little endian array starting at offset. */
  static byte[] longToLittleEndian(byte[] buf, int offset, long value) {
    return integerToLittleEndian(buf, offset, value, 8);
  }

  /** Reads 16 bits in little-endian byte order from the buffer at the given offset. */
  static short get16(byte[] source, int offset) {
    int a = source[offset + 0] & 0xff;
    int b = source[offset + 1] & 0xff;
    return (short) ((b << 8) | a);
  }

  /** Reads 32 bits in little-endian byte order from the buffer at the given offset. */
  static int get32(byte[] source, int offset) {
    int a = source[offset + 0] & 0xff;
    int b = source[offset + 1] & 0xff;
    int c = source[offset + 2] & 0xff;
    int d = source[offset + 3] & 0xff;
    return (d << 24) | (c << 16) | (b << 8) | a;
  }

  /** Reads 64 bits in little-endian byte order from the buffer at the given offset. */
  static long get64(byte[] source, int offset) {
    long a = source[offset + 0] & 0xffL;
    long b = source[offset + 1] & 0xffL;
    long c = source[offset + 2] & 0xffL;
    long d = source[offset + 3] & 0xffL;
    long e = source[offset + 4] & 0xffL;
    long f = source[offset + 5] & 0xffL;
    long g = source[offset + 6] & 0xffL;
    long h = source[offset + 7] & 0xffL;
    return (h << 56) | (g << 48) | (f << 40) | (e << 32) | (d << 24) | (c << 16) | (b << 8) | a;
  }

  /**
   * Reads an unsigned short in little-endian byte order from the buffer at the given offset.
   * Casts to an int to allow proper numerical comparison.
   */
  static int getUnsignedShort(byte[] source, int offset) {
    return get16(source, offset) & 0xffff;
  }

  /**
   * Reads an unsigned int in little-endian byte order from the buffer at the given offset.
   * Casts to a long to allow proper numerical comparison.
   */
  static long getUnsignedInt(byte[] source, int offset) {
    return get32(source, offset) & 0xffffffffL;
  }

  /**
   * Reads an unsigned long in little-endian byte order from the buffer at the given offset.
   * Performs bounds checking to see if the unsigned long will be properly represented in Java's
   * signed value.
   */
  static long getUnsignedLong(byte[] source, int offset) throws ZipException {
    long result = get64(source, offset);
    if (result < 0) {
      throw new ZipException("The requested unsigned long value is too large for Java's signed"
          + "values. This Zip file is unsupported");
    }
    return result;
  }

  /** Checks if the unix timestamp is representable as a valid DOS timestamp.
   *
   * <p>See <a href="http://www.pkware.com/documents/casestudies/APPNOTE.TXT">ZIP Format</a> for
   * a general description of the date a time fields (Section 4.4.6) and
   * <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/ms724247.aspx">DOS date
   * format</a> for a detailed description of the format.
   */
  static boolean isValidInDos(long timeMillis) {
    Calendar time = Calendar.getInstance();
    time.setTimeInMillis(timeMillis);
    Calendar minTime = Calendar.getInstance();
    minTime.setTimeInMillis(DOS_EPOCH);
    Calendar maxTime = Calendar.getInstance();
    maxTime.setTimeInMillis(MAX_DOS_DATE);
    return (!time.before(minTime) && !time.after(maxTime));
  }

  /** Converts a unix timestamp into a 32-bit DOS timestamp. */
  static int unixToDosTime(long timeMillis) {
    Calendar time = Calendar.getInstance();
    time.setTimeInMillis(timeMillis);

    if (!isValidInDos(timeMillis)) {
      DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
      throw new IllegalArgumentException(String.format("%s is not representable in the DOS time"
          + " format. It must be in the range %s to %s", df.format(time.getTime()),
          df.format(new Date(DOS_EPOCH)), df.format(new Date(MAX_DOS_DATE))));
    }

    int dos = time.get(Calendar.SECOND) / 2;
    dos |= time.get(Calendar.MINUTE) << DOS_MINUTE_OFFSET;
    dos |= time.get(Calendar.HOUR_OF_DAY) << DOS_HOUR_OFFSET;
    dos |= time.get(Calendar.DAY_OF_MONTH) << DOS_DAY_OFFSET;
    dos |= (time.get(Calendar.MONTH) + 1) << DOS_MONTH_OFFSET;
    dos |= (time.get(Calendar.YEAR) - 1980) << DOS_YEAR_OFFSET;
    return dos;
  }

  /** Converts a 32-bit DOS timestamp into a unix timestamp. */
  static long dosToUnixTime(int timestamp) {
    Calendar time = Calendar.getInstance();
    time.clear();
    time.set(Calendar.SECOND, (timestamp & 0x1f) * 2);
    time.set(Calendar.MINUTE, (timestamp >> DOS_MINUTE_OFFSET) & 0x3f);
    time.set(Calendar.HOUR_OF_DAY, (timestamp >> DOS_HOUR_OFFSET) & 0x1f);
    time.set(Calendar.DAY_OF_MONTH, (timestamp >> DOS_DAY_OFFSET) & 0x1f);
    time.set(Calendar.MONTH, ((timestamp >> DOS_MONTH_OFFSET) & 0x0f) - 1);
    time.set(Calendar.YEAR, ((timestamp >> DOS_YEAR_OFFSET) & 0x7f) + 1980);
    return time.getTimeInMillis();
  }

  /** Checks if array starts with target. */
  static boolean arrayStartsWith(byte[] array, byte[] target) {
    if (array == null) {
      return false;
    }
    if (target == null) {
      return true;
    }
    if (target.length > array.length) {
      return false;
    }
    for (int i = 0; i < target.length; i++) {
      if (array[i] != target[i]) {
        return false;
      }
    }
    return true;
  }

  /** Read from the input stream into the array until it is full. */
  static int readFully(InputStream in, byte[] b) throws IOException {
    return readFully(in, b, 0, b.length);
  }

  /** Read from the input stream into the array starting at off until len bytes have been read. */
  static int readFully(InputStream in, byte[] b, int off, int len) throws IOException {
    if (len < 0) {
      throw new IndexOutOfBoundsException();
    }
    int n = 0;
    while (n < len) {
      int count = in.read(b, off + n, len - n);
      if (count < 0) {
        return n;
      }
      n += count;
    }
    return n;
  }
}