// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

const int _UTF8_ONE_BYTE_MAX = 0x7f;
const int _UTF8_TWO_BYTE_MAX = 0x7ff;
const int _UTF8_THREE_BYTE_MAX = 0xffff;

const int _UTF8_LO_SIX_BIT_MASK = 0x3f;

const int _UTF8_FIRST_BYTE_OF_TWO_BASE = 0xc0;
const int _UTF8_FIRST_BYTE_OF_THREE_BASE = 0xe0;
const int _UTF8_FIRST_BYTE_OF_FOUR_BASE = 0xf0;
const int _UTF8_FIRST_BYTE_OF_FIVE_BASE = 0xf8;
const int _UTF8_FIRST_BYTE_OF_SIX_BASE = 0xfc;

const int _UTF8_FIRST_BYTE_OF_TWO_MASK = 0x1f;
const int _UTF8_FIRST_BYTE_OF_THREE_MASK = 0xf;
const int _UTF8_FIRST_BYTE_OF_FOUR_MASK = 0x7;

const int _UTF8_FIRST_BYTE_BOUND_EXCL = 0xfe;
const int _UTF8_SUBSEQUENT_BYTE_BASE = 0x80;

/**
 * Decodes the UTF-8 bytes as an iterable. Thus, the consumer can only convert
 * as much of the input as needed. Set the replacementCharacter to null to
 * throw an ArgumentError rather than replace the bad value.
 */
IterableUtf8Decoder decodeUtf8AsIterable(List<int> bytes, [int offset = 0,
    int length,
    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
  return new IterableUtf8Decoder(bytes, offset, length, replacementCodepoint);
}

/**
 * Produce a String from a List of UTF-8 encoded bytes. The parameters
 * can set an offset into a list of bytes (as int), limit the length of the
 * values to be decoded, and override the default Unicode replacement character.
 * Set the replacementCharacter to null to throw an ArgumentError
 * rather than replace the bad value.
 */
String decodeUtf8(List<int> bytes, [int offset = 0, int length,
    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
  return codepointsToString(
      (new Utf8Decoder(bytes, offset, length, replacementCodepoint))
      .decodeRest());
}

/**
 * Produce a sequence of UTF-8 encoded bytes from the provided string.
 */
List<int> encodeUtf8(String str) =>
  codepointsToUtf8(stringToCodepoints(str));

int _addToEncoding(int offset, int bytes, int value, List<int> buffer) {
  while (bytes > 0) {
    buffer[offset + bytes] = _UTF8_SUBSEQUENT_BYTE_BASE |
        (value & _UTF8_LO_SIX_BIT_MASK);
    value = value >> 6;
    bytes--;
  }
  return value;
}

/**
 * Encode code points as UTF-8 code units.
 */
List<int> codepointsToUtf8(
    List<int> codepoints, [int offset = 0, int length]) {
  _ListRange source = new _ListRange(codepoints, offset, length);

  int encodedLength = 0;
  for (int value in source) {
    if (value < 0 || value > UNICODE_VALID_RANGE_MAX) {
      encodedLength += 3;
    } else if (value <= _UTF8_ONE_BYTE_MAX) {
      encodedLength++;
    } else if (value <= _UTF8_TWO_BYTE_MAX) {
      encodedLength += 2;
    } else if (value <= _UTF8_THREE_BYTE_MAX) {
      encodedLength += 3;
    } else if (value <= UNICODE_VALID_RANGE_MAX) {
      encodedLength += 4;
    }
  }

  List<int> encoded = new List<int>(encodedLength);
  int insertAt = 0;
  for (int value in source) {
    if (value < 0 || value > UNICODE_VALID_RANGE_MAX) {
      encoded.setRange(insertAt, 3, [0xef, 0xbf, 0xbd]);
      insertAt += 3;
    } else if (value <= _UTF8_ONE_BYTE_MAX) {
      encoded[insertAt] = value;
      insertAt++;
    } else if (value <= _UTF8_TWO_BYTE_MAX) {
      encoded[insertAt] = _UTF8_FIRST_BYTE_OF_TWO_BASE | (
          _UTF8_FIRST_BYTE_OF_TWO_MASK &
          _addToEncoding(insertAt, 1, value, encoded));
      insertAt += 2;
    } else if (value <= _UTF8_THREE_BYTE_MAX) {
      encoded[insertAt] = _UTF8_FIRST_BYTE_OF_THREE_BASE | (
          _UTF8_FIRST_BYTE_OF_THREE_MASK &
          _addToEncoding(insertAt, 2, value, encoded));
      insertAt += 3;
    } else if (value <= UNICODE_VALID_RANGE_MAX) {
      encoded[insertAt] = _UTF8_FIRST_BYTE_OF_FOUR_BASE | (
          _UTF8_FIRST_BYTE_OF_FOUR_MASK &
          _addToEncoding(insertAt, 3, value, encoded));
      insertAt += 4;
    }
  }
  return encoded;
}

// Because UTF-8 specifies byte order, we do not have to follow the pattern
// used by UTF-16 & UTF-32 regarding byte order.
List<int> utf8ToCodepoints(
    List<int> utf8EncodedBytes, [int offset = 0, int length,
    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
  return new Utf8Decoder(utf8EncodedBytes, offset, length,
      replacementCodepoint).decodeRest();
}

/**
 * Return type of [decodeUtf8AsIterable] and variants. The Iterable type
 * provides an iterator on demand and the iterator will only translate bytes
 * as requested by the user of the iterator. (Note: results are not cached.)
 */
class IterableUtf8Decoder implements Iterable<int> {
  final List<int> bytes;
  final int offset;
  final int length;
  final int replacementCodepoint;

  IterableUtf8Decoder(this.bytes, [this.offset = 0, this.length = null,
      this.replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]);

  Utf8Decoder iterator() => new Utf8Decoder(bytes, offset, length,
          replacementCodepoint);
}

/**
 * Provides an iterator of Unicode codepoints from UTF-8 encoded bytes. The
 * parameters can set an offset into a list of bytes (as int), limit the length
 * of the values to be decoded, and override the default Unicode replacement
 * character. Set the replacementCharacter to null to throw an
 * ArgumentError rather than replace the bad value. The return value
 * from this method can be used as an Iterable (e.g. in a for-loop).
 */
class Utf8Decoder implements Iterator<int> {
  final _ListRangeIterator utf8EncodedBytesIterator;
  final int replacementCodepoint;

  Utf8Decoder(List<int> utf8EncodedBytes, [int offset = 0, int length,
      this.replacementCodepoint =
      UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) :
      utf8EncodedBytesIterator = (new _ListRange(utf8EncodedBytes, offset,
          length)).iterator();


  Utf8Decoder._fromListRangeIterator(_ListRange source, [
      this.replacementCodepoint =
      UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) :
      utf8EncodedBytesIterator = source.iterator();

  /** Decode the remaininder of the characters in this decoder
    * into a [List<int>].
    */
  List<int> decodeRest() {
    List<int> codepoints = new List<int>(utf8EncodedBytesIterator.remaining);
    int i = 0;
    while (hasNext()) {
      codepoints[i++] = next();
    }
    if (i == codepoints.length) {
      return codepoints;
    } else {
      List<int> truncCodepoints = new List<int>(i);
      truncCodepoints.setRange(0, i, codepoints);
      return truncCodepoints;
    }
  }

  bool hasNext() => utf8EncodedBytesIterator.hasNext();

  int next() {
    int value = utf8EncodedBytesIterator.next();
    int additionalBytes = 0;

    if (value < 0) {
      if (replacementCodepoint != null) {
        return replacementCodepoint;
      } else {
        throw new ArgumentError(
            "Invalid UTF8 at ${utf8EncodedBytesIterator.position}");
      }
    } else if (value <= _UTF8_ONE_BYTE_MAX) {
      return value;
    } else if (value < _UTF8_FIRST_BYTE_OF_TWO_BASE) {
      if (replacementCodepoint != null) {
        return replacementCodepoint;
      } else {
        throw new ArgumentError(
            "Invalid UTF8 at ${utf8EncodedBytesIterator.position}");
      }
    } else if (value < _UTF8_FIRST_BYTE_OF_THREE_BASE) {
      value -= _UTF8_FIRST_BYTE_OF_TWO_BASE;
      additionalBytes = 1;
    } else if (value < _UTF8_FIRST_BYTE_OF_FOUR_BASE) {
      value -= _UTF8_FIRST_BYTE_OF_THREE_BASE;
      additionalBytes = 2;
    } else if (value < _UTF8_FIRST_BYTE_OF_FIVE_BASE) {
      value -= _UTF8_FIRST_BYTE_OF_FOUR_BASE;
      additionalBytes = 3;
    } else if (value < _UTF8_FIRST_BYTE_OF_SIX_BASE) {
      value -= _UTF8_FIRST_BYTE_OF_FIVE_BASE;
      additionalBytes = 4;
    } else if (value < _UTF8_FIRST_BYTE_BOUND_EXCL) {
      value -= _UTF8_FIRST_BYTE_OF_SIX_BASE;
      additionalBytes = 5;
    } else if (replacementCodepoint != null) {
      return replacementCodepoint;
    } else {
      throw new ArgumentError(
          "Invalid UTF8 at ${utf8EncodedBytesIterator.position}");
    }
    int j = 0;
    while (j < additionalBytes && utf8EncodedBytesIterator.hasNext()) {
      int nextValue = utf8EncodedBytesIterator.next();
      if (nextValue > _UTF8_ONE_BYTE_MAX &&
          nextValue < _UTF8_FIRST_BYTE_OF_TWO_BASE) {
        value = ((value << 6) | (nextValue & _UTF8_LO_SIX_BIT_MASK));
      } else {
        // if sequence-starting code unit, reposition cursor to start here
        if (nextValue >= _UTF8_FIRST_BYTE_OF_TWO_BASE) {
          utf8EncodedBytesIterator.backup();
        }
        break;
      }
      j++;
    }
    bool validSequence = (j == additionalBytes && (
        value < UNICODE_UTF16_RESERVED_LO ||
        value > UNICODE_UTF16_RESERVED_HI));
    bool nonOverlong =
        (additionalBytes == 1 && value > _UTF8_ONE_BYTE_MAX) ||
        (additionalBytes == 2 && value > _UTF8_TWO_BYTE_MAX) ||
        (additionalBytes == 3 && value > _UTF8_THREE_BYTE_MAX);
    bool inRange = value <= UNICODE_VALID_RANGE_MAX;
    if (validSequence && nonOverlong && inRange) {
      return value;
    } else if (replacementCodepoint != null) {
      return replacementCodepoint;
    } else {
      throw new ArgumentError(
          "Invalid UTF8 at ${utf8EncodedBytesIterator.position - j}");
    }
  }
}