'use strict';
var Buffer = require('safer-buffer').Buffer;

// UTF-7 codec, according to https://tools.ietf.org/html/rfc2152
// See also below a UTF-7-IMAP codec, according to http://tools.ietf.org/html/rfc3501#section-5.1.3

exports.utf7 = Utf7Codec;
exports.unicode11utf7 = 'utf7'; // Alias UNICODE-1-1-UTF-7
function Utf7Codec(codecOptions, iconv) {
  this.iconv = iconv;
}

Utf7Codec.prototype.encoder = Utf7Encoder;
Utf7Codec.prototype.decoder = Utf7Decoder;
Utf7Codec.prototype.bomAware = true;

// -- Encoding

var nonDirectChars = /[^A-Za-z0-9'\(\),-\.\/:\? \n\r\t]+/g;

function Utf7Encoder(options, codec) {
  this.iconv = codec.iconv;
}

Utf7Encoder.prototype.write = function (str) {
  // Naive implementation.
  // Non-direct chars are encoded as "+<base64>-"; single "+" char is encoded as "+-".
  return Buffer.from(
    str.replace(
      nonDirectChars,
      function (chunk) {
        return (
          '+' +
          (chunk === '+' ? '' : (
            this.iconv
              .encode(chunk, 'utf16-be')
              .toString('base64')
              .replace(/=+$/, '')
          )) +
          '-'
        );
      }.bind(this)
    )
  );
};

Utf7Encoder.prototype.end = function () {};

// -- Decoding

function Utf7Decoder(options, codec) {
  this.iconv = codec.iconv;
  this.inBase64 = false;
  this.base64Accum = '';
}

var base64Regex = /[A-Za-z0-9\/+]/;
var base64Chars = [];
for (var i = 0; i < 256; i++)
  base64Chars[i] = base64Regex.test(String.fromCharCode(i));

var plusChar = '+'.charCodeAt(0),
  minusChar = '-'.charCodeAt(0),
  andChar = '&'.charCodeAt(0);

Utf7Decoder.prototype.write = function (buf) {
  var res = '',
    lastI = 0,
    inBase64 = this.inBase64,
    base64Accum = this.base64Accum;

  // The decoder is more involved as we must handle chunks in stream.

  for (var i = 0; i < buf.length; i++) {
    if (!inBase64) {
      // We're in direct mode.
      // Write direct chars until '+'
      if (buf[i] == plusChar) {
        res += this.iconv.decode(buf.slice(lastI, i), 'ascii'); // Write direct chars.
        lastI = i + 1;
        inBase64 = true;
      }
    } else {
      // We decode base64.
      if (!base64Chars[buf[i]]) {
        // Base64 ended.
        if (i == lastI && buf[i] == minusChar) {
          // "+-" -> "+"
          res += '+';
        } else {
          var b64str =
            base64Accum + this.iconv.decode(buf.slice(lastI, i), 'ascii');
          res += this.iconv.decode(Buffer.from(b64str, 'base64'), 'utf16-be');
        }

        if (buf[i] != minusChar)
          // Minus is absorbed after base64.
          i--;

        lastI = i + 1;
        inBase64 = false;
        base64Accum = '';
      }
    }
  }

  if (!inBase64) {
    res += this.iconv.decode(buf.slice(lastI), 'ascii'); // Write direct chars.
  } else {
    var b64str = base64Accum + this.iconv.decode(buf.slice(lastI), 'ascii');

    var canBeDecoded = b64str.length - (b64str.length % 8); // Minimal chunk: 2 quads -> 2x3 bytes -> 3 chars.
    base64Accum = b64str.slice(canBeDecoded); // The rest will be decoded in future.
    b64str = b64str.slice(0, canBeDecoded);

    res += this.iconv.decode(Buffer.from(b64str, 'base64'), 'utf16-be');
  }

  this.inBase64 = inBase64;
  this.base64Accum = base64Accum;

  return res;
};

Utf7Decoder.prototype.end = function () {
  var res = '';
  if (this.inBase64 && this.base64Accum.length > 0)
    res = this.iconv.decode(
      Buffer.from(this.base64Accum, 'base64'),
      'utf16-be'
    );

  this.inBase64 = false;
  this.base64Accum = '';
  return res;
};

// UTF-7-IMAP codec.
// RFC3501 Sec. 5.1.3 Modified UTF-7 (http://tools.ietf.org/html/rfc3501#section-5.1.3)
// Differences:
//  * Base64 part is started by "&" instead of "+"
//  * Direct characters are 0x20-0x7E, except "&" (0x26)
//  * In Base64, "," is used instead of "/"
//  * Base64 must not be used to represent direct characters.
//  * No implicit shift back from Base64 (should always end with '-')
//  * String must end in non-shifted position.
//  * "-&" while in base64 is not allowed.

exports.utf7imap = Utf7IMAPCodec;
function Utf7IMAPCodec(codecOptions, iconv) {
  this.iconv = iconv;
}

Utf7IMAPCodec.prototype.encoder = Utf7IMAPEncoder;
Utf7IMAPCodec.prototype.decoder = Utf7IMAPDecoder;
Utf7IMAPCodec.prototype.bomAware = true;

// -- Encoding

function Utf7IMAPEncoder(options, codec) {
  this.iconv = codec.iconv;
  this.inBase64 = false;
  this.base64Accum = Buffer.alloc(6);
  this.base64AccumIdx = 0;
}

Utf7IMAPEncoder.prototype.write = function (str) {
  var inBase64 = this.inBase64,
    base64Accum = this.base64Accum,
    base64AccumIdx = this.base64AccumIdx,
    buf = Buffer.alloc(str.length * 5 + 10),
    bufIdx = 0;

  for (var i = 0; i < str.length; i++) {
    var uChar = str.charCodeAt(i);
    if (0x20 <= uChar && uChar <= 0x7e) {
      // Direct character or '&'.
      if (inBase64) {
        if (base64AccumIdx > 0) {
          bufIdx += buf.write(
            base64Accum
              .slice(0, base64AccumIdx)
              .toString('base64')
              .replace(/\//g, ',')
              .replace(/=+$/, ''),
            bufIdx
          );
          base64AccumIdx = 0;
        }

        buf[bufIdx++] = minusChar; // Write '-', then go to direct mode.
        inBase64 = false;
      }

      if (!inBase64) {
        buf[bufIdx++] = uChar; // Write direct character

        if (uChar === andChar)
          // Ampersand -> '&-'
          buf[bufIdx++] = minusChar;
      }
    } else {
      // Non-direct character
      if (!inBase64) {
        buf[bufIdx++] = andChar; // Write '&', then go to base64 mode.
        inBase64 = true;
      }
      if (inBase64) {
        base64Accum[base64AccumIdx++] = uChar >> 8;
        base64Accum[base64AccumIdx++] = uChar & 0xff;

        if (base64AccumIdx == base64Accum.length) {
          bufIdx += buf.write(
            base64Accum.toString('base64').replace(/\//g, ','),
            bufIdx
          );
          base64AccumIdx = 0;
        }
      }
    }
  }

  this.inBase64 = inBase64;
  this.base64AccumIdx = base64AccumIdx;

  return buf.slice(0, bufIdx);
};

Utf7IMAPEncoder.prototype.end = function () {
  var buf = Buffer.alloc(10),
    bufIdx = 0;
  if (this.inBase64) {
    if (this.base64AccumIdx > 0) {
      bufIdx += buf.write(
        this.base64Accum
          .slice(0, this.base64AccumIdx)
          .toString('base64')
          .replace(/\//g, ',')
          .replace(/=+$/, ''),
        bufIdx
      );
      this.base64AccumIdx = 0;
    }

    buf[bufIdx++] = minusChar; // Write '-', then go to direct mode.
    this.inBase64 = false;
  }

  return buf.slice(0, bufIdx);
};

// -- Decoding

function Utf7IMAPDecoder(options, codec) {
  this.iconv = codec.iconv;
  this.inBase64 = false;
  this.base64Accum = '';
}

var base64IMAPChars = base64Chars.slice();
base64IMAPChars[','.charCodeAt(0)] = true;

Utf7IMAPDecoder.prototype.write = function (buf) {
  var res = '',
    lastI = 0,
    inBase64 = this.inBase64,
    base64Accum = this.base64Accum;

  // The decoder is more involved as we must handle chunks in stream.
  // It is forgiving, closer to standard UTF-7 (for example, '-' is optional at the end).

  for (var i = 0; i < buf.length; i++) {
    if (!inBase64) {
      // We're in direct mode.
      // Write direct chars until '&'
      if (buf[i] == andChar) {
        res += this.iconv.decode(buf.slice(lastI, i), 'ascii'); // Write direct chars.
        lastI = i + 1;
        inBase64 = true;
      }
    } else {
      // We decode base64.
      if (!base64IMAPChars[buf[i]]) {
        // Base64 ended.
        if (i == lastI && buf[i] == minusChar) {
          // "&-" -> "&"
          res += '&';
        } else {
          var b64str =
            base64Accum +
            this.iconv.decode(buf.slice(lastI, i), 'ascii').replace(/,/g, '/');
          res += this.iconv.decode(Buffer.from(b64str, 'base64'), 'utf16-be');
        }

        if (buf[i] != minusChar)
          // Minus may be absorbed after base64.
          i--;

        lastI = i + 1;
        inBase64 = false;
        base64Accum = '';
      }
    }
  }

  if (!inBase64) {
    res += this.iconv.decode(buf.slice(lastI), 'ascii'); // Write direct chars.
  } else {
    var b64str =
      base64Accum +
      this.iconv.decode(buf.slice(lastI), 'ascii').replace(/,/g, '/');

    var canBeDecoded = b64str.length - (b64str.length % 8); // Minimal chunk: 2 quads -> 2x3 bytes -> 3 chars.
    base64Accum = b64str.slice(canBeDecoded); // The rest will be decoded in future.
    b64str = b64str.slice(0, canBeDecoded);

    res += this.iconv.decode(Buffer.from(b64str, 'base64'), 'utf16-be');
  }

  this.inBase64 = inBase64;
  this.base64Accum = base64Accum;

  return res;
};

Utf7IMAPDecoder.prototype.end = function () {
  var res = '';
  if (this.inBase64 && this.base64Accum.length > 0)
    res = this.iconv.decode(
      Buffer.from(this.base64Accum, 'base64'),
      'utf16-be'
    );

  this.inBase64 = false;
  this.base64Accum = '';
  return res;
};