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

// Single-byte codec. Needs a 'chars' string parameter that contains 256 or 128 chars that
// correspond to encoded bytes (if 128 - then lower half is ASCII).

exports._sbcs = SBCSCodec;
function SBCSCodec(codecOptions, iconv) {
  if (!codecOptions) throw new Error('SBCS codec is called without the data.');

  // Prepare char buffer for decoding.
  if (
    !codecOptions.chars ||
    (codecOptions.chars.length !== 128 && codecOptions.chars.length !== 256)
  )
    throw new Error(
      "Encoding '" +
        codecOptions.type +
        "' has incorrect 'chars' (must be of len 128 or 256)"
    );

  if (codecOptions.chars.length === 128) {
    var asciiString = '';
    for (var i = 0; i < 128; i++) asciiString += String.fromCharCode(i);
    codecOptions.chars = asciiString + codecOptions.chars;
  }

  this.decodeBuf = Buffer.from(codecOptions.chars, 'ucs2');

  // Encoding buffer.
  var encodeBuf = Buffer.alloc(
    65536,
    iconv.defaultCharSingleByte.charCodeAt(0)
  );

  for (var i = 0; i < codecOptions.chars.length; i++)
    encodeBuf[codecOptions.chars.charCodeAt(i)] = i;

  this.encodeBuf = encodeBuf;
}

SBCSCodec.prototype.encoder = SBCSEncoder;
SBCSCodec.prototype.decoder = SBCSDecoder;

function SBCSEncoder(options, codec) {
  this.encodeBuf = codec.encodeBuf;
}

SBCSEncoder.prototype.write = function (str) {
  var buf = Buffer.alloc(str.length);
  for (var i = 0; i < str.length; i++)
    buf[i] = this.encodeBuf[str.charCodeAt(i)];

  return buf;
};

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

function SBCSDecoder(options, codec) {
  this.decodeBuf = codec.decodeBuf;
}

SBCSDecoder.prototype.write = function (buf) {
  // Strings are immutable in JS -> we use ucs2 buffer to speed up computations.
  var decodeBuf = this.decodeBuf;
  var newBuf = Buffer.alloc(buf.length * 2);
  var idx1 = 0,
    idx2 = 0;
  for (var i = 0; i < buf.length; i++) {
    idx1 = buf[i] * 2;
    idx2 = i * 2;
    newBuf[idx2] = decodeBuf[idx1];
    newBuf[idx2 + 1] = decodeBuf[idx1 + 1];
  }
  return newBuf.toString('ucs2');
};

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