//Intel Hex record types
const DATA = 0,
  END_OF_FILE = 1,
  EXT_SEGMENT_ADDR = 2,
  START_SEGMENT_ADDR = 3,
  EXT_LINEAR_ADDR = 4,
  START_LINEAR_ADDR = 5;

const EMPTY_VALUE = 0xff;

/* intel_hex.parse(data)
	`data` - Intel Hex file (string in ASCII format or Buffer Object)
	`bufferSize` - the size of the Buffer containing the data (optional)
	
	returns an Object with the following properties:
		- data - data as a Buffer Object, padded with 0xFF
			where data is empty.
		- startSegmentAddress - the address provided by the last
			start segment address record; null, if not given
		- startLinearAddress - the address provided by the last
			start linear address record; null, if not given
	Special thanks to: http://en.wikipedia.org/wiki/Intel_HEX
*/
export function parseIntelHex(data: Buffer | string, bufferSize?: number) {
  if (data instanceof Buffer) data = data.toString("ascii");
  //Initialization
  var buf = Buffer.alloc(bufferSize || 8192),
    bufLength = 0, //Length of data in the buffer
    highAddress = 0, //upper address
    startSegmentAddress = null,
    startLinearAddress = null,
    lineNum = 0, //Line number in the Intel Hex string
    pos = 0; //Current position in the Intel Hex string
  const SMALLEST_LINE = 11;
  while (pos + SMALLEST_LINE <= data.length) {
    //Parse an entire line
    if (data.charAt(pos++) != ":")
      throw new Error(
        "Line " + (lineNum + 1) + " does not start with a colon (:)."
      );
    else lineNum++;
    //Number of bytes (hex digit pairs) in the data field
    var dataLength = parseInt(data.substr(pos, 2), 16);
    pos += 2;
    //Get 16-bit address (big-endian)
    var lowAddress = parseInt(data.substr(pos, 4), 16);
    pos += 4;
    //Record type
    var recordType = parseInt(data.substr(pos, 2), 16);
    pos += 2;
    //Data field (hex-encoded string)
    var dataField = data.substr(pos, dataLength * 2),
      dataFieldBuf = Buffer.from(dataField, "hex");
    pos += dataLength * 2;
    //Checksum
    var checksum = parseInt(data.substr(pos, 2), 16);
    pos += 2;
    //Validate checksum
    var calcChecksum =
      (dataLength + (lowAddress >> 8) + lowAddress + recordType) & 0xff;
    for (var i = 0; i < dataLength; i++)
      calcChecksum = (calcChecksum + dataFieldBuf[i]) & 0xff;
    calcChecksum = (0x100 - calcChecksum) & 0xff;
    if (checksum != calcChecksum)
      throw new Error(
        "Invalid checksum on line " +
          lineNum +
          ": got " +
          checksum +
          ", but expected " +
          calcChecksum
      );
    //Parse the record based on its recordType
    switch (recordType) {
      case DATA:
        var absoluteAddress = highAddress + lowAddress;
        //Expand buf, if necessary
        if (absoluteAddress + dataLength >= buf.length) {
          var tmp = Buffer.alloc((absoluteAddress + dataLength) * 2);
          buf.copy(tmp, 0, 0, bufLength);
          buf = tmp;
        }
        //Write over skipped bytes with EMPTY_VALUE
        if (absoluteAddress > bufLength)
          buf.fill(EMPTY_VALUE, bufLength, absoluteAddress);
        //Write the dataFieldBuf to buf
        dataFieldBuf.copy(buf, absoluteAddress);
        bufLength = Math.max(bufLength, absoluteAddress + dataLength);
        break;
      case END_OF_FILE:
        if (dataLength != 0)
          throw new Error("Invalid EOF record on line " + lineNum + ".");
        return {
          data: buf.slice(0, bufLength),
          startSegmentAddress: startSegmentAddress,
          startLinearAddress: startLinearAddress,
        };
      case EXT_SEGMENT_ADDR:
        if (dataLength != 2 || lowAddress != 0)
          throw new Error(
            "Invalid extended segment address record on line " + lineNum + "."
          );
        highAddress = parseInt(dataField, 16) << 4;
        break;
      case START_SEGMENT_ADDR:
        if (dataLength != 4 || lowAddress != 0)
          throw new Error(
            "Invalid start segment address record on line " + lineNum + "."
          );
        startSegmentAddress = parseInt(dataField, 16);
        break;
      case EXT_LINEAR_ADDR:
        if (dataLength != 2 || lowAddress != 0)
          throw new Error(
            "Invalid extended linear address record on line " + lineNum + "."
          );
        highAddress = parseInt(dataField, 16) << 16;
        break;
      case START_LINEAR_ADDR:
        if (dataLength != 4 || lowAddress != 0)
          throw new Error(
            "Invalid start linear address record on line " + lineNum + "."
          );
        startLinearAddress = parseInt(dataField, 16);
        break;
      default:
        throw new Error(
          "Invalid record type (" + recordType + ") on line " + lineNum
        );
    }
    //Advance to the next line
    if (data.charAt(pos) == "\r") pos++;
    if (data.charAt(pos) == "\n") pos++;
  }
  throw new Error("Unexpected end of input: missing or invalid EOF record.");
}