'use strict';

const assert = require('assert'),
  bitUtil = require('bit-util');

const GPS_13 = 0x13;

/**
 * RAPParser is responsible for parsing RAP binary records
 */
class RAPParser {

  constructor() {
    // Using these local vars to avoid GC for more memory efficency
    this._hour = 0;
    this._minute = 0;
    this._second = 0;
    this._year = 0;
    this._month = 0;
    this._day = 0;
    this._byte = 0;
  }

  /**
   * Parse RAP binary response package
   * @param {*} rapPkg The binary package data in Buffer. Structure: <Cmd><Len><Data>, Cmd = 0x13
   * @returns a GPS data object
   */
  parse(rapPkg) {
    let record;
    if (rapPkg && rapPkg[0] >= GPS_13) {
      assert.ok(Buffer.isBuffer(rapPkg), 'rapPkg argument must be an instance of Buffer'); // prettier-ignore

      // Byte 19th, if bit 4 is set -> has GPS Fix
      if (rapPkg[18] && bitUtil.isBitOn(rapPkg[18], 4)) {
        record = {};
        let offset = 2; // Add 2 to skip the data package header <Cmd><Len> to read the data

        record.lat = rapPkg.readInt32LE(offset) * 1e-5; offset += 4;
        record.lon = rapPkg.readInt32LE(offset) * 1e-5; offset += 4;
        record.speed = rapPkg.readUInt8(offset); offset += 1;
        // GPS Direction in 2 Degree Increasements
        record.head = rapPkg.readUInt8(offset) << 1; offset += 1;

        this._hour = rapPkg.readUInt8(offset); offset += 1;
        this._minute = rapPkg.readUInt8(offset); offset += 1;
        this._second = rapPkg.readUInt8(offset); offset += 1;
        this._year = 2000 + rapPkg.readUInt8(offset); offset += 1;
        this._month = rapPkg.readUInt8(offset); offset += 1;
        this._day = rapPkg.readUInt8(offset); offset += 1;

        // Month in JS 0 => 11
        record.gdt = new Date(Date.UTC(this._year, this._month - 1, this._day, this._hour, this._minute, this._second));

        record.inputs = 0;

        // Cmd 0x13. Byte 19th
        this._byte = rapPkg.readUInt8(offset); offset += 1;

        // Cmd 0x13. Byte 19th. Bits 0-3: numbers of GPS setellites
        record.sats = bitUtil.extractBits(this._byte, 4, 0);

        // Cmd 0x13. Byte 20th
        this._byte = rapPkg.readUInt8(offset);

        // Cmd 0x13. Byte 20th. Bit 3: Inputs+
        if (bitUtil.isBitOn(this._byte, 3)) {

          // Cmd 0x13. Byte 20th. Bit 0: 1 => extra inputs (21-24)
          offset += bitUtil.isBitOn(this._byte, 0) ? 4 : 1;

          // Skip reading Odometer data

          // Cmd 0x13. Byte 21th/25th
          this._byte = rapPkg.readUInt8(offset); offset += 1;

          if (bitUtil.isBitOn(this._byte, 0)) {
            // Cmd 0x13. Byte 22th/25th: Whether Digital input state present
            this._byte = rapPkg.readUInt8(offset); offset += 1;

            // Digital inputs (Up to 5, use only input 1 for Spray on/off, 0: spray on and 1 is off)
            // Check Input 1 (bit 0) for spray on/off
            record.inputs = bitUtil.isBitOn(this._byte, 0) ? 0 : 1;
          }
        }

      }
    }
    return record;
  }
}

module.exports = RAPParser;