import { describe, it, expect } from 'vitest';
import { crc16Ibm } from '../src/adapters/teltonika/crc.js';

describe('crc16Ibm', () => {
  it('returns 0x0000 for an empty buffer', () => {
    expect(crc16Ibm(Buffer.alloc(0))).toBe(0x0000);
  });

  it('matches the canonical Teltonika Codec 8 first example (0xC7CF)', () => {
    // Full frame (hex stream from the Teltonika doc, first example):
    //   000000000000003608010000016B40D8EA30010000000000000000000000000000000105021503010101425E0F01F10000601A014E0000000000000000010000C7CF
    //
    // Structure:
    //   00 00 00 00         preamble
    //   00 00 00 36         DataFieldLength = 0x36 = 54
    //   08 01 ...           body (CodecID through N2) — 54 bytes
    //   00 00 C7 CF         CRC field
    //
    // CRC is computed over the 54-byte body only.
    const body = Buffer.from(
      '08' +                         // CodecID
      '01' +                         // N1 = 1
      '0000016B40D8EA30' +            // Timestamp
      '01' +                         // Priority
      '00000000' +                   // Longitude
      '00000000' +                   // Latitude
      '0000' +                       // Altitude
      '0000' +                       // Angle
      '00' +                         // Satellites
      '0000' +                       // Speed
      '01' +                         // Event IO ID
      '05' +                         // N total IO
      '02' +                         // N1 IO (1-byte values)
      '15' + '03' +                  // IO 21 = 3
      '01' + '01' +                  // IO 1 = 1
      '01' +                         // N2 IO (2-byte values)
      '42' + '5E0F' +                // IO 66 = 0x5E0F
      '01' +                         // N4 IO (4-byte values)
      'F1' + '0000601A' +            // IO 241 = 0x0000601A
      '01' +                         // N8 IO (8-byte values)
      '4E' + '0000000000000000' +    // IO 78 = 0
      '01',                          // N2 = 1
      'hex',
    );

    expect(body.length).toBe(0x36); // sanity-check: must be 54 bytes
    expect(crc16Ibm(body)).toBe(0xc7cf);
  });

  it('matches the second Teltonika Codec 8 example (0xF22A)', () => {
    // Full frame hex:
    //   000000000000002808010000016B40D9AD80010000000000000000000000000000000103021503010101425E100000010000F22A
    // Body = bytes from CodecID through N2 (0x28 = 40 bytes)
    const body = Buffer.from(
      '08' +
      '01' +
      '0000016B40D9AD80' +
      '01' +
      '00000000' +
      '00000000' +
      '0000' +
      '0000' +
      '00' +
      '0000' +
      '01' +
      '03' +
      '02' +
      '15' + '03' +
      '01' + '01' +
      '01' +
      '42' + '5E10' +
      '00' +
      '00' +
      '01',
      'hex',
    );

    expect(body.length).toBe(0x28); // 40 bytes
    expect(crc16Ibm(body)).toBe(0xf22a);
  });

  it('produces a non-zero CRC for a single 0xFF byte', () => {
    expect(crc16Ibm(Buffer.from([0xff]))).not.toBe(0);
  });
});