import { describe, it, expect } from 'vitest';
import { Buffer } from 'node:buffer';
import { encodeVarint, decodeVarint } from '../src/connection.js';

describe('varint encoding', () => {
  it('round-trips small numbers', () => {
    for (const n of [0, 1, 5, 100, 127]) {
      const encoded = encodeVarint(n);
      const [decoded, consumed] = decodeVarint(encoded);
      expect(decoded).toBe(n);
      expect(consumed).toBe(encoded.length);
    }
  });

  it('round-trips numbers requiring 2 bytes', () => {
    for (const n of [128, 200, 16383, 16384, 100_000]) {
      const encoded = encodeVarint(n);
      const [decoded, consumed] = decodeVarint(encoded);
      expect(decoded).toBe(n);
      expect(consumed).toBe(encoded.length);
    }
  });

  it('round-trips numbers requiring 4-5 bytes', () => {
    for (const n of [2 ** 20, 2 ** 28, 2 ** 31 - 1, 2 ** 32]) {
      const encoded = encodeVarint(n);
      const [decoded, consumed] = decodeVarint(encoded);
      expect(decoded).toBe(n);
      expect(consumed).toBe(encoded.length);
    }
  });

  it('encodes correctly per the protobuf spec', () => {
    // Reference values from the protobuf documentation
    expect([...encodeVarint(0)]).toEqual([0x00]);
    expect([...encodeVarint(1)]).toEqual([0x01]);
    expect([...encodeVarint(127)]).toEqual([0x7f]);
    expect([...encodeVarint(128)]).toEqual([0x80, 0x01]);
    expect([...encodeVarint(300)]).toEqual([0xac, 0x02]);
  });

  it('decodes from a multi-byte buffer correctly', () => {
    // decodeVarint should stop at the varint boundary
    const buf = Buffer.concat([encodeVarint(42), Buffer.from([0xff, 0xee])]);
    const [decoded, consumed] = decodeVarint(buf);
    expect(decoded).toBe(42);
    expect(consumed).toBe(1); // only the first byte was the varint
  });

  it('rejects negative numbers', () => {
    expect(() => encodeVarint(-1)).toThrow();
  });
});

describe('varint edge cases', () => {
  it('decodes 0', () => {
    const [v, c] = decodeVarint(Buffer.from([0]));
    expect(v).toBe(0);
    expect(c).toBe(1);
  });

  it('decodes max uint32', () => {
    const n = 0xffffffff;
    const [v, c] = decodeVarint(encodeVarint(n));
    expect(v).toBe(n);
    expect(c).toBe(encodeVarint(n).length);
  });
});