import { describe, it, expect, beforeEach } from 'vitest';
import { addChunk, trimAged, getBuffer, resetBuffer } from '../../src/offscreen/recorder';

describe('ring buffer', () => {
  beforeEach(() => resetBuffer());

  it('first chunk is header', () => {
    addChunk({ size: 1024 } as unknown as Blob, 1_000);
    const buf = getBuffer();
    expect(buf.length).toBe(1);
    expect(buf[0].isFirst).toBe(true);
  });

  it('second chunk is NOT header', () => {
    addChunk({ size: 1024 } as unknown as Blob, 1_000);
    addChunk({ size: 512 } as unknown as Blob, 2_000);
    const buf = getBuffer();
    expect(buf.length).toBe(2);
    expect(buf[0].isFirst).toBe(true);
    expect(buf[1].isFirst).toBeFalsy();
  });

  it('trim 30s — keeps header, evicts aged tail', () => {
    addChunk({ size: 1024 } as unknown as Blob, 0);          // header at t=0
    addChunk({ size: 512 } as unknown as Blob, 10_000);      // t=10s
    addChunk({ size: 512 } as unknown as Blob, 35_000);      // t=35s
    trimAged(40_000);                                        // now=40s
    const buf = getBuffer();
    expect(buf[0].isFirst).toBe(true);                       // header survives unconditionally
    expect(buf.length).toBeGreaterThanOrEqual(2);            // header + at least the t=35s chunk
    // The header chunk's age (40s) does NOT cause it to be trimmed.
    const headerStillThere = buf.some((c) => c.isFirst);
    expect(headerStillThere).toBe(true);
  });

  it('trim with empty buffer does not throw', () => {
    expect(() => trimAged(0)).not.toThrow();
    expect(getBuffer()).toEqual([]);
  });
});