import { describe, expect, test, afterAll } from 'bun:test';
import { mkdtempSync, rmSync, readFileSync, existsSync, writeFileSync } from 'node:fs';
import { tmpdir } from 'node:os';
import { join } from 'node:path';
import { writeAgentBrief } from './agent-brief';

/**
 * Both harnesses have to find the brief.
 *
 * Claude Code discovers `CLAUDE.md`, opencode discovers `AGENTS.md` and nothing else. Every brief the
 * platform wrote was `CLAUDE.md`, so under opencode a commander, a bot and a plugin chat were each
 * briefed with nothing — silently, which is why it lasted.
 */

const root = mkdtempSync(join(tmpdir(), 'agent-brief-'));
afterAll(() => rmSync(root, { recursive: true, force: true }));

const dir = (name: string) => {
  const d = join(root, name);
  rmSync(d, { recursive: true, force: true });
  Bun.spawnSync(['mkdir', '-p', d]);
  return d;
};

describe('writeAgentBrief', () => {
  test('writes the content as AGENTS.md and a POINTER as CLAUDE.md', async () => {
    const d = dir('both');
    await writeAgentBrief(d, '# Brief\n\nthe real instructions\n');

    expect(readFileSync(join(d, 'AGENTS.md'), 'utf8')).toContain('the real instructions');
    const pointer = readFileSync(join(d, 'CLAUDE.md'), 'utf8');
    expect(pointer).toContain('AGENTS.md');
    // The pointer must NOT be a second copy — two copies of a file rewritten every turn will disagree,
    // and the stale one is the one somebody reads.
    expect(pointer).not.toContain('the real instructions');
  });

  test('is idempotent — an unchanged brief writes nothing', async () => {
    const d = dir('idempotent');
    expect(await writeAgentBrief(d, 'same\n')).toBe(true);
    expect(await writeAgentBrief(d, 'same\n')).toBe(false);
  });

  test('rewrites when the content changes, because that is how a template reaches a bot', async () => {
    const d = dir('rewrite');
    await writeAgentBrief(d, 'v1\n');
    expect(await writeAgentBrief(d, 'v2\n')).toBe(true);
    expect(readFileSync(join(d, 'AGENTS.md'), 'utf8')).toBe('v2\n');
  });

  test('onlyIfAbsent never touches a brief the agent has extended', async () => {
    // A commander writes its own job into this file over days. Rewriting it because the template
    // changed would delete what it agreed with the owner.
    const d = dir('extended');
    await writeAgentBrief(d, 'generated\n');
    writeFileSync(join(d, 'AGENTS.md'), 'generated\n\n## JOB\n\nwatch the thing\n');

    expect(await writeAgentBrief(d, 'a new template\n', { onlyIfAbsent: true })).toBe(false);
    expect(readFileSync(join(d, 'AGENTS.md'), 'utf8')).toContain('watch the thing');
  });

  test('onlyIfAbsent still creates both files the first time', async () => {
    const d = dir('first');
    expect(await writeAgentBrief(d, 'generated\n', { onlyIfAbsent: true })).toBe(true);
    expect(existsSync(join(d, 'AGENTS.md'))).toBe(true);
    expect(existsSync(join(d, 'CLAUDE.md'))).toBe(true);
  });
});