import { describe, test, expect, beforeEach, afterEach } from 'vitest';
import { mkdtempSync, writeFileSync, rmSync, utimesSync } from 'node:fs';
import { tmpdir } from 'node:os';
import { join } from 'node:path';
import { GraphCache } from '../src/cache.js';

describe('GraphCache (mtime revalidation)', () => {
  let dir: string;

  beforeEach(() => {
    dir = mkdtempSync(join(tmpdir(), 'wiki-graph-cache-'));
    writeFileSync(join(dir, 'a.md'), '# A\n[[b]]\n');
    writeFileSync(join(dir, 'b.md'), '# B\n');
  });

  afterEach(() => {
    rmSync(dir, { recursive: true, force: true });
  });

  test('returns the same graph instance when nothing changed', () => {
    const cache = new GraphCache();
    const g1 = cache.load(dir);
    const g2 = cache.load(dir);
    expect(g2).toBe(g1);
    expect(g1.stats().nodes).toBe(2);
  });

  test('rebuilds when a new file appears', () => {
    const cache = new GraphCache();
    const g1 = cache.load(dir);
    writeFileSync(join(dir, 'c.md'), '# C\n');
    const g2 = cache.load(dir);
    expect(g2).not.toBe(g1);
    expect(g2.stats().nodes).toBe(3);
  });

  test('rebuilds when a file is modified (mtime bump)', () => {
    const cache = new GraphCache();
    const g1 = cache.load(dir);
    expect(g1.backlinks('c')).toEqual([]);
    writeFileSync(join(dir, 'a.md'), '# A\n[[b]] [[c]]\n');
    writeFileSync(join(dir, 'c.md'), '# C\n');
    const future = new Date(Date.now() + 5000);
    utimesSync(join(dir, 'a.md'), future, future);
    const g2 = cache.load(dir);
    expect(g2).not.toBe(g1);
    expect(g2.backlinks('c')).toEqual(['a']);
  });

  test('only changed files are re-read', () => {
    const cache = new GraphCache();
    cache.load(dir);
    writeFileSync(join(dir, 'c.md'), '# C\n');
    const before = cache.reads;
    cache.load(dir);
    // a.md and b.md unchanged → only c.md read on the second build
    expect(cache.reads - before).toBe(1);
  });
});