import test from 'node:test'
import assert from 'node:assert/strict'
import { readdirSync, readFileSync } from 'node:fs'
import { fileURLToPath } from 'node:url'
import { dirname, join, basename } from 'node:path'

const srcDir = join(dirname(fileURLToPath(import.meta.url)), '..', 'src')

// Files that are allowed to touch the outside world.
const excluded = (file) => ['runtime.js', 'browser.js', 'main.js'].includes(basename(file))

const banned = [
  ['let', /\blet\b/],
  ['var', /\bvar\b/],
  ['++', /\+\+/],
  ['--', /--/],
  ['.push(', /\.push\(/],
  ['.pop(', /\.pop\(/],
  ['.shift(', /\.shift\(/],
  ['.unshift(', /\.unshift\(/],
  ['.splice(', /\.splice\(/],
  ['.sort(', /\.sort\(/],
  ['.reverse(', /\.reverse\(/],
  ['Math.random', /\bMath\.random\b/],
  ['Date.now', /\bDate\.now\b/],
  ['performance.now', /\bperformance\.now\b/],
  ['document', /\bdocument\b/],
  ['window', /\bwindow\b/],
  ['addEventListener', /\baddEventListener\b/],
]

const stripComments = (code) => code.replace(/\/\*[\s\S]*?\*\//g, '').replace(/\/\/.*$/gm, '')
const violations = (code) => banned.filter(([, re]) => re.test(stripComments(code))).map(([name]) => name)

const jsFiles = (dir) =>
  readdirSync(dir, { withFileTypes: true }).flatMap((e) =>
    e.isDirectory() ? jsFiles(join(dir, e.name)) : e.name.endsWith('.js') ? [join(dir, e.name)] : [])

banned.forEach(([name]) =>
  test(`purity scanner flags a known-bad sample using ${name}`, () => {
    const samples = {
      let: 'let n = 0',
      var: 'var n = 0',
      '++': 'n++',
      '--': 'n--',
      '.push(': 'xs.push(1)',
      '.pop(': 'xs.pop()',
      '.shift(': 'xs.shift()',
      '.unshift(': 'xs.unshift(1)',
      '.splice(': 'xs.splice(0, 1)',
      '.sort(': 'xs.sort()',
      '.reverse(': 'xs.reverse()',
      'Math.random': 'const r = Math.random()',
      'Date.now': 'const t = Date.now()',
      'performance.now': 'const t = performance.now()',
      document: 'document.title',
      window: 'window.alert(1)',
      addEventListener: 'x.addEventListener("click", f)',
    }
    assert.ok(violations(samples[name]).includes(name))
  }))

test('purity scanner ignores banned words inside comments', () => {
  const code = '// let var Math.random()\n/* xs.push(1); document; n++ */\nconst a = 1 // window\n'
  assert.deepEqual(violations(code), [])
})

test('purity scanner accepts ordinary pure code', () =>
  assert.deepEqual(violations('export const f = (xs) => xs.map((x) => x + 1)'), []))

jsFiles(srcDir)
  .filter((f) => !excluded(f))
  .forEach((f) =>
    test(`purity: ${f.slice(srcDir.length + 1)} has no banned constructs`, () =>
      assert.deepEqual(violations(readFileSync(f, 'utf8')), [])))

// helpers.js is loaded by every test file; importing src/ there would make all tests fail at load time against the stubs.
test('test/helpers.js imports nothing from src/', () =>
  assert.doesNotMatch(readFileSync(join(dirname(fileURLToPath(import.meta.url)), 'helpers.js'), 'utf8'), /from\s+['"][^'"]*src\//))