import { mkdir, readFile, writeFile } from 'node:fs/promises'
import { dirname, resolve } from 'node:path'
import { fileURLToPath } from 'node:url'

const __dirname = dirname(fileURLToPath(import.meta.url))
const CACHE_DIR = resolve(__dirname, '../../.cache/og')

let ensured = false

async function ensureCacheDir() {
  if (ensured) return
  await mkdir(CACHE_DIR, { recursive: true })
  ensured = true
}

// Returns cached PNG buffer or null. Key must be safe for a filename.
export async function getCachedOG(key) {
  await ensureCacheDir()
  try {
    return await readFile(resolve(CACHE_DIR, `${key}.png`))
  } catch {
    return null
  }
}

export async function setCachedOG(key, buffer) {
  await ensureCacheDir()
  await writeFile(resolve(CACHE_DIR, `${key}.png`), buffer)
}

// Build a safe, deterministic cache key from event slug + updatedAt timestamp.
// Slug is already URL-safe; updatedAt busts the cache on any edit.
export function eventCacheKey(event) {
  const slug = String(event.slug || event._id).replace(/[^a-zA-Z0-9_-]/g, '_')
  const stamp = event.updatedAt ? new Date(event.updatedAt).getTime() : 0
  return `event-${slug}-${stamp}`
}