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

const CACHE_PATH = '.import-cache/og.json'
type Cache = Record<string, OgMeta>
export type OgMeta = { title?: string; description?: string; image?: string }

async function load(): Promise<Cache> {
  try {
    return JSON.parse(await readFile(CACHE_PATH, 'utf8'))
  } catch {
    return {}
  }
}

async function save(c: Cache) {
  await mkdir(dirname(CACHE_PATH), { recursive: true })
  await writeFile(CACHE_PATH, JSON.stringify(c, null, 2))
}

function pick(html: string, prop: string): string | undefined {
  const re = new RegExp(
    `<meta[^>]+(?:property|name)=["']${prop}["'][^>]+content=["']([^"']+)["']`,
    'i',
  )
  return html.match(re)?.[1]
}

export async function fetchOg(url: string, cache: Cache): Promise<OgMeta> {
  if (cache[url]) return cache[url]
  try {
    const res = await fetch(url, { headers: { 'user-agent': 'arter-blog-importer/1.0' } })
    if (!res.ok) throw new Error(`HTTP ${res.status}`)
    const html = await res.text()
    const meta: OgMeta = {
      title: pick(html, 'og:title') ?? pick(html, 'twitter:title'),
      description: pick(html, 'og:description') ?? pick(html, 'twitter:description'),
      image: pick(html, 'og:image') ?? pick(html, 'twitter:image'),
    }
    cache[url] = meta
    return meta
  } catch (err) {
    console.warn(`[og] failed for ${url}: ${(err as Error).message}`)
    cache[url] = {}
    return {}
  }
}

export async function loadOgCache() {
  return load()
}
export async function persistOgCache(c: Cache) {
  await save(c)
}