import { createHash } from 'node:crypto'
import { existsSync } from 'node:fs'
import { readFile, rename, writeFile } from 'node:fs/promises'
import path from 'node:path'

const TYPES = {
  png: 'image/png',
  jpg: 'image/jpeg',
  gif: 'image/gif',
  webp: 'image/webp',
  avif: 'image/avif',
  bmp: 'image/bmp',
  svg: 'image/svg+xml',
} as const

type ImageExtension = keyof typeof TYPES

const FILE_NAME = /^[a-f0-9]{40}\.(png|jpg|gif|webp|avif|bmp|svg)$/

/** 根据文件头判断真实格式，不信任浏览器给的 Content-Type。 */
export function detectImageType(bytes: Uint8Array): ImageExtension | null {
  const ascii = (start: number, end: number) => String.fromCharCode(...bytes.subarray(start, end))
  if (bytes.length < 12) return null
  if (bytes[0] === 0x89 && ascii(1, 4) === 'PNG') return 'png'
  if (bytes[0] === 0xff && bytes[1] === 0xd8 && bytes[2] === 0xff) return 'jpg'
  if (ascii(0, 4) === 'GIF8') return 'gif'
  if (ascii(0, 4) === 'RIFF' && ascii(8, 12) === 'WEBP') return 'webp'
  if (ascii(4, 8) === 'ftyp' && ['avif', 'avis'].includes(ascii(8, 12))) return 'avif'
  if (ascii(0, 2) === 'BM') return 'bmp'
  const head = new TextDecoder().decode(bytes.subarray(0, 1024)).trimStart().toLowerCase()
  if ((head.startsWith('<svg') || head.startsWith('<?xml')) && head.includes('<svg')) return 'svg'
  return null
}

export class ImageStore {
  private readonly dir: string

  constructor(dir: string) {
    this.dir = dir
  }

  /** 按内容哈希命名，同一张图片重复上传只存一份。 */
  async save(bytes: Uint8Array) {
    const ext = detectImageType(bytes)
    if (!ext) return null
    const hash = createHash('sha1').update(bytes).digest('hex')
    const name = `${hash}.${ext}`
    const file = path.join(this.dir, name)
    if (!existsSync(file)) {
      const temp = `${file}.${process.pid}.tmp`
      await writeFile(temp, bytes)
      await rename(temp, file)
    }
    return name
  }

  async read(name: string) {
    if (!FILE_NAME.test(name)) return null
    try {
      const data = await readFile(path.join(this.dir, name))
      const ext = name.slice(name.lastIndexOf('.') + 1) as ImageExtension
      return { data, type: TYPES[ext] }
    } catch {
      return null
    }
  }
}