import { TWebMetadata } from '@/types'
import DataLoader from 'dataloader'

class WebService {
  static instance: WebService

  private proxyUrl(url: string): string {
    const proxyServer = import.meta.env.VITE_PROXY_SERVER
    if (proxyServer) {
      return `${proxyServer}/sites/${encodeURIComponent(url)}`
    }
    return url
  }

  private webMetadataDataLoader = new DataLoader<string, TWebMetadata>(
    async (urls) => {
      return await Promise.all(
        urls.map(async (url) => {
          try {
            const res = await fetch(this.proxyUrl(url))
            const html = await res.text()
            const parser = new DOMParser()
            const doc = parser.parseFromString(html, 'text/html')

            const title =
              doc.querySelector('meta[property="og:title"]')?.getAttribute('content') ||
              doc.querySelector('title')?.textContent
            const description =
              doc.querySelector('meta[property="og:description"]')?.getAttribute('content') ||
              (doc.querySelector('meta[name="description"]') as HTMLMetaElement | null)?.content
            const image = (doc.querySelector('meta[property="og:image"]') as HTMLMetaElement | null)
              ?.content

            return { title, description, image }
          } catch {
            return {}
          }
        })
      )
    },
    { maxBatchSize: 1 }
  )

  constructor() {
    if (!WebService.instance) {
      WebService.instance = this
    }
    return WebService.instance
  }

  async fetchWebMetadata(url: string) {
    return await this.webMetadataDataLoader.load(url)
  }
}

const instance = new WebService()

export default instance