import isNodeJs from 'detect-node'
import { PDFWorker } from '../dist/cache/worker'
import { PDFWorkerHelper } from './worker-helper'
import { getFileUrl } from './file'
import { ScoreInfo, SheetInfo, Dimensions } from './scoreinfo'
import { fetchBuffer } from './utils'

type _ExFn = (imgURLs: string[], imgType: 'svg' | 'png', dimensions: Dimensions) => Promise<ArrayBuffer>

const _exportPDFBrowser: _ExFn = async (imgURLs, imgType, dimensions) => {
  const worker = new PDFWorkerHelper()
  const pdfArrayBuffer = await worker.generatePDF(imgURLs, imgType, dimensions.width, dimensions.height)
  worker.terminate()
  return pdfArrayBuffer
}

const _exportPDFNode: _ExFn = async (imgURLs, imgType, dimensions) => {
  const imgBufs = await Promise.all(imgURLs.map(url => fetchBuffer(url)))

  const { generatePDF } = PDFWorker()
  const pdfArrayBuffer = await generatePDF(
    imgBufs,
    imgType,
    dimensions.width,
    dimensions.height,
  ) as ArrayBuffer

  return pdfArrayBuffer
}

export const exportPDF = async (scoreinfo: ScoreInfo, sheet: SheetInfo): Promise<ArrayBuffer> => {
  const imgType = sheet.imgType
  const pageCount = sheet.pageCount

  const rs = Array.from({ length: pageCount }).map((_, i) => {
    if (i === 0) { // The url to the first page is static. We don't need to use API to obtain it.
      return sheet.thumbnailUrl
    } else { // obtain image urls using the API
      return getFileUrl(scoreinfo.id, 'img', i)
    }
  })
  const sheetImgURLs = await Promise.all(rs)

  const args = [sheetImgURLs, imgType, sheet.dimensions] as const
  if (!isNodeJs) {
    return _exportPDFBrowser(...args)
  } else {
    return _exportPDFNode(...args)
  }
}

let pdfBlob: Blob
export const downloadPDF = async (scoreinfo: ScoreInfo, sheet: SheetInfo, saveAs: typeof import('file-saver').saveAs): Promise<void> => {
  const name = scoreinfo.fileName
  if (pdfBlob) {
    return saveAs(pdfBlob, `${name}.pdf`)
  }

  const pdfArrayBuffer = await exportPDF(scoreinfo, sheet)

  pdfBlob = new Blob([pdfArrayBuffer])
  saveAs(pdfBlob, `${name}.pdf`)
}