import { assertUint8 } from './assert.js'
import { typedView } from './array.js'
import { isHermes, nativeDecoder, nativeEncoder, E_STRING } from './fallback/_utils.js'
import { asciiPrefix, decodeLatin1 } from './fallback/latin1.js'
import * as js from './fallback/utf8.js'

const { TextDecoder, decodeURIComponent, escape } = globalThis // Buffer is optional
// ignoreBOM: true means that BOM will be left as-is, i.e. will be present in the output
// We don't want to strip anything unexpectedly
const decoderLoose = nativeDecoder
const decoderFatal = nativeDecoder
  ? new TextDecoder('utf-8', { ignoreBOM: true, fatal: true })
  : null
const { isWellFormed } = String.prototype

const { E_STRICT, E_STRICT_UNICODE } = js

const shouldUseEscapePath = isHermes // faster only on Hermes, js path beats it on normal engines

function deLoose(str, loose, res) {
  if (loose || str.length === res.length) return res // length is equal only for ascii, which is automatically fine
  if (isWellFormed) {
    // We have a fast native method
    if (isWellFormed.call(str)) return res
    throw new TypeError(E_STRICT_UNICODE)
  }

  // Recheck if the string was encoded correctly
  let start = 0
  const last = res.length - 2
  // Search for EFBFBD
  while (start < last) {
    const pos = res.indexOf(0xef, start)
    if (pos === -1) break
    start = pos + 1
    if (res[pos + 1] === 0xbf && res[pos + 2] === 0xbd) {
      // Found a replacement char in output, need to recheck if we encoded the input correctly
      if (str !== decode(res)) throw new TypeError(E_STRICT_UNICODE)
      return res
    }
  }

  return res
}

function encode(str, loose = false) {
  if (typeof str !== 'string') throw new TypeError(E_STRING)
  if (str.length === 0) return new Uint8Array() // faster than Uint8Array.of
  if (nativeEncoder) return deLoose(str, loose, nativeEncoder.encode(str))
  // No reason to use unescape + encodeURIComponent: it's slower than JS on normal engines, and modern Hermes already has TextEncoder
  return js.encode(str, loose)
}

function decode(arr, loose = false) {
  assertUint8(arr)
  if (arr.byteLength === 0) return ''
  if (nativeDecoder) return loose ? decoderLoose.decode(arr) : decoderFatal.decode(arr) // Node.js and browsers

  // Fast path for ASCII prefix, this is faster than all alternatives below
  const prefix = decodeLatin1(arr, 0, asciiPrefix(arr)) // No native decoder to use, so decodeAscii is useless here
  if (prefix.length === arr.length) return prefix

  // This codepath gives a ~3x perf boost on Hermes
  if (shouldUseEscapePath && escape && decodeURIComponent) {
    const o = escape(decodeLatin1(arr, prefix.length, arr.length))
    try {
      return prefix + decodeURIComponent(o) // Latin1 to utf8
    } catch {
      if (!loose) throw new TypeError(E_STRICT)
      // Ok, we have to use manual implementation for loose decoder
    }
  }

  return prefix + js.decode(arr, loose, prefix.length)
}

export const utf8fromString = (str, format = 'uint8') => typedView(encode(str, false), format)
export const utf8fromStringLoose = (str, format = 'uint8') => typedView(encode(str, true), format)
export const utf8toString = (arr) => decode(arr, false)
export const utf8toStringLoose = (arr) => decode(arr, true)