type HtmlEscapedCallbackOpts = { error?: Error; buffer?: [string] }
export type HtmlEscapedCallback = (opts: HtmlEscapedCallbackOpts) => Promise<string>
export type HtmlEscaped = {
  isEscaped: true
  callbacks?: HtmlEscapedCallback[]
}
export type HtmlEscapedString = string & HtmlEscaped

/**
 * StringBuffer contains string and Promise<string> alternately
 * The length of the array will be odd, the odd numbered element will be a string,
 * and the even numbered element will be a Promise<string>.
 * When concatenating into a single string, it must be processed from the tail.
 * @example
 * [
 *   'framework.',
 *   Promise.resolve('ultra fast'),
 *   'a ',
 *   Promise.resolve('is '),
 *   'Hono',
 * ]
 */
export type StringBuffer = (string | Promise<string>)[]

import { raw } from '../helper/html/index.ts'

// The `escapeToBuffer` implementation is based on code from the MIT licensed `react-dom` package.
// https://github.com/facebook/react/blob/main/packages/react-dom-bindings/src/server/escapeTextForBrowser.js

const escapeRe = /[&<>'"]/

export const stringBufferToString = async (buffer: StringBuffer): Promise<HtmlEscapedString> => {
  let str = ''
  const callbacks: HtmlEscapedCallback[] = []
  for (let i = buffer.length - 1; ; i--) {
    str += buffer[i]
    i--
    if (i < 0) {
      break
    }

    let r = await buffer[i]
    if (typeof r === 'object') {
      callbacks.push(...((r as HtmlEscapedString).callbacks || []))
    }

    const isEscaped = (r as HtmlEscapedString).isEscaped
    r = await (typeof r === 'object' ? (r as HtmlEscapedString).toString() : r)
    if (typeof r === 'object') {
      callbacks.push(...((r as HtmlEscapedString).callbacks || []))
    }

    if ((r as HtmlEscapedString).isEscaped ?? isEscaped) {
      str += r
    } else {
      const buf = [str]
      escapeToBuffer(r, buf)
      str = buf[0]
    }
  }

  return raw(str, callbacks)
}

export const escapeToBuffer = (str: string, buffer: StringBuffer): void => {
  const match = str.search(escapeRe)
  if (match === -1) {
    buffer[0] += str
    return
  }

  let escape
  let index
  let lastIndex = 0

  for (index = match; index < str.length; index++) {
    switch (str.charCodeAt(index)) {
      case 34: // "
        escape = '&quot;'
        break
      case 39: // '
        escape = '&#39;'
        break
      case 38: // &
        escape = '&amp;'
        break
      case 60: // <
        escape = '&lt;'
        break
      case 62: // >
        escape = '&gt;'
        break
      default:
        continue
    }

    buffer[0] += str.substring(lastIndex, index) + escape
    lastIndex = index + 1
  }

  buffer[0] += str.substring(lastIndex, index)
}

export const resolveStream = (
  str: string | HtmlEscapedString,
  buffer?: [string]
): Promise<string> => {
  if (!(str as HtmlEscapedString).callbacks?.length) {
    return Promise.resolve(str)
  }
  const callbacks = (str as HtmlEscapedString).callbacks as HtmlEscapedCallback[]
  if (buffer) {
    buffer[0] += str
  } else {
    buffer = [str]
  }
  return Promise.all(callbacks.map((c) => c({ buffer }))).then((res) =>
    Promise.all(res.map((str) => resolveStream(str, buffer))).then(() => (buffer as [string])[0])
  )
}