import type { ChangeEvent, KeyboardEvent, ReactElement } from 'react'
import type { BlockView } from './types'
import { useEffect, useLayoutEffect, useRef, useState } from 'react'
import { recolor } from './segments'
import { SegmentText } from './SegmentText'
import { postMessage } from './vscode'

const EDIT_DEBOUNCE_MS = 200

interface CodeEditorProps {
  block: BlockView
  /** 文档版本：每来一份新文档都要对一次输入框内容，哪怕这一块的代码没变 */
  version: number
  autoFocus: boolean
  onAutoFocused: () => void
  onExit: () => void
}

/** 一块源码的编辑状态：着色层显示，透明输入框接收输入，改动防抖后整行替换回文件。 */
export function CodeEditor({ block, version, autoFocus, onAutoFocused, onExit }: CodeEditorProps): ReactElement {
  const [text, setText] = useState(block.code)
  const textareaRef = useRef<HTMLTextAreaElement>(null)
  const blockRef = useRef(block)
  blockRef.current = block
  const textRef = useRef(text)
  textRef.current = text
  /** 本地改过、还没在新文档里看到的文字；有它时新文档不能覆盖有焦点的输入框 */
  const unconfirmed = useRef<string | null>(null)
  /** 最近发出的文字在文件里占几行：新文档到之前，下一次替换要盖住这么多行，而不是旧文档里的行数 */
  const sentLineCount = useRef<number | null>(null)
  const timer = useRef<number | undefined>(undefined)
  const unsent = useRef(false)
  const restoreSelection = useRef<[number, number] | null>(null)

  function flush(): void {
    window.clearTimeout(timer.current)
    if (!unsent.current)
      return
    unsent.current = false
    const { startLine, endLine } = blockRef.current
    const value = textRef.current
    postMessage({
      type: 'edit',
      startLine,
      endLine: sentLineCount.current === null ? endLine : startLine + sentLineCount.current - 1,
      text: value,
    })
    sentLineCount.current = value.split('\n').length
  }

  useEffect(() => {
    const el = textareaRef.current
    const focused = el !== null && document.activeElement === el
    if (focused && unconfirmed.current !== null && unconfirmed.current !== block.code)
      return
    unconfirmed.current = null
    sentLineCount.current = null
    if (block.code === textRef.current)
      return
    if (focused)
      restoreSelection.current = [el.selectionStart, el.selectionEnd]
    setText(block.code)
  }, [version, block.code])

  useLayoutEffect(() => {
    const el = textareaRef.current
    const selection = restoreSelection.current
    if (!el || !selection)
      return
    restoreSelection.current = null
    el.setSelectionRange(Math.min(selection[0], text.length), Math.min(selection[1], text.length))
  }, [text])

  useEffect(() => {
    const el = textareaRef.current
    if (!autoFocus || !el)
      return
    el.focus()
    el.setSelectionRange(el.value.length, el.value.length)
    onAutoFocused()
  }, [autoFocus, onAutoFocused])

  // 卸载（切回预览、块消失）前把没发出去的改动发掉
  useEffect(() => flush, [])

  function onChange(e: ChangeEvent<HTMLTextAreaElement>): void {
    const value = e.target.value
    setText(value)
    unconfirmed.current = value
    unsent.current = true
    window.clearTimeout(timer.current)
    timer.current = window.setTimeout(flush, EDIT_DEBOUNCE_MS)
  }

  function onKeyDown(e: KeyboardEvent<HTMLTextAreaElement>): void {
    if (e.key === 'Escape') {
      e.preventDefault()
      flush()
      onExit()
    }
    // ⌘S 由 VS Code 接管保存：先把还在防抖里的改动发出去，免得存的是旧内容
    else if (e.key === 's' && (e.metaKey || e.ctrlKey)) {
      flush()
    }
  }

  return (
    <div className="cr-editor">
      <textarea
        ref={textareaRef}
        className="cr-code"
        value={text}
        rows={1}
        spellCheck={false}
        autoCapitalize="off"
        autoComplete="off"
        autoCorrect="off"
        aria-label="源码"
        onChange={onChange}
        onKeyDown={onKeyDown}
        onBlur={flush}
      />
      <pre className="cr-code" aria-hidden="true">
        <SegmentText segments={recolor(block.codeTokens, block.code, text)} />
        {text === '' || text.endsWith('\n') ? ' ' : ''}
      </pre>
    </div>
  )
}