import React, { useRef, useEffect, useState, useCallback } from 'react'
import ExerciseInlineFileMediaModal from './ExerciseInlineFileMediaModal'
import ExerciseInlineEmbedModal from './ExerciseInlineEmbedModal'

function exec(cmd, value = null) {
  try {
    return document.execCommand(cmd, false, value)
  } catch (_) {
    return false
  }
}

/** Selection speichern, bevor Toolbar-Klicks sie zerstört (mousedown + preventDefault allein reicht nicht überall). */
function saveSelectionInside(editorEl) {
  const sel = window.getSelection()
  if (!sel || sel.rangeCount === 0 || !editorEl) return null
  try {
    const range = sel.getRangeAt(0)
    if (!editorEl.contains(range.commonAncestorContainer)) return null
    return range.cloneRange()
  } catch {
    return null
  }
}

function restoreSelection(range) {
  if (!range) return
  try {
    const sel = window.getSelection()
    sel.removeAllRanges()
    sel.addRange(range)
  } catch {
    /* noop */
  }
}

/** Browser: formatBlock erwartet oft Tag in Großschreibung. */
function formatBlock(tag) {
  const t = String(tag).toUpperCase()
  if (!exec('formatBlock', t)) {
    exec('formatBlock', tag.toLowerCase())
  }
}

function normalText() {
  exec('removeFormat')
  formatBlock('p')
}

function buildInlineExerciseMediaHtml(mediaId, displaySize = 'medium') {
  const sid = parseInt(String(mediaId), 10)
  if (!Number.isFinite(sid) || sid < 1) return null
  const sz = ['small', 'medium', 'full'].includes(displaySize) ? displaySize : 'medium'
  return `<span data-shinkan-exercise-media="${sid}" data-shinkan-exercise-media-size="${sz}" class="shinkan-inline-media">\u2060</span>`
}

function insertExerciseMediaPlaceholder(editorEl, mediaId, displaySize = 'medium') {
  if (!editorEl || mediaId == null) return false
  const html = buildInlineExerciseMediaHtml(mediaId, displaySize)
  if (!html) return false

  editorEl.focus()
  const sel = window.getSelection()
  if (!sel) return false

  let caretInside = false
  if (sel.rangeCount > 0) {
    try {
      const r0 = sel.getRangeAt(0)
      caretInside = editorEl.contains(r0.commonAncestorContainer)
    } catch {
      caretInside = false
    }
  }
  if (!caretInside) {
    const anchor = document.createRange()
    try {
      anchor.selectNodeContents(editorEl)
      anchor.collapse(false)
    } catch {
      return false
    }
    sel.removeAllRanges()
    sel.addRange(anchor)
  }

  let inserted = false
  try {
    inserted = document.execCommand('insertHTML', false, html)
  } catch {
    inserted = false
  }
  if (inserted) return true

  let range = null
  try {
    range = sel.rangeCount ? sel.getRangeAt(0).cloneRange() : null
  } catch {
    range = null
  }
  if (!range || !editorEl.contains(range.commonAncestorContainer)) {
    range = document.createRange()
    range.selectNodeContents(editorEl)
    range.collapse(false)
    sel.removeAllRanges()
    sel.addRange(range)
  }
  try {
    const tpl = document.createElement('template')
    tpl.innerHTML = html
    const span = tpl.content.firstChild
    if (!span) return false
    range.deleteContents()
    range.insertNode(span)
    range.setStartAfter(span)
    range.collapse(true)
    sel.removeAllRanges()
    sel.addRange(range)
    return true
  } catch {
    return false
  }
}

/**
 * Leichter WYSIWYG (contenteditable).
 * @param {{ inlineExerciseId?: number|null, onExerciseMediaListChanged?: () => Promise<void> }} [extra]
 */
export default function RichTextEditor({
  value,
  onChange,
  placeholder,
  minHeight = '140px',
  inlineExerciseId = null,
  onExerciseMediaListChanged,
}) {
  const ref = useRef(null)
  const pendingRangeRef = useRef(null)
  const [focused, setFocused] = useState(false)
  const [fileModalOpen, setFileModalOpen] = useState(false)
  const [embedModalOpen, setEmbedModalOpen] = useState(false)

  useEffect(() => {
    const el = ref.current
    if (!el || focused) return
    const next = value ?? ''
    if (el.innerHTML !== next) {
      el.innerHTML = next
    }
  }, [value, focused])

  const sync = useCallback(() => {
    if (!ref.current) return
    onChange(ref.current.innerHTML)
  }, [onChange])

  const refreshExerciseMedia = useCallback(async () => {
    if (onExerciseMediaListChanged) {
      await onExerciseMediaListChanged()
    }
  }, [onExerciseMediaListChanged])

  const stashRangeAndOpen = useCallback((openFn) => (e) => {
    e.preventDefault()
    e.stopPropagation()
    const el = ref.current
    pendingRangeRef.current = el ? saveSelectionInside(el) : null
    openFn()
  }, [])

  const finalizeInsertFromModal = useCallback(
    (mediaId, displaySize) => {
      queueMicrotask(() => {
        const shell = ref.current
        if (!shell) return
        shell.focus()
        restoreSelection(pendingRangeRef.current)
        const ok = insertExerciseMediaPlaceholder(shell, mediaId, displaySize)
        if (!ok) {
          alert(
            'Einfügen ist fehlgeschlagen — bitte Cursor ins Textfeld setzen und den Schalter erneut verwenden.',
          )
          return
        }
        sync()
        shell.focus()
      })
    },
    [sync],
  )

  const run = (fn) => (e) => {
    e.preventDefault()
    e.stopPropagation()
    const el = ref.current
    if (!el) return
    const saved = saveSelectionInside(el)
    el.focus()
    restoreSelection(saved)
    try {
      document.execCommand('styleWithCSS', false, false)
    } catch {
      /* optional */
    }
    fn()
    sync()
  }

  const onLink = (e) => {
    e.preventDefault()
    e.stopPropagation()
    const el = ref.current
    if (!el) return
    const saved = saveSelectionInside(el)
    el.focus()
    restoreSelection(saved)
    const url = window.prompt('Link-URL (https://…)')
    if (url) {
      exec('createLink', url)
      sync()
    }
  }

  const showInlineToolbar = inlineExerciseId != null && Number(inlineExerciseId) > 0

  return (
    <div className="rich-text-editor-wrap">
      <div className="rich-text-toolbar" role="toolbar" aria-label="Formatierung">
        <button type="button" className="rte-btn" title="Fett" onMouseDown={run(() => exec('bold'))}>
          <strong>B</strong>
        </button>
        <button type="button" className="rte-btn" title="Kursiv" onMouseDown={run(() => exec('italic'))}>
          <em>I</em>
        </button>
        <button type="button" className="rte-btn" title="Unterstrichen" onMouseDown={run(() => exec('underline'))}>
          U
        </button>
        <span className="rte-sep" />
        <button type="button" className="rte-btn" title="Normaler Absatz" onMouseDown={run(normalText)}>
          Normal
        </button>
        <button type="button" className="rte-btn" title="Zwischenüberschrift" onMouseDown={run(() => formatBlock('h3'))}>
          Ü3
        </button>
        <span className="rte-sep" />
        <button
          type="button"
          className="rte-btn"
          title="Aufzählung (Mehrzeilen-Markierung möglich)"
          onMouseDown={run(() => exec('insertUnorderedList'))}
        >
          • Liste
        </button>
        <button type="button" className="rte-btn" title="Nummerierte Liste" onMouseDown={run(() => exec('insertOrderedList'))}>
          1. Liste
        </button>
        <span className="rte-sep" />
        <button type="button" className="rte-btn" title="Link einfügen" onMouseDown={onLink}>
          Link
        </button>
        {showInlineToolbar ? (
          <>
            <button
              type="button"
              className="rte-btn"
              title="Datei aus Mediathek oder neu hochladen, in den Text einfügen"
              onMouseDown={stashRangeAndOpen(() => setFileModalOpen(true))}
            >
              Medien im Text
            </button>
            <button
              type="button"
              className="rte-btn"
              title="Embed-URL hinzufügen und im Text einfügen"
              onMouseDown={stashRangeAndOpen(() => setEmbedModalOpen(true))}
            >
              Embed im Text
            </button>
          </>
        ) : null}
        <button
          type="button"
          className="rte-btn"
          title="Zeichenformatierung am Cursor entfernen"
          onMouseDown={run(() => {
            exec('removeFormat')
            exec('unlink')
          })}
        >
          ␡
        </button>
      </div>
      <div
        ref={ref}
        className="rich-text-editor"
        contentEditable
        suppressContentEditableWarning
        data-placeholder={placeholder || ''}
        style={{ minHeight }}
        onFocus={() => setFocused(true)}
        onBlur={() => {
          setFocused(false)
          sync()
        }}
        onInput={sync}
      />

      {showInlineToolbar ? (
        <ExerciseInlineFileMediaModal
          open={fileModalOpen}
          onClose={() => setFileModalOpen(false)}
          exerciseId={Number(inlineExerciseId)}
          onMediaListChanged={refreshExerciseMedia}
          onInserted={(mid, sz) => finalizeInsertFromModal(mid, sz)}
        />
      ) : null}
      {showInlineToolbar ? (
        <ExerciseInlineEmbedModal
          open={embedModalOpen}
          onClose={() => setEmbedModalOpen(false)}
          exerciseId={Number(inlineExerciseId)}
          onMediaListChanged={refreshExerciseMedia}
          onInserted={(mid, sz) => finalizeInsertFromModal(mid, sz)}
        />
      ) : null}
    </div>
  )
}