import React, { useCallback, useEffect, useRef, useState } from 'react'
import axios from 'axios'
import ReactMarkdown from 'react-markdown'
import EmojiPickerButton from './EmojiPickerButton'

/* ── Toolbar icon components ──────────────────────────────────────────────── */
function BoldIcon() {
  return (
    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth={2.5} className="h-4 w-4">
      <path strokeLinecap="round" strokeLinejoin="round" d="M6 4h8a4 4 0 0 1 0 8H6zM6 12h9a4 4 0 0 1 0 8H6z" />
    </svg>
  )
}

function ItalicIcon() {
  return (
    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth={2.5} className="h-4 w-4">
      <line x1="19" y1="4" x2="10" y2="4" />
      <line x1="14" y1="20" x2="5" y2="20" />
      <line x1="15" y1="4" x2="9" y2="20" />
    </svg>
  )
}

function CodeIcon() {
  return (
    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth={2} className="h-4 w-4">
      <polyline points="16 18 22 12 16 6" />
      <polyline points="8 6 2 12 8 18" />
    </svg>
  )
}

function LinkIcon() {
  return (
    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth={2} className="h-4 w-4">
      <path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71" />
      <path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71" />
    </svg>
  )
}

function ListIcon() {
  return (
    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth={2} className="h-4 w-4">
      <line x1="8" y1="6" x2="21" y2="6" />
      <line x1="8" y1="12" x2="21" y2="12" />
      <line x1="8" y1="18" x2="21" y2="18" />
      <circle cx="3" cy="6" r="1" fill="currentColor" stroke="none" />
      <circle cx="3" cy="12" r="1" fill="currentColor" stroke="none" />
      <circle cx="3" cy="18" r="1" fill="currentColor" stroke="none" />
    </svg>
  )
}

function QuoteIcon() {
  return (
    <svg viewBox="0 0 24 24" fill="currentColor" className="h-4 w-4">
      <path d="M4.583 17.321C3.553 16.227 3 15 3 13.011c0-3.5 2.457-6.637 6.03-8.188l.893 1.378c-3.335 1.804-3.987 4.145-4.247 5.621.537-.278 1.24-.375 1.929-.311C9.591 11.68 11 13.176 11 15c0 1.933-1.567 3.5-3.5 3.5-1.073 0-2.099-.456-2.917-1.179zM15.583 17.321C14.553 16.227 14 15 14 13.011c0-3.5 2.457-6.637 6.03-8.188l.893 1.378c-3.335 1.804-3.987 4.145-4.247 5.621.537-.278 1.24-.375 1.929-.311C20.591 11.68 22 13.176 22 15c0 1.933-1.567 3.5-3.5 3.5-1.073 0-2.099-.456-2.917-1.179z" />
    </svg>
  )
}

/* ── Toolbar button wrapper ───────────────────────────────────────────────── */
function ToolbarBtn({ title, onClick, children }) {
  return (
    <button
      type="button"
      title={title}
      onMouseDown={(e) => { e.preventDefault(); onClick() }}
      className="flex h-7 w-7 items-center justify-center rounded-md text-white/40 transition-colors hover:bg-white/[0.08] hover:text-white/70"
    >
      {children}
    </button>
  )
}

/* ── Main component ───────────────────────────────────────────────────────── */
export default function CommentForm({
  artworkId,
  onPosted,
  isLoggedIn = false,
  loginUrl = '/login',
  parentId = null,
  replyTo = null,
  onCancelReply = null,
  compact = false,
}) {
  const [content, setContent] = useState('')
  const [tab, setTab] = useState('write') // 'write' | 'preview'
  const [submitting, setSubmitting] = useState(false)
  const [errors, setErrors] = useState([])
  const textareaRef = useRef(null)
  const formRef = useRef(null)

  // Auto-focus when entering reply mode
  useEffect(() => {
    if (replyTo && textareaRef.current) {
      textareaRef.current.focus()
      formRef.current?.scrollIntoView({ behavior: 'smooth', block: 'nearest' })
    }
  }, [replyTo])

  /* ── Helpers to wrap selected text ────────────────────────────────────── */
  const wrapSelection = useCallback((before, after) => {
    const el = textareaRef.current
    if (!el) return

    const start = el.selectionStart
    const end = el.selectionEnd
    const selected = content.slice(start, end)
    const replacement = before + (selected || 'text') + after

    const next = content.slice(0, start) + replacement + content.slice(end)
    setContent(next)

    requestAnimationFrame(() => {
      const cursorPos = selected
        ? start + replacement.length
        : start + before.length
      const cursorEnd = selected
        ? start + replacement.length
        : start + before.length + 4
      el.selectionStart = cursorPos
      el.selectionEnd = cursorEnd
      el.focus()
    })
  }, [content])

  const prefixLines = useCallback((prefix) => {
    const el = textareaRef.current
    if (!el) return

    const start = el.selectionStart
    const end = el.selectionEnd
    const selected = content.slice(start, end)
    const lines = selected ? selected.split('\n') : ['']
    const prefixed = lines.map(l => prefix + l).join('\n')

    const next = content.slice(0, start) + prefixed + content.slice(end)
    setContent(next)

    requestAnimationFrame(() => {
      el.selectionStart = start
      el.selectionEnd = start + prefixed.length
      el.focus()
    })
  }, [content])

  const insertLink = useCallback(() => {
    const el = textareaRef.current
    if (!el) return

    const start = el.selectionStart
    const end = el.selectionEnd
    const selected = content.slice(start, end)
    const isUrl = /^https?:\/\//.test(selected)
    const replacement = isUrl
      ? `[link](${selected})`
      : `[${selected || 'link'}](https://)`

    const next = content.slice(0, start) + replacement + content.slice(end)
    setContent(next)

    requestAnimationFrame(() => {
      if (isUrl) {
        el.selectionStart = start + 1
        el.selectionEnd = start + 5
      } else {
        const urlStart = start + replacement.length - 1
        el.selectionStart = urlStart - 8
        el.selectionEnd = urlStart - 1
      }
      el.focus()
    })
  }, [content])

  // Insert text at cursor (for emoji picker)
  const insertAtCursor = useCallback((text) => {
    const el = textareaRef.current
    if (!el) {
      setContent((v) => v + text)
      return
    }

    const start = el.selectionStart ?? content.length
    const end   = el.selectionEnd ?? content.length
    const next  = content.slice(0, start) + text + content.slice(end)
    setContent(next)

    requestAnimationFrame(() => {
      el.selectionStart = start + text.length
      el.selectionEnd   = start + text.length
      el.focus()
    })
  }, [content])

  const handleEmojiSelect = useCallback((emoji) => {
    insertAtCursor(emoji)
  }, [insertAtCursor])

  /* ── Keyboard shortcuts ───────────────────────────────────────────────── */
  const handleKeyDown = useCallback((e) => {
    const mod = e.ctrlKey || e.metaKey
    if (!mod) return

    switch (e.key.toLowerCase()) {
      case 'b':
        e.preventDefault()
        wrapSelection('**', '**')
        break
      case 'i':
        e.preventDefault()
        wrapSelection('*', '*')
        break
      case 'k':
        e.preventDefault()
        insertLink()
        break
      case 'e':
        e.preventDefault()
        wrapSelection('`', '`')
        break
      default:
        break
    }
  }, [wrapSelection, insertLink])

  /* ── Submit ───────────────────────────────────────────────────────────── */
  const handleSubmit = useCallback(
    async (e) => {
      e.preventDefault()

      if (!isLoggedIn) {
        window.location.href = loginUrl
        return
      }

      const trimmed = content.trim()
      if (!trimmed) return

      setSubmitting(true)
      setErrors([])

      try {
        const { data } = await axios.post(`/api/artworks/${artworkId}/comments`, {
          content: trimmed,
          parent_id: parentId || null,
        })

        setContent('')
        setTab('write')
        onPosted?.(data.data)
        onCancelReply?.()
      } catch (err) {
        if (err.response?.status === 422) {
          const fieldErrors = err.response.data?.errors ?? {}
          const allErrors = Object.values(fieldErrors).flat()
          setErrors(allErrors.length ? allErrors : ['Invalid content.'])
        } else {
          setErrors(['Something went wrong. Please try again.'])
        }
      } finally {
        setSubmitting(false)
      }
    },
    [artworkId, content, isLoggedIn, loginUrl, onPosted, parentId, onCancelReply],
  )

  /* ── Logged-out state ─────────────────────────────────────────────────── */
  if (!isLoggedIn) {
    return (
      <div className="flex items-center gap-3 rounded-2xl border border-white/[0.06] bg-white/[0.03] px-5 py-4 backdrop-blur-sm">
        <svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" strokeWidth={1.5} stroke="currentColor" className="h-5 w-5 shrink-0 text-white/25">
          <path strokeLinecap="round" strokeLinejoin="round" d="M16.5 10.5V6.75a4.5 4.5 0 1 0-9 0v3.75m-.75 11.25h10.5a2.25 2.25 0 0 0 2.25-2.25v-6.75a2.25 2.25 0 0 0-2.25-2.25H6.75a2.25 2.25 0 0 0-2.25 2.25v6.75a2.25 2.25 0 0 0 2.25 2.25Z" />
        </svg>
        <p className="text-sm text-white/40">
          <a href={loginUrl} className="font-medium text-accent transition-colors hover:text-accent/80">
            Sign in
          </a>{' '}
          to join the conversation.
        </p>
      </div>
    )
  }

  /* ── Editor ───────────────────────────────────────────────────────────── */
  return (
    <form id={parentId ? `reply-form-${parentId}` : 'comment-form'} ref={formRef} onSubmit={handleSubmit} className="space-y-3">
      {/* Reply indicator */}
      {replyTo && (
        <div className="flex items-center gap-2 rounded-lg bg-accent/[0.06] px-3 py-2">
          <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20" fill="currentColor" className="h-3.5 w-3.5 text-accent/60 shrink-0">
            <path fillRule="evenodd" d="M7.793 2.232a.75.75 0 0 1-.025 1.06L3.622 7.25h10.003a5.375 5.375 0 0 1 0 10.75H10.75a.75.75 0 0 1 0-1.5h2.875a3.875 3.875 0 0 0 0-7.75H3.622l4.146 3.957a.75.75 0 0 1-1.036 1.085l-5.5-5.25a.75.75 0 0 1 0-1.085l5.5-5.25a.75.75 0 0 1 1.06.025Z" clipRule="evenodd" />
          </svg>
          <span className="text-xs text-white/50">
            Replying to <span className="font-semibold text-white/70">{replyTo}</span>
          </span>
          <button
            type="button"
            onClick={onCancelReply}
            className="ml-auto text-[11px] font-medium text-white/30 transition-colors hover:text-white/60"
          >
            Cancel
          </button>
        </div>
      )}

      <div className={`rounded-2xl border border-white/[0.06] bg-white/[0.03] transition-all duration-200 focus-within:border-white/[0.12] focus-within:shadow-lg focus-within:shadow-black/20 ${compact ? 'rounded-xl' : ''}`}>

        {/* ── Top bar: tabs + emoji ─────────────────────────────────────── */}
        <div className="flex items-center justify-between border-b border-white/[0.06] px-3 py-1.5">
          {/* Tabs */}
          <div className="flex items-center gap-1">
            <button
              type="button"
              onClick={() => setTab('write')}
              className={[
                'rounded-md px-3 py-1 text-xs font-medium transition-colors',
                tab === 'write'
                  ? 'bg-white/[0.08] text-white'
                  : 'text-white/40 hover:text-white/60',
              ].join(' ')}
            >
              Write
            </button>
            <button
              type="button"
              onClick={() => setTab('preview')}
              className={[
                'rounded-md px-3 py-1 text-xs font-medium transition-colors',
                tab === 'preview'
                  ? 'bg-white/[0.08] text-white'
                  : 'text-white/40 hover:text-white/60',
              ].join(' ')}
            >
              Preview
            </button>
          </div>

          <div className="flex items-center gap-1.5">
            <span
              className={[
                'text-[11px] tabular-nums font-medium transition-colors',
                content.length > 9000 ? 'text-amber-400/80' : 'text-white/20',
              ].join(' ')}
            >
              {content.length > 0 && `${content.length.toLocaleString()}/10,000`}
            </span>
            <EmojiPickerButton onEmojiSelect={handleEmojiSelect} disabled={submitting} />
          </div>
        </div>

        {/* ── Formatting toolbar (write mode only) ──────────────────────── */}
        {tab === 'write' && (
          <div className="flex items-center gap-0.5 border-b border-white/[0.04] px-3 py-1">
            <ToolbarBtn title="Bold (Ctrl+B)" onClick={() => wrapSelection('**', '**')}>
              <BoldIcon />
            </ToolbarBtn>
            <ToolbarBtn title="Italic (Ctrl+I)" onClick={() => wrapSelection('*', '*')}>
              <ItalicIcon />
            </ToolbarBtn>
            <ToolbarBtn title="Inline code (Ctrl+E)" onClick={() => wrapSelection('`', '`')}>
              <CodeIcon />
            </ToolbarBtn>
            <ToolbarBtn title="Link (Ctrl+K)" onClick={insertLink}>
              <LinkIcon />
            </ToolbarBtn>

            <div className="mx-1 h-4 w-px bg-white/[0.08]" />

            <ToolbarBtn title="Bulleted list" onClick={() => prefixLines('- ')}>
              <ListIcon />
            </ToolbarBtn>
            <ToolbarBtn title="Quote" onClick={() => prefixLines('> ')}>
              <QuoteIcon />
            </ToolbarBtn>
          </div>
        )}

        {/* ── Write tab ─────────────────────────────────────────────────── */}
        {tab === 'write' && (
          <textarea
            ref={textareaRef}
            value={content}
            onChange={(e) => setContent(e.target.value)}
            onKeyDown={handleKeyDown}
            placeholder={replyTo ? `Reply to ${replyTo}…` : 'Share your thoughts…'}
            rows={compact ? 2 : 4}
            maxLength={10000}
            disabled={submitting}
            aria-label="Comment text"
            className="w-full resize-none bg-transparent px-4 py-3 text-[13px] leading-relaxed text-white/90 placeholder-white/25 focus:outline-none disabled:opacity-50"
          />
        )}

        {/* ── Preview tab ───────────────────────────────────────────────── */}
        {tab === 'preview' && (
          <div className="min-h-[7rem] px-4 py-3">
            {content.trim() ? (
              <div className="prose prose-invert prose-sm max-w-none text-[13px] leading-relaxed text-white/80 [&_a]:text-accent [&_a]:no-underline hover:[&_a]:underline [&_code]:rounded [&_code]:bg-white/[0.08] [&_code]:px-1.5 [&_code]:py-0.5 [&_code]:text-[12px] [&_code]:text-amber-300/80 [&_blockquote]:border-l-2 [&_blockquote]:border-accent/40 [&_blockquote]:pl-3 [&_blockquote]:text-white/50 [&_ul]:list-disc [&_ul]:pl-4 [&_ol]:list-decimal [&_ol]:pl-4 [&_li]:text-white/70 [&_strong]:text-white [&_em]:text-white/70 [&_p]:mb-2 [&_p:last-child]:mb-0">
                <ReactMarkdown
                  allowedElements={['p', 'strong', 'em', 'a', 'code', 'pre', 'ul', 'ol', 'li', 'blockquote', 'br']}
                  unwrapDisallowed
                  components={{
                    a: ({ href, children }) => (
                      <a href={href} target="_blank" rel="noopener noreferrer nofollow">{children}</a>
                    ),
                  }}
                >
                  {content}
                </ReactMarkdown>
              </div>
            ) : (
              <p className="text-sm text-white/25 italic">Nothing to preview</p>
            )}
          </div>
        )}

        {/* ── Bottom hint ───────────────────────────────────────────────── */}
        {tab === 'write' && (
          <div className="px-4 pb-2">
            <p className="text-[11px] text-white/15">
              Markdown supported · <kbd className="rounded bg-white/[0.06] px-1 py-0.5 text-[10px] text-white/25">Ctrl+B</kbd> bold · <kbd className="rounded bg-white/[0.06] px-1 py-0.5 text-[10px] text-white/25">Ctrl+I</kbd> italic · <kbd className="rounded bg-white/[0.06] px-1 py-0.5 text-[10px] text-white/25">Ctrl+K</kbd> link
            </p>
          </div>
        )}
      </div>

      {/* Errors */}
      {errors.length > 0 && (
        <ul className="space-y-1 rounded-xl border border-red-500/20 bg-red-500/[0.06] px-4 py-2.5" role="alert">
          {errors.map((e, i) => (
            <li key={i} className="text-xs font-medium text-red-400">
              {e}
            </li>
          ))}
        </ul>
      )}

      {/* Submit */}
      <div className="flex justify-end">
        <button
          type="submit"
          disabled={submitting || !content.trim()}
          className="rounded-full bg-accent px-6 py-2 text-sm font-semibold text-white shadow-lg shadow-accent/20 transition-all duration-200 hover:bg-accent/90 hover:shadow-xl hover:shadow-accent/25 focus:outline-none focus-visible:ring-2 focus-visible:ring-accent/60 focus-visible:ring-offset-2 focus-visible:ring-offset-deep disabled:pointer-events-none disabled:opacity-40 disabled:shadow-none"
        >
          {submitting ? (
            <span className="inline-flex items-center gap-2">
              <svg className="h-3.5 w-3.5 animate-spin" viewBox="0 0 24 24" fill="none">
                <circle className="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" strokeWidth="3" />
                <path className="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4z" />
              </svg>
              Posting…
            </span>
          ) : (
            'Post comment'
          )}
        </button>
      </div>
    </form>
  )
}
