import { useEffect, useRef, useState } from 'react';
import { BotIcon, SendIcon, SparklesIcon, XIcon } from 'lucide-react';
import { track } from '../analytics';

type ChatMessage = {
  role: 'user' | 'assistant';
  content: string;
  streaming?: boolean;
  error?: boolean;
};

type SseFrame = {
  content?: string;
  error?: string;
  done?: boolean;
};

/** شناسه گفتگو برای هر نشست — در sessionStorage می‌ماند تا رفرش صفحه تاریخچه را نگه دارد */
function getThreadId(): string {
  const KEY = 'chat_thread_id';
  let id = sessionStorage.getItem(KEY);
  if (!id) {
    id = `t_${Date.now()}_${Math.random().toString(36).slice(2, 11)}`;
    sessionStorage.setItem(KEY, id);
  }
  return id;
}

/** خواندن فریم‌های SSE از پاسخ fetch (استریم توکن‌به‌توکن) */
async function readSse(response: Response, onFrame: (frame: SseFrame) => void) {
  const reader = response.body?.getReader();
  if (!reader) throw new Error('پاسخ استریمی ندارد');
  const decoder = new TextDecoder();
  let buffer = '';

  for (;;) {
    const { done, value } = await reader.read();
    if (done) break;
    buffer += decoder.decode(value, { stream: true });
    const lines = buffer.split('\n');
    buffer = lines.pop() ?? '';
    for (const line of lines) {
      const trimmed = line.trim();
      if (trimmed.startsWith('data: ')) {
        try {
          onFrame(JSON.parse(trimmed.slice(6)) as SseFrame);
        } catch {
          // فریم ناقص — نادیده بگیر
        }
      }
    }
  }
}

export function ChatWidget() {
  const [open, setOpen] = useState(false);
  const [messages, setMessages] = useState<ChatMessage[]>([]);
  const [input, setInput] = useState('');
  const [isLoading, setIsLoading] = useState(false);
  const [suggestions, setSuggestions] = useState<string[]>([]);
  const scrollEndRef = useRef<HTMLDivElement>(null);
  const inputRef = useRef<HTMLInputElement>(null);
  const assistantIndexRef = useRef<number | null>(null);

  // پیشنهاد پرسش‌ها فقط یک بار برای هر بازشدن اول
  useEffect(() => {
    if (!open || suggestions.length > 0) return;
    fetch('/chat/suggestions')
      .then((r) => (r.ok ? r.json() : Promise.reject(new Error(String(r.status)))))
      .then((d) => setSuggestions((d.questions ?? []).slice(0, 4)))
      .catch(() => setSuggestions([]));
  }, [open, suggestions.length]);

  useEffect(() => {
    scrollEndRef.current?.scrollIntoView({ behavior: 'smooth', block: 'end' });
  }, [messages, open]);

  const sendMessage = async (text: string) => {
    const question = text.trim();
    if (!question || isLoading) return;
    track('chat-question')
    setInput('');
    setIsLoading(true);
    setMessages((prev) => {
      const next: ChatMessage[] = [
        ...prev,
        { role: 'user', content: question },
        { role: 'assistant', content: '', streaming: true },
      ];
      assistantIndexRef.current = next.length - 1;
      return next;
    });

    const patchAssistant = (patch: Partial<ChatMessage>) => {
      setMessages((prev) => {
        const idx = assistantIndexRef.current;
        if (idx === null || !prev[idx]) return prev;
        const updated = [...prev];
        updated[idx] = { ...updated[idx], ...patch };
        return updated;
      });
    };

    try {
      const params = new URLSearchParams({ message: question, thread_id: getThreadId() });
      const response = await fetch(`/chat/stream?${params.toString()}`, {
        headers: { Accept: 'text/event-stream' },
      });
      if (!response.ok) throw new Error(`HTTP ${response.status}`);

      let accumulated = '';
      await readSse(response, (frame) => {
        if (frame.error) {
          patchAssistant({ content: frame.error, streaming: false, error: true });
          return;
        }
        if (frame.content) {
          accumulated += frame.content;
          patchAssistant({ content: accumulated });
        }
        if (frame.done) patchAssistant({ content: accumulated || 'پاسخی دریافت نشد.', streaming: false });
      });
      patchAssistant({ streaming: false });
    } catch (err) {
      patchAssistant({
        content: 'سرویس گفتگو در دسترس نیست؛ لطفاً کمی بعد دوباره تلاش کنید.',
        streaming: false,
        error: true,
      });
    } finally {
      setIsLoading(false);
      inputRef.current?.focus();
    }
  };

  return (
    <>
      {/* دکمه شناور — گوشه راست‌پایین (دکمه تماس سمت چپ است) */}
      <button
        type="button"
        onClick={() => {
          setOpen((v) => {
            if (!v) track('chat-open');
            return !v;
          });
        }}
        aria-label={open ? 'بستن گفتگو' : 'گفتگو با دستیار هوشمند'}
        className="group fixed bottom-8 right-8 z-40 flex h-14 w-14 items-center justify-center rounded-full bg-ivory text-ink shadow-[0_10px_30px_rgba(0,0,0,0.45)] transition-transform duration-200 ease-lux hover:scale-105">
        <span className="absolute inset-0 rounded-full border border-ivory/60 opacity-0 transition-transform duration-300 ease-lux group-hover:scale-125 group-hover:opacity-100" />
        {open ? <XIcon className="h-5 w-5" /> : <BotIcon className="h-5 w-5" />}
      </button>

      {/* پنل گفتگو */}
      {open && (
        <div
          className="fixed bottom-24 right-4 z-40 flex h-[min(560px,72vh)] w-[min(380px,calc(100vw-2rem))] flex-col overflow-hidden rounded-2xl border border-copper/30 bg-char shadow-lux sm:right-8">
          {/* سربرگ */}
          <div className="flex items-center gap-3 border-b border-ivory/10 bg-ink px-4 py-3">
            <span className="flex h-9 w-9 items-center justify-center rounded-full bg-copper/15 text-copper">
              <SparklesIcon className="h-4 w-4" />
            </span>
            <div className="flex-1">
              <p className="text-sm font-bold text-ivory">دستیار هوشمند آرامش</p>
              <p className="text-[11px] font-light text-ivory/50">پاسخ از محتوای همین سایت</p>
            </div>
            <button
              type="button"
              onClick={() => setOpen(false)}
              aria-label="بستن"
              className="rounded-full p-1.5 text-ivory/50 transition-colors hover:bg-ivory/10 hover:text-ivory">
              <XIcon className="h-4 w-4" />
            </button>
          </div>

          {/* پیام‌ها */}
          <div className="flex-1 space-y-3 overflow-y-auto px-4 py-4">
            {messages.length === 0 && (
              <div className="mt-6 text-center">
                <BotIcon className="mx-auto h-8 w-8 text-copper/60" />
                <p className="mt-3 text-sm font-light leading-7 text-ivory/60">
                  سلام! هر سؤالی درباره خدمات، پروژه‌ها و مقالات
                  <span className="font-bold text-ivory"> گروه ساختمانی آرامش </span>
                  دارید بپرسید.
                </p>
              </div>
            )}

            {messages.map((msg, i) => (
              <div key={i} className={`flex ${msg.role === 'user' ? 'justify-end' : 'justify-start'}`}>
                <div
                  className={`max-w-[85%] whitespace-pre-wrap rounded-2xl px-3.5 py-2.5 text-[13px] leading-6 ${
                    msg.role === 'user'
                      ? 'rounded-bl-md bg-copper text-char'
                      : msg.error
                        ? 'rounded-br-md border border-red-400/30 bg-red-400/10 text-red-200'
                        : 'rounded-br-md border border-ivory/10 bg-ink text-ivory'
                  }`}>
                  {msg.content || (msg.streaming ? '…' : '')}
                  {msg.streaming && msg.content && (
                    <span className="ms-1 inline-block h-1.5 w-1.5 animate-pulse rounded-full bg-copper align-middle" />
                  )}
                </div>
              </div>
            ))}
            <div ref={scrollEndRef} />
          </div>

          {/* پیشنهاد پرسش‌ها */}
          {suggestions.length > 0 && messages.length === 0 && (
            <div className="flex flex-wrap gap-1.5 border-t border-ivory/10 px-3 py-2.5">
              {suggestions.map((q) => (
                <button
                  key={q}
                  type="button"
                  onClick={() => sendMessage(q)}
                  className="rounded-full border border-copper/30 px-2.5 py-1 text-[11px] text-copper transition-colors hover:bg-copper hover:text-char">
                  {q}
                </button>
              ))}
            </div>
          )}

          {/* ورودی */}
          <form
            onSubmit={(e) => {
              e.preventDefault();
              sendMessage(input);
            }}
            className="flex items-center gap-2 border-t border-ivory/10 bg-ink px-3 py-3">
            <input
              ref={inputRef}
              type="text"
              value={input}
              onChange={(e) => setInput(e.target.value)}
              placeholder="پرسش خود را بنویسید…"
              disabled={isLoading}
              className="flex-1 rounded-full border border-ivory/15 bg-char px-4 py-2 text-[13px] text-ivory placeholder:text-ivory/30 focus:border-copper/60 focus:outline-none disabled:opacity-50"
            />
            <button
              type="submit"
              disabled={isLoading || !input.trim()}
              aria-label="ارسال"
              className="flex h-9 w-9 shrink-0 items-center justify-center rounded-full bg-copper text-char transition-transform hover:scale-105 disabled:bg-ivory/15 disabled:text-ivory/40 disabled:hover:scale-100">
              <SendIcon className="h-4 w-4 -scale-x-100" />
            </button>
          </form>
        </div>
      )}
    </>
  );
}