"use client";

import { useEffect, useRef, useState, useCallback } from "react";
import { useParams, useRouter } from "next/navigation";
import { ChevronRight, Send, User, Lock } from "lucide-react";
import { cn } from "@/lib/utils";
import { formatApiError } from "@/lib/hooks";
import { ErrorBanner } from "@/components/ui/ErrorBanner";
import { FullScreenLoader } from "@/components/ui/FullScreenLoader";
import {
  MessageView,
  MatchView,
  listMatches,
  listMessages,
  sendMessage,
  photoUrl,
} from "@/lib/api";
import { ensureKeyPair, encryptMessage, decryptMessage } from "@/lib/e2ee";

const POLL_MS = 4000;
const UNREADABLE = "🔒 این پیام رو نمی‌تونی روی این دستگاه بخونی";

// پیام رمزنگاری‌شده رو برای نمایش رمزگشایی می‌کنه؛ پیام قدیمیِ قبل از E2EE
// همینجوری برگردونده می‌شه.
function messageText(
  m: MessageView,
  partnerPublicKey: string | undefined,
  mySecretKey: Uint8Array | null
): string {
  if (m.cipher_text && m.nonce) {
    if (!mySecretKey || !partnerPublicKey) return UNREADABLE;
    return decryptMessage(m.cipher_text, m.nonce, partnerPublicKey, mySecretKey) ?? UNREADABLE;
  }
  return m.text ?? "";
}

export default function ChatPage() {
  const params = useParams<{ id: string }>();
  const router = useRouter();
  const matchId = Number(params.id);

  const [match, setMatch] = useState<MatchView | null>(null);
  const [messages, setMessages] = useState<MessageView[] | null>(null);
  const [error, setError] = useState<string | null>(null);
  const [draft, setDraft] = useState("");
  const [sending, setSending] = useState(false);
  const [mySecretKey, setMySecretKey] = useState<Uint8Array | null>(null);
  const bottomRef = useRef<HTMLDivElement>(null);
  const pollRef = useRef<ReturnType<typeof setInterval> | null>(null);

  const refreshMessages = useCallback(async () => {
    try {
      const msgs = await listMessages(matchId);
      setMessages(msgs);
    } catch (err) {
      setError(formatApiError(err));
    }
  }, [matchId]);

  useEffect(() => {
    listMatches()
      .then((matches) => {
        const found = matches.find((m) => m.id === matchId);
        setMatch(found ?? null);
      })
      .catch(() => {});
    // eslint-disable-next-line react-hooks/set-state-in-effect
    refreshMessages();
    ensureKeyPair()
      .then((kp) => setMySecretKey(kp.secretKey))
      .catch(() => {});

    pollRef.current = setInterval(refreshMessages, POLL_MS);
    return () => {
      if (pollRef.current) clearInterval(pollRef.current);
    };
  }, [matchId, refreshMessages]);

  useEffect(() => {
    bottomRef.current?.scrollIntoView({ block: "end" });
  }, [messages?.length]);

  const canEncrypt = !!mySecretKey && !!match?.partner_public_key;

  async function handleSend() {
    const text = draft.trim();
    if (!text || sending || !mySecretKey || !match?.partner_public_key) return;
    setSending(true);
    setDraft("");
    try {
      const { cipherText, nonce } = encryptMessage(text, match.partner_public_key, mySecretKey);
      const msg = await sendMessage(matchId, cipherText, nonce);
      setMessages((prev) => (prev ? [...prev, msg] : [msg]));
    } catch (err) {
      setError(formatApiError(err));
    } finally {
      setSending(false);
    }
  }

  if (error && !messages) {
    return (
      <div className="flex-1 flex flex-col items-center justify-center gap-4 p-6 text-center">
        <ErrorBanner message={error} />
        <button
          onClick={() => router.push("/messages")}
          className="text-[13px] font-bold text-(--color-brand-600)"
        >
          برگرد به پیام‌ها
        </button>
      </div>
    );
  }
  if (!messages) return <FullScreenLoader />;

  return (
    <div className="flex flex-col min-h-full">
      <header className="flex items-center gap-3 px-4 pt-[calc(env(safe-area-inset-top)+12px)] pb-3 border-b border-(--color-border-subtle) sticky top-0 bg-(--color-surface-default) z-10">
        <button
          onClick={() => router.push("/messages")}
          className="w-9 h-9 rounded-full flex items-center justify-center hover:bg-(--color-bg-secondary) shrink-0"
        >
          <ChevronRight size={20} className="text-(--color-content-secondary)" />
        </button>
        <button
          onClick={() => match && router.push(`/home/${match.user_id}`)}
          className="flex items-center gap-2.5 flex-1 min-w-0"
        >
          <div className="w-10 h-10 rounded-full overflow-hidden bg-(--color-bg-tertiary) flex items-center justify-center shrink-0">
            {match?.photos[0] ? (
              // eslint-disable-next-line @next/next/no-img-element
              <img src={photoUrl(match.photos[0])} alt={match.first_name} className="w-full h-full object-cover" />
            ) : (
              <User size={18} className="text-(--color-content-disabled)" />
            )}
          </div>
          <p className="font-bold text-[15px] text-(--color-content-primary) truncate">
            {match?.first_name ?? "..."}
          </p>
        </button>
      </header>

      <div className="flex-1 flex flex-col gap-3 px-4 py-4 overflow-y-auto">
        <p className="flex items-center justify-center gap-1.5 text-[11px] text-(--color-content-tertiary) text-center py-2 px-4 mx-auto">
          <Lock size={11} />
          پیام‌ها با رمزنگاری سرتاسری محافظت می‌شن؛ هیچ‌کس جز شما دو نفر، حتی ادمین‌های دلدل، نمی‌تونه بخوندشون.
        </p>
        {messages.length === 0 ? (
          <p className="text-[13px] text-(--color-content-tertiary) text-center py-8">
            هنوز پیامی نیست؛ اولین نفر باش که سلام می‌ده 👋
          </p>
        ) : (
          messages.map((m) => (
            <div
              key={m.id}
              className={cn("flex flex-col max-w-[75%]", m.is_mine ? "self-start items-start" : "self-end items-end")}
            >
              <div
                className={cn(
                  "px-4 py-2.5 text-[14px] leading-6",
                  m.is_mine
                    ? "bg-(--color-brand-500) text-white rounded-2xl rounded-br-md"
                    : "bg-(--color-bg-secondary) text-(--color-content-primary) rounded-2xl rounded-bl-md"
                )}
              >
                {messageText(m, match?.partner_public_key, mySecretKey)}
              </div>
            </div>
          ))
        )}
        <div ref={bottomRef} />
      </div>

      <ErrorBanner message={error} />

      {!canEncrypt && (
        <p className="text-[12px] text-(--color-content-tertiary) text-center px-4 pb-1 flex items-center justify-center gap-1.5">
          <Lock size={12} />
          طرف مقابل هنوز رمزنگاری سرتاسری رو فعال نکرده؛ تا فعال نشه نمی‌تونی پیام بفرستی.
        </p>
      )}
      <div className="flex items-center gap-2 px-4 py-3 border-t border-(--color-border-subtle) pb-[calc(env(safe-area-inset-bottom)+12px)]">
        <input
          value={draft}
          onChange={(e) => setDraft(e.target.value)}
          onKeyDown={(e) => e.key === "Enter" && handleSend()}
          placeholder="پیامت رو بنویس..."
          disabled={!canEncrypt}
          className="flex-1 h-11 rounded-(--radius-full) bg-(--color-bg-secondary) px-4 text-[14px] focus:outline-none focus:ring-2 focus:ring-(--color-brand-200) disabled:opacity-50"
        />
        <button
          onClick={handleSend}
          disabled={!draft.trim() || sending || !canEncrypt}
          className="w-11 h-11 rounded-full bg-(--color-brand-500) text-white flex items-center justify-center disabled:opacity-40 shrink-0"
        >
          <Send size={17} />
        </button>
      </div>
    </div>
  );
}