"use client";

import { useState, useRef, useEffect } from "react";
import { useRouter } from "next/navigation";
import { useAuth } from "@/lib/auth";

interface ChatMessage {
  id: string;
  role: "user" | "assistant";
  content: string;
  timestamp: Date;
}

export default function ChatPage() {
  const { token, user } = useAuth();
  const router = useRouter();
  const [messages, setMessages] = useState<ChatMessage[]>([]);
  const [input, setInput] = useState("");
  const [loading, setLoading] = useState(false);
  const messagesEndRef = useRef<HTMLDivElement>(null);
  const inputRef = useRef<HTMLTextAreaElement>(null);

  useEffect(() => {
    if (!token) {
      router.replace("/login");
    }
  }, [token, router]);

  useEffect(() => {
    messagesEndRef.current?.scrollIntoView({ behavior: "smooth" });
  }, [messages]);

  async function handleSend() {
    const text = input.trim();
    if (!text || loading || !token) return;

    const userMsg: ChatMessage = {
      id: Date.now().toString(),
      role: "user",
      content: text,
      timestamp: new Date(),
    };

    setMessages((prev) => [...prev, userMsg]);
    setInput("");
    setLoading(true);

    try {
      const res = await fetch("/api/v1/chat", {
        method: "POST",
        headers: {
          "Content-Type": "application/json",
          Authorization: `Bearer ${token}`,
        },
        body: JSON.stringify({ message: text }),
      });

      if (!res.ok) {
        throw new Error(`HTTP ${res.status}`);
      }

      const data = await res.json();
      const assistantMsg: ChatMessage = {
        id: (Date.now() + 1).toString(),
        role: "assistant",
        content: data.reply || data.message || "Omlouvám se, nemohl jsem zpracovat vaši zprávu.",
        timestamp: new Date(),
      };
      setMessages((prev) => [...prev, assistantMsg]);
    } catch {
      const errorMsg: ChatMessage = {
        id: (Date.now() + 1).toString(),
        role: "assistant",
        content: "Chat asistent je momentálně nedostupný. Zkuste to prosím později.",
        timestamp: new Date(),
      };
      setMessages((prev) => [...prev, errorMsg]);
    } finally {
      setLoading(false);
      inputRef.current?.focus();
    }
  }

  function handleKeyDown(e: React.KeyboardEvent) {
    if (e.key === "Enter" && !e.shiftKey) {
      e.preventDefault();
      handleSend();
    }
  }

  if (!token) return null;

  return (
    <div className="flex flex-col h-[calc(100vh-8rem)] max-w-2xl mx-auto px-4">
      {/* Chat header */}
      <div className="flex items-center gap-3 py-4 border-b border-gray-200 dark:border-gray-800">
        <div className="w-10 h-10 bg-purple-100 dark:bg-purple-900/30 text-purple-700 dark:text-purple-300 rounded-full flex items-center justify-center">
          <svg className="w-5 h-5" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
            <path strokeLinecap="round" strokeLinejoin="round" d="M8 12h.01M12 12h.01M16 12h.01M21 12c0 4.418-4.03 8-9 8a9.863 9.863 0 01-4.255-.949L3 20l1.395-3.72C3.512 15.042 3 13.574 3 12c0-4.418 4.03-8 9-8s9 3.582 9 8z" />
          </svg>
        </div>
        <div>
          <h1 className="font-semibold">AI Asistent</h1>
          <p className="text-xs text-muted">Zeptejte se na cokoliv ohledně vašich úkolů</p>
        </div>
      </div>

      {/* Messages area */}
      <div className="flex-1 overflow-y-auto py-4 space-y-4">
        {messages.length === 0 && (
          <div className="text-center py-16">
            <div className="text-5xl mb-4 opacity-40">
              <svg className="w-16 h-16 mx-auto text-muted" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={1}>
                <path strokeLinecap="round" strokeLinejoin="round" d="M8 12h.01M12 12h.01M16 12h.01M21 12c0 4.418-4.03 8-9 8a9.863 9.863 0 01-4.255-.949L3 20l1.395-3.72C3.512 15.042 3 13.574 3 12c0-4.418 4.03-8 9-8s9 3.582 9 8z" />
              </svg>
            </div>
            <p className="text-muted text-lg font-medium">Začněte konverzaci</p>
            <p className="text-muted text-sm mt-1">
              Napište zprávu a AI asistent vám pomůže s úkoly
            </p>
          </div>
        )}

        {messages.map((msg) => (
          <div
            key={msg.id}
            className={`flex ${msg.role === "user" ? "justify-end" : "justify-start"}`}
          >
            <div
              className={`max-w-[80%] rounded-2xl px-4 py-3 ${
                msg.role === "user"
                  ? "bg-blue-600 text-white rounded-br-md"
                  : "bg-gray-100 dark:bg-gray-800 rounded-bl-md"
              }`}
            >
              <p className="text-sm whitespace-pre-wrap leading-relaxed">{msg.content}</p>
              <p
                className={`text-[10px] mt-1 ${
                  msg.role === "user" ? "text-blue-200" : "text-muted"
                }`}
              >
                {msg.timestamp.toLocaleTimeString("cs-CZ", { hour: "2-digit", minute: "2-digit" })}
              </p>
            </div>
          </div>
        ))}

        {loading && (
          <div className="flex justify-start">
            <div className="bg-gray-100 dark:bg-gray-800 rounded-2xl rounded-bl-md px-4 py-3">
              <div className="flex gap-1.5">
                <div className="w-2 h-2 bg-gray-400 rounded-full animate-bounce" style={{ animationDelay: "0ms" }} />
                <div className="w-2 h-2 bg-gray-400 rounded-full animate-bounce" style={{ animationDelay: "150ms" }} />
                <div className="w-2 h-2 bg-gray-400 rounded-full animate-bounce" style={{ animationDelay: "300ms" }} />
              </div>
            </div>
          </div>
        )}

        <div ref={messagesEndRef} />
      </div>

      {/* Input area */}
      <div className="border-t border-gray-200 dark:border-gray-800 py-3 pb-20 sm:pb-4">
        <div className="flex items-end gap-2">
          <textarea
            ref={inputRef}
            value={input}
            onChange={(e) => setInput(e.target.value)}
            onKeyDown={handleKeyDown}
            placeholder="Napište zprávu..."
            rows={1}
            className="flex-1 px-4 py-3 border border-gray-300 dark:border-gray-600 rounded-2xl bg-white dark:bg-gray-800 focus:ring-2 focus:ring-blue-500 focus:border-transparent outline-none resize-none text-sm"
            style={{ maxHeight: "120px" }}
          />
          <button
            onClick={handleSend}
            disabled={loading || !input.trim()}
            className="p-3 bg-blue-600 hover:bg-blue-700 disabled:opacity-50 text-white rounded-full transition-colors flex-shrink-0"
            aria-label="Odeslat"
          >
            <svg className="w-5 h-5" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
              <path strokeLinecap="round" strokeLinejoin="round" d="M12 19l9 2-9-18-9 18 9-2zm0 0v-8" />
            </svg>
          </button>
        </div>
      </div>
    </div>
  );
}