import React, { useState, useEffect, useRef } from "react";
import { Send, Bot, User } from "lucide-react";
import { motion } from "framer-motion";
import { mbaFaqs } from "../data/mbaData";

const API_BASE_URL = import.meta.env.VITE_API_BASE_URL || "";

export default function ICFAIChatbot() {
  // Local program/semester/course data
  const programs = [
    { id: "mba_online", name: "Online MBA" },
    { id: "bba_online", name: "Online BBA" },
  ];

  const allSemesters = [
    {
      id: "sem1",
      name: "Semester I",
      courses: [
        { id: "mob", name: "Management and Organization Behavior" },
        { id: "ba", name: "Business Analytics" },
        { id: "faf", name: "Foundations of Accounting and Finance" },
        { id: "be", name: "Business Environment" },
        { id: "itm", name: "IT for Managers" },
      ],
    },
    { id: "sem2", name: "Semester II", courses: [] },
    { id: "sem3", name: "Semester III", courses: [] },
    { id: "sem4", name: "Semester IV", courses: [] },
  ];

  const faqs = mbaFaqs || [];

  // Flow state: program -> semester -> course -> units
  const [flowStep, setFlowStep] = useState("program");
  const [selectedProgram, setSelectedProgram] = useState(null);
  const [selectedSemester, setSelectedSemester] = useState(null);
  const [selectedCourse, setSelectedCourse] = useState(null);
  const [openUnit, setOpenUnit] = useState(null); // when a unit is selected, sidebar shows unit content

  // Chat state
  const [messages, setMessages] = useState([]);
  const [inputValue, setInputValue] = useState("");
  const [isTyping, setIsTyping] = useState(false);
  const messagesEndRef = useRef(null);

  useEffect(() => {
    if (messages.length === 0) addBotMessage("Hello! 👋 Welcome — choose a program from the left.");
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  const addBotMessage = (text, delay = 300) => {
    setIsTyping(true);
    setTimeout(() => {
      setMessages((m) => [...m, { type: "bot", text }]);
      setIsTyping(false);
      scrollToBottom();
    }, delay);
  };

  const addUserMessage = (text) => {
    setMessages((m) => [...m, { type: "user", text }]);
    scrollToBottom();
  };

  const scrollToBottom = () => messagesEndRef.current?.scrollIntoView({ behavior: "smooth" });

  // Flow handlers
  const onSelectProgram = (p) => {
    addUserMessage(p.name);
    setSelectedProgram(p);
    setSelectedSemester(null);
    setSelectedCourse(null);
    setOpenUnit(null);
    setFlowStep("semester");
    addBotMessage(`Great — ${p.name} selected. Choose a semester.`);
  };

  const onSelectSemester = (s) => {
    addUserMessage(s.name);
    setSelectedSemester(s);
    setSelectedCourse(null);
    setOpenUnit(null);
    setFlowStep("course");
    addBotMessage(`You selected ${s.name}. Pick a course.`);
  };

  const onSelectCourse = (c) => {
    addUserMessage(c.name);
    setSelectedCourse(c);
    setOpenUnit(null);
    if (c.id === "itm") {
      setFlowStep("units");
      addBotMessage(`You selected ${c.name}. Choose a unit from the left.`);
    } else {
      setFlowStep("chat");
      addBotMessage(`You selected ${c.name}. Ask academic questions or open Units if available.`);
    }
  };

  const onSelectUnit = (n) => setOpenUnit(n);

  const onBack = () => {
    if (openUnit) {
      setOpenUnit(null);
      return;
    }
    if (flowStep === "units") {
      setFlowStep("course");
      setSelectedCourse(null);
      return;
    }
    if (flowStep === "course") {
      setFlowStep("semester");
      setSelectedSemester(null);
      return;
    }
    if (flowStep === "semester") {
      setFlowStep("program");
      setSelectedProgram(null);
      return;
    }
  };

  const onFaqClick = (faq) => {
    // show FAQ answer in chat (keeps sidebar focused on FAQs)
    addUserMessage(faq.question);
    addBotMessage(faq.answer, 400);
  };

  const handleSendMessage = async () => {
    if (!inputValue.trim()) return;
    const q = inputValue.trim();
    addUserMessage(q);
    setInputValue("");
    setIsTyping(true);
    try {
      const fd = new FormData();
      fd.append("user_message", q);
      const res = await fetch(`${API_BASE_URL}/digital_icfai_chat`, { method: "POST", body: fd });
      const data = await res.json().catch(() => ({}));
      const answer = (data && (data.answer || data.response)) || "I couldn't find an exact answer in the FAQs.";
      addBotMessage(answer, 200);
    } catch (err) {
      addBotMessage("Sorry, knowledge server unreachable. Try again later.");
    } finally {
      setIsTyping(false);
    }
  };

  // Sidebar renderer — only one section visible at a time, and unit content expands inside sidebar
  const SidebarContent = () => {
    if (!flowStep || flowStep === "program") {
      return (
        <>
          <h3 className="font-bold text-lg">Programs</h3>
          <div className="mt-4 space-y-3">
            {programs.map((p) => (
              <button key={p.id} onClick={() => onSelectProgram(p)} className="w-full text-left px-4 py-3 rounded-lg bg-white border border-gray-100 hover:bg-blue-50">
                {p.name}
              </button>
            ))}
          </div>
        </>
      );
    }

    if (flowStep === "semester") {
      return (
        <>
          <div className="flex items-center justify-between">
            <h3 className="font-bold text-lg">Semesters</h3>
            <button onClick={onBack} className="text-sm text-gray-600">Back</button>
          </div>
          <div className="mt-4 space-y-3">
            {allSemesters.map((s) => (
              <button key={s.id} onClick={() => onSelectSemester(s)} className="w-full text-left px-4 py-3 rounded-lg bg-white border border-gray-100 hover:bg-blue-50">
                {s.name}
              </button>
            ))}
          </div>
        </>
      );
    }

    if (flowStep === "course") {
      return (
        <>
          <div className="flex items-center justify-between">
            <h3 className="font-bold text-lg">Courses in {selectedSemester?.name}</h3>
            <button onClick={onBack} className="text-sm text-gray-600">Back</button>
          </div>
          <div className="mt-4 space-y-3">
            {(selectedSemester?.courses || []).length > 0 ? (
              selectedSemester.courses.map((c) => (
                <button key={c.id} onClick={() => onSelectCourse(c)} className="w-full text-left px-4 py-3 rounded-lg bg-white border border-gray-100 hover:bg-blue-50">
                  {c.name}
                </button>
              ))
            ) : (
              <div className="text-sm text-gray-500">No courses listed for this semester</div>
            )}
          </div>
        </>
      );
    }

    if (flowStep === "units") {
      // If no unit selected, show unit buttons. If unit selected, show its FAQ(s) in the sidebar content area.
      if (!openUnit) {
        return (
          <>
            <div className="flex items-center justify-between">
              <h3 className="font-bold text-lg">ITM Units</h3>
              <button onClick={onBack} className="text-sm text-gray-600">Back</button>
            </div>
            <div className="mt-4 space-y-3">
              {[1,2,3,4,5].map((n) => (
                <button key={n} onClick={() => onSelectUnit(n)} className="w-full text-left px-4 py-3 rounded-lg bg-white border border-gray-100 hover:bg-blue-50">
                  Unit {n}
                </button>
              ))}
            </div>
          </>
        );
      }

      // openUnit: render the unit content inside the sidebar (fixed header + scrollable FAQ list)
      return (
        <>
          <div className="flex items-center justify-between">
            <h3 className="font-bold text-lg">Unit {openUnit}</h3>
            <div className="space-x-2">
              <button onClick={() => setOpenUnit(null)} className="text-sm text-gray-600">Back to Units</button>
              <button onClick={onBack} className="text-sm text-gray-600">Back</button>
            </div>
          </div>

          <div className="mt-4 flex-1 overflow-auto pr-2">
            {openUnit === 1 ? (
              <div className="space-y-2">
                {faqs.map((q,i) => (
                  <button key={i} onClick={() => onFaqClick(q)} className="w-full text-left px-3 py-2 rounded-md bg-white border border-gray-100 hover:bg-gray-50">
                    {q.question}
                  </button>
                ))}
              </div>
            ) : (
              <div>
                {faqs[openUnit - 2] ? (
                  <button onClick={() => onFaqClick(faqs[openUnit - 2])} className="w-full text-left px-3 py-2 rounded-md bg-white border border-gray-100 hover:bg-gray-50">
                    {faqs[openUnit - 2].question}
                  </button>
                ) : (
                  <div className="text-xs text-gray-400">No FAQ assigned</div>
                )}
              </div>
            )}
          </div>
        </>
      );
    }

    return null;
  };

  return (
    <div className="flex w-full h-screen min-w-0 bg-gradient-to-br from-indigo-500 via-violet-500 to-pink-500">
      {/* Sidebar: 600px, vertical layout, header fixed, content scrolls, footer fixed */}
      <aside style={{ width: 600, minWidth: 600 }} className="flex-shrink-0 bg-white border border-gray-200 rounded-l-xl p-6 shadow-lg h-screen flex flex-col">
        {/* Sidebar header */}
        <div className="flex items-start justify-between mb-3">
          <div>
            <h2 className="text-xl font-bold">ICFAI Online Assistant</h2>
            <p className="text-xs text-gray-500">Select program → semester → course → unit</p>
          </div>
          <div>
            <button onClick={() => { setFlowStep("program"); setSelectedProgram(null); setSelectedSemester(null); setSelectedCourse(null); setOpenUnit(null); }} className="text-sm text-gray-600">Reset</button>
          </div>
        </div>

        {/* Sidebar content area: this is the scrollable region */}
        <div className="flex-1 overflow-auto">
          <SidebarContent />
        </div>

        {/* Sidebar footer (fixed) */}
        <div className="mt-4">
          <button onClick={() => { setFlowStep("program"); setSelectedProgram(null); setSelectedSemester(null); setSelectedCourse(null); setOpenUnit(null); }} className="w-full bg-blue-600 text-white px-4 py-3 rounded-lg">Main Menu</button>
        </div>
      </aside>

      {/* Right panel: always shows chat */}
      <div className="flex-1 flex flex-col h-screen bg-white rounded-r-xl shadow-lg overflow-hidden min-w-0">
        <motion.div className="bg-gradient-to-r from-blue-600 to-blue-700 text-white p-6 flex items-center justify-between">
          <div className="flex items-center gap-4">
            <div className="bg-white p-3 rounded-full"><Bot size={22} className="text-blue-600" /></div>
            <div>
              <h3 className="font-bold text-lg">ICFAI Online Assistant</h3>
              <p className="text-sm text-blue-100">Chat / Answers</p>
            </div>
          </div>
          <div className="flex items-center gap-3">
            <button onClick={onBack} className="text-sm bg-white/10 px-4 py-2 rounded-full">← Go Back</button>
            <button onClick={() => { setFlowStep("program"); setSelectedProgram(null); setSelectedSemester(null); setSelectedCourse(null); setOpenUnit(null); }} className="text-sm bg-white/10 px-4 py-2 rounded-full">Main Menu</button>
          </div>
        </motion.div>

        {/* Chat messages */}
        <div className="flex-1 overflow-auto p-8 space-y-6" style={{ paddingBottom: 140 }}>
          {messages.map((m, i) => (
            <div key={i} className={`flex ${m.type === "user" ? "justify-end" : "justify-start"}`}>
              {m.type !== "user" && <div className="bg-blue-600 p-3 rounded-full h-12 w-12 mr-3"><Bot size={18} className="text-white" /></div>}
              <div className={`${m.type === "user" ? "bg-blue-600 text-white" : "bg-white text-gray-800"} p-4 rounded-2xl shadow-sm max-w-[85%]`}>
                {m.text}
              </div>
              {m.type === "user" && <div className="bg-gray-300 p-2 rounded-full h-9 w-9 ml-3"><User size={16} className="text-gray-700" /></div>}
            </div>
          ))}

          {isTyping && (
            <div className="flex gap-3">
              <div className="bg-blue-600 p-3 rounded-full h-12 w-12"><Bot size={18} className="text-white" /></div>
              <div className="bg-white p-3 rounded-2xl shadow-sm border border-gray-100">
                <div className="flex gap-1">
                  <div className="w-2 h-2 bg-gray-400 rounded-full animate-bounce" />
                  <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="p-6 bg-gray-50 border-t border-gray-200" style={{ position: 'relative', zIndex: 2 }}>
          <div className="flex gap-3 items-center">
            <input value={inputValue} onChange={(e) => setInputValue(e.target.value)} placeholder="Ask academic questions about the selected course..." className="flex-1 p-4 border border-gray-300 rounded-2xl focus:outline-none focus:ring-2 focus:ring-blue-600 text-sm" />
            <button onClick={handleSendMessage} disabled={!inputValue.trim()} className="bg-blue-600 text-white p-4 rounded-full disabled:opacity-50"><Send size={20} /></button>
          </div>
          <p className="text-xs text-gray-400 mt-3 text-center">Powered by ICFAI Online</p>
        </div>
      </div>
    </div>
  );
}