/* ========================================
   App Component — padhle (Backend-Connected)
   ======================================== */

import { useState, useRef, useCallback, useEffect } from "react";
import Sidebar from "./components/sidebar/Sidebar";
import TopNav from "./components/top-nav/TopNav";
import ChatHistory from "./components/chat-history/ChatHistory";
import ChatInput from "./components/chat-input/ChatInput";
import SelectorFlow from "./components/selector-flow/SelectorFlow";
import { useAuth } from "./lib/auth/SupabaseAuth";
import SignInModal from "./lib/auth/SignIn";
import { resetAppState } from "./appState";
const API_BASE = ""; // Uses Vite proxy → localhost:3001 in dev

// Default selectors
const DEFAULTS = {
  grade: "Choose standard",
  subject: "choose-subject",
  chapter: "choose-chapter",
};

/* ─── Selector data ─── */

const gradeItems = [
  { id: "grade-6", label: "Grade 6", icon: "backpack" },
  { id: "grade-7", label: "Grade 7", icon: "auto_stories" },
  { id: "grade-8", label: "Grade 8", icon: "menu_book" },
  { id: "grade-9", label: "Grade 9", icon: "science" },
  { id: "grade-10", label: "Grade 10", icon: "calculate" },
  { id: "grade-11", label: "Grade 11", icon: "psychology" },
  { id: "grade-12", label: "Grade 12", icon: "school" },
];

const subjectItems = [
  { id: "math", label: "Mathematics" },
  { id: "science", label: "Science" },
  { id: "history", label: "History" },
  { id: "language", label: "Language Arts" },
  { id: "english", label: "English" },
  { id: "geography", label: "Geography" },
];

const chapterData = {
  math: [
    { id: "ch-1", label: "Chapter 1: Rational Numbers" },
    { id: "ch-2", label: "Chapter 2: Linear Equations" },
    { id: "ch-3", label: "Chapter 3: Coordinate Geometry" },
    { id: "ch-4", label: "Chapter 4: Algebra" },
    { id: "ch-5", label: "Chapter 5: Geometry" },
    { id: "ch-6", label: "Chapter 6: Trigonometry" },
  ],
  science: [
    { id: "ch-1", label: "Chapter 1: Nutrition in Plants" },
    { id: "ch-2", label: "Chapter 2: Photosynthesis" },
    { id: "ch-3", label: "Chapter 3: Human Physiology" },
    { id: "ch-4", label: "Chapter 4: Chemistry Basics" },
    { id: "ch-5", label: "Chapter 5: Motion & Force" },
    { id: "ch-6", label: "Chapter 6: Electricity" },
  ],
  history: [
    { id: "ch-1", label: "Chapter 1: Early Civilizations" },
    { id: "ch-2", label: "Chapter 2: Ancient India" },
    { id: "ch-3", label: "Chapter 3: Medieval Period" },
    { id: "ch-4", label: "Chapter 4: Modern India" },
    { id: "ch-5", label: "Chapter 5: World Wars" },
    { id: "ch-6", label: "Chapter 6: Independence Movement" },
  ],
  language: [
    { id: "ch-1", label: "Chapter 1: Grammar Basics" },
    { id: "ch-2", label: "Chapter 2: Comprehension" },
    { id: "ch-3", label: "Chapter 3: Creative Writing" },
    { id: "ch-4", label: "Chapter 4: Literature" },
    { id: "ch-5", label: "Chapter 5: Vocabulary" },
    { id: "ch-6", label: "Chapter 6: Composition" },
  ],
  english: [
    { id: "ch-1", label: "Chapter 1: Reading Skills" },
    { id: "ch-2", label: "Chapter 2: Writing Skills" },
    { id: "ch-3", label: "Chapter 3: Grammar" },
    { id: "ch-4", label: "Chapter 4: Poetry" },
    { id: "ch-5", label: "Chapter 5: Prose" },
    { id: "ch-6", label: "Chapter 6: Drama" },
  ],
  geography: [
    { id: "ch-1", label: "Chapter 1: Earth & Universe" },
    { id: "ch-2", label: "Chapter 2: Landforms" },
    { id: "ch-3", label: "Chapter 3: Climate & Weather" },
    { id: "ch-4", label: "Chapter 4: Natural Resources" },
    { id: "ch-5", label: "Chapter 5: Maps & Atlas" },
    { id: "ch-6", label: "Chapter 6: Human Geography" },
  ],
};

function App() {
  const { isAuthenticated, user, signIn, signUp, signOut, getToken } = useAuth();
  const [messages, setMessages] = useState([]);
  const [activeSubject, setActiveSubject] = useState(DEFAULTS.subject);

  /* ─── Subject label resolution (ID → display name) ─── */
  const getSubjectLabel = (id) => {
    if (!id || id === "choose-subject") return "Choose Subject";
    return subjectItems.find((s) => s.id === id)?.label || id;
  };

  /* ─── Chapter list resolution (subject ID → array) ─── */
  const getChaptersForSubject = (subjectId) => {
    return chapterData[subjectId] || [];
  };

  /* ─── Chapter label resolution (ID → display name) ─── */
  const getChapterLabel = (chapterId) => {
    if (!chapterId || chapterId === "choose-chapter") return "Choose Chapter";
    return chapterId;
  };
  const [activeChat, setActiveChat] = useState(null);
  const [activeGrade, setActiveGrade] = useState(DEFAULTS.grade);
  const [activeChapter, setActiveChapter] = useState(DEFAULTS.chapter);
  const [isTyping, setIsTyping] = useState(false);
  const [sessions, setSessions] = useState([]);
  const [isLoadingSessions, setIsLoadingSessions] = useState(false);
  const [selectorStep, setSelectorStep] = useState("grade"); // grade → subject → chapter → chat
  const abortRef = useRef(null);
  const hasMountedRef = useRef(false); // track first mount to avoid resetting on initial load

  // Reset all user-scoped state whenever authentication changes.
  useEffect(() => {
    if (!hasMountedRef.current) {
      hasMountedRef.current = true;
      if (isAuthenticated) loadSessions();
      return;
    }

    if (abortRef.current) {
      abortRef.current.abort();
      abortRef.current = null;
    }

    const next = resetAppState();
    setMessages(next.messages);
    setActiveChat(next.activeChat);
    setActiveGrade(next.activeGrade);
    setActiveSubject(next.activeSubject);
    setActiveChapter(next.activeChapter);
    setIsTyping(next.isTyping);
    setSelectorStep(next.selectorStep);
    setSessions(next.sessions);

    if (isAuthenticated) loadSessions();
  }, [isAuthenticated]);



  // ─── Auth handlers ───
  const handleAuthError = (msg) => {
    setMessages((prev) => [
      ...prev,
      { id: Date.now(), role: "assistant", text: `⚠️ ${msg}` },
    ]);
  };

  const loadSessions = async () => {
    setIsLoadingSessions(true);
    try {
      const token = await getToken();
      const headers = {};
      if (token) headers["Authorization"] = `Bearer ${token}`;

      const res = await fetch(`${API_BASE}/api/sessions`, { headers, credentials: "include" });
      if (res.ok) {
        const data = await res.json();
        setSessions(data);
      }
    } catch (err) {
      console.error("Failed to load sessions:", err);
    } finally {
      setIsLoadingSessions(false);
    }
  };

  const handleNewChat = () => {
    // Abort any in-flight request
    if (abortRef.current) {
      abortRef.current.abort();
      abortRef.current = null;
    }

    // Clear everything
    setMessages([]);
    setActiveChat(null);
    setActiveGrade(DEFAULTS.grade);
    setActiveSubject(DEFAULTS.subject);
    setActiveChapter(DEFAULTS.chapter);
    setIsTyping(false);

    // Reset selector to grade step
    setSelectorStep("grade");

    // Refresh sessions list from backend
    loadSessions();
  };

  const handleChatSelect = async (sessionId) => {
    // Abort any in-flight request
    if (abortRef.current) {
      abortRef.current.abort();
      abortRef.current = null;
    }

    setIsTyping(true);
    setMessages([]);

    try {
      const token = await getToken();
      const headers = {};
      if (token) headers["Authorization"] = `Bearer ${token}`;

      const res = await fetch(`${API_BASE}/api/chat/${sessionId}`, { headers, credentials: "include" });
      if (!res.ok) {
        throw new Error("Session not found");
      }
      const data = await res.json();

      // Set the session's context (grade, subject, chapter)
      if (data.session) {
        setActiveGrade(data.session.grade || DEFAULTS.grade);
        setActiveSubject(data.session.subject || DEFAULTS.subject);
        setActiveChapter(data.session.chapter || DEFAULTS.chapter);
      }

      // Move to chat view
      setSelectorStep("chat");

      // Load the messages
      if (data.messages) {
        setMessages(data.messages.map((m) => ({ ...m, streaming: false })));
      }

      setActiveChat(sessionId);
    } catch (err) {
      console.error("Failed to load session:", err);
      setMessages([
        {
          id: Date.now(),
          role: "assistant",
          text: `⚠️ Could not load that chat. It may have been deleted.`,
        },
      ]);
    } finally {
      setIsTyping(false);
    }
  };

  const handleDeleteChat = async (sessionId) => {
    try {
      const token = await getToken();
      const headers = {};
      if (token) headers["Authorization"] = `Bearer ${token}`;

      const res = await fetch(`${API_BASE}/api/sessions/${sessionId}`, {
        method: "DELETE",
        headers,
        credentials: "include",
      });
      if (res.ok) {
        // If we were on the deleted chat, clear it
        if (activeChat === sessionId) {
          handleNewChat();
        } else {
          loadSessions();
        }
      }
    } catch (err) {
      console.error("Failed to delete session:", err);
    }
  };

  const handleSend = useCallback(
    async (text) => {
      if (!text.trim() || isTyping) return;

      // Abort any previous in-flight request
      if (abortRef.current) {
        abortRef.current.abort();
      }

      // Add user message immediately
      const userMsg = { id: Date.now(), role: "user", text };
      setMessages((prev) => [...prev, userMsg]);
      setIsTyping(true);

      const fetchChatId = activeChat;

      // Build request body
      const body = {
        text: text.trim(),
        chatId: fetchChatId,
        grade: activeGrade !== DEFAULTS.grade ? activeGrade : undefined,
        subject: activeSubject !== DEFAULTS.subject ? activeSubject : undefined,
        chapter: activeChapter !== DEFAULTS.chapter ? activeChapter : undefined,
      };

      // Open SSE connection
      const controller = new AbortController();
      abortRef.current = controller;

      const token = await getToken();
      const headers = { "Content-Type": "application/json" };
      if (token) headers["Authorization"] = `Bearer ${token}`;

      fetch(`${API_BASE}/api/chat`, {
        method: "POST",
        headers,
        credentials: "include",
        body: JSON.stringify(body),
        signal: controller.signal,
      })
        .then(async (response) => {
          if (!response.ok) {
            throw new Error(`Server error: ${response.status}`);
          }

          const reader = response.body.getReader();
          const decoder = new TextDecoder();
          let buffer = "";
          let assistantText = "";

          // Create placeholder assistant message
          const assistantId = Date.now() + 1;
          setMessages((prev) => [
            ...prev,
            { id: assistantId, role: "assistant", text: "", streaming: true },
          ]);

          while (true) {
            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) {
              if (!line.startsWith("data: ")) continue;
              const jsonStr = line.slice(6);
              if (jsonStr === "[DONE]") continue;

              try {
                const data = JSON.parse(jsonStr);
                if (data.type === "chunk") {
                  assistantText += data.content;
                  setMessages((prev) =>
                    prev.map((m) =>
                      m.id === assistantId
                        ? { ...m, text: assistantText }
                        : m
                    )
                  );
                } else if (data.type === "done") {
                  // Mark as non-streaming
                  setMessages((prev) =>
                    prev.map((m) =>
                      m.id === assistantId
                        ? { ...m, streaming: false }
                        : m
                    )
                  );
                } else if (data.type === "error") {
                  setMessages((prev) =>
                    prev.map((m) =>
                      m.id === assistantId
                        ? {
                            ...m,
                            text: `⚠️ Error: ${data.message}`,
                            streaming: false,
                          }
                        : m
                    )
                  );
                }
              } catch {
                // Skip malformed SSE frames
              }
            }
          }

          setIsTyping(false);
          abortRef.current = null;

          // Refresh sessions to update timestamps
          loadSessions();
        })
        .catch((err) => {
          if (err.name === "AbortError") return; // intentional abort
          setIsTyping(false);
          setMessages((prev) => [
            ...prev,
            {
              id: Date.now() + 1,
              role: "assistant",
              text: `⚠️ Connection error: ${err.message}. Make sure the backend is running on port 3001.`,
            },
          ]);
          abortRef.current = null;
        });
    },
    [isTyping, activeChat, activeGrade, activeSubject, activeChapter]
  );

  const handlePromptClick = useCallback(
    (promptText) => {
      handleSend(promptText);
    },
    [handleSend]
  );

  /* ─── Selector step handlers ─── */

  const handleGradeSelect = (item) => {
    setActiveGrade(item.label);
    setSelectorStep("subject");
  };

  const handleSubjectSelect = (item) => {
    setActiveSubject(item.id);
    setActiveChapter(DEFAULTS.chapter);
    setSelectorStep("chapter");
  };

  const handleChapterSelect = (item) => {
    setActiveChapter(item.label);
    setSelectorStep("chat");
  };

  /* ─── Selector step data ─── */

  const selectorData = {
    grade: {
      title: "Select your standard",
      subtitle: "Choose the grade you are studying in",
      items: gradeItems,
      selected: activeGrade,
      onSelect: handleGradeSelect,
    },
    subject: {
      title: "Select your subject",
      subtitle: `Chose by grade – ${activeGrade}`,
      items: subjectItems,
      selectedValue: activeSubject,
      onSelect: handleSubjectSelect,
      compareField: "id",
    },
    chapter: {
      title: "Select a chapter",
      subtitle: `Subject – ${getSubjectLabel(activeSubject)}`,
      items: getChaptersForSubject(activeSubject),
      selectedValue: activeChapter,
      onSelect: handleChapterSelect,
      compareField: "label",
    },
  };

  // ─── Not authenticated → show sign-in modal ───
  if (!isAuthenticated) {
    return (
      <SignInModal
        onSignIn={async (email, password) => {
          try {
            await signIn(email, password);
          } catch (err) {
            handleAuthError(err.message || "Sign in failed");
          }
        }}
        onSignUp={async (email, password) => {
          try {
            await signUp(email, password);
          } catch (err) {
            handleAuthError(err.message || "Sign up failed");
          }
        }}
        onError={handleAuthError}
      />
    );
  }

  return (
    <div className="page">
      <Sidebar
        activeSubject={activeSubject}
        onSubjectChange={(id) => {
          setActiveSubject(id);
          setActiveChapter(DEFAULTS.chapter);
          if (selectorStep !== "chat") {
            setSelectorStep("subject");
          }
        }}
        activeChat={activeChat}
        onChatSelect={handleChatSelect}
        onNewChat={handleNewChat}
        sessions={sessions}
        onDeleteChat={handleDeleteChat}
        isLoadingSessions={isLoadingSessions}
        showUpgrade={false}
        user={user}
        onSignOut={signOut}
      />

      <div className="page__main">
        <TopNav
          activeGrade={activeGrade}
          onGradeChange={(g) => setActiveGrade(g)}
          subjectItems={subjectItems}
          chapterData={chapterData}
          activeSubject={activeSubject}
          activeChapter={activeChapter}
          onChapterChange={(ch) => {
            setActiveChapter(ch);
            if (selectorStep !== "chat") {
              setSelectorStep("chapter");
            }
          }}
          onSubjectChange={(id) => {
            setActiveSubject(id);
            setActiveChapter(DEFAULTS.chapter);
            if (selectorStep !== "chat") {
              setSelectorStep("subject");
            }
          }}
          user={user}
          onSignOut={signOut}
        />

        <div className="main-content">
          <ChatHistory
            messages={messages}
            activeSubject={activeSubject}
            activeGrade={activeGrade}
            activeChapter={activeChapter}
            onPromptClick={handlePromptClick}
            isTyping={isTyping}
            selectorStep={selectorStep}
            selectorData={selectorStep !== "chat" ? selectorData[selectorStep] : null}
          />
        </div>

        <ChatInput
          onSend={handleSend}
          placeholder={`Ask anything about ${activeGrade} ${getSubjectLabel(activeSubject)} – ${getChapterLabel(activeChapter)}...`}
          disabled={isTyping}
        />
      </div>
    </div>
  );
}

export default App;