import { db } from "./firebase.js";
import {
    collection,
    doc,
    setDoc,
    getDoc,
    addDoc,
    onSnapshot,
    serverTimestamp,
    query,
    where,
    getDocs,
    orderBy,
    updateDoc,
    getCountFromServer,
    deleteDoc
} from "https://www.gstatic.com/firebasejs/10.7.1/firebase-firestore.js";

// Collection references
const ROOMS_COLLECTION = "classrooms";
const USERS_COLLECTION = "users";
const PROGRESS_COLLECTION = "progress";
const CHALLENGES_COLLECTION = "challenges";

/**
 * Creates a new classroom room
 * @param {string} promotedCode - Optional custom code
 * @param {string} hostName - Optional host name
 * @returns {Promise<string>} The room code
 */
export async function createRoom(promotedCode = null, hostName = 'Unknown') {
    const roomCode = promotedCode || Math.floor(1000 + Math.random() * 9000).toString();
    const roomRef = doc(db, ROOMS_COLLECTION, roomCode);

    await setDoc(roomRef, {
        createdAt: serverTimestamp(),
        active: true,
        host: hostName
    });

    return roomCode;
}

/**
 * Cleans up rooms older than 14 days (inactive)
 */
export async function cleanupOldRooms() {
    try {
        const fourteenDaysAgo = new Date();
        fourteenDaysAgo.setDate(fourteenDaysAgo.getDate() - 14);

        const roomsRef = collection(db, ROOMS_COLLECTION);
        const q = query(roomsRef, where("createdAt", "<", fourteenDaysAgo));

        const snapshot = await getDocs(q);
        if (snapshot.empty) return;

        const deletePromises = snapshot.docs.map(doc => deleteDoc(doc.ref));
        await Promise.all(deletePromises);
        console.log(`Cleaned up ${snapshot.size} old rooms.`);
    } catch (e) {
        console.error("Cleanup failed:", e);
    }
}

/**
 * Verifies instructor password against Firestore (Auto-seeds if missing)
 * @param {string} inputPassword 
 * @returns {Promise<boolean>}
 */
export async function verifyInstructorPassword(inputPassword) {
    const settingsRef = doc(db, "settings", "instructor_auth");
    const snap = await getDoc(settingsRef);

    if (!snap.exists()) {
        // Auto-seed default password for migration
        await setDoc(settingsRef, { password: "88300" });
        return inputPassword === "88300";
    }

    return snap.data().password === inputPassword;
}

/**
 * Joins a room with Dual-Role Auth / Session Persistence logic
 * @param {string} roomCode 
 * @param {string} nickname 
 * @returns {Promise<string>} The student ID (userId)
 */
export async function joinRoom(roomCode, nickname) {
    // 1. Verify Room Exists
    const roomRef = doc(db, ROOMS_COLLECTION, roomCode);
    const roomSnap = await getDoc(roomRef);

    if (!roomSnap.exists()) {
        throw new Error("教室代碼不存在");
    }

    // 2. Check if user already exists in this room (Cross-device sync)
    const usersRef = collection(db, USERS_COLLECTION);
    const q = query(
        usersRef,
        where("current_room", "==", roomCode),
        where("nickname", "==", nickname)
    );

    const querySnapshot = await getDocs(q);

    if (!querySnapshot.empty) {
        // User exists, return existing ID
        const userDoc = querySnapshot.docs[0];
        // Update last active
        await updateDoc(userDoc.ref, { last_active: serverTimestamp() });
        return userDoc.id;
    }

    // 3. Create new user if not exists
    const newUserRef = await addDoc(usersRef, {
        nickname,
        current_room: roomCode,
        role: 'student',
        joinedAt: serverTimestamp(),
        last_active: serverTimestamp()
    });

    return newUserRef.id;
}

/**
 * Submits a prompt for a specific level
 * @param {string} userId 
 * @param {string} roomCode 
 * @param {string} challengeId 
 * @param {string} prompt 
 */
export async function submitPrompt(userId, roomCode, challengeId, prompt) {
    const text = prompt.trim();
    if (!text) return;

    // Check if submission already exists to update it, or add new
    // For simplicity, we can just use a composite ID or query first.
    // Let's use addDoc for history, or setDoc with custom ID for latest state.
    // Requirement says "progress/{docId}", let's query first to see if we should update.

    const progressRef = collection(db, PROGRESS_COLLECTION);
    const q = query(
        progressRef,
        where("userId", "==", userId),
        where("challengeId", "==", challengeId)
    );
    const snapshot = await getDocs(q);

    if (!snapshot.empty) {
        // Update existing
        const docRef = snapshot.docs[0].ref;
        await updateDoc(docRef, {
            status: "completed",
            submission_prompt: text,
            roomCode: roomCode, // Ensure roomCode is updated for legacy docs
            timestamp: serverTimestamp()
        });
    } else {
        // Create new
        await addDoc(progressRef, {
            userId,
            roomCode, // Added for easier querying by instructor
            challengeId,
            status: "completed",
            submission_prompt: text,
            timestamp: serverTimestamp()
        });
    }

    // Update user last active
    const userRef = doc(db, USERS_COLLECTION, userId);
    await updateDoc(userRef, { last_active: serverTimestamp() });
}

/**
 * Records that a user has started a challenge
 * @param {string} userId 
 * @param {string} roomCode 
 * @param {string} challengeId 
 */
export async function startChallenge(userId, roomCode, challengeId) {
    const progressRef = collection(db, PROGRESS_COLLECTION);
    const q = query(
        progressRef,
        where("userId", "==", userId),
        where("challengeId", "==", challengeId)
    );
    const snapshot = await getDocs(q);

    if (!snapshot.empty) {
        // Already exists (maybe started or completed)
        const docData = snapshot.docs[0].data();
        if (docData.status === 'completed') return; // Don't overwrite completed status

        // If already started, maybe just update timestamp? Or do nothing.
        // Let's update timestamp to reflect "last worked on"
        await updateDoc(snapshot.docs[0].ref, {
            status: 'started',
            roomCode: String(roomCode), // Ensure roomCode is updated
            timestamp: serverTimestamp()
        });
    } else {
        // Create new progress entry with 'started' status
        await addDoc(progressRef, {
            userId,
            roomCode: String(roomCode),
            challengeId,
            status: 'started',
            startedAt: serverTimestamp(), // Keep original start time if we want to track duration
            timestamp: serverTimestamp()  // Last update time
        });
    }

    // Update user last active
    const userRef = doc(db, USERS_COLLECTION, userId);
    await updateDoc(userRef, { last_active: serverTimestamp() });
}

/**
 * Subscribes to room users and their progress
 * @param {string} roomCode 
 * @param {Function} callback (studentsWithProgress) => void
 * @returns {Function} Unsubscribe function
 */
export function subscribeToRoom(roomCode, callback) {
    // Listen to users in the room
    const usersQuery = query(collection(db, USERS_COLLECTION), where("current_room", "==", roomCode));

    // We also need progress. Real-time listening to TWO collections and joining them 
    // is complex in NoSQL. 
    // Strategy: Listen to Users. When Users change, fetch all progress for this room (or listen to it).
    // Simpler efficient approach for dashboard: 
    // Listen to Progress independent of users? No, we need user list.

    // Let's listen to Users, and inside, listen to Progress for this room.

    let unsubscribeProgress = () => { };

    const unsubscribeUsers = onSnapshot(usersQuery, (userSnap) => {
        const users = [];
        userSnap.forEach((doc) => {
            users.push({ id: doc.id, ...doc.data() });
        });

        // Now listen to progress for this room
        const progressQuery = query(collection(db, PROGRESS_COLLECTION), where("roomCode", "==", roomCode));

        unsubscribeProgress(); // Detach previous listener if any

        unsubscribeProgress = onSnapshot(progressQuery, (progressSnap) => {
            const progressMap = {}; // { userId: { challengeId: { status, prompt } } }

            progressSnap.forEach(doc => {
                const data = doc.data();
                if (!progressMap[data.userId]) progressMap[data.userId] = {};
                progressMap[data.userId][data.challengeId] = {
                    status: data.status,
                    prompt: data.submission_prompt,
                    timestamp: data.timestamp,
                    likes: data.likes || 0 // Include likes
                };
            });

            // Merge back to users
            const combinedData = users.map(user => ({
                ...user,
                progress: progressMap[user.id] || {}
            }));

            callback(combinedData);
        });
    });

    return () => {
        unsubscribeUsers();
        unsubscribeProgress();
    };
}

/**
 * Fetches prompts for Peer Learning
 */
export async function getPeerPrompts(roomCode, challengeId) {
    const progressRef = collection(db, PROGRESS_COLLECTION);

    // Query completions (filtered by challenge, status)
    const q = query(
        progressRef,
        where("challengeId", "==", challengeId),
        where("status", "==", "completed")
    );

    try {
        const snapshot = await getDocs(q);
        const entries = [];

        for (const docSnapshot of snapshot.docs) {
            const data = docSnapshot.data();

            // Fetch nickname & user room info
            // We fetch user first to verify room if needed
            const userSnap = await getDoc(doc(db, USERS_COLLECTION, data.userId));
            if (!userSnap.exists()) continue;

            const userData = userSnap.data();

            // Room Code Check
            // 1. Check direct reference in progress (Fastest)
            // 2. Fallback to user's current room (Legacy support)
            const targetRoom = data.roomCode || userData.current_room;

            if (String(targetRoom) !== String(roomCode)) {
                continue;
            }

            entries.push({
                id: docSnapshot.id,
                userId: data.userId,
                nickname: userData.nickname,
                prompt: data.submission_prompt,
                timestamp: data.timestamp,
                likes: data.likes || 0,
                likedBy: data.likedBy || []
            });
        }
        return entries;

    } catch (e) {
        console.error("Error fetching peer prompts:", e);
        return [];
    }
}

/**
 * Resets a user's progress for a specific challenge (sets status to 'started')
 * @param {string} userId 
 * @param {string} roomCode 
 * @param {string} challengeId 
 */
export async function resetProgress(userId, roomCode, challengeId) {
    const progressRef = collection(db, PROGRESS_COLLECTION);
    const q = query(
        progressRef,
        where("userId", "==", userId),
        where("challengeId", "==", challengeId)
    );
    const snapshot = await getDocs(q);

    if (!snapshot.empty) {
        // Reset status to 'started' so they can submit again
        await updateDoc(snapshot.docs[0].ref, {
            status: 'started',
            timestamp: serverTimestamp()
        });
    }
}

/**
 * Validates and gets progress for a specific user
 * @param {string} userId 
 * @returns {Promise<Object>} Map of challengeId -> { status, prompt, timestamp }
 */
export async function getUserProgress(userId) {
    const progressRef = collection(db, PROGRESS_COLLECTION);
    const q = query(progressRef, where("userId", "==", userId));
    const snapshot = await getDocs(q);

    const progressMap = {};
    snapshot.forEach(doc => {
        const data = doc.data();
        progressMap[data.challengeId] = data;
    });
    return progressMap;
}

// --- Admin / Challenge Services ---

export async function getChallenges() {
    const q = query(collection(db, CHALLENGES_COLLECTION), orderBy("order", "asc"));
    const snapshot = await getDocs(q);
    return snapshot.docs.map(doc => ({ id: doc.id, ...doc.data() }));
}

export async function createChallenge(data) {
    // data: { level, title, description, link, order }
    await addDoc(collection(db, CHALLENGES_COLLECTION), data);
}

export async function updateChallenge(id, data) {
    await updateDoc(doc(db, CHALLENGES_COLLECTION, id), data);
}

export async function deleteChallenge(id) {
    await deleteDoc(doc(db, CHALLENGES_COLLECTION, id));
}

// --- Social Features ---

const NOTIFICATIONS_COLLECTION = "notifications";

/**
 * Toggles like on a progress submission
 */
export async function toggleLike(progressId, currentUserId, currentNickname, targetUserId, challengeTitle) {
    const progressRef = doc(db, PROGRESS_COLLECTION, progressId);
    const progressSnap = await getDoc(progressRef);

    if (!progressSnap.exists()) return;

    const data = progressSnap.data();
    const likedBy = data.likedBy || [];
    const isLiked = likedBy.includes(currentUserId);

    if (isLiked) {
        // Unlike
        await updateDoc(progressRef, {
            likes: (data.likes || 1) - 1,
            likedBy: likedBy.filter(id => id !== currentUserId)
        });
    } else {
        // Like
        await updateDoc(progressRef, {
            likes: (data.likes || 0) + 1,
            likedBy: [...likedBy, currentUserId]
        });

        // Send Notification if not liking self
        if (targetUserId !== currentUserId) {
            await addDoc(collection(db, NOTIFICATIONS_COLLECTION), {
                recipientId: targetUserId,
                senderNickname: currentNickname,
                challengeTitle: challengeTitle,
                type: 'like',
                timestamp: serverTimestamp(),
                read: false
            });
        }
    }
}

/**
 * Listen to notifications for a user
 */
export function subscribeToNotifications(userId, callback) {
    const q = query(
        collection(db, NOTIFICATIONS_COLLECTION),
        where("recipientId", "==", userId),
        where("read", "==", false),
        orderBy("timestamp", "desc")
    );

    return onSnapshot(q, (snapshot) => {
        const notifications = [];
        snapshot.forEach(doc => {
            notifications.push({ id: doc.id, ...doc.data() });
        });
        callback(notifications);
    });
}

/**
 * Mark notification as read
 */
export async function markNotificationRead(notificationId) {
    await updateDoc(doc(db, NOTIFICATIONS_COLLECTION, notificationId), {
        read: true
    });
}

/**
 * Gets the number of users in a room
 * @param {string} roomCode 
 * @returns {Promise<number>}
 */
/**
 * Gets the number of users in a room
 * @param {string} roomCode 
 * @returns {Promise<number>}
 */
export async function getClassSize(roomCode) {
    const q = query(
        collection(db, USERS_COLLECTION),
        where("current_room", "==", roomCode)
    );
    const snapshot = await getCountFromServer(q);
    return snapshot.data().count;
}

/**
 * Gets the number of students who have reached a higher or equal stage
 * Used for determining percentile ranking
 * @param {string} roomCode
 * @param {number} targetStage
 * @returns {Promise<number>}
 */
export async function getHigherStageCount(roomCode, targetStage) {
    const q = query(
        collection(db, USERS_COLLECTION),
        where("current_room", "==", roomCode),
        where("monster_stage", ">=", targetStage)
    );
    const snapshot = await getCountFromServer(q);
    return snapshot.data().count;
}

/**
 * Updates a student's monster stage and specific form
 * @param {string} userId
 * @param {number} newStage
 * @param {string} monsterId (Optional, for persisting specific form)
 */
export async function updateUserMonster(userId, newStage, monsterId = undefined) {
    const userRef = doc(db, USERS_COLLECTION, userId);
    const data = { monster_stage: newStage };
    // If monsterId is explicitly provided (including null/empty string), update it.
    // If undefined, leave as is. 
    // We want to allow clearing it (null) or setting 'Egg'.
    if (monsterId !== undefined) {
        data.monster_id = monsterId;
    }

    await updateDoc(userRef, data);
}

/**
 * Gets user profile data
 * @param {string} userId
 * @returns {Promise<Object>}
 */
export async function getUser(userId) {
    const userRef = doc(db, USERS_COLLECTION, userId);
    const snap = await getDoc(userRef);
    return snap.exists() ? snap.data() : null;
}

/**
 * Removes a user from the classroom (Kick)
 * @param {string} userId 
 */
/**
 * Subscribes to a single user's progress for real-time updates
 * @param {string} userId 
 * @param {Function} callback (progressMap) => void
 * @returns {Function} unsubscribe
 */
export function subscribeToUserProgress(userId, callback) {
    const q = query(
        collection(db, PROGRESS_COLLECTION),
        where("userId", "==", userId)
    );

    return onSnapshot(q, (snapshot) => {
        const progressMap = {};
        snapshot.forEach(doc => {
            const data = doc.data();
            progressMap[data.challengeId] = data;
        });
        callback(progressMap);
    });
}

export async function removeUser(userId) {
    if (!userId) return;
    await deleteDoc(doc(db, USERS_COLLECTION, userId));
}