backend/services/credit.js

import { db } from '@/backend/services/firebase';

export async function checkEligibility(sessionId, toolKey, isOwnKey) {
    if (!sessionId) throw new Error("Authentication failed. No session ID provided.");

    const now = new Date();
    const today = now.toLocaleDateString('en-CA'); // Robust YYYY-MM-DD
    
    // Map toolKey to prefix-aware usage key
    const usageKey = isOwnKey ? `own_${toolKey}` : `app_${toolKey}`;

    // 1. Fetch System Tier Settings
    const sysSnapshot = await db.ref('system/settings/tiers').once('value');
    const tiers = sysSnapshot.val() || {};

    const toolMapper = {
        'count_transcript': 'transcript',
        'count_translate': 'translate',
        'count_srt_translate': 'srt_translator',
        'count_tts': 'tts',
        'count_subtitle': 'subtitle_gen',
        'count_creator_text': 'content_creator',
        'count_creator_image': 'ai_image'
    };
    const tierToolKey = toolMapper[toolKey] || toolKey;

    let userKey, userData, userClass;

    if (sessionId === 'free_access') {
        userClass = 'FREE';
        userData = { Usage: {}, Credits: 0, Class: 'FREE' };
    } else {
        const snapshot = await db.ref('users').orderByChild('Active_Session_ID').equalTo(sessionId).once('value');
        if (!snapshot.exists()) throw new Error("Invalid Membership ID. Please login again.");
        userKey = Object.keys(snapshot.val())[0];
        userData = snapshot.val()[userKey];
        if (userData.Status !== 'ACTIVE') throw new Error("Account suspended. Please contact admin.");
        userClass = userData.Class === 'MEMBER+' ? 'MEMBER_PLUS' : 'MEMBER';
    }

    const tierConfig = tiers[userClass] || { tools: {}, ownTools: {}, limits: {}, ownLimits: {}, apiAccess: { app: true, own: true } };

    // 2. CHECK API ACCESS PERMISSIONS
    if (isOwnKey && tierConfig.apiAccess?.own === false) {
        throw new Error(`OWN_API_RESTRICTED: Your ${userClass} class is not allowed to use private API keys.`);
    }
    if (!isOwnKey && tierConfig.apiAccess?.app === false) {
        throw new Error(`APP_API_RESTRICTED: Shared App API is currently disabled for your class.`);
    }

    // 3. CHECK SPECIFIC TOOL STATUS FOR TIER (Mode Specific)
    const toolMap = isOwnKey ? (tierConfig.ownTools || {}) : (tierConfig.tools || {});
    if (toolMap[tierToolKey] === false) {
        throw new Error(`TOOL_DISABLED: This tool is disabled in ${isOwnKey ? 'Own API' : 'App API'} mode for ${userClass} class.`);
    }

    const usage = (userData.Last_Usage_Date === today) ? (userData.Usage || {}) : {};
    
    // 4. CHECK LIMITS (Mode Specific)
    const limit = isOwnKey ? (tierConfig.ownLimits?.[tierToolKey] ?? -1) : (tierConfig.limits?.[tierToolKey] ?? -1);
    
    if (limit !== -1) {
        const currentCount = parseInt(usage[usageKey] || 0);
        if (currentCount >= limit) {
            throw new Error(`DAILY_QUOTA_REACHED: Your ${userClass} daily limit for ${isOwnKey ? 'Own' : 'App'} API has been reached.`);
        }
    }

    // 5. CHECK CREDITS (Only if using App API)
    let cost = 0;
    if (!isOwnKey) {
        const costMap = {
            'count_transcript': 1, 'count_translate': 1, 'count_srt_translate': 5,
            'count_tts': 3, 'count_subtitle': 1, 'count_creator_text': 1, 'count_creator_image': 5
        };
        cost = costMap[toolKey] || 1;
        
        if (userClass === 'MEMBER_PLUS') {
            const freeTools = ['count_transcript', 'count_translate', 'count_subtitle', 'count_creator_text'];
            if (freeTools.includes(toolKey)) cost = 0;
        }
        if (userClass === 'FREE') cost = 0;

        const currentCredits = userData.Credits || 0;
        if (cost > 0 && currentCredits < cost) {
            throw new Error(`INSUFFICIENT_BALANCE: This task costs ${cost} credits. Your balance is ${currentCredits}.`);
        }
    }

    return { userKey, userData, usageKey, cost, today, isGuest: (userClass === 'FREE'), isOwnKey };
}

export async function commitDeduction(eligibilityData, toolKey) {
    if (!eligibilityData) return; 
    const { userKey, userData, usageKey, cost, today, isGuest } = eligibilityData;
    
    if (isGuest) return;

    const updates = {};
    if (cost > 0) {
        const newBalance = (userData.Credits || 0) - cost;
        updates[`users/${userKey}/Credits`] = newBalance >= 0 ? newBalance : 0;
    }

    if (userData.Last_Usage_Date !== today) {
        updates[`users/${userKey}/Last_Usage_Date`] = today;
        updates[`users/${userKey}/Usage`] = { [usageKey]: 1 };
    } else {
        const currentUsage = (userData.Usage && userData.Usage[usageKey]) || 0;
        updates[`users/${userKey}/Usage/${usageKey}`] = currentUsage + 1;
    }

    await db.ref().update(updates);
}

export async function processFreePool(toolKey) {
    const today = new Date().toLocaleDateString('en-CA');
    const poolPath = `system/daily_pool/${today}/app_${toolKey}`; // Default to app prefix for free pool
    const snapshot = await db.ref(poolPath).once('value');
    const current = snapshot.val() || 0;
    await db.ref(poolPath).set(current + 1);
}