/**
 * Cache Manager - ระบบจัดการ Cache
 * Chahua Development Thailand
 * CEO: Saharath C.
 * 
 * Purpose: จัดการการ cache ข้อมูลเพื่อประสิทธิภาพ
 */

const fs = require('fs');
const path = require('path');

class CacheManager {
    constructor(options = {}) {
        this.config = {
            defaultTTL: options.defaultTTL || 300, // 5 minutes
            maxSize: options.maxSize || 1000, // Max 1000 items
            persistPath: options.persistPath || './logs/cache',
            enablePersistence: options.enablePersistence || false,
            cleanupInterval: options.cleanupInterval || 60000, // 1 minute
            compressionEnabled: options.compressionEnabled || false
        };
        
        this.cache = new Map();
        this.accessTimes = new Map();
        this.stats = {
            hits: 0,
            misses: 0,
            sets: 0,
            deletes: 0,
            cleanups: 0
        };
        
        this.setupCleanupTimer();
        
        if (this.config.enablePersistence) {
            this.loadFromDisk();
        }
        
        console.log('Cache Manager initialized');
    }

    async set(key, value, options = {}) {
        try {
            const ttl = options.ttl || this.config.defaultTTL;
            const expiry = Date.now() + (ttl * 1000);
            
            const cacheItem = {
                key,
                value,
                expiry,
                size: this.calculateSize(value),
                created: Date.now(),
                accessed: Date.now(),
                hits: 0
            };
            
            // Check if we need to make space
            if (this.cache.size >= this.config.maxSize) {
                this.evictLRU();
            }
            
            this.cache.set(key, cacheItem);
            this.accessTimes.set(key, Date.now());
            this.stats.sets++;
            
            if (this.config.enablePersistence) {
                await this.persistToDisk();
            }
            
            console.log(`Cache SET: ${key} (TTL: ${ttl}s)`);
            return true;
            
        } catch (error) {
            console.error('Cache set error:', error.message);
            return false;
        }
    }

    async get(key) {
        try {
            const item = this.cache.get(key);
            
            if (!item) {
                this.stats.misses++;
                console.log(`Cache MISS: ${key}`);
                return null;
            }
            
            // Check if expired
            if (Date.now() > item.expiry) {
                this.cache.delete(key);
                this.accessTimes.delete(key);
                this.stats.misses++;
                console.log(`Cache EXPIRED: ${key}`);
                return null;
            }
            
            // Update access info
            item.accessed = Date.now();
            item.hits++;
            this.accessTimes.set(key, Date.now());
            this.stats.hits++;
            
            console.log(`Cache HIT: ${key}`);
            return item.value;
            
        } catch (error) {
            console.error('Cache get error:', error.message);
            this.stats.misses++;
            return null;
        }
    }

    async delete(key) {
        try {
            const deleted = this.cache.delete(key);
            this.accessTimes.delete(key);
            
            if (deleted) {
                this.stats.deletes++;
                console.log(`Cache DELETE: ${key}`);
                
                if (this.config.enablePersistence) {
                    await this.persistToDisk();
                }
            }
            
            return deleted;
            
        } catch (error) {
            console.error('Cache delete error:', error.message);
            return false;
        }
    }

    async clear() {
        try {
            const size = this.cache.size;
            this.cache.clear();
            this.accessTimes.clear();
            
            if (this.config.enablePersistence) {
                await this.persistToDisk();
            }
            
            console.log(`Cache CLEARED: ${size} items removed`);
            return true;
            
        } catch (error) {
            console.error('Cache clear error:', error.message);
            return false;
        }
    }

    has(key) {
        const item = this.cache.get(key);
        if (!item) return false;
        
        // Check if expired
        if (Date.now() > item.expiry) {
            this.cache.delete(key);
            this.accessTimes.delete(key);
            return false;
        }
        
        return true;
    }

    keys() {
        const validKeys = [];
        const now = Date.now();
        
        for (const [key, item] of this.cache.entries()) {
            if (now <= item.expiry) {
                validKeys.push(key);
            }
        }
        
        return validKeys;
    }

    size() {
        this.cleanup(); // Clean expired items first
        return this.cache.size;
    }

    evictLRU() {
        // Find least recently used item
        let oldestKey = null;
        let oldestTime = Date.now();
        
        for (const [key, time] of this.accessTimes.entries()) {
            if (time < oldestTime) {
                oldestTime = time;
                oldestKey = key;
            }
        }
        
        if (oldestKey) {
            this.cache.delete(oldestKey);
            this.accessTimes.delete(oldestKey);
            console.log(`Cache LRU EVICTED: ${oldestKey}`);
        }
    }

    cleanup() {
        const now = Date.now();
        let cleanedCount = 0;
        
        for (const [key, item] of this.cache.entries()) {
            if (now > item.expiry) {
                this.cache.delete(key);
                this.accessTimes.delete(key);
                cleanedCount++;
            }
        }
        
        if (cleanedCount > 0) {
            this.stats.cleanups++;
            console.log(`Cache CLEANUP: ${cleanedCount} expired items removed`);
        }
        
        return cleanedCount;
    }

    setupCleanupTimer() {
        this.cleanupTimer = setInterval(() => {
            this.cleanup();
        }, this.config.cleanupInterval);
    }

    stopCleanupTimer() {
        if (this.cleanupTimer) {
            clearInterval(this.cleanupTimer);
            this.cleanupTimer = null;
        }
    }

    calculateSize(value) {
        try {
            return JSON.stringify(value).length;
        } catch (error) {
            return 0;
        }
    }

    async persistToDisk() {
        try {
            const cacheDir = path.dirname(this.config.persistPath);
            if (!fs.existsSync(cacheDir)) {
                fs.mkdirSync(cacheDir, { recursive: true });
            }
            
            const cacheData = {
                timestamp: Date.now(),
                cache: Array.from(this.cache.entries()),
                accessTimes: Array.from(this.accessTimes.entries()),
                stats: this.stats
            };
            
            fs.writeFileSync(this.config.persistPath, JSON.stringify(cacheData));
            
        } catch (error) {
            console.error('Cache persist error:', error.message);
        }
    }

    loadFromDisk() {
        try {
            if (!fs.existsSync(this.config.persistPath)) {
                return;
            }
            
            const data = JSON.parse(fs.readFileSync(this.config.persistPath, 'utf8'));
            
            // Restore cache
            this.cache = new Map(data.cache || []);
            this.accessTimes = new Map(data.accessTimes || []);
            this.stats = { ...this.stats, ...data.stats };
            
            // Clean expired items
            this.cleanup();
            
            console.log('Cache loaded from disk');
            
        } catch (error) {
            console.error('Cache load error:', error.message);
        }
    }

    getStats() {
        const totalRequests = this.stats.hits + this.stats.misses;
        const hitRate = totalRequests > 0 ? Math.round((this.stats.hits / totalRequests) * 100) : 0;
        
        return {
            size: this.cache.size,
            hitRate: `${hitRate}%`,
            totalHits: this.stats.hits,
            totalMisses: this.stats.misses,
            totalSets: this.stats.sets,
            totalDeletes: this.stats.deletes,
            totalCleanups: this.stats.cleanups,
            totalRequests
        };
    }

    getDetailedStats() {
        const stats = this.getStats();
        const items = [];
        
        for (const [key, item] of this.cache.entries()) {
            items.push({
                key,
                size: item.size,
                hits: item.hits,
                created: new Date(item.created).toISOString(),
                accessed: new Date(item.accessed).toISOString(),
                expiresIn: Math.max(0, Math.round((item.expiry - Date.now()) / 1000))
            });
        }
        
        // Sort by most accessed
        items.sort((a, b) => b.hits - a.hits);
        
        return {
            ...stats,
            items: items.slice(0, 10) // Top 10 most accessed
        };
    }

    exportCache() {
        const exportData = {
            exportTime: new Date().toISOString(),
            config: this.config,
            stats: this.getStats(),
            items: Array.from(this.cache.entries()).map(([key, item]) => ({
                key,
                value: item.value,
                created: new Date(item.created).toISOString(),
                accessed: new Date(item.accessed).toISOString(),
                hits: item.hits,
                size: item.size
            }))
        };
        
        return exportData;
    }
}

module.exports = CacheManager;