/**
 * ╔══════════════════════════════════════════════════════════════════════════════╗
 * ║                    PATTERN MEMORY SERVICE - ENTERPRISE A+                      ║
 * ║                                                                                ║
 * ║  Records and analyzes query patterns with persistent SQLite storage.          ║
 * ║  Enables:                                                                      ║
 * ║    • Learning which sources are best for which queries                        ║
 * ║    • Predictive pre-fetching based on historical patterns                     ║
 * ║    • Performance optimization recommendations                                  ║
 * ║    • Cross-session memory persistence                                          ║
 * ║                                                                                ║
 * ║  Schema: mcp_query_patterns table (defined in schema.sql)                     ║
 * ╚══════════════════════════════════════════════════════════════════════════════╝
 */

import { v4 as uuidv4 } from 'uuid';
import crypto from 'crypto';
import type { StorageAdapter } from './StorageAdapter.js';
import { logger } from '../../utils/logger.js';
import { eventBus, type EventType } from '../EventBus.js';

// ═══════════════════════════════════════════════════════════════════════════════
// INTERFACES
// ═══════════════════════════════════════════════════════════════════════════════

export interface QueryPattern {
    id: string;
    widgetId: string;
    queryType: string;
    querySignature: string;
    sourceUsed: string;
    latencyMs: number;
    resultSize?: number;
    success: boolean;
    userContext?: {
        userId?: string;
        timeOfDay: number;
        dayOfWeek: number;
    };
    timestamp: Date;
}

export interface SimilarQuery {
    pattern: QueryPattern;
    similarity: number;
}

export interface UsagePattern {
    widgetId: string;
    commonSources: string[];
    averageLatency: number;
    successRate: number;
    queryCount: number;
    timePatterns: {
        hour: number;
        frequency: number;
    }[];
    lastActivity: Date | null;
}

export interface PatternStatistics {
    totalPatterns: number;
    uniqueWidgets: number;
    uniqueSources: number;
    avgLatencyMs: number;
    successRate: number;
    queriesLast24h: number;
    queriesLast7d: number;
    topSources: { source: string; count: number; avgLatency: number }[];
    topWidgets: { widget: string; count: number }[];
}

// ═══════════════════════════════════════════════════════════════════════════════
// PATTERN MEMORY SERVICE - ENTERPRISE IMPLEMENTATION
// ═══════════════════════════════════════════════════════════════════════════════

export class PatternMemory {
    private storage: StorageAdapter | null = null;
    private initialized: boolean = false;
    private writeQueue: QueryPattern[] = [];
    private flushInterval: ReturnType<typeof setInterval> | null = null;

    // In-memory cache for hot data (last 1000 patterns)
    private cache: QueryPattern[] = [];
    private readonly CACHE_SIZE = 1000;
    private readonly FLUSH_INTERVAL_MS = 5000; // Batch writes every 5 seconds
    private readonly MAX_DB_PATTERNS = 100000;

    constructor(storage?: StorageAdapter) {
        if (storage) {
            this.storage = storage;
            this.initialize();
        }
    }

    /**
     * Initialize with storage adapter
     */
    public setStorage(storage: StorageAdapter): void {
        this.storage = storage;
        this.initialize();
    }

    /**
     * Initialize the service
     */
    private async initialize(): Promise<void> {
        if (this.initialized || !this.storage) return;

        try {
            // Postgres uses different syntax for some things, but basic CREATE TABLE is mostly compatible
            // except for DATETIME DEFAULT CURRENT_TIMESTAMP vs TIMESTAMP WITH TIME ZONE
            const isPostgres = this.storage.mode === 'postgres';
            const timestampType = isPostgres ? 'TIMESTAMP WITH TIME ZONE' : 'DATETIME';

            await this.storage.execute(`
                CREATE TABLE IF NOT EXISTS mcp_query_patterns (
                    id TEXT PRIMARY KEY,
                    widget_id TEXT NOT NULL,
                    query_type TEXT NOT NULL,
                    query_signature TEXT NOT NULL,
                    source_used TEXT NOT NULL,
                    latency_ms INTEGER NOT NULL,
                    result_size INTEGER,
                    success BOOLEAN NOT NULL,
                    user_context TEXT,
                    timestamp ${timestampType} NOT NULL DEFAULT CURRENT_TIMESTAMP
                )
            `);

            // Create indexes for fast queries
            await this.storage.execute(`CREATE INDEX IF NOT EXISTS idx_query_patterns_widget 
                ON mcp_query_patterns(widget_id, timestamp DESC)`);
            await this.storage.execute(`CREATE INDEX IF NOT EXISTS idx_query_patterns_signature 
                ON mcp_query_patterns(query_signature)`);
            await this.storage.execute(`CREATE INDEX IF NOT EXISTS idx_query_patterns_source 
                ON mcp_query_patterns(source_used, timestamp DESC)`);

            // Load recent patterns into cache
            await this.loadCacheFromDb();

            // Start background flush
            this.flushInterval = setInterval(() => this.flushWriteQueue(), this.FLUSH_INTERVAL_MS);

            this.initialized = true;
            logger.info(`🧠 PatternMemory initialized with ${this.storage.mode} storage`);
        } catch (error) {
            logger.error('❌ PatternMemory initialization failed:', error);
            // Fall back to in-memory only
            this.initialized = true;
        }
    }

    /**
     * Load recent patterns from database into cache
     */

    private async loadCacheFromDb(): Promise<void> {
        if (!this.storage) return;

        try {
            const rows = await this.storage.queryAll(`
                SELECT * FROM mcp_query_patterns 
                ORDER BY timestamp DESC 
                LIMIT ?
            `, [this.CACHE_SIZE]);

            for (const row of rows) {
                this.cache.push(this.rowToPattern(row));
            }

            logger.info(`📦 Loaded ${this.cache.length} patterns into memory cache`);
        } catch (error) {
            logger.warn('⚠️ Failed to load pattern cache:', error);
        }
    }

    /**
     * Convert database row to QueryPattern
     */
    private rowToPattern(row: any): QueryPattern {
        return {
            id: row.id,
            widgetId: row.widget_id,
            queryType: row.query_type,
            querySignature: row.query_signature,
            sourceUsed: row.source_used,
            latencyMs: row.latency_ms,
            resultSize: row.result_size || undefined,
            success: Boolean(row.success),
            userContext: row.user_context ? JSON.parse(row.user_context) : undefined,
            timestamp: new Date(row.timestamp)
        };
    }

    /**
     * Record a query pattern for learning (async, batched)
     */
    async recordQuery(params: {
        widgetId: string;
        queryType: string;
        queryParams: any;
        sourceUsed: string;
        latencyMs: number;
        resultSize?: number;
        success: boolean;
        userId?: string;
    }): Promise<void> {
        const id = uuidv4();
        const signature = this.generateSignature(params.queryType, params.queryParams);

        const userContext = {
            userId: params.userId,
            timeOfDay: new Date().getHours(),
            dayOfWeek: new Date().getDay()
        };

        const pattern: QueryPattern = {
            id,
            widgetId: params.widgetId,
            queryType: params.queryType,
            querySignature: signature,
            sourceUsed: params.sourceUsed,
            latencyMs: params.latencyMs,
            resultSize: params.resultSize,
            success: params.success,
            userContext,
            timestamp: new Date()
        };

        // Add to cache (hot data)
        this.cache.unshift(pattern);
        if (this.cache.length > this.CACHE_SIZE) {
            this.cache.pop();
        }

        // Queue for database write
        this.writeQueue.push(pattern);

        // Emit event for real-time monitoring
        eventBus.emit('pattern:recorded' as EventType, {
            widgetId: params.widgetId,
            sourceUsed: params.sourceUsed,
            latencyMs: params.latencyMs,
            success: params.success
        });
    }

    /**
     * Flush write queue to database (batched writes)
     */
    private async flushWriteQueue(): Promise<void> {
        if (!this.storage || this.writeQueue.length === 0) return;

        const patterns = [...this.writeQueue];
        this.writeQueue = [];

        try {
            const columns = [
                'id', 'widget_id', 'query_type', 'query_signature', 'source_used',
                'latency_ms', 'result_size', 'success', 'user_context', 'timestamp'
            ];

            const rows = patterns.map(p => [
                p.id,
                p.widgetId,
                p.queryType,
                p.querySignature,
                p.sourceUsed,
                p.latencyMs,
                p.resultSize ?? null,
                p.success, // Use boolean directly for Postgres compatibility
                p.userContext ? JSON.stringify(p.userContext) : null,
                p.timestamp.toISOString()
            ]);

            await this.storage.batchInsert('mcp_query_patterns', columns, rows);

            // Cleanup old patterns periodically
            if (Math.random() < 0.01) { // 1% chance per flush
                this.cleanupOldPatterns(); // No await to keep it background
            }

        } catch (error) {
            logger.error('❌ Failed to flush pattern write queue:', error);
            // Put patterns back in queue
            this.writeQueue.unshift(...patterns);
        }
    }

    /**
     * Cleanup old patterns to prevent database bloat
     */
    private async cleanupOldPatterns(): Promise<void> {
        if (!this.storage) return;

        try {
            const thirtyDaysAgo = new Date();
            thirtyDaysAgo.setDate(thirtyDaysAgo.getDate() - 30);

            // Need to fix this query for Postgres compatibility if nested subquery limit issues arise
            // But standard SQL roughly supports DELETE...
            // Postgres supports DELETE FROM ... WHERE id NOT IN (...)
            await this.storage.execute(`
                DELETE FROM mcp_query_patterns 
                WHERE timestamp < ?
                AND id NOT IN (
                    SELECT id FROM mcp_query_patterns 
                    ORDER BY timestamp DESC 
                    LIMIT ?
                )
            `, [thirtyDaysAgo.toISOString(), this.MAX_DB_PATTERNS]);

            logger.debug('🧹 Cleaned up old query patterns');
        } catch (error) {
            logger.warn('⚠️ Pattern cleanup failed:', error);
        }
    }

    /**
     * Find similar queries based on signature
     */
    async findSimilarQueries(
        queryType: string,
        queryParams: any,
        limit: number = 10
    ): Promise<SimilarQuery[]> {
        const signature = this.generateSignature(queryType, queryParams);

        // Check cache first
        const cacheMatches = this.cache
            .filter(p => p.querySignature === signature)
            .slice(0, limit);

        let results: SimilarQuery[] = cacheMatches.map(p => ({ pattern: p, similarity: 1.0 }));

        if (results.length >= limit) {
            return results;
        }

        // Query database for more
        if (this.storage) {
            try {
                const remaining = limit - results.length;
                const rows = await this.storage.queryAll(`
                    SELECT * FROM mcp_query_patterns 
                    WHERE query_signature = ?
                    AND id NOT IN (${results.map(() => '?').join(',') || '\'\''})
                    ORDER BY timestamp DESC
                    LIMIT ?
                `, [...results.map(r => r.pattern.id), signature, remaining]);

                const dbMatches = rows.map(row => ({
                    pattern: this.rowToPattern(row),
                    similarity: 1.0
                }));

                results = [...results, ...dbMatches];
            } catch (error) {
                logger.warn('⚠️ Database query failed, using cache:', error);
            }
        }

        return results;
    }

    /**
     * Get widget usage patterns (comprehensive analysis)
     */
    async getWidgetPatterns(widgetId: string): Promise<UsagePattern> {
        const sevenDaysAgo = new Date();
        sevenDaysAgo.setDate(sevenDaysAgo.getDate() - 7);

        let patterns: QueryPattern[] = [];

        // Try database first
        if (this.storage) {
            try {
                const rows = await this.storage.queryAll(`
                    SELECT * FROM mcp_query_patterns 
                    WHERE widget_id = ? AND timestamp > ?
                    ORDER BY timestamp DESC
                `, [widgetId, sevenDaysAgo.toISOString()]);

                patterns = rows.map(row => this.rowToPattern(row));
            } catch (error) {
                logger.warn('⚠️ Database query failed, using cache');
            }
        }

        // Fall back to cache
        if (patterns.length === 0) {
            patterns = this.cache.filter(
                p => p.widgetId === widgetId && p.timestamp > sevenDaysAgo
            );
        }

        // Aggregate statistics
        const sourceCounts = new Map<string, number>();
        const timePatterns = new Map<number, number>();
        let totalLatency = 0;
        let successCount = 0;
        let lastActivity: Date | null = null;

        for (const p of patterns) {
            sourceCounts.set(
                p.sourceUsed,
                (sourceCounts.get(p.sourceUsed) || 0) + 1
            );

            const hour = p.userContext?.timeOfDay || 0;
            timePatterns.set(hour, (timePatterns.get(hour) || 0) + 1);
            totalLatency += p.latencyMs;

            if (p.success) successCount++;
            if (!lastActivity || p.timestamp > lastActivity) {
                lastActivity = p.timestamp;
            }
        }

        const commonSources = Array.from(sourceCounts.entries())
            .sort((a, b) => b[1] - a[1])
            .slice(0, 5)
            .map(([source]) => source);

        const timePatternArray = Array.from(timePatterns.entries())
            .map(([hour, frequency]) => ({ hour, frequency }))
            .sort((a, b) => b.frequency - a.frequency);

        return {
            widgetId,
            commonSources,
            averageLatency: patterns.length > 0 ? totalLatency / patterns.length : 0,
            successRate: patterns.length > 0 ? successCount / patterns.length : 0,
            queryCount: patterns.length,
            timePatterns: timePatternArray,
            lastActivity
        };
    }

    /**
     * Get average latency for a source
     */
    async getAverageLatency(sourceName: string): Promise<number> {
        if (this.storage) {
            try {
                const oneDayAgo = new Date();
                oneDayAgo.setDate(oneDayAgo.getDate() - 1);

                const result = await this.storage.queryOne<{ avg_latency: number }>(`
                    SELECT AVG(latency_ms) as avg_latency 
                    FROM mcp_query_patterns 
                    WHERE source_used = ? AND success = 1 AND timestamp > ?
                `, [sourceName, oneDayAgo.toISOString()]);

                if (result && result.avg_latency !== null) {
                    return result.avg_latency;
                }
                // If DB has no data (result is null or avg_latency is null), fall back to cache
            } catch (error) {
                logger.warn('⚠️ Latency query failed:', error);
            }
        }

        // Fall back to cache
        const oneDayAgo = new Date();
        oneDayAgo.setDate(oneDayAgo.getDate() - 1);

        const sourcePatterns = this.cache.filter(
            p => p.sourceUsed === sourceName && p.success && p.timestamp > oneDayAgo
        );

        if (sourcePatterns.length === 0) return 0;
        return sourcePatterns.reduce((sum, p) => sum + p.latencyMs, 0) / sourcePatterns.length;
    }

    /**
     * Get success rate for a source and query type
     */
    async getSuccessRate(sourceName: string, queryType: string): Promise<number> {
        if (this.storage) {
            try {
                const sevenDaysAgo = new Date();
                sevenDaysAgo.setDate(sevenDaysAgo.getDate() - 7);

                const result = await this.storage.queryOne<{ total: number; successes: number }>(`
                    SELECT 
                        COUNT(*) as total,
                        SUM(CASE WHEN success = 1 THEN 1 ELSE 0 END) as successes
                    FROM mcp_query_patterns 
                    WHERE source_used = ? AND query_type = ? AND timestamp > ?
                `, [sourceName, queryType, sevenDaysAgo.toISOString()]);

                if (result && result.total > 0) {
                    return result.successes / result.total;
                }
                // Fall back to cache if DB yields no matching rows
            } catch (error) {
                logger.warn('⚠️ Success rate query failed:', error);
            }
        }

        // Fall back to cache
        const sevenDaysAgo = new Date();
        sevenDaysAgo.setDate(sevenDaysAgo.getDate() - 7);

        const matching = this.cache.filter(
            p => p.sourceUsed === sourceName &&
                p.queryType === queryType &&
                p.timestamp > sevenDaysAgo
        );

        if (matching.length === 0) return 0;
        return matching.filter(p => p.success).length / matching.length;
    }

    /**
     * Get comprehensive statistics
     */
    async getStatistics(): Promise<PatternStatistics> {
        const now = new Date();
        const oneDayAgo = new Date(now.getTime() - 24 * 60 * 60 * 1000);
        const sevenDaysAgo = new Date(now.getTime() - 7 * 24 * 60 * 60 * 1000);

        if (this.storage) {
            try {
                // Total patterns
                const total = await this.storage.queryScalar<number>('SELECT COUNT(*) FROM mcp_query_patterns') || 0;

                // Unique widgets
                const uniqueWidgets = await this.storage.queryScalar<number>('SELECT COUNT(DISTINCT widget_id) FROM mcp_query_patterns') || 0;

                // Unique sources
                const uniqueSources = await this.storage.queryScalar<number>('SELECT COUNT(DISTINCT source_used) FROM mcp_query_patterns') || 0;

                // Average latency
                const avgLatency = await this.storage.queryScalar<number>('SELECT AVG(latency_ms) FROM mcp_query_patterns WHERE success = 1') || 0;

                // Success rate
                const successRate = await this.storage.queryScalar<number>('SELECT AVG(CAST(success AS FLOAT)) FROM mcp_query_patterns') || 0;

                // Queries last 24h
                const last24h = await this.storage.queryScalar<number>(
                    'SELECT COUNT(*) FROM mcp_query_patterns WHERE timestamp > ?',
                    [oneDayAgo.toISOString()]
                ) || 0;

                // Queries last 7d
                const last7d = await this.storage.queryScalar<number>(
                    'SELECT COUNT(*) FROM mcp_query_patterns WHERE timestamp > ?',
                    [sevenDaysAgo.toISOString()]
                ) || 0;

                // Top sources
                const topSourcesRows = await this.storage.queryAll<{ source_used: string; count: number; avg_latency: number }>(`
                    SELECT source_used, COUNT(*) as count, AVG(latency_ms) as avg_latency
                    FROM mcp_query_patterns
                    GROUP BY source_used
                    ORDER BY count DESC
                    LIMIT 10
                `);
                const topSources = topSourcesRows.map(row => ({
                    source: row.source_used,
                    count: row.count,
                    avgLatency: row.avg_latency || 0
                }));

                // Top widgets
                const topWidgetsRows = await this.storage.queryAll<{ widget_id: string; count: number }>(`
                    SELECT widget_id, COUNT(*) as count
                    FROM mcp_query_patterns
                    GROUP BY widget_id
                    ORDER BY count DESC
                    LIMIT 10
                `);
                const topWidgets = topWidgetsRows.map(row => ({
                    widget: row.widget_id,
                    count: row.count
                }));

                return {
                    totalPatterns: total,
                    uniqueWidgets,
                    uniqueSources,

                    avgLatencyMs: avgLatency,
                    successRate,
                    queriesLast24h: last24h,
                    queriesLast7d: last7d,
                    topSources,
                    topWidgets
                };
            } catch (error) {
                logger.warn('⚠️ Statistics query failed:', error);
            }
        }

        // Fallback to cache-based stats
        const widgets = new Set(this.cache.map(p => p.widgetId));
        const sources = new Set(this.cache.map(p => p.sourceUsed));

        return {
            totalPatterns: this.cache.length,
            uniqueWidgets: widgets.size,
            uniqueSources: sources.size,
            avgLatencyMs: this.cache.length > 0
                ? this.cache.reduce((sum, p) => sum + p.latencyMs, 0) / this.cache.length
                : 0,
            successRate: this.cache.length > 0
                ? this.cache.filter(p => p.success).length / this.cache.length
                : 0,
            queriesLast24h: this.cache.filter(p => p.timestamp > oneDayAgo).length,
            queriesLast7d: this.cache.filter(p => p.timestamp > sevenDaysAgo).length,
            topSources: [],
            topWidgets: []
        };
    }

    /**
     * Force flush all pending writes
     */
    async flush(): Promise<void> {
        this.flushWriteQueue();
    }

    /**
     * Shutdown gracefully
     */
    async shutdown(): Promise<void> {
        if (this.flushInterval) {
            clearInterval(this.flushInterval);
            this.flushInterval = null;
        }
        this.flushWriteQueue();
        logger.info('🧠 PatternMemory shut down gracefully');
    }

    /**
     * Generate query signature for pattern matching
     */
    private generateSignature(queryType: string, queryParams: any): string {
        const normalized = JSON.stringify({
            type: queryType,
            params: this.normalizeParams(queryParams)
        });

        return crypto.createHash('sha256')
            .update(normalized)
            .digest('hex')
            .substring(0, 16);
    }

    /**
     * Normalize query params for signature generation
     */
    private normalizeParams(params: any): any {
        if (!params) return {};

        // Remove volatile params (timestamps, random IDs, etc.)
        const { timestamp, requestId, _t, _ts, ...stable } = params;

        // Sort keys for consistent hashing
        const sorted: any = {};
        Object.keys(stable).sort().forEach(key => {
            sorted[key] = stable[key];
        });

        return sorted;
    }
}