/**
 * ╔══════════════════════════════════════════════════════════════════════════════╗
 * ║                    FAILURE MEMORY SERVICE - ENTERPRISE A+                     ║
 * ║                                                                                ║
 * ║  Records and learns from failures with persistent SQLite storage.             ║
 * ║  Enables:                                                                      ║
 * ║    • Self-healing by remembering successful recovery paths                    ║
 * ║    • Avoiding known failure scenarios                                          ║
 * ║    • Predicting failures before they happen                                   ║
 * ║    • Cross-session failure memory persistence                                  ║
 * ║                                                                                ║
 * ║  Schema: mcp_failure_memory table (defined in schema.sql)                     ║
 * ╚══════════════════════════════════════════════════════════════════════════════╝
 */

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

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

export interface Failure {
    id: string;
    sourceName: string;
    errorType: string;
    errorMessage: string;
    errorContext: any;
    queryContext: any;
    recoveryAction?: string;
    recoverySuccess?: boolean;
    recoveryTimeMs?: number;
    occurredAt: Date;
}

export interface RecoveryPath {
    action: string;
    successRate: number;
    averageRecoveryTime: number;
    occurrences: number;
    lastSuccessAt?: Date;
}

export interface FailureStatistics {
    totalFailures: number;
    uniqueErrorTypes: number;
    uniqueSources: number;
    overallRecoveryRate: number;
    averageRecoveryTimeMs: number;
    failuresLast24h: number;
    failuresLast7d: number;
    topErrorTypes: { type: string; count: number; recoveryRate: number }[];
    topFailingSources: { source: string; count: number }[];
    recentRecoveries: { action: string; success: boolean; timeMs: number; at: Date }[];
}

export interface SourceHealthSummary {
    sourceName: string;
    totalFailures: number;
    uniqueErrorTypes: number;
    recoverySuccessRate: number;
    averageRecoveryTime: number;
    isRecurring: boolean;
    lastFailure?: Date;
    recommendedAction?: string;
}

// ═══════════════════════════════════════════════════════════════════════════════
// FAILURE MEMORY SERVICE - ENTERPRISE IMPLEMENTATION
// ═══════════════════════════════════════════════════════════════════════════════

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

    // In-memory cache for hot failures (recent 500)
    private cache: Failure[] = [];
    private readonly CACHE_SIZE = 500;
    private readonly FLUSH_INTERVAL_MS = 3000; // Faster flush for failures
    private readonly MAX_DB_FAILURES = 50000;

    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 {
            const isPostgres = this.storage.mode === 'postgres';
            const timestampType = isPostgres ? 'TIMESTAMP WITH TIME ZONE' : 'DATETIME';

            // Ensure table exists - use exec for DDL statements (more compatible)
            await this.storage.execute(`
                CREATE TABLE IF NOT EXISTS mcp_failure_memory (
                    id TEXT PRIMARY KEY,
                    source_name TEXT NOT NULL,
                    error_type TEXT NOT NULL,
                    error_message TEXT,
                    error_context TEXT,
                    query_context TEXT,
                    recovery_action TEXT,
                    recovery_success BOOLEAN,
                    recovery_time_ms INTEGER,
                    occurred_at ${timestampType} NOT NULL DEFAULT CURRENT_TIMESTAMP
                )
            `);

            // Create indexes
            await this.storage.execute(`CREATE INDEX IF NOT EXISTS idx_failure_memory_source 
                ON mcp_failure_memory(source_name, occurred_at DESC)`);
            await this.storage.execute(`CREATE INDEX IF NOT EXISTS idx_failure_memory_error 
                ON mcp_failure_memory(error_type, occurred_at DESC)`);
            await this.storage.execute(`CREATE INDEX IF NOT EXISTS idx_failure_memory_recovery 
                ON mcp_failure_memory(recovery_action, recovery_success)`);

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

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

            this.initialized = true;
            logger.info(`🛡️ FailureMemory initialized with ${this.storage.mode} persistence`);
        } catch (error) {
            logger.error('❌ FailureMemory initialization failed:', error);
            this.initialized = true;
        }
    }

    /**
     * Load recent failures from database into cache
     */
    private async loadCacheFromDb(): Promise<void> {
        if (!this.storage) return;

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

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

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

    /**
     * Convert database row to Failure
     */
    private rowToFailure(row: any): Failure {
        return {
            id: row.id,
            sourceName: row.source_name,
            errorType: row.error_type,
            errorMessage: row.error_message || '',
            errorContext: row.error_context ? JSON.parse(row.error_context) : {},
            queryContext: row.query_context ? JSON.parse(row.query_context) : {},
            recoveryAction: row.recovery_action || undefined,
            recoverySuccess: row.recovery_success != null ? Boolean(row.recovery_success) : undefined,
            recoveryTimeMs: row.recovery_time_ms || undefined,
            occurredAt: new Date(row.occurred_at)
        };
    }

    /**
     * Record a failure for learning
     */
    async recordFailure(params: {
        sourceName: string;
        error: Error;
        queryContext?: any;
        recoveryAction?: string;
        recoverySuccess?: boolean;
        recoveryTimeMs?: number;
    }): Promise<string> {
        const id = uuidv4();

        const failure: Failure = {
            id,
            sourceName: params.sourceName,
            errorType: params.error.name || 'Error',
            errorMessage: params.error.message,
            errorContext: {
                stack: params.error.stack?.substring(0, 1000), // Limit stack size
                ...this.extractErrorContext(params.error)
            },
            queryContext: params.queryContext || {},
            recoveryAction: params.recoveryAction,
            recoverySuccess: params.recoverySuccess,
            recoveryTimeMs: params.recoveryTimeMs,
            occurredAt: new Date()
        };

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

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

        // Emit event for monitoring
        eventBus.emit('failure:recorded' as EventType, {
            id,
            sourceName: params.sourceName,
            errorType: failure.errorType,
            recoveryAction: params.recoveryAction,
            recoverySuccess: params.recoverySuccess
        });

        // Check if this is a recurring failure
        const isRecurring = await this.isRecurringFailure(params.sourceName, failure.errorType, 30);
        if (isRecurring) {
            eventBus.emit('failure:recurring' as EventType, {
                sourceName: params.sourceName,
                errorType: failure.errorType,
                message: `Recurring failure detected for ${params.sourceName}: ${failure.errorType}`
            });
        }

        return id;
    }

    /**
     * Update a failure with recovery result
     */
    async updateRecovery(
        failureId: string,
        recoveryAction: string,
        success: boolean,
        recoveryTimeMs: number
    ): Promise<void> {
        // Update cache
        const cachedFailure = this.cache.find(f => f.id === failureId);
        if (cachedFailure) {
            cachedFailure.recoveryAction = recoveryAction;
            cachedFailure.recoverySuccess = success;
            cachedFailure.recoveryTimeMs = recoveryTimeMs;
        }

        // Update database
        // Update database
        if (this.storage) {
            try {
                await this.storage.execute(`
                    UPDATE mcp_failure_memory 
                    SET recovery_action = ?, recovery_success = ?, recovery_time_ms = ?
                    WHERE id = ?
                `, [recoveryAction, success ? 1 : 0, recoveryTimeMs, failureId]);
            } catch (error) {
                logger.warn('⚠️ Failed to update recovery:', error);
            }
        }

        eventBus.emit('recovery:completed' as EventType, {
            failureId,
            recoveryAction,
            success,
            recoveryTimeMs
        });
    }

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

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

        try {
            const columns = [
                'id', 'source_name', 'error_type', 'error_message', 'error_context',
                'query_context', 'recovery_action', 'recovery_success', 'recovery_time_ms', 'occurred_at'
            ];

            const rows = failures.map(f => [
                f.id,
                f.sourceName,
                f.errorType,
                f.errorMessage,
                JSON.stringify(f.errorContext),
                JSON.stringify(f.queryContext),
                f.recoveryAction || null,
                f.recoverySuccess != null ? f.recoverySuccess : null, // Use boolean directly
                f.recoveryTimeMs || null,
                f.occurredAt.toISOString()
            ]);

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

            // Cleanup old failures periodically
            if (Math.random() < 0.02) { // 2% chance per flush
                this.cleanupOldFailures(); // Background
            }

        } catch (error) {
            logger.error('❌ Failed to flush failure write queue:', error);
            this.writeQueue.unshift(...failures);
        }
    }

    /**
     * Cleanup old failures
     */
    private async cleanupOldFailures(): Promise<void> {
        if (!this.storage) return;

        try {
            const ninetyDaysAgo = new Date();
            ninetyDaysAgo.setDate(ninetyDaysAgo.getDate() - 90);

            await this.storage.execute(`
                DELETE FROM mcp_failure_memory 
                WHERE occurred_at < ?
                AND id NOT IN (
                    SELECT id FROM mcp_failure_memory 
                    ORDER BY occurred_at DESC 
                    LIMIT ?
                )
            `, [ninetyDaysAgo.toISOString(), this.MAX_DB_FAILURES]);

            logger.debug('🧹 Cleaned up old failure records');
        } catch (error) {
            logger.warn('⚠️ Failure cleanup failed:', error);
        }
    }

    /**
     * Get failure history for a source
     */
    async getFailureHistory(
        sourceName: string,
        limit: number = 50
    ): Promise<Failure[]> {
        if (this.storage) {
            try {
                const rows = await this.storage.queryAll(`
                    SELECT * FROM mcp_failure_memory 
                    WHERE source_name = ?
                    ORDER BY occurred_at DESC
                    LIMIT ?
                `, [sourceName, limit]);

                if (rows.length > 0) {
                    return rows.map(row => this.rowToFailure(row));
                }
                // Fall back to cache if DB empty (e.g. write queue not flushed)
            } catch (error) {
                logger.warn('⚠️ Database query failed:', error);
            }
        }

        return this.cache
            .filter(f => f.sourceName === sourceName)
            .slice(0, limit);
    }

    /**
     * Get successful recovery paths for an error type
     */
    async getRecoveryPaths(
        sourceName: string,
        errorType: string
    ): Promise<RecoveryPath[]> {
        if (this.storage) {
            try {
                const rows = await this.storage.queryAll<{
                    recovery_action: string;
                    total: number;
                    successes: number;
                    avg_time: number;
                    last_success: string | null;
                }>(`
                    SELECT 
                        recovery_action,
                        COUNT(*) as total,
                        SUM(CASE WHEN recovery_success = 1 THEN 1 ELSE 0 END) as successes,
                        AVG(CASE WHEN recovery_success = 1 THEN recovery_time_ms ELSE NULL END) as avg_time,
                        MAX(CASE WHEN recovery_success = 1 THEN occurred_at ELSE NULL END) as last_success
                    FROM mcp_failure_memory 
                    WHERE source_name = ? AND error_type = ?
                    GROUP BY recovery_action
                `, [sourceName, errorType]);

                if (rows.length > 0) {
                    return rows.map(row => ({
                        action: row.recovery_action,
                        successRate: row.total > 0 ? row.successes / row.total : 0,
                        averageRecoveryTime: row.avg_time || 0,
                        occurrences: row.total,
                        lastSuccessAt: row.last_success ? new Date(row.last_success) : undefined
                    }));
                }
                // Fall back to cache
            } catch (error) {
                logger.warn('⚠️ Database query failed:', error);
            }
        }

        // Fallback to in-memory calculation from cache
        const relevant = this.cache.filter(
            f => f.sourceName === sourceName && f.errorType === errorType && f.recoveryAction
        );


        const actionGroups = new Map<string, Failure[]>();
        for (const f of relevant) {
            const action = f.recoveryAction!;
            if (!actionGroups.has(action)) {
                actionGroups.set(action, []);
            }
            actionGroups.get(action)!.push(f);
        }

        return Array.from(actionGroups.entries()).map(([action, failures]) => {
            const successes = failures.filter(f => f.recoverySuccess).length;
            const withTime = failures.filter(f => f.recoveryTimeMs);
            const totalTime = withTime.reduce((sum, f) => sum + (f.recoveryTimeMs || 0), 0);
            const lastSuccess = failures
                .filter(f => f.recoverySuccess)
                .sort((a, b) => b.occurredAt.getTime() - a.occurredAt.getTime())[0];

            return {
                action,
                successRate: failures.length > 0 ? successes / failures.length : 0,
                averageRecoveryTime: withTime.length > 0 ? totalTime / withTime.length : 0,
                occurrences: failures.length,
                lastSuccessAt: lastSuccess?.occurredAt
            };
        }).sort((a, b) => b.successRate - a.successRate);
    }

    /**
     * Get best recovery action for an error
     */
    async getBestRecoveryAction(
        sourceName: string,
        errorType: string
    ): Promise<RecoveryPath | null> {
        const paths = await this.getRecoveryPaths(sourceName, errorType);

        // Find path with best success rate and at least 2 occurrences
        const reliable = paths.filter(p => p.occurrences >= 2 && p.successRate > 0.5);

        if (reliable.length > 0) {
            return reliable[0];
        }

        // Fall back to any successful recovery
        const anySuccess = paths.find(p => p.successRate > 0);
        return anySuccess || null;
    }

    /**
     * Check if a failure pattern is recurring
     */
    async isRecurringFailure(
        sourceName: string,
        errorType: string,
        withinMinutes: number = 60
    ): Promise<boolean> {
        const cutoff = new Date();
        cutoff.setMinutes(cutoff.getMinutes() - withinMinutes);

        if (this.storage) {
            try {
                const count = await this.storage.queryScalar<number>(`
                    SELECT COUNT(*) 
                    FROM mcp_failure_memory 
                    WHERE source_name = ? AND error_type = ? AND occurred_at > ?
                `, [sourceName, errorType, cutoff.toISOString()]);

                if ((count || 0) >= 3) return true;
            } catch (error) {
                logger.warn('⚠️ Recurring check failed:', error);
            }
        }

        const recentCount = this.cache.filter(
            f => f.sourceName === sourceName &&
                f.errorType === errorType &&
                f.occurredAt > cutoff
        ).length;

        return recentCount >= 3;
    }

    /**
     * Get source health summary
     */
    async getSourceHealthSummary(sourceName: string): Promise<SourceHealthSummary> {
        const sevenDaysAgo = new Date();
        sevenDaysAgo.setDate(sevenDaysAgo.getDate() - 7);

        let failures: Failure[] = [];

        if (this.storage) {
            try {
                const rows = await this.storage.queryAll(`
                    SELECT * FROM mcp_failure_memory 
                    WHERE source_name = ? AND occurred_at > ?
                    ORDER BY occurred_at DESC
                `, [sourceName, sevenDaysAgo.toISOString()]);

                failures = rows.map(row => this.rowToFailure(row));
            } catch (error) {
                logger.warn('⚠️ Health summary query failed:', error);
            }
        }

        if (failures.length === 0) {
            failures = this.cache.filter(
                f => f.sourceName === sourceName && f.occurredAt > sevenDaysAgo
            );
        }

        const errorTypes = new Set(failures.map(f => f.errorType));
        const withRecovery = failures.filter(f => f.recoveryAction);
        const successfulRecoveries = withRecovery.filter(f => f.recoverySuccess);
        const recoveryTimes = successfulRecoveries
            .filter(f => f.recoveryTimeMs)
            .map(f => f.recoveryTimeMs!);

        // Check for recurring failures
        const recentErrorTypes = [...errorTypes];
        let isRecurring = false;
        for (const errorType of recentErrorTypes) {
            if (await this.isRecurringFailure(sourceName, errorType, 60)) {
                isRecurring = true;
                break;
            }
        }

        // Get recommended action
        let recommendedAction: string | undefined;
        if (failures.length > 0) {
            const mostCommonError = failures
                .map(f => f.errorType)
                .reduce((acc, type) => {
                    acc[type] = (acc[type] || 0) + 1;
                    return acc;
                }, {} as Record<string, number>);

            const topError = Object.entries(mostCommonError)
                .sort((a, b) => b[1] - a[1])[0];

            if (topError) {
                const bestRecovery = await this.getBestRecoveryAction(sourceName, topError[0]);
                recommendedAction = bestRecovery?.action;
            }
        }

        return {
            sourceName,
            totalFailures: failures.length,
            uniqueErrorTypes: errorTypes.size,
            recoverySuccessRate: withRecovery.length > 0
                ? successfulRecoveries.length / withRecovery.length
                : 0,
            averageRecoveryTime: recoveryTimes.length > 0
                ? recoveryTimes.reduce((a, b) => a + b, 0) / recoveryTimes.length
                : 0,
            isRecurring,
            lastFailure: failures[0]?.occurredAt,
            recommendedAction
        };
    }

    /**
     * Get comprehensive failure statistics
     */
    async getStatistics(): Promise<FailureStatistics> {
        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 {
                const total = await this.storage.queryScalar<number>('SELECT COUNT(*) FROM mcp_failure_memory') || 0;
                const uniqueErrors = await this.storage.queryScalar<number>('SELECT COUNT(DISTINCT error_type) FROM mcp_failure_memory') || 0;
                const uniqueSources = await this.storage.queryScalar<number>('SELECT COUNT(DISTINCT source_name) FROM mcp_failure_memory') || 0;

                const recoveryRate = await this.storage.queryScalar<number>(`
                    SELECT AVG(CAST(recovery_success AS FLOAT)) 
                    FROM mcp_failure_memory 
                    WHERE recovery_action IS NOT NULL
                `) || 0;

                const avgRecoveryTime = await this.storage.queryScalar<number>(`
                    SELECT AVG(recovery_time_ms) 
                    FROM mcp_failure_memory 
                    WHERE recovery_success = 1
                `) || 0;

                const last24h = await this.storage.queryScalar<number>(
                    'SELECT COUNT(*) FROM mcp_failure_memory WHERE occurred_at > ?',
                    [oneDayAgo.toISOString()]
                ) || 0;

                const last7d = await this.storage.queryScalar<number>(
                    'SELECT COUNT(*) FROM mcp_failure_memory WHERE occurred_at > ?',
                    [sevenDaysAgo.toISOString()]
                ) || 0;

                // Top error types
                const topErrorRows = await this.storage.queryAll<{ error_type: string; count: number; recovery_rate: number }>(`
                    SELECT 
                        error_type, 
                        COUNT(*) as count,
                        AVG(CASE WHEN recovery_success = 1 THEN 1.0 ELSE 0.0 END) as recovery_rate
                    FROM mcp_failure_memory
                    GROUP BY error_type
                    ORDER BY count DESC
                    LIMIT 10
                `);
                const topErrors = topErrorRows.map(row => ({
                    type: row.error_type,
                    count: row.count,
                    recoveryRate: row.recovery_rate || 0
                }));

                // Top failing sources
                const topSourceRows = await this.storage.queryAll<{ source_name: string; count: number }>(`
                    SELECT source_name, COUNT(*) as count
                    FROM mcp_failure_memory
                    GROUP BY source_name
                    ORDER BY count DESC
                    LIMIT 10
                `);
                const topSources = topSourceRows.map(row => ({
                    source: row.source_name,
                    count: row.count
                }));

                // Recent recoveries
                const recentRecoveryRows = await this.storage.queryAll<{
                    recovery_action: string;
                    recovery_success: number;
                    recovery_time_ms: number;
                    occurred_at: string;
                }>(`
                    SELECT recovery_action, recovery_success, recovery_time_ms, occurred_at
                    FROM mcp_failure_memory
                    WHERE recovery_action IS NOT NULL
                    ORDER BY occurred_at DESC
                    LIMIT 10
                `);
                const recentRecoveries = recentRecoveryRows.map(row => ({
                    action: row.recovery_action,
                    success: Boolean(row.recovery_success),
                    timeMs: row.recovery_time_ms || 0,
                    at: new Date(row.occurred_at)
                }));

                return {
                    totalFailures: total,
                    uniqueErrorTypes: uniqueErrors,
                    uniqueSources,
                    overallRecoveryRate: recoveryRate,
                    averageRecoveryTimeMs: avgRecoveryTime,
                    failuresLast24h: last24h,
                    failuresLast7d: last7d,
                    topErrorTypes: topErrors,
                    topFailingSources: topSources,
                    recentRecoveries
                };
            } catch (error) {
                logger.warn('⚠️ Statistics query failed:', error);
            }
        }

        // Cache-based fallback
        return {
            totalFailures: this.cache.length,
            uniqueErrorTypes: new Set(this.cache.map(f => f.errorType)).size,
            uniqueSources: new Set(this.cache.map(f => f.sourceName)).size,
            overallRecoveryRate: 0,
            averageRecoveryTimeMs: 0,
            failuresLast24h: this.cache.filter(f => f.occurredAt > oneDayAgo).length,
            failuresLast7d: this.cache.filter(f => f.occurredAt > sevenDaysAgo).length,
            topErrorTypes: [],
            topFailingSources: [],
            recentRecoveries: []
        };
    }

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

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

    /**
     * Extract useful context from error
     */
    private extractErrorContext(error: any): any {
        const context: any = {};

        // Network errors
        if (error.code) context.code = error.code;
        if (error.errno) context.errno = error.errno;
        if (error.syscall) context.syscall = error.syscall;
        if (error.hostname) context.hostname = error.hostname;
        if (error.port) context.port = error.port;

        // HTTP errors
        if (error.statusCode) context.statusCode = error.statusCode;
        if (error.status) context.status = error.status;
        if (error.response?.status) context.responseStatus = error.response.status;
        if (error.response?.statusText) context.responseText = error.response.statusText;

        // Database errors
        if (error.sql) context.sql = error.sql.substring(0, 200);
        if (error.constraint) context.constraint = error.constraint;

        // Timeout errors
        if (error.timeout) context.timeout = error.timeout;

        return context;
    }
}