/**
 * Centralized Error Handling Utility
 * 
 * This module provides standardized error handling patterns across the application,
 * ensuring consistent error responses, proper logging, and appropriate error
 * classification. It implements error handling best practices including:
 * 
 * 1. Standardized error response format for API consistency
 * 2. Error classification for appropriate handling strategies
 * 3. Context-aware logging for debugging and monitoring
 * 4. Request ID tracking for error correlation
 * 5. Severity-based error routing and alerting
 * 
 * Design Rationale:
 * - Centralizes error handling logic to reduce code duplication
 * - Provides consistent user experience across all endpoints
 * - Enables comprehensive error monitoring and debugging
 * - Supports multiple error handling strategies based on error type
 * - Maintains backward compatibility with existing error patterns
 */

const { qerrors } = require('qerrors');
const { sendJsonResponse } = require('./responseUtils');
const { getRequestId } = require('./requestUtils');

/**
 * Error type classification for appropriate handling strategies
 * 
 * Rationale: Different error types require different handling approaches.
 * This classification enables appropriate response codes, user messages,
 * logging levels, and recovery strategies.
 */
const ErrorTypes = {
    VALIDATION: 'validation',           // User input errors (400)
    AUTHENTICATION: 'authentication',   // Auth failures (401)
    AUTHORIZATION: 'authorization',     // Permission errors (403)
    NOT_FOUND: 'not_found',            // Resource not found (404)
    RATE_LIMIT: 'rate_limit',          // Rate limiting (429)
    NETWORK: 'network',                // External service errors (502/503)
    DATABASE: 'database',              // Database errors (500)
    SYSTEM: 'system',                  // Internal system errors (500)
    CONFIGURATION: 'configuration'      // Config/setup errors (500)
};

/**
 * Error severity levels for logging and alerting
 * 
 * Rationale: Different error severities require different response strategies.
 * This classification enables appropriate logging, alerting, and escalation.
 */
const ErrorSeverity = {
    LOW: 'low',           // Expected errors, user mistakes
    MEDIUM: 'medium',     // Operational issues, recoverable
    HIGH: 'high',         // Service degradation, requires attention
    CRITICAL: 'critical'  // Service disruption, immediate response needed
};

/**
 * Maps error types to appropriate HTTP status codes
 * 
 * Rationale: Consistent HTTP status code mapping ensures proper client
 * behavior and follows REST API conventions.
 */
const ERROR_STATUS_MAP = {
    [ErrorTypes.VALIDATION]: 400,
    [ErrorTypes.AUTHENTICATION]: 401,
    [ErrorTypes.AUTHORIZATION]: 403,
    [ErrorTypes.NOT_FOUND]: 404,
    [ErrorTypes.RATE_LIMIT]: 429,
    [ErrorTypes.NETWORK]: 502,
    [ErrorTypes.DATABASE]: 500,
    [ErrorTypes.SYSTEM]: 500,
    [ErrorTypes.CONFIGURATION]: 500
};

/**
 * Maps error types to severity levels for monitoring
 * 
 * Rationale: Automatic severity classification enables appropriate
 * alerting and escalation without manual intervention.
 */
const ERROR_SEVERITY_MAP = {
    [ErrorTypes.VALIDATION]: ErrorSeverity.LOW,
    [ErrorTypes.AUTHENTICATION]: ErrorSeverity.LOW,
    [ErrorTypes.AUTHORIZATION]: ErrorSeverity.MEDIUM,
    [ErrorTypes.NOT_FOUND]: ErrorSeverity.LOW,
    [ErrorTypes.RATE_LIMIT]: ErrorSeverity.MEDIUM,
    [ErrorTypes.NETWORK]: ErrorSeverity.MEDIUM,
    [ErrorTypes.DATABASE]: ErrorSeverity.HIGH,
    [ErrorTypes.SYSTEM]: ErrorSeverity.HIGH,
    [ErrorTypes.CONFIGURATION]: ErrorSeverity.CRITICAL
};

/**
 * Creates a standardized error object with consistent format
 * 
 * Rationale: Standardized error format ensures consistent API responses
 * and enables proper error handling on the client side. Includes all
 * necessary information for debugging and user feedback.
 * 
 * @param {string} code - Error code for programmatic handling
 * @param {string} message - Human-readable error message
 * @param {string} type - Error type from ErrorTypes enum
 * @param {Object} context - Additional context for debugging
 * @returns {Object} Standardized error object
 */
function createError(code, message, type, context = {}) { // build standard error object
    return {
        code,
        message,
        type,
        timestamp: new Date().toISOString(),
        requestId: context.requestId || getRequestId(context.req),
        context: {
            ...context,
            req: undefined, // Remove req object to prevent circular references
            res: undefined  // Remove res object to prevent circular references
        }
    };
}

/**
 * Logs error with appropriate severity and context
 * 
 * Rationale: Centralized error logging ensures consistent log format
 * and enables proper monitoring and alerting. Different severities
 * can be routed to different logging destinations.
 * 
 * @param {Object} error - Error object or Error instance
 * @param {string} functionName - Name of function where error occurred
 * @param {Object} context - Request context and additional information
 * @param {string} severity - Error severity level
 */
function logError(error, functionName, context = {}, severity = ErrorSeverity.MEDIUM) { // log with severity context
    const logContext = {
        ...context,
        severity,
        timestamp: new Date().toISOString(),
        requestId: context.requestId || getRequestId(context.req)
    };

    // Use existing qerrors for consistent logging
    qerrors(error, functionName, logContext);

    // Additional logging based on severity
    if (severity === ErrorSeverity.CRITICAL) {
        console.error(`CRITICAL ERROR in ${functionName}:`, {
            error: error.message || error,
            context: logContext
        });
    } else if (severity === ErrorSeverity.HIGH) {
        console.error(`HIGH SEVERITY ERROR in ${functionName}:`, {
            error: error.message || error,
            context: logContext
        });
    }
}

/**
 * Handles controller errors with standardized response
 * 
 * Rationale: Provides consistent error handling across all controllers
 * while maintaining existing responseUtils integration. Automatically
 * determines appropriate status codes and response format.
 * 
 * @param {Object} res - Express response object
 * @param {Object} error - Error object or Error instance
 * @param {string} functionName - Name of function where error occurred
 * @param {Object} context - Request context
 * @param {string} userMessage - Optional user-friendly message override
 */
function handleControllerError(res, error, functionName, context = {}, userMessage = null) { // send standardized error response
    const errorType = error.type || ErrorTypes.SYSTEM;
    const severity = ERROR_SEVERITY_MAP[errorType];
    const statusCode = ERROR_STATUS_MAP[errorType];

    // Log the error with appropriate severity
    logError(error, functionName, context, severity);

    // Create standardized error response
    const errorResponse = createError(
        error.code || 'INTERNAL_ERROR',
        userMessage || error.message || 'An internal error occurred',
        errorType,
        context
    );

    // Send standardized JSON response
    sendJsonResponse(res, statusCode, { error: errorResponse });
}

/**
 * Wraps async operations with standardized error handling
 * 
 * Rationale: Reduces boilerplate code in controllers while ensuring
 * consistent error handling. Automatically catches and handles errors
 * according to their type and severity.
 * 
 * @param {Function} operation - Async operation to execute
 * @param {string} functionName - Name for logging purposes
 * @param {Object} context - Request context
 * @param {*} fallback - Fallback value on error (optional)
 * @returns {*} Operation result or fallback value
 */
async function withErrorHandling(operation, functionName, context = {}, fallback = null) { // execute operation with safety net
    try {
        const result = await operation();
        console.log(`${functionName} is returning result`);
        return result;
    } catch (error) {
        logError(error, functionName, context);
        return fallback;
    }
}