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logger.ts
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/**
* Structured Logging Framework
* Provides consistent, structured logging across the application
*/
export enum LogLevel {
DEBUG = 'debug',
INFO = 'info',
WARN = 'warn',
ERROR = 'error',
}
export interface LogContext {
[key: string]: any;
}
export interface LogEntry {
timestamp: string;
level: LogLevel;
message: string;
context?: LogContext;
error?: {
name: string;
message: string;
stack?: string;
};
}
/**
* Logger class for structured logging
*/
export class Logger {
private context: LogContext;
private minLevel: LogLevel;
constructor(context: LogContext = {}, minLevel: LogLevel = LogLevel.INFO) {
this.context = context;
this.minLevel = minLevel;
}
/**
* Create child logger with additional context
*/
child(additionalContext: LogContext): Logger {
return new Logger({ ...this.context, ...additionalContext }, this.minLevel);
}
/**
* Set minimum log level
*/
setLevel(level: LogLevel): void {
this.minLevel = level;
}
/**
* Check if level should be logged
*/
private shouldLog(level: LogLevel): boolean {
const levels = [LogLevel.DEBUG, LogLevel.INFO, LogLevel.WARN, LogLevel.ERROR];
return levels.indexOf(level) >= levels.indexOf(this.minLevel);
}
/**
* Format and output log entry
*/
private log(level: LogLevel, message: string, context?: LogContext, error?: Error): void {
if (!this.shouldLog(level)) {
return;
}
const entry: LogEntry = {
timestamp: new Date().toISOString(),
level,
message,
context: { ...this.context, ...context },
};
if (error) {
entry.error = {
name: error.name,
message: error.message,
stack: error.stack,
};
}
// In production, you might want to send this to a logging service
// For now, we'll use console with structured output
const output = this.formatOutput(entry);
switch (level) {
case LogLevel.DEBUG:
console.debug(output);
break;
case LogLevel.INFO:
console.info(output);
break;
case LogLevel.WARN:
console.warn(output);
break;
case LogLevel.ERROR:
console.error(output);
break;
}
}
/**
* Format log entry for output
*/
private formatOutput(entry: LogEntry): string {
// Development: Pretty print
if (process.env.NODE_ENV !== 'production') {
const emoji = this.getLevelEmoji(entry.level);
let output = `${emoji} [${entry.timestamp}] ${entry.level.toUpperCase()}: ${entry.message}`;
if (entry.context && Object.keys(entry.context).length > 0) {
try {
output += `\n Context: ${JSON.stringify(entry.context, null, 2)}`;
} catch (e) {
// Handle objects with null prototypes
output += `\n Context: [Unable to serialize context]`;
}
}
if (entry.error) {
output += `\n Error: ${entry.error.name}: ${entry.error.message}`;
if (entry.error.stack) {
output += `\n${entry.error.stack}`;
}
}
return output;
}
// Production: JSON output for log aggregation services
try {
return JSON.stringify(entry);
} catch (e) {
// Fallback for objects that can't be stringified
return JSON.stringify({
timestamp: entry.timestamp,
level: entry.level,
message: entry.message,
error: 'Unable to serialize log entry'
});
}
}
/**
* Get emoji for log level
*/
private getLevelEmoji(level: LogLevel): string {
switch (level) {
case LogLevel.DEBUG:
return '🔍';
case LogLevel.INFO:
return 'ℹ️';
case LogLevel.WARN:
return '⚠️';
case LogLevel.ERROR:
return '❌';
}
}
/**
* Log debug message
*/
debug(message: string, context?: LogContext): void {
this.log(LogLevel.DEBUG, message, context);
}
/**
* Log info message
*/
info(message: string, context?: LogContext): void {
this.log(LogLevel.INFO, message, context);
}
/**
* Log warning message
*/
warn(message: string, context?: LogContext): void {
this.log(LogLevel.WARN, message, context);
}
/**
* Log error message
*/
error(message: string, error?: Error, context?: LogContext): void {
this.log(LogLevel.ERROR, message, context, error);
}
/**
* Log with custom level
*/
logWithLevel(level: LogLevel, message: string, context?: LogContext, error?: Error): void {
this.log(level, message, context, error);
}
}
// Global logger instance
let globalLogger: Logger | null = null;
/**
* Get global logger instance
*/
export function getLogger(context?: LogContext): Logger {
if (!globalLogger) {
const level = process.env.LOG_LEVEL as LogLevel ||
(process.env.NODE_ENV === 'production' ? LogLevel.INFO : LogLevel.DEBUG);
globalLogger = new Logger({}, level);
}
if (context) {
return globalLogger.child(context);
}
return globalLogger;
}
/**
* Create a logger with specific context
*/
export function createLogger(context: LogContext): Logger {
return getLogger(context);
}