/**
* ApplicationLoggerService - Structured JSON logging to stderr with log level support
*
* This service provides logging functions that output structured JSON exclusively to process.stderr.
* It respects the LOG_LEVEL environment variable for filtering logs based on severity.
*/
// Log levels with numeric values for comparison
const LOG_LEVELS = {
debug: 0,
info: 1,
warn: 2,
error: 3,
};
// Get log level from environment or default to 'info'
const getCurrentLogLevel = () => {
const logLevel = process.env.LOG_LEVEL?.toLowerCase() || "info";
return LOG_LEVELS[logLevel] !== undefined ? logLevel : "info";
};
/**
* Check if a given log level should be logged based on the current log level setting
* @param {string} level - The log level to check
* @returns {boolean} - Whether the log should be output
*/
const shouldLog = (level) => {
const currentLevel = LOG_LEVELS[getCurrentLogLevel()];
const targetLevel = LOG_LEVELS[level];
return targetLevel >= currentLevel;
};
/**
* Process message or error object to ensure proper serialization
* @param {string|Error} message - Message string or Error object
* @returns {Object} - Processed message object
*/
const processMessage = (message) => {
if (message instanceof Error) {
return {
message: message.message,
stack: message.stack,
};
}
return { message };
};
/**
* Process context object, handling Error objects specially
* @param {Object|Error|undefined} context - Optional context object
* @returns {Object|undefined} - Processed context
*/
const processContext = (context) => {
if (!context) return undefined;
if (context instanceof Error) {
return {
error: {
message: context.message,
stack: context.stack,
},
};
}
return context;
};
/**
* Core logging function
* @param {string} level - Log level
* @param {string|Error} message - Log message or Error object
* @param {Object} [context] - Optional context data
*/
const log = (level, message, context) => {
if (!shouldLog(level)) return;
const processedMessage = processMessage(message);
const processedContext = processContext(context);
const logObject = {
timestamp: new Date().toISOString(),
level,
...processedMessage,
...(processedContext ? { context: processedContext } : {}),
};
// Write to stderr as JSON with newline
process.stderr.write(JSON.stringify(logObject) + "\n");
};
/**
* Logger object with methods for different log levels
*/
const logger = {
/**
* Log debug message
* @param {string|Error} message - Debug message or Error
* @param {Object} [context] - Optional context
*/
debug: (message, context) => log("debug", message, context),
/**
* Log informational message
* @param {string|Error} message - Info message or Error
* @param {Object} [context] - Optional context
*/
info: (message, context) => log("info", message, context),
/**
* Log warning message
* @param {string|Error} message - Warning message or Error
* @param {Object} [context] - Optional context
*/
warn: (message, context) => log("warn", message, context),
/**
* Log error message
* @param {string|Error} message - Error message or Error object
* @param {Object} [context] - Optional context
*/
error: (message, context) => log("error", message, context),
};
// Export the logger instance
export default logger;
