- added fileNameFormat

- fixed up some logic aka duplicate logic
- actually verify config
-add more ansiColors
-default to no max files

README.md

@@ -4,7 +4,7 @@ A minimal, flexible logger for Node with:
 
 - Colored console output
 - Daily `.jsonl` file logging
-- Configurable output patterns
+- Configurable output patterns and file naming
 - Structured logs with caller metadata
 - Fully typed config with environment/file/constructor override
 
@@ -14,7 +14,7 @@ A minimal, flexible logger for Node with:
 
 - Console and file logging with level-based filtering
 - Colored output with ANSI formatting
-- Daily rotated `.jsonl` files
+- Daily rotated `.jsonl` files with custom naming patterns
 - Supports runtime configuration merging
 - Auto-formatted output using custom patterns
 - Includes caller file, line, and column
@@ -75,6 +75,7 @@ constructor > environment > logger.json > defaults
 
 	"rotate": true,
 	"maxFiles": 3,
+	"fileNameFormat": "yyyy-MM-dd",
 
 	"console": true,
 	"consoleColor": true,
@@ -121,6 +122,7 @@ constructor > environment > logger.json > defaults
 | `LOG_DISABLE_FILE`     | Disable file output (`true` or `false`)       |
 | `LOG_ROTATE`           | Enable daily rotation                         |
 | `LOG_MAX_FILES`        | Max rotated files to keep                     |
+| `LOG_FILE_NAME_FORMAT` | Custom file name format (default: yyyy-MM-dd) |
 | `LOG_CONSOLE`          | Enable console output                         |
 | `LOG_CONSOLE_COLOR`    | Enable ANSI color in console output           |
 | `LOG_DATE_FORMAT`      | Date format for display timestamp             |
@@ -133,6 +135,17 @@ constructor > environment > logger.json > defaults
 
 ---
 
+### Custom File Naming
+```json
+{
+  "fileNameFormat": "yyyy-MM-dd",        // 2025-06-03.jsonl
+  "fileNameFormat": "yyyy-MM-dd_HH-mm",  // 2025-06-03_18-30.jsonl
+  "fileNameFormat": "yyyyMMdd",          // 20250603.jsonl
+}
+```
+
+---
+
 ## Pattern Tokens
 
 These tokens are replaced in the log pattern:

biome.json

@@ -7,7 +7,7 @@
 	},
 	"files": {
 		"ignoreUnknown": true,
-		"ignore": ["dist", "types"]
+		"ignore": ["dist"]
 	},
 	"formatter": {
 		"enabled": true,
@@ -29,14 +29,14 @@
 			"recommended": true,
 			"correctness": {
 				"noUnusedImports": "error",
-				"useJsxKeyInIterable": "off",
 				"noUnusedVariables": "error"
 			},
 			"style": {
 				"useConst": "error",
 				"noVar": "error"
 			}
-		}
+		},
+		"ignore": ["types"]
 	},
 	"javascript": {
 		"formatter": {

package.json

@@ -46,6 +46,12 @@
 		"type": "git",
 		"url": "https://git.creations.works/atums/echo"
 	},
+	"keywords": ["logger", "logging", "typescript", "nodejs", "structured"],
+	"author": "creations.works",
+	"homepage": "https://git.creations.works/atums/echo",
+	"bugs": {
+		"url": "https://git.creations.works/atums/echo/issues"
+	},
 	"dependencies": {
 		"date-fns-tz": "^3.2.0"
 	}

src/index.ts

@@ -7,17 +7,24 @@ import {
 	statSync,
 } from "node:fs";
 import { resolve } from "node:path";
-import { format, inspect } from "node:util";
-import { getCallerInfo, getTimestamp, parsePattern } from "@lib/char";
 import {
-	ansiColors,
+	formatData,
+	getCallerInfo,
+	getConsoleMethod,
+	getTimestamp,
+	parsePattern,
+	processPattern,
+} from "@lib/char";
+import {
 	defaultConfig,
 	loadEnvConfig,
 	loadLoggerConfig,
 	logLevelValues,
+	validateAndSanitizeConfig,
 } from "@lib/config";
 import { FileLogger } from "@lib/file";
-import type { LogLevel, LoggerConfig } from "@types";
+
+import type { LogLevel, LoggerConfig, PatternTokens } from "@types";
 
 class Echo {
 	private readonly directory: string;
@@ -35,12 +42,18 @@ class Echo {
 
 		const envConfig: LoggerConfig = loadEnvConfig();
 
-		this.config = {
+		const mergedConfig = {
 			...defaultConfig,
 			...fileConfig,
 			...envConfig,
 			...overrideConfig,
 		};
+		const finalConfig = validateAndSanitizeConfig(
+			mergedConfig,
+			"merged configuration",
+		);
+
+		this.config = finalConfig as Required<LoggerConfig>;
 
 		this.directory = resolve(this.config.directory);
 
@@ -75,9 +88,7 @@ class Echo {
 		const line = parsePattern({ level, data, config: this.config });
 
 		if (this.config.console) {
-			console[level === "error" ? "error" : level === "warn" ? "warn" : "log"](
+			console[getConsoleMethod(level)](line);
-				line,
-			);
 		}
 
 		if (!this.config.disableFile && this.fileLogger) {
@@ -113,39 +124,21 @@ class Echo {
 		if (this.config.silent) return;
 
 		const timestamps = getTimestamp(this.config);
-
+		const resolvedData = formatData(data, this.config);
-		const normalizedTag = tag.toUpperCase();
-		const tagColor = this.config.consoleColor
-			? (ansiColors[this.config.customColors?.[normalizedTag] ?? "green"] ?? "")
-			: "";
-		const contextColor = this.config.consoleColor ? ansiColors.cyan : "";
-		const gray = this.config.consoleColor ? ansiColors.gray : "";
-		const reset = this.config.consoleColor ? ansiColors.reset : "";
-
-		const resolvedData =
-			this.config.prettyPrint && typeof data === "object" && data !== null
-				? inspect(data, {
-						depth: null,
-						colors: this.config.consoleColor,
-						breakLength: 1,
-						compact: false,
-					})
-				: format(data);
 
 		const pattern =
 			this.config.customPattern ??
 			"{color:gray}{pretty-timestamp}{reset} {color:tagColor}[{tag}]{reset} {color:contextColor}({context}){reset} {data}";
 
-		const line = pattern
+		const tokens: PatternTokens = {
-			.replace(/{timestamp}/g, timestamps.timestamp)
+			timestamp: timestamps.timestamp,
-			.replace(/{pretty-timestamp}/g, timestamps.prettyTimestamp)
+			prettyTimestamp: timestamps.prettyTimestamp,
-			.replace(/{tag}/g, tag)
+			tag,
-			.replace(/{context}/g, context)
+			context,
-			.replace(/{data}/g, resolvedData)
+			data: resolvedData,
-			.replace(/{color:gray}/g, gray)
+		};
-			.replace(/{color:tagColor}/g, tagColor)
+
-			.replace(/{color:contextColor}/g, contextColor)
+		const line = processPattern(pattern, tokens, this.config, undefined, tag);
-			.replace(/{reset}/g, reset);
 
 		if (this.config.console) {
 			console.log(line);

src/lib/char.ts

@@ -8,6 +8,7 @@ import type {
 	LogLevelValue,
 	LoggerConfig,
 	PatternContext,
+	PatternTokens,
 } from "@types";
 
 function getTimestamp(config: Required<LoggerConfig>): {
@@ -113,22 +114,121 @@ function generateShortId(length = 8): string {
 	return id;
 }
 
-function replaceColorTokens(
+function formatData(data: unknown, config: Required<LoggerConfig>): string {
-	input: string,
+	return config.prettyPrint && typeof data === "object" && data !== null
-	level: LogLevel,
+		? inspect(data, {
+				depth: null,
+				colors: config.consoleColor,
+				breakLength: 1,
+				compact: false,
+			})
+		: format(data);
+}
+
+function getConsoleMethod(level: LogLevel): "log" | "warn" | "error" {
+	if (level === "error" || level === "fatal") return "error";
+	if (level === "warn") return "warn";
+	return "log";
+}
+
+function resolveColor(
+	colorKey: string,
 	config: Required<LoggerConfig>,
+	level?: LogLevel,
+	tag?: string,
 ): string {
-	return input
+	if (!config.consoleColor) return "";
-		.replace(/{color:(\w+)}/g, (_, colorKey) => {
+
-			if (!config.consoleColor) return "";
+	if (colorKey === "levelColor" && level) {
-			if (colorKey === "levelColor") {
+		const colorForLevel =
-				const colorForLevel =
+			config.levelColor?.[level] ?? defaultLevelColor[level];
-					config.levelColor?.[level] ?? defaultLevelColor[level];
+		return ansiColors[colorForLevel ?? ""] ?? "";
-				return ansiColors[colorForLevel ?? ""] ?? "";
+	}
-			}
+
-			return ansiColors[colorKey] ?? "";
+	if (colorKey === "tagColor" && tag) {
-		})
+		const normalizedTag = tag.toUpperCase();
-		.replace(/{reset}/g, config.consoleColor ? ansiColors.reset : "");
+		return ansiColors[config.customColors?.[normalizedTag] ?? "green"] ?? "";
+	}
+
+	if (colorKey === "contextColor") {
+		return ansiColors.cyan ?? "";
+	}
+
+	return ansiColors[colorKey] ?? "";
+}
+
+function serializeLogData(data: unknown): unknown {
+	if (data instanceof Error) {
+		return {
+			name: data.name,
+			message: data.message,
+			stack: data.stack,
+		};
+	}
+
+	if (typeof data === "string" || typeof data === "number") {
+		return data;
+	}
+
+	return data;
+}
+
+function processPattern(
+	pattern: string,
+	tokens: PatternTokens,
+	config: Required<LoggerConfig>,
+	level?: LogLevel,
+	tag?: string,
+): string {
+	let processed = pattern;
+
+	if (tokens.timestamp) {
+		processed = processed.replace(/{timestamp}/g, tokens.timestamp);
+	}
+	if (tokens.prettyTimestamp) {
+		processed = processed.replace(
+			/{pretty-timestamp}/g,
+			tokens.prettyTimestamp,
+		);
+	}
+	if (tokens.levelName) {
+		processed = processed.replace(/{level-name}/g, tokens.levelName);
+	}
+	if (tokens.level) {
+		processed = processed.replace(/{level}/g, tokens.level);
+	}
+	if (tokens.fileName) {
+		processed = processed.replace(/{file-name}/g, tokens.fileName);
+	}
+	if (tokens.line) {
+		processed = processed.replace(/{line}/g, tokens.line);
+	}
+	if (tokens.column) {
+		processed = processed.replace(/{column}/g, tokens.column);
+	}
+	if (tokens.data) {
+		processed = processed.replace(/{data}/g, tokens.data);
+	}
+	if (tokens.id) {
+		processed = processed.replace(/{id}/g, tokens.id);
+	}
+	if (tokens.tag) {
+		processed = processed.replace(/{tag}/g, tokens.tag);
+	}
+	if (tokens.context) {
+		processed = processed.replace(/{context}/g, tokens.context);
+	}
+
+	processed = processed.replace(/{color:(\w+)}/g, (_, colorKey) => {
+		return resolveColor(colorKey, config, level, tag);
+	});
+
+	processed = processed.replace(
+		/{reset}/g,
+		config.consoleColor ? ansiColors.reset : "",
+	);
+
+	return processed;
 }
 
 function parsePattern(ctx: PatternContext): string {
@@ -136,30 +236,33 @@ function parsePattern(ctx: PatternContext): string {
 
 	const { id, fileName, line, column, timestamp, prettyTimestamp } =
 		getCallerInfo(config);
-	const resolvedData: string =
-		config.prettyPrint && typeof data === "object" && data !== null
-			? inspect(data, {
-					depth: null,
-					colors: config.consoleColor,
-					breakLength: 1,
-					compact: false,
-				})
-			: format(data);
 
+	const resolvedData: string = formatData(data, config);
 	const numericLevel: LogLevelValue = logLevelValues[level];
 
-	const final = config.pattern
+	const tokens: PatternTokens = {
-		.replace(/{timestamp}/g, timestamp)
+		timestamp,
-		.replace(/{pretty-timestamp}/g, prettyTimestamp)
+		prettyTimestamp,
-		.replace(/{level-name}/g, level.toUpperCase())
+		levelName: level.toUpperCase(),
-		.replace(/{level}/g, String(numericLevel))
+		level: String(numericLevel),
-		.replace(/{file-name}/g, fileName)
+		fileName,
-		.replace(/{line}/g, line)
+		line,
-		.replace(/{data}/g, resolvedData)
+		column,
-		.replace(/{id}/g, id)
+		data: resolvedData,
-		.replace(/{column}/g, column);
+		id,
+	};
 
-	return replaceColorTokens(final, level, config);
+	return processPattern(config.pattern, tokens, config, level);
 }
 
-export { parsePattern, getCallerInfo, getTimestamp, generateShortId };
+export {
+	parsePattern,
+	getCallerInfo,
+	getTimestamp,
+	generateShortId,
+	formatData,
+	getConsoleMethod,
+	resolveColor,
+	serializeLogData,
+	processPattern,
+};

src/lib/config.ts

@@ -10,7 +10,7 @@ const logLevelValues = {
 	error: 50,
 	fatal: 60,
 	silent: 70,
-};
+} as const;
 
 const defaultLevelColor: Record<LogLevel, keyof typeof ansiColors> = {
 	trace: "cyan",
@@ -35,7 +35,12 @@ const ansiColors: Record<string, string> = {
 	cyan: "\x1b[36m",
 	white: "\x1b[37m",
 	gray: "\x1b[90m",
-};
+	bold: "\x1b[1m",
+	underline: "\x1b[4m",
+	inverse: "\x1b[7m",
+	hidden: "\x1b[8m",
+	strikethrough: "\x1b[9m",
+} as const;
 
 const defaultConfig: Required<LoggerConfig> = {
 	directory: "logs",
@@ -43,7 +48,8 @@ const defaultConfig: Required<LoggerConfig> = {
 	disableFile: false,
 
 	rotate: true,
-	maxFiles: 3,
+	maxFiles: null,
+	fileNameFormat: "yyyy-MM-dd",
 
 	console: true,
 	consoleColor: true,
@@ -72,12 +78,129 @@ const defaultConfig: Required<LoggerConfig> = {
 	prettyPrint: true,
 };
 
+function isValidLogLevel(level: string): level is LogLevel {
+	return level in logLevelValues;
+}
+
+function isValidColor(color: string): color is keyof typeof ansiColors {
+	return color in ansiColors;
+}
+
+function parseNumericEnv(
+	value: string | undefined,
+	min = 0,
+): number | undefined {
+	if (!value) return undefined;
+
+	const parsed = Number.parseInt(value, 10);
+	if (Number.isNaN(parsed) || parsed < min) {
+		return undefined;
+	}
+
+	return parsed;
+}
+
+function parseBooleanEnv(value: string | undefined): boolean | undefined {
+	if (!value) return undefined;
+	return value.toLowerCase() === "true";
+}
+
+function validateAndSanitizeConfig(
+	config: LoggerConfig,
+	source: string,
+): LoggerConfig {
+	const sanitized = { ...config };
+	const warnings: string[] = [];
+
+	if (sanitized.level && !isValidLogLevel(sanitized.level)) {
+		warnings.push(
+			`Invalid log level "${sanitized.level}" in ${source}, using default "info"`,
+		);
+		sanitized.level = "info";
+	}
+
+	if (sanitized.maxFiles !== undefined && sanitized.maxFiles !== null) {
+		if (
+			typeof sanitized.maxFiles !== "number" ||
+			sanitized.maxFiles < 1 ||
+			!Number.isInteger(sanitized.maxFiles)
+		) {
+			warnings.push(
+				`Invalid maxFiles value "${sanitized.maxFiles}" in ${source}, setting to null`,
+			);
+			sanitized.maxFiles = null;
+		}
+	}
+
+	if (sanitized.levelColor) {
+		const validLevelColors: Partial<Record<LogLevel, keyof typeof ansiColors>> =
+			{};
+
+		for (const [level, color] of Object.entries(sanitized.levelColor)) {
+			if (!isValidLogLevel(level)) {
+				warnings.push(
+					`Invalid log level "${level}" in levelColor from ${source}, skipping`,
+				);
+				continue;
+			}
+			if (!isValidColor(color)) {
+				warnings.push(
+					`Invalid color "${color}" for level "${level}" in ${source}, using default`,
+				);
+				validLevelColors[level as LogLevel] =
+					defaultLevelColor[level as LogLevel];
+			} else {
+				validLevelColors[level as LogLevel] = color;
+			}
+		}
+
+		sanitized.levelColor = validLevelColors;
+	}
+
+	if (sanitized.customColors) {
+		const validCustomColors: Record<string, keyof typeof ansiColors> = {};
+
+		for (const [tag, color] of Object.entries(sanitized.customColors)) {
+			if (!isValidColor(color)) {
+				warnings.push(
+					`Invalid color "${color}" for tag "${tag}" in ${source}, skipping`,
+				);
+				continue;
+			}
+			validCustomColors[tag] = color;
+		}
+
+		sanitized.customColors = validCustomColors;
+	}
+
+	if (warnings.length > 0) {
+		console.warn(
+			`[@atums/echo] Configuration warnings:\n  ${warnings.join("\n  ")}`,
+		);
+	}
+
+	return sanitized;
+}
+
 function loadLoggerConfig(configPath = "logger.json"): LoggerConfig {
 	try {
 		const fullPath: string = resolve(process.cwd(), configPath);
 		const raw: string = readFileSync(fullPath, "utf-8");
-		return JSON.parse(raw);
+		const parsed = JSON.parse(raw);
-	} catch {
+
+		if (typeof parsed !== "object" || parsed === null) {
+			console.warn(`[@atums/echo] Invalid config file format: ${configPath}`);
+			return {};
+		}
+
+		return validateAndSanitizeConfig(parsed, `config file "${configPath}"`);
+	} catch (error) {
+		if (error instanceof Error && !error.message.includes("ENOENT")) {
+			console.warn(
+				`[@atums/echo] Failed to load config file ${configPath}:`,
+				error.message,
+			);
+		}
 		return {};
 	}
 }
@@ -85,50 +208,97 @@ function loadLoggerConfig(configPath = "logger.json"): LoggerConfig {
 function loadEnvConfig(): LoggerConfig {
 	const config: LoggerConfig = {};
 
-	if (process.env.LOG_LEVEL) config.level = process.env.LOG_LEVEL as LogLevel;
+	if (process.env.LOG_LEVEL && isValidLogLevel(process.env.LOG_LEVEL)) {
-	if (process.env.LOG_DIRECTORY) config.directory = process.env.LOG_DIRECTORY;
+		config.level = process.env.LOG_LEVEL;
-	if (process.env.LOG_DISABLE_FILE)
+	}
-		config.disableFile = process.env.LOG_DISABLE_FILE === "true";
+
-	if (process.env.LOG_ROTATE) config.rotate = process.env.LOG_ROTATE === "true";
+	if (process.env.LOG_DIRECTORY) {
-	if (process.env.LOG_MAX_FILES)
+		config.directory = process.env.LOG_DIRECTORY;
-		config.maxFiles = Number.parseInt(process.env.LOG_MAX_FILES, 10);
+	}
-	if (process.env.LOG_CONSOLE)
+
-		config.console = process.env.LOG_CONSOLE === "true";
+	config.disableFile = parseBooleanEnv(process.env.LOG_DISABLE_FILE);
-	if (process.env.LOG_CONSOLE_COLOR)
+	config.rotate = parseBooleanEnv(process.env.LOG_ROTATE);
-		config.consoleColor = process.env.LOG_CONSOLE_COLOR === "true";
+	config.console = parseBooleanEnv(process.env.LOG_CONSOLE);
-	if (process.env.LOG_DATE_FORMAT)
+	config.consoleColor = parseBooleanEnv(process.env.LOG_CONSOLE_COLOR);
+	config.silent = parseBooleanEnv(process.env.LOG_SILENT);
+	config.prettyPrint = parseBooleanEnv(process.env.LOG_PRETTY_PRINT);
+
+	const maxFiles = parseNumericEnv(process.env.LOG_MAX_FILES, 1);
+	if (maxFiles !== undefined) {
+		config.maxFiles = maxFiles;
+	}
+
+	if (process.env.LOG_FILE_NAME_FORMAT) {
+		config.fileNameFormat = process.env.LOG_FILE_NAME_FORMAT;
+	}
+
+	if (process.env.LOG_DATE_FORMAT) {
 		config.dateFormat = process.env.LOG_DATE_FORMAT;
-	if (process.env.LOG_TIMEZONE) config.timezone = process.env.LOG_TIMEZONE;
+	}
-	if (process.env.LOG_SILENT) config.silent = process.env.LOG_SILENT === "true";
+
-	if (process.env.LOG_PATTERN) config.pattern = process.env.LOG_PATTERN;
+	if (process.env.LOG_TIMEZONE) {
-	if (process.env.LOG_PRETTY_PRINT)
+		config.timezone = process.env.LOG_TIMEZONE;
-		config.prettyPrint = process.env.LOG_PRETTY_PRINT === "true";
+	}
+
+	if (process.env.LOG_PATTERN) {
+		config.pattern = process.env.LOG_PATTERN;
+	}
+
+	if (process.env.LOG_CUSTOM_PATTERN) {
+		config.customPattern = process.env.LOG_CUSTOM_PATTERN;
+	}
 
 	if (process.env.LOG_LEVEL_COLOR) {
 		const colors = process.env.LOG_LEVEL_COLOR.split(",");
-		for (const color of colors) {
+		const levelColor: Partial<Record<LogLevel, keyof typeof ansiColors>> = {};
-			const [level, colorName] = color.split(":");
+
-			if (logLevelValues[level as LogLevel] !== undefined) {
+		for (const colorPair of colors) {
-				config.levelColor = {
+			const [level, colorName] = colorPair.split(":");
-					...config.levelColor,
+
-					[level as LogLevel]: colorName as keyof typeof ansiColors,
+			if (
-				};
+				level &&
+				colorName &&
+				isValidLogLevel(level) &&
+				isValidColor(colorName)
+			) {
+				levelColor[level] = colorName;
+			} else {
+				console.warn(`[@atums/echo] Invalid level color pair: ${colorPair}`);
 			}
 		}
+
+		if (Object.keys(levelColor).length > 0) {
+			config.levelColor = levelColor;
+		}
 	}
 
 	if (process.env.LOG_CUSTOM_COLORS) {
 		const colors = process.env.LOG_CUSTOM_COLORS.split(",");
-		for (const color of colors) {
+		const customColors: Record<string, keyof typeof ansiColors> = {};
-			const [tag, colorName] = color.split(":");
+
-			config.customColors = {
+		for (const colorPair of colors) {
-				...config.customColors,
+			const [tag, colorName] = colorPair.split(":");
-				[tag]: colorName as keyof typeof ansiColors,
+
-			};
+			if (tag && colorName && isValidColor(colorName)) {
+				customColors[tag] = colorName;
+			} else {
+				console.warn(`[@atums/echo] Invalid custom color pair: ${colorPair}`);
+			}
+		}
+
+		if (Object.keys(customColors).length > 0) {
+			config.customColors = customColors;
 		}
 	}
 
-	return config;
+	const sanitizedConfig = validateAndSanitizeConfig(
+		config,
+		"environment variables",
+	);
+
+	return Object.fromEntries(
+		Object.entries(sanitizedConfig).filter(([_, value]) => value !== undefined),
+	) as LoggerConfig;
 }
 
 export {
@@ -138,4 +308,7 @@ export {
 	loadEnvConfig,
 	logLevelValues,
 	ansiColors,
+	validateAndSanitizeConfig,
+	isValidLogLevel,
+	isValidColor,
 };

src/lib/file.ts

@@ -7,6 +7,7 @@ import {
 	unlinkSync,
 } from "node:fs";
 import { join } from "node:path";
+import { serializeLogData } from "@lib/char";
 import type { LogLevel, LoggerConfig } from "@types";
 import { format } from "date-fns-tz";
 
@@ -14,15 +15,30 @@ class FileLogger {
 	private stream: WriteStream | null = null;
 	private filePath = "";
 	private date = "";
+	private fileNameFormat = "yyyy-MM-dd";
 
 	constructor(private readonly config: Required<LoggerConfig>) {
 		if (!existsSync(this.config.directory)) {
 			mkdirSync(this.config.directory, { recursive: true });
 		}
+
+		if (this.config.fileNameFormat) {
+			try {
+				format(new Date(), this.config.fileNameFormat, {
+					timeZone: this.config.timezone,
+				});
+				this.fileNameFormat = this.config.fileNameFormat;
+			} catch (error) {
+				throw new Error(
+					`[@atums/echo] Invalid fileNameFormat: ${this.config.fileNameFormat}. Error: ${error instanceof Error ? error.message : "Unknown error"}`,
+				);
+			}
+		}
 	}
 
 	private getLogFilePath(dateStr: string): string {
-		return join(this.config.directory, `${dateStr}.jsonl`);
+		const fileName = `${dateStr}.jsonl`;
+		return join(this.config.directory, fileName);
 	}
 
 	private resetStream(path: string): void {
@@ -31,13 +47,32 @@ class FileLogger {
 		this.filePath = path;
 	}
 
+	private generateFileRegex(): RegExp {
+		const pattern = this.fileNameFormat
+			.replace(/[.*+?^${}()|[\]\\]/g, "\\$&")
+			.replace(/\\y\\y\\y\\y/g, "\\d{4}")
+			.replace(/\\M\\M/g, "\\d{2}")
+			.replace(/\\d\\d/g, "\\d{2}")
+			.replace(/\\H\\H/g, "\\d{2}")
+			.replace(/\\m\\m/g, "\\d{2}")
+			.replace(/\\s\\s/g, "\\d{2}")
+			.replace(/\\S\\S\\S/g, "\\d{3}");
+
+		return new RegExp(`^${pattern}\\.jsonl$`);
+	}
+
 	private pruneOldLogs(): void {
-		if (this.config.maxFiles && this.config.maxFiles < 1) {
+		if (this.config.maxFiles === null) {
+			return;
+		}
+
+		if (this.config.maxFiles < 1) {
 			throw new Error("[@atums/echo] maxFiles must be >= 1 if set.");
 		}
 
+		const fileRegex = this.generateFileRegex();
 		const files = readdirSync(this.config.directory)
-			.filter((file) => /^\d{4}-\d{2}-\d{2}\.jsonl$/.test(file))
+			.filter((file) => fileRegex.test(file))
 			.sort();
 
 		const excess = files.slice(
@@ -52,6 +87,13 @@ class FileLogger {
 		}
 	}
 
+	private getFilePath(dateStr?: string): string {
+		if (this.config.rotate && dateStr) {
+			return this.getLogFilePath(dateStr);
+		}
+		return join(this.config.directory, "log.jsonl");
+	}
+
 	public write(
 		level: LogLevel | string,
 		data: unknown,
@@ -67,27 +109,6 @@ class FileLogger {
 		if (this.config.disableFile) return;
 
 		const now = new Date();
-		let path: string;
-
-		if (this.config.rotate) {
-			const dateStr = format(now, "yyyy-MM-dd", {
-				timeZone: this.config.timezone,
-			});
-			path = this.getLogFilePath(dateStr);
-
-			if (!this.stream || this.filePath !== path || this.date !== dateStr) {
-				this.date = dateStr;
-				this.resetStream(path);
-				this.pruneOldLogs();
-			}
-		} else {
-			path = join(this.config.directory, "log.jsonl");
-
-			if (!this.stream || this.filePath !== path) {
-				this.resetStream(path);
-			}
-		}
-
 		const line = `${JSON.stringify({
 			timestamp: new Date(meta.timestamp).getTime(),
 			level,
@@ -95,18 +116,28 @@ class FileLogger {
 			file: meta.fileName,
 			line: meta.line,
 			column: meta.column,
-			data:
+			data: serializeLogData(data),
-				data instanceof Error
-					? {
-							name: data.name,
-							message: data.message,
-							stack: data.stack,
-						}
-					: typeof data === "string" || typeof data === "number"
-						? data
-						: data,
 		})}\n`;
 
+		let path: string;
+		const dateStr = this.config.rotate
+			? format(now, this.fileNameFormat, { timeZone: this.config.timezone })
+			: undefined;
+
+		const needsRotation = this.config.rotate && this.date !== dateStr;
+		path = this.getFilePath(dateStr);
+
+		if (!this.stream || needsRotation || this.filePath !== path) {
+			if (this.config.rotate && dateStr) {
+				this.date = dateStr;
+			}
+			this.resetStream(path);
+
+			if (needsRotation) {
+				this.pruneOldLogs();
+			}
+		}
+
 		try {
 			this.stream?.write(line);
 		} catch (err) {

types/index.ts

@@ -1,6 +1,6 @@
-import { ansiColors, logLevelValues } from "@lib/config";
+import type { ansiColors, logLevelValues } from "@lib/config";
 
-type LogLevelValue = typeof logLevelValues[keyof typeof logLevelValues];
+type LogLevelValue = (typeof logLevelValues)[keyof typeof logLevelValues];
 type LogLevel = keyof typeof logLevelValues;
 
 type LoggerConfig = {
@@ -9,7 +9,8 @@ type LoggerConfig = {
 	disableFile?: boolean;
 
 	rotate?: boolean;
-	maxFiles?: number;
+	maxFiles?: number | null;
+	fileNameFormat?: string;
 
 	console?: boolean;
 	consoleColor?: boolean;
@@ -28,10 +29,30 @@ type LoggerConfig = {
 	prettyPrint?: boolean;
 };
 
-interface PatternContext {
+type PatternContext = {
 	level: LogLevel;
 	data: unknown;
 	config: Required<LoggerConfig>;
+};
+
+interface PatternTokens {
+	timestamp?: string;
+	prettyTimestamp?: string;
+	levelName?: string;
+	level?: string;
+	fileName?: string;
+	line?: string;
+	column?: string;
+	data?: string;
+	id?: string;
+	tag?: string;
+	context?: string;
 }
 
-export type { LogLevel, LogLevelValue, LoggerConfig, PatternContext };
+export type {
+	LogLevel,
+	LogLevelValue,
+	LoggerConfig,
+	PatternContext,
+	PatternTokens,
+};