add file logging, readme, so on

src/lib/file.ts

@@ -0,0 +1,105 @@
+import {
+	type WriteStream,
+	createWriteStream,
+	existsSync,
+	mkdirSync,
+} from "node:fs";
+import { join } from "node:path";
+import type { LogLevel, LoggerConfig } from "@types";
+import { format } from "date-fns-tz";
+
+let currentStream: WriteStream | null = null;
+let currentFilePath = "";
+let currentDate = "";
+
+function getLogFilePath(
+	config: Required<LoggerConfig>,
+	dateStr: string,
+): string {
+	return join(config.directory, `${dateStr}.jsonl`);
+}
+
+function resetStream(path: string): void {
+	currentStream?.end();
+	currentStream = createWriteStream(path, { flags: "a", encoding: "utf-8" });
+	currentFilePath = path;
+}
+
+export function writeLogJson(
+	level: LogLevel,
+	data: unknown,
+	meta: {
+		id: string;
+		fileName: string;
+		line: string;
+		column: string;
+		timestamp: string;
+		prettyTimestamp: string;
+	},
+	config: Required<LoggerConfig>,
+): void {
+	if (config.disableFile) return;
+
+	const now = new Date();
+
+	if (!existsSync(config.directory)) {
+		mkdirSync(config.directory, { recursive: true });
+	}
+
+	let filePath: string;
+
+	if (config.rotate) {
+		const dateStr = format(now, "yyyy-MM-dd", {
+			timeZone: config.timezone,
+		});
+		filePath = getLogFilePath(config, dateStr);
+
+		if (
+			currentStream === null ||
+			currentFilePath !== filePath ||
+			currentDate !== dateStr
+		) {
+			currentDate = dateStr;
+			resetStream(filePath);
+		}
+	} else {
+		filePath = join(config.directory, "log.jsonl");
+
+		if (currentStream === null || currentFilePath !== filePath) {
+			resetStream(filePath);
+		}
+	}
+
+	const line = `${JSON.stringify({
+		timestamp: new Date(meta.timestamp).getTime(),
+		level,
+		id: meta.id,
+		file: meta.fileName,
+		line: meta.line,
+		column: meta.column,
+		data:
+			data instanceof Error
+				? {
+						name: data.name,
+						message: data.message,
+						stack: data.stack,
+					}
+				: typeof data === "string" || typeof data === "number"
+					? data
+					: data,
+	})}\n`;
+
+	if (currentStream === null) {
+		throw new Error("Logger stream is not initialized");
+	}
+
+	currentStream.write(line);
+}
+
+process.on("exit", () => {
+	currentStream?.end();
+});
+process.on("SIGINT", () => {
+	currentStream?.end();
+	process.exit();
+});