From 8a013b0e626cec532fbcd81936773474186e414b Mon Sep 17 00:00:00 2001
From: Yuzu <yuzu@kirameki.cafe>
Date: Mon, 13 Jul 2026 16:59:30 +0700
Subject: [PATCH] =?UTF-8?q?=E2=9C=A8=20feat:=20add=20a=20leveled=20logger?=
 =?UTF-8?q?=20with=20control-char=20sanitization?=
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---
 src/logger.ts | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 src/logger.ts

diff --git a/src/logger.ts b/src/logger.ts
new file mode 100644
index 0000000..27b2cc6
--- /dev/null
+++ b/src/logger.ts
@@ -0,0 +1,58 @@
+export type LogLevel = "debug" | "info" | "warn" | "error";
+
+const LEVEL_ORDER: Record<LogLevel, number> = {
+    debug: 10,
+    info: 20,
+    warn: 30,
+    error: 40,
+};
+
+function resolveThreshold(): number {
+    const raw = (globalThis.process.env.LOG_LEVEL ?? "info")
+        .trim()
+        .toLowerCase();
+    return LEVEL_ORDER[raw as LogLevel] ?? LEVEL_ORDER.info;
+}
+
+let threshold = resolveThreshold();
+
+export function sanitize(value: unknown, maxLength = 200): string {
+    let str =
+        typeof value === "string"
+            ? value
+            : value === undefined
+              ? ""
+              : String(value);
+    // eslint-disable-next-line no-control-regex
+    str = str.replace(/[\x00-\x1f\x7f-\x9f]/g, "�");
+    if (str.length > maxLength) str = str.slice(0, maxLength) + "…";
+    return str;
+}
+
+function emit(
+    level: LogLevel,
+    stream: NodeJS.WriteStream,
+    args: unknown[]
+): void {
+    if (LEVEL_ORDER[level] < threshold) return;
+    const ts = new Date().toISOString();
+    const line =
+        `[${ts}] ${level.toUpperCase().padEnd(5)} ` +
+        args
+            .map((a) => (typeof a === "string" ? a : JSON.stringify(a)))
+            .join(" ");
+    stream.write(line + "\n");
+}
+
+export const logger = {
+    debug: (...args: unknown[]) =>
+        emit("debug", globalThis.process.stdout, args),
+    info: (...args: unknown[]) => emit("info", globalThis.process.stdout, args),
+    warn: (...args: unknown[]) => emit("warn", globalThis.process.stderr, args),
+    error: (...args: unknown[]) =>
+        emit("error", globalThis.process.stderr, args),
+    refresh: () => {
+        threshold = resolveThreshold();
+    },
+    sanitize,
+};