type Level = "debug" | "info" | "warn" | "error";

const PRIORITY: Record<Level, number> = {
  debug: 0,
  info: 1,
  warn: 2,
  error: 3,
};

function getMinLevel(): Level {
  const env = process.env.LOG_LEVEL as Level | undefined;
  if (env && env in PRIORITY) return env;
  const appEnv = process.env.APP_ENV;
  return appEnv === "production" ? "info" : "debug";
}

function shouldLog(level: Level): boolean {
  return PRIORITY[level] >= PRIORITY[getMinLevel()];
}

// TZ 환경변수 기준 로컬 시간 (toISOString은 항상 UTC라 사용하지 않음)
export function timestamp(): string {
  const d = new Date();
  const pad = (n: number, w = 2) => String(n).padStart(w, "0");
  const offMin = -d.getTimezoneOffset();
  const sign = offMin >= 0 ? "+" : "-";
  const abs = Math.abs(offMin);
  return (
    `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())}` +
    `T${pad(d.getHours())}:${pad(d.getMinutes())}:${pad(d.getSeconds())}` +
    `.${pad(d.getMilliseconds(), 3)}` +
    `${sign}${pad(Math.floor(abs / 60))}:${pad(abs % 60)}`
  );
}

function write(
  level: Level,
  ctx: string,
  message: string,
  data?: Record<string, unknown>
): void {
  if (!shouldLog(level)) return;
  const ts = timestamp();
  const tag = level.toUpperCase().padEnd(5);
  const line = data
    ? `[${ts}] [${tag}] [${ctx}] ${message} ${JSON.stringify(data)}`
    : `[${ts}] [${tag}] [${ctx}] ${message}`;
  if (level === "warn" || level === "error") {
    console.error(line);
  } else {
    console.log(line);
  }
}

export const logger = {
  debug: (ctx: string, message: string, data?: Record<string, unknown>) =>
    write("debug", ctx, message, data),
  info: (ctx: string, message: string, data?: Record<string, unknown>) =>
    write("info", ctx, message, data),
  warn: (ctx: string, message: string, data?: Record<string, unknown>) =>
    write("warn", ctx, message, data),
  error: (ctx: string, message: string, data?: Record<string, unknown>) =>
    write("error", ctx, message, data),
  isEnabled: (level: Level): boolean => shouldLog(level),
};