export type LogLevel = "trace" | "debug" | "info" | "warn" | "error" | "fatal";

export interface LogEntry {
  level: LogLevel;
  msg: string;
  time: number;
  [key: string]: unknown;
}

export interface LoggerOptions {
  level?: LogLevel;
  name?: string;
  base?: Record<string, unknown>;
  transport?: (entry: LogEntry) => void;
}

export interface KittenLogger {
  trace(msg: string, data?: Record<string, unknown>): void;
  debug(msg: string, data?: Record<string, unknown>): void;
  info(msg: string, data?: Record<string, unknown>): void;
  warn(msg: string, data?: Record<string, unknown>): void;
  error(msg: string, data?: Record<string, unknown>): void;
  fatal(msg: string, data?: Record<string, unknown>): void;
  child(bindings: Record<string, unknown>): KittenLogger;
}

const LEVELS: Record<LogLevel, number> = {
  trace: 10,
  debug: 20,
  info: 30,
  warn: 40,
  error: 50,
  fatal: 60,
};

const defaultTransport = (entry: LogEntry) => {
  const out = JSON.stringify(entry);
  if (entry.level === "error" || entry.level === "fatal") console.error(out);
  else console.log(out);
};

export class Logger implements KittenLogger {
  private readonly minLevel: number;
  private readonly base: Record<string, unknown>;
  private readonly transport: (entry: LogEntry) => void;

  constructor(private readonly options: LoggerOptions = {}) {
    this.minLevel = LEVELS[options.level ?? "info"];
    this.base = {
      ...(options.name ? { name: options.name } : {}),
      ...options.base,
    };
    this.transport = options.transport ?? defaultTransport;
  }

  private write(level: LogLevel, msg: string, data?: Record<string, unknown>) {
    if (LEVELS[level] < this.minLevel) return;
    this.transport({
      level,
      msg,
      time: Date.now(),
      ...this.base,
      ...data,
    });
  }

  trace(msg: string, data?: Record<string, unknown>) {
    this.write("trace", msg, data);
  }
  debug(msg: string, data?: Record<string, unknown>) {
    this.write("debug", msg, data);
  }
  info(msg: string, data?: Record<string, unknown>) {
    this.write("info", msg, data);
  }
  warn(msg: string, data?: Record<string, unknown>) {
    this.write("warn", msg, data);
  }
  error(msg: string, data?: Record<string, unknown>) {
    this.write("error", msg, data);
  }
  fatal(msg: string, data?: Record<string, unknown>) {
    this.write("fatal", msg, data);
  }

  child(bindings: Record<string, unknown>): KittenLogger {
    return new Logger({
      ...this.options,
      base: { ...this.base, ...bindings },
    });
  }
}

const baseLogger = new Logger();
export { baseLogger };