EllyDiscordBot/crates/shared/src/logger/sinks.ts

/**
 * Logger sink implementations.
 *
 * - `ConsoleSink`: synchronous writes to stdout/stderr, optionally
 *   ANSI-colorized for `console` format or compact JSON for `json` format.
 * - `RotatingFileSink`: asynchronous, append-only JSON lines with size-based
 *   rotation. Writes are serialized through a promise queue so concurrent
 *   `write()` calls cannot interleave.
 *
 * Both sinks survive transient errors (logged to stderr) — a failing log
 * sink must never crash the host process.
 */

import { dirname } from "@std/path";
import { ensureDir } from "@std/fs";
import {
  bold,
  cyan,
  gray,
  green,
  magenta,
  red,
  yellow,
} from "@std/fmt/colors";
import {
  LOG_LEVEL_ORDER,
  type LogLevel,
  type LogRecord,
  type LogSink,
} from "./types.ts";

const encoder = new TextEncoder();

const LEVEL_COLOR: Record<LogLevel, (s: string) => string> = {
  debug: cyan,
  info: green,
  warn: yellow,
  error: red,
  fatal: (s) => bold(magenta(s)),
};

// =====================================================================
// ConsoleSink
// =====================================================================

export class ConsoleSink implements LogSink {
  constructor(private readonly format: "console" | "json") {}

  write(record: LogRecord): void {
    const line = this.format === "json"
      ? JSON.stringify(record) + "\n"
      : this.formatConsole(record) + "\n";

    const useStderr = LOG_LEVEL_ORDER[record.level] >= LOG_LEVEL_ORDER.warn;
    const writer = useStderr ? Deno.stderr : Deno.stdout;
    try {
      writer.writeSync(encoder.encode(line));
    } catch {
      // Never propagate sink failures to user code.
    }
  }

  flush(): Promise<void> {
    return Promise.resolve();
  }

  private formatConsole(record: LogRecord): string {
    const { time, level, logger, msg, ...rest } = record;
    const ts = gray(time);
    const lvl = LEVEL_COLOR[level](level.toUpperCase().padEnd(5));
    const name = cyan(`[${logger}]`);

    let fields = "";
    const keys = Object.keys(rest);
    if (keys.length > 0) {
      const parts: string[] = [];
      for (const k of keys) {
        parts.push(`${k}=${formatValue(rest[k])}`);
      }
      fields = " " + gray(parts.join(" "));
    }

    return `${ts} ${lvl} ${name} ${msg}${fields}`;
  }
}

function formatValue(v: unknown): string {
  if (v === null) return "null";
  if (v === undefined) return "undefined";
  switch (typeof v) {
    case "string":
      return /\s/.test(v) ? JSON.stringify(v) : v;
    case "number":
    case "boolean":
    case "bigint":
      return String(v);
    case "function":
      return "[function]";
  }
  if (v instanceof Error) {
    return `${v.name}: ${v.message}`;
  }
  try {
    return JSON.stringify(v);
  } catch {
    return String(v);
  }
}

// =====================================================================
// RotatingFileSink
// =====================================================================

export class RotatingFileSink implements LogSink {
  private queue: Promise<void> = Promise.resolve();
  private readonly maxBytes: number;
  private readonly maxBackups: number;
  private dirEnsured = false;

  constructor(
    private readonly path: string,
    options: { maxBytes?: number; maxBackups?: number } = {},
  ) {
    this.maxBytes = options.maxBytes ?? 10 * 1024 * 1024;
    this.maxBackups = options.maxBackups ?? 5;
  }

  write(record: LogRecord): void {
    const line = JSON.stringify(record) + "\n";
    this.queue = this.queue.then(() => this.doWrite(line)).catch((err) => {
      const msg = err instanceof Error ? err.message : String(err);
      try {
        Deno.stderr.writeSync(
          encoder.encode(`[logger] RotatingFileSink write failed: ${msg}\n`),
        );
      } catch {
        // give up
      }
    });
  }

  async flush(): Promise<void> {
    await this.queue;
  }

  private async doWrite(line: string): Promise<void> {
    if (!this.dirEnsured) {
      await ensureDir(dirname(this.path));
      this.dirEnsured = true;
    }

    try {
      const stat = await Deno.stat(this.path);
      if (stat.size + line.length > this.maxBytes) {
        await this.rotate();
      }
    } catch (err) {
      if (!(err instanceof Deno.errors.NotFound)) throw err;
    }

    await Deno.writeTextFile(this.path, line, { append: true });
  }

  private async rotate(): Promise<void> {
    // Remove the oldest backup if it would be pushed past the retention limit.
    if (this.maxBackups > 0) {
      const oldest = `${this.path}.${this.maxBackups}`;
      try {
        await Deno.remove(oldest);
      } catch (err) {
        if (!(err instanceof Deno.errors.NotFound)) throw err;
      }
    }

    // Shift .{i} -> .{i+1} for i in [maxBackups-1 .. 1].
    for (let i = this.maxBackups - 1; i >= 1; i--) {
      const src = `${this.path}.${i}`;
      const dst = `${this.path}.${i + 1}`;
      try {
        await Deno.rename(src, dst);
      } catch (err) {
        if (!(err instanceof Deno.errors.NotFound)) throw err;
      }
    }

    // Rotate the active log to .1 (only if there is at least one backup slot).
    if (this.maxBackups > 0) {
      try {
        await Deno.rename(this.path, `${this.path}.1`);
      } catch (err) {
        if (!(err instanceof Deno.errors.NotFound)) throw err;
      }
    } else {
      // No retention — just truncate.
      try {
        await Deno.remove(this.path);
      } catch (err) {
        if (!(err instanceof Deno.errors.NotFound)) throw err;
      }
    }
  }
}