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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.import { type LevelName, LogLevels } from "./levels.ts";import type { LogRecord } from "./logger.ts";import { BaseHandler, type BaseHandlerOptions } from "./base_handler.ts";import { writeAllSync } from "../io/write_all.ts";
const PAGE_SIZE = 4096;export type LogMode = "a" | "w" | "x";
export interface FileHandlerOptions extends BaseHandlerOptions {  filename: string;  mode?: LogMode;}
/** * This handler will output to a file using an optional mode (default is `a`, * e.g. append). The file will grow indefinitely. It uses a buffer for writing * to file. Logs can be manually flushed with `fileHandler.flush()`. Log * messages with a log level greater than error are immediately flushed. Logs * are also flushed on process completion. * * Behavior of the log modes is as follows: * * - `'a'` - Default mode. Appends new log messages to the end of an existing log *   file, or create a new log file if none exists. * - `'w'` - Upon creation of the handler, any existing log file will be removed *   and a new one created. * - `'x'` - This will create a new log file and throw an error if one already *   exists. * * This handler requires `--allow-write` permission on the log file. */export class FileHandler extends BaseHandler {  protected _file: Deno.FsFile | undefined;  protected _buf: Uint8Array = new Uint8Array(PAGE_SIZE);  protected _pointer = 0;  protected _filename: string;  protected _mode: LogMode;  protected _openOptions: Deno.OpenOptions;  protected _encoder: TextEncoder = new TextEncoder();  #unloadCallback = (() => {    this.destroy();  }).bind(this);
  constructor(levelName: LevelName, options: FileHandlerOptions) {    super(levelName, options);    this._filename = options.filename;    // default to append mode, write only    this._mode = options.mode ? options.mode : "a";    this._openOptions = {      createNew: this._mode === "x",      create: this._mode !== "x",      append: this._mode === "a",      truncate: this._mode !== "a",      write: true,    };  }
  override setup() {    this._file = Deno.openSync(this._filename, this._openOptions);    this.#resetBuffer();
    addEventListener("unload", this.#unloadCallback);  }
  override handle(logRecord: LogRecord) {    super.handle(logRecord);
    // Immediately flush if log level is higher than ERROR    if (logRecord.level > LogLevels.ERROR) {      this.flush();    }  }
  override log(msg: string) {    const bytes = this._encoder.encode(msg + "\n");    if (bytes.byteLength > this._buf.byteLength - this._pointer) {      this.flush();    }    if (bytes.byteLength > this._buf.byteLength) {      writeAllSync(this._file!, bytes);    } else {      this._buf.set(bytes, this._pointer);      this._pointer += bytes.byteLength;    }  }
  flush() {    if (this._pointer > 0 && this._file) {      let written = 0;      while (written < this._pointer) {        written += this._file.writeSync(          this._buf.subarray(written, this._pointer),        );      }      this.#resetBuffer();    }  }
  #resetBuffer() {    this._pointer = 0;  }
  override destroy() {    this.flush();    this._file?.close();    this._file = undefined;    removeEventListener("unload", this.#unloadCallback);  }}