const debug = require("debug")("streamroller:RollingFileWriteStream");
const fs = require("fs-extra");
const path = require("path");
const newNow = require("./now");
const format = require("date-format");
const { Writable } = require("stream");
const fileNameFormatter = require("./fileNameFormatter");
const fileNameParser = require("./fileNameParser");
const moveAndMaybeCompressFile = require("./moveAndMaybeCompressFile");

/**
 * RollingFileWriteStream is mainly used when writing to a file rolling by date or size.
 * RollingFileWriteStream inherits from stream.Writable
 */
class RollingFileWriteStream extends Writable {
  /**
   * Create a RollingFileWriteStream
   * @constructor
   * @param {string} filePath - The file path to write.
   * @param {object} options - The extra options
   * @param {number} options.numToKeep - The max numbers of files to keep.
   * @param {number} options.maxSize - The maxSize one file can reach. Unit is Byte.
   *                                   This should be more than 1024. The default is Number.MAX_SAFE_INTEGER.
   * @param {string} options.mode - The mode of the files. The default is '0644'. Refer to stream.writable for more.
   * @param {string} options.flags - The default is 'a'. Refer to stream.flags for more.
   * @param {boolean} options.compress - Whether to compress backup files.
   * @param {boolean} options.keepFileExt - Whether to keep the file extension.
   * @param {string} options.pattern - The date string pattern in the file name.
   * @param {boolean} options.alwaysIncludePattern - Whether to add date to the name of the first file.
   */
  constructor(filePath, options) {
    debug(`constructor: creating RollingFileWriteStream. path=${filePath}`);
    super(options);
    this.options = this._parseOption(options);
    this.fileObject = path.parse(filePath);
    if (this.fileObject.dir === "") {
      this.fileObject = path.parse(path.join(process.cwd(), filePath));
    }
    this.fileFormatter = fileNameFormatter({
      file: this.fileObject,
      alwaysIncludeDate: this.options.alwaysIncludePattern,
      needsIndex: this.options.maxSize < Number.MAX_SAFE_INTEGER,
      compress: this.options.compress,
      keepFileExt: this.options.keepFileExt
    });

    this.fileNameParser = fileNameParser({
      file: this.fileObject,
      keepFileExt: this.options.keepFileExt,
      pattern: this.options.pattern
    });

    this.state = {
      currentSize: 0
    };

    if (this.options.pattern) {
      this.state.currentDate = format(this.options.pattern, newNow());
    }

    this.filename = this.fileFormatter({
      index: 0,
      date: this.state.currentDate
    });
    if (["a", "a+", "as", "as+"].includes(this.options.flags)) {
      this._setExistingSizeAndDate();
    }

    debug(
      `constructor: create new file ${this.filename}, state=${JSON.stringify(
        this.state
      )}`
    );
    this._renewWriteStream();
  }

  _setExistingSizeAndDate() {
    try {
      const stats = fs.statSync(this.filename);
      this.state.currentSize = stats.size;
      if (this.options.pattern) {
        this.state.currentDate = format(this.options.pattern, stats.mtime);
      }
    } catch (e) {
      //file does not exist, that's fine - move along
      return;
    }
  }

  _parseOption(rawOptions) {
    const defaultOptions = {
      maxSize: Number.MAX_SAFE_INTEGER,
      numToKeep: Number.MAX_SAFE_INTEGER,
      encoding: "utf8",
      mode: parseInt("0644", 8),
      flags: "a",
      compress: false,
      keepFileExt: false,
      alwaysIncludePattern: false
    };
    const options = Object.assign({}, defaultOptions, rawOptions);
    if (options.maxSize <= 0) {
      throw new Error(`options.maxSize (${options.maxSize}) should be > 0`);
    }
    if (options.numToKeep <= 0) {
      throw new Error(`options.numToKeep (${options.numToKeep}) should be > 0`);
    }
    debug(
      `_parseOption: creating stream with option=${JSON.stringify(options)}`
    );
    return options;
  }

  _final(callback) {
    this.currentFileStream.end("", this.options.encoding, callback);
  }

  _write(chunk, encoding, callback) {
    this._shouldRoll().then(() => {
      debug(
        `_write: writing chunk. ` +
          `file=${this.currentFileStream.path} ` +
          `state=${JSON.stringify(this.state)} ` +
          `chunk=${chunk}`
      );
      this.currentFileStream.write(chunk, encoding, e => {
        this.state.currentSize += chunk.length;
        callback(e);
      });
    });
  }

  async _shouldRoll() {
    if (this._dateChanged() || this._tooBig()) {
      debug(
        `_shouldRoll: rolling because dateChanged? ${this._dateChanged()} or tooBig? ${this._tooBig()}`
      );
      await this._roll();
    }
  }

  _dateChanged() {
    return (
      this.state.currentDate &&
      this.state.currentDate !== format(this.options.pattern, newNow())
    );
  }

  _tooBig() {
    return this.state.currentSize >= this.options.maxSize;
  }

  _roll() {
    debug(`_roll: closing the current stream`);
    return new Promise((resolve, reject) => {
      this.currentFileStream.end("", this.options.encoding, () => {
        this._moveOldFiles()
          .then(resolve)
          .catch(reject);
      });
    });
  }

  async _moveOldFiles() {
    const files = await this._getExistingFiles();
    const todaysFiles = this.state.currentDate
      ? files.filter(f => f.date === this.state.currentDate)
      : files;
    for (let i = todaysFiles.length; i >= 0; i--) {
      debug(`_moveOldFiles: i = ${i}`);
      const sourceFilePath = this.fileFormatter({
        date: this.state.currentDate,
        index: i
      });
      const targetFilePath = this.fileFormatter({
        date: this.state.currentDate,
        index: i + 1
      });

      await moveAndMaybeCompressFile(
        sourceFilePath,
        targetFilePath,
        this.options.compress && i === 0
      );
    }

    this.state.currentSize = 0;
    this.state.currentDate = this.state.currentDate
      ? format(this.options.pattern, newNow())
      : null;
    debug(
      `_moveOldFiles: finished rolling files. state=${JSON.stringify(
        this.state
      )}`
    );
    this._renewWriteStream();
    // wait for the file to be open before cleaning up old ones,
    // otherwise the daysToKeep calculations can be off
    await new Promise((resolve, reject) => {
      this.currentFileStream.write("", "utf8", () => {
        this._clean()
          .then(resolve)
          .catch(reject);
      });
    });
  }

  // Sorted from the oldest to the latest
  async _getExistingFiles() {
    const files = await fs.readdir(this.fileObject.dir).catch(() => []);

    debug(`_getExistingFiles: files=${files}`);
    const existingFileDetails = files
      .map(n => this.fileNameParser(n))
      .filter(n => n);

    const getKey = n =>
      (n.timestamp ? n.timestamp : newNow().getTime()) - n.index;
    existingFileDetails.sort((a, b) => getKey(a) - getKey(b));

    return existingFileDetails;
  }

  _renewWriteStream() {
    fs.ensureDirSync(this.fileObject.dir);
    const filePath = this.fileFormatter({
      date: this.state.currentDate,
      index: 0
    });
    const ops = {
      flags: this.options.flags,
      encoding: this.options.encoding,
      mode: this.options.mode
    };
    this.currentFileStream = fs.createWriteStream(filePath, ops);
    this.currentFileStream.on("error", e => {
      this.emit("error", e);
    });
  }

  async _clean() {
    const existingFileDetails = await this._getExistingFiles();
    debug(
      `_clean: numToKeep = ${this.options.numToKeep}, existingFiles = ${existingFileDetails.length}`
    );
    debug("_clean: existing files are: ", existingFileDetails);
    if (this._tooManyFiles(existingFileDetails.length)) {
      const fileNamesToRemove = existingFileDetails
        .slice(0, existingFileDetails.length - this.options.numToKeep - 1)
        .map(f => path.format({ dir: this.fileObject.dir, base: f.filename }));
      await deleteFiles(fileNamesToRemove);
    }
  }

  _tooManyFiles(numFiles) {
    return this.options.numToKeep > 0 && numFiles > this.options.numToKeep;
  }
}

const deleteFiles = fileNames => {
  debug(`deleteFiles: files to delete: ${fileNames}`);
  return Promise.all(fileNames.map(f => fs.unlink(f).catch((e) => {
    debug(`deleteFiles: error when unlinking ${f}, ignoring. Error was ${e}`);
  })));
};

module.exports = RollingFileWriteStream;