/**
 * Way data is stored for this database.
 * This version is the Node.js/Node Webkit version.
 * It's essentially fs, mkdirp and crash safe write and read functions.
 *
 * @see module:storageBrowser
 * @see module:storageReactNative
 * @module storage
 * @private
 */
const fs = require('fs')
const fsPromises = fs.promises
const path = require('path')
const { Readable } = require('stream')

/**
 * Returns true if file exists.
 * @param {string} file
 * @return {Promise<boolean>}
 * @async
 * @alias module:storage.existsAsync
 * @see module:storage.exists
 */
const existsAsync = file => fsPromises.access(file, fs.constants.F_OK).then(() => true, () => false)

/**
 * Node.js' [fsPromises.rename]{@link https://nodejs.org/api/fs.html#fspromisesrenameoldpath-newpath}
 * @function
 * @param {string} oldPath
 * @param {string} newPath
 * @return {Promise<void>}
 * @alias module:storage.renameAsync
 * @async
 */
const renameAsync = fsPromises.rename

/**
 * Node.js' [fsPromises.writeFile]{@link https://nodejs.org/api/fs.html#fspromiseswritefilefile-data-options}.
 * @function
 * @param {string} path
 * @param {string} data
 * @param {object} [options]
 * @return {Promise<void>}
 * @alias module:storage.writeFileAsync
 * @async
 */
const writeFileAsync = fsPromises.writeFile

/**
 * Node.js' [fs.createWriteStream]{@link https://nodejs.org/api/fs.html#fscreatewritestreampath-options}.
 * @function
 * @param {string} path
 * @param {Object} [options]
 * @return {fs.WriteStream}
 * @alias module:storage.writeFileStream
 */
const writeFileStream = fs.createWriteStream

/**
 * Node.js' [fsPromises.unlink]{@link https://nodejs.org/api/fs.html#fspromisesunlinkpath}.
 * @function
 * @param {string} path
 * @return {Promise<void>}
 * @async
 * @alias module:storage.unlinkAsync
 */
const unlinkAsync = fsPromises.unlink

/**
 * Node.js' [fsPromises.appendFile]{@link https://nodejs.org/api/fs.html#fspromisesappendfilepath-data-options}.
 * @function
 * @param {string} path
 * @param {string} data
 * @param {object} [options]
 * @return {Promise<void>}
 * @alias module:storage.appendFileAsync
 * @async
 */
const appendFileAsync = fsPromises.appendFile

/**
 * Node.js' [fsPromises.readFile]{@link https://nodejs.org/api/fs.html#fspromisesreadfilepath-options}.
 * @function
 * @param {string} path
 * @param {object} [options]
 * @return {Promise<Buffer>}
 * @alias module:storage.readFileAsync
 * @async
 */
const readFileAsync = fsPromises.readFile

/**
 * Node.js' [fs.createReadStream]{@link https://nodejs.org/api/fs.html#fscreatereadstreampath-options}.
 * @function
 * @param {string} path
 * @param {Object} [options]
 * @return {fs.ReadStream}
 * @alias module:storage.readFileStream
 */
const readFileStream = fs.createReadStream

/**
 * Node.js' [fsPromises.mkdir]{@link https://nodejs.org/api/fs.html#fspromisesmkdirpath-options}.
 * @function
 * @param {string} path
 * @param {object} options
 * @return {Promise<void|string>}
 * @alias module:storage.mkdirAsync
 * @async
 */
const mkdirAsync = fsPromises.mkdir

/**
 * Removes file if it exists.
 * @param {string} file
 * @return {Promise<void>}
 * @alias module:storage.ensureFileDoesntExistAsync
 * @async
 */
const ensureFileDoesntExistAsync = async file => {
  if (await existsAsync(file)) await unlinkAsync(file)
}

/**
 * Flush data in OS buffer to storage if corresponding option is set.
 * @param {object|string} options If options is a string, it is assumed that the flush of the file (not dir) called options was requested
 * @param {string} [options.filename]
 * @param {boolean} [options.isDir = false] Optional, defaults to false
 * @return {Promise<void>}
 * @alias module:storage.flushToStorageAsync
 * @async
 */
const flushToStorageAsync = async (options) => {
  let filename
  let flags
  if (typeof options === 'string') {
    filename = options
    flags = 'r+'
  } else {
    filename = options.filename
    flags = options.isDir ? 'r' : 'r+'
  }

  /**
   * Some OSes and/or storage backends (augmented node fs) do not support fsync (FlushFileBuffers) directories,
   * or calling open() on directories at all. Flushing fails silently in this case, supported by following heuristics:
   *  + isDir === true
   *  |-- open(<dir>) -> (err.code === 'EISDIR'): can't call open() on directories (eg. BrowserFS)
   *  `-- fsync(<dir>) -> (errFS.code === 'EPERM' || errFS.code === 'EISDIR'): can't fsync directory: permissions are checked
   *        on open(); EPERM error should only occur on fsync incapability and not for general lack of permissions (e.g. Windows)
   *
   * We can live with this as it cannot cause 100% dataloss except in the very rare event of the first time
   * database is loaded and a crash happens.
   */

  let filehandle, errorOnFsync, errorOnClose
  try {
    filehandle = await fsPromises.open(filename, flags)
    try {
      await filehandle.sync()
    } catch (errFS) {
      errorOnFsync = errFS
    }
  } catch (error) {
    if (error.code !== 'EISDIR' || !options.isDir) throw error
  } finally {
    try {
      await filehandle.close()
    } catch (errC) {
      errorOnClose = errC
    }
  }
  if ((errorOnFsync || errorOnClose) && !((errorOnFsync.code === 'EPERM' || errorOnClose.code === 'EISDIR') && options.isDir)) {
    const e = new Error('Failed to flush to storage')
    e.errorOnFsync = errorOnFsync
    e.errorOnClose = errorOnClose
    throw e
  }
}

/**
 * Fully write or rewrite the datafile.
 * @param {string} filename
 * @param {string[]} lines
 * @return {Promise<void>}
 * @alias module:storage.writeFileLinesAsync
 * @async
 */
const writeFileLinesAsync = (filename, lines) => new Promise((resolve, reject) => {
  try {
    const stream = writeFileStream(filename)
    const readable = Readable.from(lines)
    readable.on('data', (line) => {
      try {
        stream.write(line + '\n')
      } catch (err) {
        reject(err)
      }
    })
    readable.on('end', () => {
      stream.close(err => {
        if (err) reject(err)
        else resolve()
      })
    })

    readable.on('error', err => {
      reject(err)
    })

    stream.on('error', err => {
      reject(err)
    })
  } catch (err) {
    reject(err)
  }
})

/**
 * Fully write or rewrite the datafile, immune to crashes during the write operation (data will not be lost).
 * @param {string} filename
 * @param {string[]} lines
 * @return {Promise<void>}
 * @alias module:storage.crashSafeWriteFileLinesAsync
 */
const crashSafeWriteFileLinesAsync = async (filename, lines) => {
  const tempFilename = filename + '~'

  await flushToStorageAsync({ filename: path.dirname(filename), isDir: true })

  const exists = await existsAsync(filename)
  if (exists) await flushToStorageAsync({ filename })

  await writeFileLinesAsync(tempFilename, lines)

  await flushToStorageAsync(tempFilename)

  await renameAsync(tempFilename, filename)

  await flushToStorageAsync({ filename: path.dirname(filename), isDir: true })
}

/**
 * Ensure the datafile contains all the data, even if there was a crash during a full file write.
 * @param {string} filename
 * @return {Promise<void>}
 * @alias module:storage.ensureDatafileIntegrityAsync
 */
const ensureDatafileIntegrityAsync = async filename => {
  const tempFilename = filename + '~'

  const filenameExists = await existsAsync(filename)
  // Write was successful
  if (filenameExists) return

  const oldFilenameExists = await existsAsync(tempFilename)
  // New database
  if (!oldFilenameExists) await writeFileAsync(filename, '', 'utf8')
  // Write failed, use old version
  else await renameAsync(tempFilename, filename)
}

// Interface
module.exports.existsAsync = existsAsync

module.exports.renameAsync = renameAsync

module.exports.writeFileAsync = writeFileAsync

module.exports.writeFileLinesAsync = writeFileLinesAsync

module.exports.crashSafeWriteFileLinesAsync = crashSafeWriteFileLinesAsync

module.exports.appendFileAsync = appendFileAsync

module.exports.readFileAsync = readFileAsync

module.exports.unlinkAsync = unlinkAsync

module.exports.mkdirAsync = mkdirAsync

module.exports.readFileStream = readFileStream

module.exports.flushToStorageAsync = flushToStorageAsync

module.exports.ensureDatafileIntegrityAsync = ensureDatafileIntegrityAsync

module.exports.ensureFileDoesntExistAsync = ensureFileDoesntExistAsync