/**
 * @module byte-size
 */

let defaultOptions = {}
const _options = new WeakMap()

class ByteSize {
  constructor (bytes, options) {
    options = Object.assign({
      units: 'metric',
      precision: 1
    }, defaultOptions, options)
    _options.set(this, options)

    const tables = {
      metric: [
        { from: 0   , to: 1e3 , unit: 'B' , long: 'bytes' },
        { from: 1e3 , to: 1e6 , unit: 'kB', long: 'kilobytes' },
        { from: 1e6 , to: 1e9 , unit: 'MB', long: 'megabytes' },
        { from: 1e9 , to: 1e12, unit: 'GB', long: 'gigabytes' },
        { from: 1e12, to: 1e15, unit: 'TB', long: 'terabytes' },
        { from: 1e15, to: 1e18, unit: 'PB', long: 'petabytes' },
        { from: 1e18, to: 1e21, unit: 'EB', long: 'exabytes' },
        { from: 1e21, to: 1e24, unit: 'ZB', long: 'zettabytes' },
        { from: 1e24, to: 1e27, unit: 'YB', long: 'yottabytes' },
      ],
      metric_octet: [
        { from: 0   , to: 1e3 , unit: 'o' , long: 'octets' },
        { from: 1e3 , to: 1e6 , unit: 'ko', long: 'kilooctets' },
        { from: 1e6 , to: 1e9 , unit: 'Mo', long: 'megaoctets' },
        { from: 1e9 , to: 1e12, unit: 'Go', long: 'gigaoctets' },
        { from: 1e12, to: 1e15, unit: 'To', long: 'teraoctets' },
        { from: 1e15, to: 1e18, unit: 'Po', long: 'petaoctets' },
        { from: 1e18, to: 1e21, unit: 'Eo', long: 'exaoctets' },
        { from: 1e21, to: 1e24, unit: 'Zo', long: 'zettaoctets' },
        { from: 1e24, to: 1e27, unit: 'Yo', long: 'yottaoctets' },
      ],
      iec: [
        { from: 0                , to: Math.pow(1024, 1), unit: 'B'  , long: 'bytes' },
        { from: Math.pow(1024, 1), to: Math.pow(1024, 2), unit: 'KiB', long: 'kibibytes' },
        { from: Math.pow(1024, 2), to: Math.pow(1024, 3), unit: 'MiB', long: 'mebibytes' },
        { from: Math.pow(1024, 3), to: Math.pow(1024, 4), unit: 'GiB', long: 'gibibytes' },
        { from: Math.pow(1024, 4), to: Math.pow(1024, 5), unit: 'TiB', long: 'tebibytes' },
        { from: Math.pow(1024, 5), to: Math.pow(1024, 6), unit: 'PiB', long: 'pebibytes' },
        { from: Math.pow(1024, 6), to: Math.pow(1024, 7), unit: 'EiB', long: 'exbibytes' },
        { from: Math.pow(1024, 7), to: Math.pow(1024, 8), unit: 'ZiB', long: 'zebibytes' },
        { from: Math.pow(1024, 8), to: Math.pow(1024, 9), unit: 'YiB', long: 'yobibytes' },
      ],
      iec_octet: [
        { from: 0                , to: Math.pow(1024, 1), unit: 'o'  , long: 'octets' },
        { from: Math.pow(1024, 1), to: Math.pow(1024, 2), unit: 'Kio', long: 'kibioctets' },
        { from: Math.pow(1024, 2), to: Math.pow(1024, 3), unit: 'Mio', long: 'mebioctets' },
        { from: Math.pow(1024, 3), to: Math.pow(1024, 4), unit: 'Gio', long: 'gibioctets' },
        { from: Math.pow(1024, 4), to: Math.pow(1024, 5), unit: 'Tio', long: 'tebioctets' },
        { from: Math.pow(1024, 5), to: Math.pow(1024, 6), unit: 'Pio', long: 'pebioctets' },
        { from: Math.pow(1024, 6), to: Math.pow(1024, 7), unit: 'Eio', long: 'exbioctets' },
        { from: Math.pow(1024, 7), to: Math.pow(1024, 8), unit: 'Zio', long: 'zebioctets' },
        { from: Math.pow(1024, 8), to: Math.pow(1024, 9), unit: 'Yio', long: 'yobioctets' },
      ],
    }
    Object.assign(tables, options.customUnits)

    const prefix = bytes < 0 ? '-' : ''
    bytes = Math.abs(bytes)
    const table = tables[options.units]
    if (table) {
      const units = table.find(u => bytes >= u.from && bytes < u.to)
      if (units) {
        const value = units.from === 0
          ? prefix + bytes
          : prefix + (bytes / units.from).toFixed(options.precision)
        this.value = value
        this.unit = units.unit
        this.long = units.long
      } else {
        this.value = prefix + bytes
        this.unit = ''
        this.long = ''
      }
    } else {
      throw new Error(`Invalid units specified: ${options.units}`)
    }
  }

  toString () {
    const options = _options.get(this)
    return options.toStringFn ? options.toStringFn.bind(this)() : `${this.value} ${this.unit}`
  }
}

/**
 * Returns an object with the spec `{ value: string, unit: string, long: string }`. The returned object defines a `toString` method meaning it can be used in any string context.
 * @param {number} - The bytes value to convert.
 * @param [options] {object} - Optional config.
 * @param [options.precision] {number} - Number of decimal places. Defaults to `1`.
 * @param [options.units] {string} - Specify `'metric'`, `'iec'`, `'metric_octet'`, `'iec_octet'` or the name of a property from the custom units table in `options.customUnits`. Defaults to `metric`.
 * @param [options.customUnits] {object} - An object containing one or more custom unit lookup tables.
 * @param [options.toStringFn] {function} - A `toString` function to override the default.
 * @returns {object}
 * @alias module:byte-size
 */
function byteSize (bytes, options) {
  return new ByteSize(bytes, options)
}

/**
 * Set the default `byteSize` options for the duration of the process.
 * @param options {object} - A `byteSize` options object.
 */
byteSize.defaultOptions = function (options) {
  defaultOptions = options
}

export default byteSize
