var fs = require('fs') var path = require('path') var util = require('util')

function Y18N (opts) {

// configurable options.
opts = opts || {}
this.directory = opts.directory || './locales'
this.updateFiles = typeof opts.updateFiles === 'boolean' ? opts.updateFiles : true
this.locale = opts.locale || 'en'
this.fallbackToLanguage = typeof opts.fallbackToLanguage === 'boolean' ? opts.fallbackToLanguage : true

// internal stuff.
this.cache = {}
this.writeQueue = []

}

Y18N.prototype.__ = function () {

if (typeof arguments[0] !== 'string') {
  return this._taggedLiteral.apply(this, arguments)
}
var args = Array.prototype.slice.call(arguments)
var str = args.shift()
var cb = function () {} // start with noop.

if (typeof args[args.length - 1] === 'function') cb = args.pop()
cb = cb || function () {} // noop.

if (!this.cache[this.locale]) this._readLocaleFile()

// we've observed a new string, update the language file.
if (!this.cache[this.locale][str] && this.updateFiles) {
  this.cache[this.locale][str] = str

  // include the current directory and locale,
  // since these values could change before the
  // write is performed.
  this._enqueueWrite([this.directory, this.locale, cb])
} else {
  cb()
}

return util.format.apply(util, [this.cache[this.locale][str] || str].concat(args))

}

Y18N.prototype._taggedLiteral = function (parts) {

var args = arguments
var str = ''
parts.forEach(function (part, i) {
  var arg = args[i + 1]
  str += part
  if (typeof arg !== 'undefined') {
    str += '%s'
  }
})
return this.__.apply(null, [str].concat([].slice.call(arguments, 1)))

}

Y18N.prototype._enqueueWrite = function (work) {

this.writeQueue.push(work)
if (this.writeQueue.length === 1) this._processWriteQueue()

}

Y18N.prototype._processWriteQueue = function () {

var _this = this
var work = this.writeQueue[0]

// destructure the enqueued work.
var directory = work[0]
var locale = work[1]
var cb = work[2]

var languageFile = this._resolveLocaleFile(directory, locale)
var serializedLocale = JSON.stringify(this.cache[locale], null, 2)

fs.writeFile(languageFile, serializedLocale, 'utf-8', function (err) {
  _this.writeQueue.shift()
  if (_this.writeQueue.length > 0) _this._processWriteQueue()
  cb(err)
})

}

Y18N.prototype._readLocaleFile = function () {

var localeLookup = {}
var languageFile = this._resolveLocaleFile(this.directory, this.locale)

try {
  localeLookup = JSON.parse(fs.readFileSync(languageFile, 'utf-8'))
} catch (err) {
  if (err instanceof SyntaxError) {
    err.message = 'syntax error in ' + languageFile
  }

  if (err.code === 'ENOENT') localeLookup = {}
  else throw err
}

this.cache[this.locale] = localeLookup

}

Y18N.prototype._resolveLocaleFile = function (directory, locale) {

var file = path.resolve(directory, './', locale + '.json')
if (this.fallbackToLanguage && !this._fileExistsSync(file) && ~locale.lastIndexOf('_')) {
  // attempt fallback to language only
  var languageFile = path.resolve(directory, './', locale.split('_')[0] + '.json')
  if (this._fileExistsSync(languageFile)) file = languageFile
}
return file

}

// this only exists because fs.existsSync() “will be deprecated” // see nodejs.org/api/fs.html#fs_fs_existssync_path Y18N.prototype._fileExistsSync = function (file) {

try {
  return fs.statSync(file).isFile()
} catch (err) {
  return false
}

}

Y18N.prototype.__n = function () {

var args = Array.prototype.slice.call(arguments)
var singular = args.shift()
var plural = args.shift()
var quantity = args.shift()

var cb = function () {} // start with noop.
if (typeof args[args.length - 1] === 'function') cb = args.pop()

if (!this.cache[this.locale]) this._readLocaleFile()

var str = quantity === 1 ? singular : plural
if (this.cache[this.locale][singular]) {
  str = this.cache[this.locale][singular][quantity === 1 ? 'one' : 'other']
}

// we've observed a new string, update the language file.
if (!this.cache[this.locale][singular] && this.updateFiles) {
  this.cache[this.locale][singular] = {
    one: singular,
    other: plural
  }

  // include the current directory and locale,
  // since these values could change before the
  // write is performed.
  this._enqueueWrite([this.directory, this.locale, cb])
} else {
  cb()
}

// if a %d placeholder is provided, add quantity
// to the arguments expanded by util.format.
var values = [str]
if (~str.indexOf('%d')) values.push(quantity)

return util.format.apply(util, values.concat(args))

}

Y18N.prototype.setLocale = function (locale) {

this.locale = locale

}

Y18N.prototype.getLocale = function () {

return this.locale

}

Y18N.prototype.updateLocale = function (obj) {

if (!this.cache[this.locale]) this._readLocaleFile()

for (var key in obj) {
  this.cache[this.locale][key] = obj[key]
}

}

module.exports = function (opts) {

var y18n = new Y18N(opts)

// bind all functions to y18n, so that
// they can be used in isolation.
for (var key in y18n) {
  if (typeof y18n[key] === 'function') {
    y18n[key] = y18n[key].bind(y18n)
  }
}

return y18n

}