local i18n = {}

local store
local locale
local pluralizeFunction
local defaultLocale = 'en'
local fallbackLocale = defaultLocale

local currentFilePath = (...):gsub("%.init$","")

local plural      = require(currentFilePath .. '.plural')
local interpolate = require(currentFilePath .. '.interpolate')
local variants    = require(currentFilePath .. '.variants')
local version     = require(currentFilePath .. '.version')

i18n.plural, i18n.interpolate, i18n.variants, i18n.version, i18n._VERSION =
  plural, interpolate, variants, version, version

-- private stuff

local function dotSplit(str)
  local fields, length = {},0
    str:gsub("[^%.]+", function(c)
    length = length + 1
    fields[length] = c
  end)
  return fields, length
end

local function isPluralTable(t)
  return type(t) == 'table' and type(t.other) == 'string'
end

local function isPresent(str)
  return type(str) == 'string' and #str > 0
end

local function assertPresent(functionName, paramName, value)
  if isPresent(value) then return end

  local msg = "i18n.%s requires a non-empty string on its %s. Got %s (a %s value). %s"
  error(msg:format(functionName, paramName, tostring(value), type(value), debug.traceback()))
end

local function assertPresentOrPlural(functionName, paramName, value)
  if isPresent(value) or isPluralTable(value) then return end

  local msg = "i18n.%s requires a non-empty string or plural-form table on its %s. Got %s (a %s value)."
  error(msg:format(functionName, paramName, tostring(value), type(value)))
end

local function assertPresentOrTable(functionName, paramName, value)
  if isPresent(value) or type(value) == 'table' then return end

  local msg = "i18n.%s requires a non-empty string or table on its %s. Got %s (a %s value)."
  error(msg:format(functionName, paramName, tostring(value), type(value)))
end

local function assertFunctionOrNil(functionName, paramName, value)
  if value == nil or type(value) == 'function' then return end

  local msg = "i18n.%s requires a function (or nil) on param %s. Got %s (a %s value)."
  error(msg:format(functionName, paramName, tostring(value), type(value)))
end

local function defaultPluralizeFunction(count)
  return plural.get(variants.root(i18n.getLocale()), count)
end

local function pluralize(t, data)
  assertPresentOrPlural('interpolatePluralTable', 't', t)
  data = data or {}
  local count = data.count or 1
  local plural_form = pluralizeFunction(count)
  return t[plural_form]
end

local function treatNode(node, data)
  if type(node) == 'string' then
    return interpolate(node, data)
  elseif isPluralTable(node) then
    return interpolate(pluralize(node, data), data)
  end
  return node
end

local function recursiveLoad(currentContext, data)
  local composedKey
  for k,v in pairs(data) do
    composedKey = (currentContext and (currentContext .. '.') or "") .. tostring(k)
    assertPresent('load', composedKey, k)
    assertPresentOrTable('load', composedKey, v)
    if type(v) == 'string' then
      i18n.set(composedKey, v)
    else
      recursiveLoad(composedKey, v)
    end
  end
end

local function localizedTranslate(key, loc, data)
  local path, length = dotSplit(loc .. "." .. key)
  local node = store

  for i=1, length do
    node = node[path[i]]
    if not node then return nil end
  end

  return treatNode(node, data)
end

-- public interface

function i18n.set(key, value)
  assertPresent('set', 'key', key)
  assertPresentOrPlural('set', 'value', value)

  local path, length = dotSplit(key)
  local node = store

  for i=1, length-1 do
    key = path[i]
    node[key] = node[key] or {}
    node = node[key]
  end

  local lastKey = path[length]
  node[lastKey] = value
end

function i18n.translate(key, data)
  assertPresent('translate', 'key', key)

  data = data or {}
  local usedLocale = data.locale or locale

  local fallbacks = variants.fallbacks(usedLocale, fallbackLocale)
  for i=1, #fallbacks do
    local value = localizedTranslate(key, fallbacks[i], data)
    if value then return value end
  end

  return data.default
end

function i18n.setLocale(newLocale, newPluralizeFunction)
  assertPresent('setLocale', 'newLocale', newLocale)
  assertFunctionOrNil('setLocale', 'newPluralizeFunction', newPluralizeFunction)
  locale = newLocale
  pluralizeFunction = newPluralizeFunction or defaultPluralizeFunction
end

function i18n.setFallbackLocale(newFallbackLocale)
  assertPresent('setFallbackLocale', 'newFallbackLocale', newFallbackLocale)
  fallbackLocale = newFallbackLocale
end

function i18n.getFallbackLocale()
  return fallbackLocale
end

function i18n.getLocale()
  return locale
end

function i18n.reset()
  store = {}
  plural.reset()
  i18n.setLocale(defaultLocale)
  i18n.setFallbackLocale(defaultLocale)
end

function i18n.load(data)
  recursiveLoad(nil, data)
end

function i18n.loadFile(path)
  local chunk = assert(loadfile(path))
  local data = chunk()
  i18n.load(data)
end

setmetatable(i18n, {__call = function(_, ...) return i18n.translate(...) end})

i18n.reset()

return i18n
