local cron = {
  __VERSION     = 'cron.lua 2.0.0',
  __DESCRIPTION = 'Time-related functions for lua',
  __URL         = 'https://github.com/kikito/cron.lua',
  __LICENSE     = [[
    Copyright (c) 2011 Enrique García Cota

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  ]]
}

-- Private functions

local function isCallable(callback)
  local tc = type(callback)
  if tc == 'function' then return true end
  if tc == 'table' then
    local mt = getmetatable(callback)
    return type(mt) == 'table' and type(mt.__call) == 'function'
  end
  return false
end

local function checkPositiveInteger(name, value)
  if type(value) ~= "number" or value < 0 then
    error(name .. " must be a positive number")
  end
end

local Clock = {}
local Clock_mt = {__index = Clock}

local function newClock(time, callback, update, ...)
  checkPositiveInteger('time', time)
  assert(isCallable(callback), "callback must be a function")

  return setmetatable({
    time     = time,
    callback = callback,
    args     = {...},
    running  = 0,
    update   = update
  }, Clock_mt)
end

local function updateAfterClock(self, dt) -- returns true if expired
  checkPositiveInteger('dt', dt)

  if self.running >= self.time then return true end

  self.running = self.running + dt

  if self.running >= self.time then
    self.callback(unpack(self.args))
    return true
  end
  return false
end

local function updateEveryClock(self, dt)
  checkPositiveInteger('dt', dt)

  self.running = self.running + dt

  while self.running >= self.time do
    self.callback(unpack(self.args))
    self.running = self.running - self.time
  end
  return false
end

function Clock:reset(running)
  running = running or 0
  checkPositiveInteger('running', running)

  self.running = running
end


function cron.after(time, callback, ...)
  return newClock(time, callback, updateAfterClock, ...)
end

function cron.every(time, callback, ...)
  return newClock(time, callback, updateEveryClock, ...)
end

return cron