local tween = {
	_VERSION     = 'tween 2.1.1',
	_DESCRIPTION = 'tweening for lua',
	_URL         = 'https://github.com/kikito/tween.lua',
	_LICENSE     = [[
		MIT LICENSE

		Copyright (c) 2014 Enrique García Cota, Yuichi Tateno, Emmanuel Oga

		license details: https://opensource.org/licenses/MIT
	]]
}

-- easing

-- Adapted from https://github.com/EmmanuelOga/easing. See LICENSE.txt for credits.
-- For all easing functions:
-- t = time == how much time has to pass for the tweening to complete
-- b = begin == starting property value
-- c = change == ending - beginning
-- d = duration == running time. How much time has passed *right now*

local pow, sin, cos, pi, sqrt, abs, asin = math.pow, math.sin, math.cos, math.pi, math.sqrt, math.abs, math.asin

-- linear
local function linear(t, b, c, d) return c * t / d + b end

-- quad
local function inQuad(t, b, c, d) return c * pow(t / d, 2) + b end
local function outQuad(t, b, c, d)
	t = t / d
	return -c * t * (t - 2) + b
end
local function inOutQuad(t, b, c, d)
	t = t / d * 2
	if t < 1 then return c / 2 * pow(t, 2) + b end
	return -c / 2 * ((t - 1) * (t - 3) - 1) + b
end
local function outInQuad(t, b, c, d)
	if t < d / 2 then return outQuad(t * 2, b, c / 2, d) end
	return inQuad((t * 2) - d, b + c / 2, c / 2, d)
end

-- cubic
local function inCubic (t, b, c, d) return c * pow(t / d, 3) + b end
local function outCubic(t, b, c, d) return c * (pow(t / d - 1, 3) + 1) + b end
local function inOutCubic(t, b, c, d)
	t = t / d * 2
	if t < 1 then return c / 2 * t * t * t + b end
	t = t - 2
	return c / 2 * (t * t * t + 2) + b
end
local function outInCubic(t, b, c, d)
	if t < d / 2 then return outCubic(t * 2, b, c / 2, d) end
	return inCubic((t * 2) - d, b + c / 2, c / 2, d)
end

-- quart
local function inQuart(t, b, c, d) return c * pow(t / d, 4) + b end
local function outQuart(t, b, c, d) return -c * (pow(t / d - 1, 4) - 1) + b end
local function inOutQuart(t, b, c, d)
	t = t / d * 2
	if t < 1 then return c / 2 * pow(t, 4) + b end
	return -c / 2 * (pow(t - 2, 4) - 2) + b
end
local function outInQuart(t, b, c, d)
	if t < d / 2 then return outQuart(t * 2, b, c / 2, d) end
	return inQuart((t * 2) - d, b + c / 2, c / 2, d)
end

-- quint
local function inQuint(t, b, c, d) return c * pow(t / d, 5) + b end
local function outQuint(t, b, c, d) return c * (pow(t / d - 1, 5) + 1) + b end
local function inOutQuint(t, b, c, d)
	t = t / d * 2
	if t < 1 then return c / 2 * pow(t, 5) + b end
	return c / 2 * (pow(t - 2, 5) + 2) + b
end
local function outInQuint(t, b, c, d)
	if t < d / 2 then return outQuint(t * 2, b, c / 2, d) end
	return inQuint((t * 2) - d, b + c / 2, c / 2, d)
end

-- sine
local function inSine(t, b, c, d) return -c * cos(t / d * (pi / 2)) + c + b end
local function outSine(t, b, c, d) return c * sin(t / d * (pi / 2)) + b end
local function inOutSine(t, b, c, d) return -c / 2 * (cos(pi * t / d) - 1) + b end
local function outInSine(t, b, c, d)
	if t < d / 2 then return outSine(t * 2, b, c / 2, d) end
	return inSine((t * 2) -d, b + c / 2, c / 2, d)
end

-- expo
local function inExpo(t, b, c, d)
	if t == 0 then return b end
	return c * pow(2, 10 * (t / d - 1)) + b - c * 0.001
end
local function outExpo(t, b, c, d)
	if t == d then return b + c end
	return c * 1.001 * (-pow(2, -10 * t / d) + 1) + b
end
local function inOutExpo(t, b, c, d)
	if t == 0 then return b end
	if t == d then return b + c end
	t = t / d * 2
	if t < 1 then return c / 2 * pow(2, 10 * (t - 1)) + b - c * 0.0005 end
	return c / 2 * 1.0005 * (-pow(2, -10 * (t - 1)) + 2) + b
end
local function outInExpo(t, b, c, d)
	if t < d / 2 then return outExpo(t * 2, b, c / 2, d) end
	return inExpo((t * 2) - d, b + c / 2, c / 2, d)
end

-- circ
local function inCirc(t, b, c, d) return(-c * (sqrt(1 - pow(t / d, 2)) - 1) + b) end
local function outCirc(t, b, c, d)  return(c * sqrt(1 - pow(t / d - 1, 2)) + b) end
local function inOutCirc(t, b, c, d)
	t = t / d * 2
	if t < 1 then return -c / 2 * (sqrt(1 - t * t) - 1) + b end
	t = t - 2
	return c / 2 * (sqrt(1 - t * t) + 1) + b
end
local function outInCirc(t, b, c, d)
	if t < d / 2 then return outCirc(t * 2, b, c / 2, d) end
	return inCirc((t * 2) - d, b + c / 2, c / 2, d)
end

-- elastic
local function calculatePAS(p,a,c,d)
	p, a = p or d * 0.3, a or 0
	if a < abs(c) then return p, c, p / 4 end -- p, a, s
	return p, a, p / (2 * pi) * asin(c/a) -- p,a,s
end
local function inElastic(t, b, c, d, a, p)
	local s
	if t == 0 then return b end
	t = t / d
	if t == 1  then return b + c end
	p,a,s = calculatePAS(p,a,c,d)
	t = t - 1
	return -(a * pow(2, 10 * t) * sin((t * d - s) * (2 * pi) / p)) + b
end
local function outElastic(t, b, c, d, a, p)
	local s
	if t == 0 then return b end
	t = t / d
	if t == 1 then return b + c end
	p,a,s = calculatePAS(p,a,c,d)
	return a * pow(2, -10 * t) * sin((t * d - s) * (2 * pi) / p) + c + b
end
local function inOutElastic(t, b, c, d, a, p)
	local s
	if t == 0 then return b end
	t = t / d * 2
	if t == 2 then return b + c end
	p,a,s = calculatePAS(p,a,c,d)
	t = t - 1
	if t < 0 then return -0.5 * (a * pow(2, 10 * t) * sin((t * d - s) * (2 * pi) / p)) + b end
	return a * pow(2, -10 * t) * sin((t * d - s) * (2 * pi) / p ) * 0.5 + c + b
end
local function outInElastic(t, b, c, d, a, p)
	if t < d / 2 then return outElastic(t * 2, b, c / 2, d, a, p) end
	return inElastic((t * 2) - d, b + c / 2, c / 2, d, a, p)
end

-- back
local function inBack(t, b, c, d, s)
	s = s or 1.70158
	t = t / d
	return c * t * t * ((s + 1) * t - s) + b
end
local function outBack(t, b, c, d, s)
	s = s or 1.70158
	t = t / d - 1
	return c * (t * t * ((s + 1) * t + s) + 1) + b
end
local function inOutBack(t, b, c, d, s)
	s = (s or 1.70158) * 1.525
	t = t / d * 2
	if t < 1 then return c / 2 * (t * t * ((s + 1) * t - s)) + b end
	t = t - 2
	return c / 2 * (t * t * ((s + 1) * t + s) + 2) + b
end
local function outInBack(t, b, c, d, s)
	if t < d / 2 then return outBack(t * 2, b, c / 2, d, s) end
	return inBack((t * 2) - d, b + c / 2, c / 2, d, s)
end

-- bounce
local function outBounce(t, b, c, d)
	t = t / d
	if t < 1 / 2.75 then return c * (7.5625 * t * t) + b end
	if t < 2 / 2.75 then
		t = t - (1.5 / 2.75)
		return c * (7.5625 * t * t + 0.75) + b
	elseif t < 2.5 / 2.75 then
		t = t - (2.25 / 2.75)
		return c * (7.5625 * t * t + 0.9375) + b
	end
	t = t - (2.625 / 2.75)
	return c * (7.5625 * t * t + 0.984375) + b
end
local function inBounce(t, b, c, d) return c - outBounce(d - t, 0, c, d) + b end
local function inOutBounce(t, b, c, d)
	if t < d / 2 then return inBounce(t * 2, 0, c, d) * 0.5 + b end
	return outBounce(t * 2 - d, 0, c, d) * 0.5 + c * .5 + b
end
local function outInBounce(t, b, c, d)
	if t < d / 2 then return outBounce(t * 2, b, c / 2, d) end
	return inBounce((t * 2) - d, b + c / 2, c / 2, d)
end

tween.easing = {
	linear    = linear,
	inQuad    = inQuad,    outQuad    = outQuad,    inOutQuad    = inOutQuad,    outInQuad    = outInQuad,
	inCubic   = inCubic,   outCubic   = outCubic,   inOutCubic   = inOutCubic,   outInCubic   = outInCubic,
	inQuart   = inQuart,   outQuart   = outQuart,   inOutQuart   = inOutQuart,   outInQuart   = outInQuart,
	inQuint   = inQuint,   outQuint   = outQuint,   inOutQuint   = inOutQuint,   outInQuint   = outInQuint,
	inSine    = inSine,    outSine    = outSine,    inOutSine    = inOutSine,    outInSine    = outInSine,
	inExpo    = inExpo,    outExpo    = outExpo,    inOutExpo    = inOutExpo,    outInExpo    = outInExpo,
	inCirc    = inCirc,    outCirc    = outCirc,    inOutCirc    = inOutCirc,    outInCirc    = outInCirc,
	inElastic = inElastic, outElastic = outElastic, inOutElastic = inOutElastic, outInElastic = outInElastic,
	inBack    = inBack,    outBack    = outBack,    inOutBack    = inOutBack,    outInBack    = outInBack,
	inBounce  = inBounce,  outBounce  = outBounce,  inOutBounce  = inOutBounce,  outInBounce  = outInBounce
}



-- private stuff

local function copyTables(destination, keysTable, valuesTable)
	valuesTable = valuesTable or keysTable
	local mt = getmetatable(keysTable)
	if mt and getmetatable(destination) == nil then
		setmetatable(destination, mt)
	end
	for k,v in pairs(keysTable) do
		if type(v) == 'table' then
			destination[k] = copyTables({}, v, valuesTable[k])
		else
			destination[k] = valuesTable[k]
		end
	end
	return destination
end

local function checkSubjectAndTargetRecursively(subject, target, path)
	path = path or {}
	local targetType, newPath
	for k,targetValue in pairs(target) do
		targetType, newPath = type(targetValue), copyTables({}, path)
		table.insert(newPath, tostring(k))
		if targetType == 'number' then
			assert(type(subject[k]) == 'number', "Parameter '" .. table.concat(newPath,'/') .. "' is missing from subject or isn't a number")
		elseif targetType == 'table' then
			checkSubjectAndTargetRecursively(subject[k], targetValue, newPath)
		else
			assert(targetType == 'number', "Parameter '" .. table.concat(newPath,'/') .. "' must be a number or table of numbers")
		end
	end
end

local function checkNewParams(duration, subject, target, easing)
	assert(type(duration) == 'number' and duration > 0, "duration must be a positive number. Was " .. tostring(duration))
	local tsubject = type(subject)
	assert(tsubject == 'table' or tsubject == 'userdata', "subject must be a table or userdata. Was " .. tostring(subject))
	assert(type(target)== 'table', "target must be a table. Was " .. tostring(target))
	assert(type(easing)=='function', "easing must be a function. Was " .. tostring(easing))
	checkSubjectAndTargetRecursively(subject, target)
end

local function getEasingFunction(easing)
	easing = easing or "linear"
	if type(easing) == 'string' then
		local name = easing
		easing = tween.easing[name]
		if type(easing) ~= 'function' then
			error("The easing function name '" .. name .. "' is invalid")
		end
	end
	return easing
end

local function performEasingOnSubject(subject, target, initial, clock, duration, easing)
	local t,b,c,d
	for k,v in pairs(target) do
		if type(v) == 'table' then
			performEasingOnSubject(subject[k], v, initial[k], clock, duration, easing)
		else
			t,b,c,d = clock, initial[k], v - initial[k], duration
			subject[k] = easing(t,b,c,d)
		end
	end
end

-- Tween methods

local Tween = {}
local Tween_mt = {__index = Tween}

function Tween:set(clock)
	assert(type(clock) == 'number', "clock must be a positive number or 0")

	self.initial = self.initial or copyTables({}, self.target, self.subject)
	self.clock = clock

	if self.clock <= 0 then

		self.clock = 0
		copyTables(self.subject, self.initial)

	elseif self.clock >= self.duration then -- the tween has expired

		self.clock = self.duration
		copyTables(self.subject, self.target)

	else

		performEasingOnSubject(self.subject, self.target, self.initial, self.clock, self.duration, self.easing)

	end

	return self.clock >= self.duration
end

function Tween:reset()
	return self:set(0)
end

function Tween:update(dt)
	assert(type(dt) == 'number', "dt must be a number")
	return self:set(self.clock + dt)
end


-- Public interface

function tween.new(duration, subject, target, easing)
	easing = getEasingFunction(easing)
	checkNewParams(duration, subject, target, easing)
	return setmetatable({
		duration  = duration,
		subject   = subject,
		target    = target,
		easing    = easing,
		clock     = 0
	}, Tween_mt)
end

return tween