-- a: amplitud
-- p: period

local function outInElastic(t, b, c, d, a, p)
  if t < d / 2 then
    return outElastic(t * 2, b, c / 2, d, a, p)
  else
    return inElastic((t * 2) - d, b + c / 2, c / 2, d, a, p)
  end
end

local function inBack(t, b, c, d, s)
  if not s then s = 1.70158 end
  t = t / d
  return c * t * t * ((s + 1) * t - s) + b
end

local function outBack(t, b, c, d, s)
  if not s then s = 1.70158 end
  t = t / d - 1
  return c * (t * t * ((s + 1) * t + s) + 1) + b
end

local function inOutBack(t, b, c, d, s)
  if not s then s = 1.70158 end
  s = s * 1.525
  t = t / d * 2
  if t < 1 then
    return c / 2 * (t * t * ((s + 1) * t - s)) + b
  else
    t = t - 2
    return c / 2 * (t * t * ((s + 1) * t + s) + 2) + b
  end
end

local function outInBack(t, b, c, d, s)
  if t < d / 2 then
    return outBack(t * 2, b, c / 2, d, s)
  else
    return inBack((t * 2) - d, b + c / 2, c / 2, d, s)
  end
end

local function outBounce(t, b, c, d)
  t = t / d
  if t < 1 / 2.75 then
    return c * (7.5625 * t * t) + b
  elseif 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
  else
    t = t - (2.625 / 2.75)
    return c * (7.5625 * t * t + 0.984375) + b
  end
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
  else
    return outBounce(t * 2 - d, 0, c, d) * 0.5 + c * .5 + b
  end
end

local function outInBounce(t, b, c, d)
  if t < d / 2 then
    return outBounce(t * 2, b, c / 2, d)
  else
    return inBounce((t * 2) - d, b + c / 2, c / 2, d)
  end
end

return {
  linear = linear,
  inQuad = inQuad,
  outQuad = outQuad,
  inOutQuad = inOutQuad,
  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,
}
