local pi = math.pi
local sin = math.sin
local cos = math.cos
local abs = math.abs

local function backIn(t, s) s = s or 1.70158; return t * t * ((s + 1) * t - s) end
local function backOut(t, s) s = s or 1.70158; t = t - 1; return 1 + t * t * ((s + 1) * t + s) end
local function backInOut(t, s)
    s = s or 1.70158
    if t < 0.5 then
        local tt = 2 * t
        return (tt * tt * ((s * 1.525 + 1) * tt - s * 1.525)) / 2
    else
        local tt = 2 * t - 2
        return (2 + tt * tt * ((s * 1.525 + 1) * tt + s * 1.525)) / 2
    end
end

-- Bounce (helper)
local function bounceOut(t)
    local n1 = 7.5625
    local d1 = 2.75
    if t < 1 / d1 then
        return n1 * t * t
    elseif t < 2 / d1 then
        t = t - 1.5 / d1
        return n1 * t * t + 0.75
    elseif t < 2.5 / d1 then
        t = t - 2.25 / d1
        return n1 * t * t + 0.9375
    else
        t = t - 2.625 / d1
        return n1 * t * t + 0.984375
    end
end

easing = {
    linear = function(t) return t end,

    -- Sine
    easeInSine = function(t) return 1 - cos((t * pi) / 2) end,
    easeOutSine = function(t) return sin((t * pi) / 2) end,
    easeInOutSine = function(t) return -(cos(pi * t) - 1) / 2 end,

    -- Quad
    easeInQuad = function(t) return t * t end,
    easeOutQuad = function(t) return 1 - (1 - t) * (1 - t) end,
    easeInOutQuad = function(t)
        if t < 0.5 then return 2 * t * t end
        return 1 - ((-2 * t + 2)^2) / 2
    end,

    -- Cubic
    easeInCubic = function(t) return t * t * t end,
    easeOutCubic = function(t) return 1 - ((1 - t)^3) end,
    easeInOutCubic = function(t)
        if t < 0.5 then return 4 * t * t * t end
        return 1 - ((-2 * t + 2)^3) / 2
    end,

    -- Expo
    easeInExpo = function(t) return (t == 0) and 0 or (2^(10 * t - 10)) end,
    easeOutExpo = function(t) return (t == 1) and 1 or 1 - (2^(-10 * t)) end,
    easeInOutExpo = function(t)
        if t == 0 then return 0 end
        if t == 1 then return 1 end
        if t < 0.5 then return (2^(20 * t - 10)) / 2 end
        return (2 - (2^(-20 * t + 10))) / 2
    end,

    -- Back (overshoot)
    easeInBack = function(t) return backIn(t) end,
    easeOutBack = function(t) return backOut(t) end,
    easeInOutBack = function(t) return backInOut(t) end,

    -- Elastic
    easeInElastic = function(t)
        if t == 0 then return 0 end
        if t == 1 then return 1 end
        local c4 = (2 * pi) / 3
        return -(2^(10 * t - 10)) * sin((t * 10 - 10.75) * c4)
    end,
    easeOutElastic = function(t)
        if t == 0 then return 0 end
        if t == 1 then return 1 end
        local c4 = (2 * pi) / 3
        return (2^(-10 * t)) * sin((t * 10 - 0.75) * c4) + 1
    end,
    easeInOutElastic = function(t)
        if t == 0 then return 0 end
        if t == 1 then return 1 end
        local c5 = (2 * pi) / 4.5
        if t < 0.5 then
            return -((2^(20 * t - 10)) * sin((20 * t - 11.125) * c5)) / 2
        end
        return ((2^(-20 * t + 10)) * sin((20 * t - 11.125) * c5)) / 2 + 1
    end,

    -- Bounce
    easeInBounce = function(t) return 1 - bounceOut(1 - t) end,
    easeOutBounce = function(t) return bounceOut(t) end,
    easeInOutBounce = function(t)
        if t < 0.5 then return (1 - bounceOut(1 - 2 * t)) / 2 end
        return (1 + bounceOut(2 * t - 1)) / 2
    end,

}

tweening = {
    list = {},

    add = function(from, to, duration, easingFun, callback)
        local tween = {
            from = from,
            to = to,
            duration = math.max(0.000001, duration or 0.001),
            easing = easingFun,
            callback = callback,
            t = 0,
        }
        tweening.list[#tweening.list + 1] = tween
        return tween
    end,

    update = function(dt)
        if #tweening.list==0 then return end

        -- iterate backwards so we can remove finished tweens safely
        for i = #tweening.list, 1, -1 do
            local tw = tweening.list[i]
            tw.t = tw.t + (dt or 0)
            local progress = tw.t / tw.duration
            if progress >= 1 then
                -- finished: ensure final value, call callback with finished=true, remove
                local value = tw.to
                if tw.callback then
                    -- callback(value, normalizedProgress, finished)
                    tw.callback(value, 1, true)
                end
                table.remove(tweening.list, i)
            else
                -- in progress
                local alpha = tw.easing(progress)
                local value = tw.from + (tw.to - tw.from) * alpha
                if tw.callback then tw.callback(value, progress, false) end
            end
        end
    end,

    clear = function()
        for i = #tweening.list, 1, -1 do table.remove(tweening.list, i) end
    end,

    -- Optional helper: cancel a specific tween (pass the tween returned by add)
    cancel = function(tween)
        for i = #tweening.list, 1, -1 do
            if tweening.list[i] == tween then
                table.remove(tweening.list, i)
                return true
            end
        end
        return false
    end
}