--// Point of the module is to offer clean and seamless transformation between two models.

local function ScaleModel(Model, TargetModel)
    local Humanoid, HumRP = Model:WaitForChild("Humanoid"), Model:WaitForChild("HumanoidRootPart")
    local Torso = Model:WaitForChild("Torso")
    local NewTorso = TargetModel:WaitForChild("Torso")

    local CharacterSize, NewModelSize = Torso.Size, NewTorso:GetExtentsSize()

    local PrimaryCFrame = Torso.CFrame
    local Scale = NewModelSize.Y / CharacterSize.Y

    Humanoid.HipHeight *= Scale
    Scale = Vector3.one * Scale

    for _,Component in ipairs(Model:GetDescendants()) do
        if Component:IsA("Part") then
            Component.Size *= Scale

        elseif Component:IsA("Motor6D") and Component.Parent ~= HumRP then
            Component.C0 = CFrame.new(Component.C0.p * Scale) * (Component.C0 - Component.C0.p)
            Component.C1 = CFrame.new(Component.C1.p * Scale) * (Component.C1 - Component.C1.p)

        elseif Component:IsA("Attachment") then
            Component.Position *= Scale
        end
    end
end

local function ChangeModelTransparency(Model, Value)
    for _,Component in Model:GetDescendants() do
        if not Component:IsA("Part") then
            continue
        end

        Component.Transparency = Value
    end
end

return function (Model, TargetModel)
    local Humanoid, HumRP = Model:WaitForChild("Humanoid"), Model:WaitForChild("HumanoidRootPart")

    --// First, we scale the "Model" to the size of the "TargetModel"
    ScaleModel(Model, TargetModel)
    ChangeModelTransparency(Model, 1)

    --// Then, we weld all the pieces of TargetModel, onto Model, like a morph.
    for _,Limb in TargetModel:GetChildren() do
        --// Every model consists of sub-models which are named after the limbs.
        if not Limb:IsA("Model") then
            continue
        end
        Limb = Limb:Clone()

        local Root = Limb.PrimaryPart
        local TargetLimb = Model:FindFirstChild(Limb.Name)
        if not TargetLimb then
            error("Couldn't find target limb: "..TargetModel.Name)
        end

        Limb:PivotTo(TargetLimb.CFrame)
        Limb.Parent = TargetLimb

        local WeldConstraint = Instance.new("WeldConstraint")
        WeldConstraint.Part0, WeldConstraint.Part1 = TargetLimb, Root
        WeldConstraint.Parent = Root
    end

    --// Guard clause to ensure our new model is fully visible.
    ChangeModelTransparency(TargetModel, 0)
end