BTtow = {}
BTtow.Create = {}
BTtow.Init = {}

local TowbarVariantSize = 24
local TowbarMaxIndex = TowbarVariantSize - 1
local TowbarFirstZ = 1.0
local TowbarSlotStep = 0.1
-- Measured from Towbar.fbx at its original 0.01 script scale. Keep this in
-- lockstep with the client selector so the enlarged mesh's inner end remains
-- on the same vehicle-hitbox contact point.
local TowbarVisualScale = 2.5
local TowbarModelLength = 0.9714089036
local TowbarScaledModelLength = TowbarModelLength * TowbarVisualScale
local TowbarModelHalfLength = TowbarScaledModelLength / 2

local function getTowbarFrontEdgeZ(script)
    if not script then return nil end

    local ok, shape = pcall(function()
        return script:getPhysicsChassisShape()
    end)
    if not ok or not shape then return nil end

    local shapeOk, shapeZ = pcall(function()
        return shape:z()
    end)
    if not shapeOk or type(shapeZ) ~= "number" or shapeZ <= 0 then
        return nil
    end

    local centerOk, center = pcall(function()
        return script:getCenterOfMassOffset()
    end)
    if not centerOk or not center then return nil end

    local zOk, centerZ = pcall(function()
        return center:z()
    end)
    if not zOk or type(centerZ) ~= "number" then return nil end

    return centerZ + shapeZ / 2
end

local function getTowbarModelSlot(script)
    local frontEdgeZ = getTowbarFrontEdgeZ(script)
    if frontEdgeZ == nil then return nil end

    -- Model offsets position the mesh origin. Move its center outward so the
    -- towbar's inner end, rather than its center, meets the vehicle hitbox.
    local modelCenterZ = frontEdgeZ + TowbarModelHalfLength
    local index = math.floor(((modelCenterZ - TowbarFirstZ) / TowbarSlotStep) + 0.5)
    return math.max(0, math.min(TowbarMaxIndex, index))
end

function BTtow.Create.towbar(vehicle, part)  
    if part == nil then return end
    for j=0, TowbarVariantSize - 1 do
        part:setModelVisible("towbar" .. j, false)        
    end
end

function BTtow.Init.towbar(vehicle, part)
    if part == nil then return end
    for j=0, TowbarVariantSize - 1 do
        part:setModelVisible("towbar" .. j, false)
    end
    local modData = vehicle:getModData()
    if modData and modData.towBarModelSwapInProgress then
        return
    end
    if modData and modData["isTowingByTowBar"] and modData["towed"] then
        local script = vehicle:getScript()
        if script then
            local index = getTowbarModelSlot(script)
            local shouldShowOnThisPart = part:getId() == "towbar"
            if shouldShowOnThisPart and index ~= nil then
                part:setModelVisible("towbar" .. index, true)
            end
        end
    end
end