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

require("TowBar/VehicleCompatibility")

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 VanillaScaleMin = 1.5
local VanillaScaleMax = 2.0

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

local function getVehicleModelScale(script)
    if not script then return nil end
    local ok, result = pcall(function() return script:getModelScale() end)
    if ok and type(result) == "number" then return result end
    ok, result = pcall(function()
        local model = script:getModel()
        return model and model:getScale() or nil
    end)
    return ok and type(result) == "number" and result or nil
end

local function isVanillaScale(script)
    local modelScale = getVehicleModelScale(script)
    if modelScale == nil then return true end
    local configuredMin = TowBarMod.Config and tonumber(TowBarMod.Config.vanillaTowbarModelScaleMin)
    local configuredMax = TowBarMod.Config and tonumber(TowBarMod.Config.vanillaTowbarModelScaleMax)
    return modelScale >= (configuredMin or VanillaScaleMin)
        and modelScale <= (configuredMax or VanillaScaleMax)
end

local function getTowbarIndexVanilla(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 zOk, shapeZ = pcall(function() return shape:z() end)
    if not zOk or type(shapeZ) ~= "number" then return nil end
    local z = shapeZ / 2 - 0.1
    local index = math.floor((z * 2 / 3 - 1) * 10)
    return math.max(0, math.min(TowbarMaxIndex, index))
end

local function getTowbarIndexSmallScale(script)
    if not script then return nil end
    local maxAbsTowZ = nil
    local trailer = script:getAttachmentById("trailer")
    if trailer then maxAbsTowZ = math.abs(trailer:getOffset():z()) end
    local trailerFront = script:getAttachmentById("trailerfront")
    if trailerFront then
        local frontAbsZ = math.abs(trailerFront:getOffset():z())
        if not maxAbsTowZ or frontAbsZ > maxAbsTowZ then maxAbsTowZ = frontAbsZ end
    end
    if maxAbsTowZ == nil then return nil end
    local index = math.floor((maxAbsTowZ + 0.1 - 1.0) * 10)
    return math.max(0, math.min(TowbarMaxIndex, index))
end

local function getLegacyTowbarModelSlot(script)
    local useNormalPart = isVanillaScale(script)
    local index = getTowbarIndexVanilla(script)
    if not useNormalPart then index = getTowbarIndexSmallScale(script) or index end
    return index, useNormalPart
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 isKi5 = TowBarMod.Compatibility.isKi5Vehicle(vehicle)
            local index, useNormalPart
            if isKi5 then
                index = getTowbarModelSlot(script)
            else
                index, useNormalPart = getLegacyTowbarModelSlot(script)
            end
            local partId = part:getId()
            local shouldShowOnThisPart = (isKi5 and partId == "towbarKI5")
                or (not isKi5 and useNormalPart and partId == "towbar")
                or (not isKi5 and not useNormalPart and partId == "towbarLarge")
            if shouldShowOnThisPart and index ~= nil then
                part:setModelVisible("towbar" .. index, true)
            end
        end
    end
end