-- A generator module is a ModuleScript that defines how a ProceduralModel builds its contents.
-- See https://create.roblox.com/docs/reference/engine/classes/ProceduralModel for details.
--
-- To be used as a generator, the ModuleScript must return a table with two fields:
--   * `Attributes`  - a table of default values. Each key becomes an attribute on every
--                     ProceduralModel that uses this generator. Users can then tweak these
--                     attributes in the Properties panel to re-run generation with new inputs.
--   * `OnGenerate`  - a function the engine calls to (re)build the model's contents.
--
-- Nothing about this script or its placement is special. It can live anywhere in the DataModel
-- and the `Generator` property on a ProceduralModel can be reassigned to point at it.

-- The type annotations below are optional but documented here so the required shape is explicit.

-- `GenerationFunctionParams` is passed to `OnGenerate` every time generation runs. It exposes:
--   * `Attributes` - the current attribute values on the ProceduralModel.
--   * `Size`       - the bounding volume to generate within (from `ProceduralModel.Size`).
--   * `Pause`      - a cooperative yield. Call `parameters:Pause()` inside long loops so large
--                    generations don't stall the calling thread; the engine may resume you later.
type GenerationFunctionParams<Attributes> = {
	Attributes: Attributes,
	Size: Vector3,
	Pause: (self: GenerationFunctionParams<Attributes>) -> (),
}

-- `GeneratorModuleDefinition` is the table the ModuleScript must return.
-- `OnGenerate` must not return a value; parent generated instances into `targetContainer` instead.
-- Anything parented to `targetContainer` (or its descendants) becomes the output of generation.
type GeneratorModuleDefinition<Attributes> = {
	Attributes: Attributes,
	OnGenerate: (
		parameters: GenerationFunctionParams<Attributes>,
		targetContainer: GeneratedFolder
	) -> (),
}

-- Default attributes. Each entry here shows up as an editable attribute on the ProceduralModel.
-- A fixed `RandomSeed` keeps generation deterministic: the same inputs always produce the same
-- output, which is important because generation may run many times as the user edits properties.
local defaultAttributes = {
	BorderThickness = 1,
	RandomSeed = 142376088,
}

local Generator: GeneratorModuleDefinition<typeof(defaultAttributes)> = {
	Attributes = defaultAttributes,
	OnGenerate = function(parameters, targetContainer)
		-- Inputs. `parameters.Attributes` reflects whatever the user has set on the
		-- ProceduralModel; `parameters.Size` is the bounding box to build into.
		local borderThickness = parameters.Attributes.BorderThickness
		local random = Random.new(parameters.Attributes.RandomSeed)
		local size = parameters.Size

		-- Derived values. Seeded `random` above makes these reproducible per RandomSeed.
		local minSize = math.min(size.X, size.Y, size.Z)
		local baseColor = Color3.fromHSV(random:NextNumber(0.5, 0.8), 0.7, 0.8)
		local outlineColor = Color3.fromHSV(random:NextNumber(), 0.4, 0.25)

		-- Small helpers to make the construction below read top-to-bottom. You don't need
		-- helpers like these to write a generator; they just cut down on repetition.
		local function assignProperties(instance: Instance, properties: { [string]: unknown })
			-- Set Parent last so other properties are in place before the instance enters
			-- the DataModel and fires Changed events.
			for name, value in properties do
				if name ~= "Parent" then
					(instance :: any)[name] = value
				end
			end
			if properties.Parent ~= nil then
				instance.Parent = properties.Parent :: Instance
			end
			return instance
		end

		local function createInstance(className: string, properties: { [string]: unknown })
			return assignProperties(Instance.new(className), properties)
		end

		local function createPartWithDefaults(properties: { [string]: unknown })
			-- Generated parts are typically anchored and non-colliding; override per-part as needed.
			local part = createInstance("Part", {
				Anchored = true,
				CanCollide = false,
				Color = baseColor,
				Material = Enum.Material.SmoothPlastic,
				BottomSurface = Enum.SurfaceType.Smooth,
				TopSurface = Enum.SurfaceType.Smooth,
			})
			return assignProperties(part, properties)
		end

		-- Everything below parents into `targetContainer`, which is how instances become
		-- part of the generated output. Instances not parented here are discarded.

		-- Invisible bounding part used as the billboard adornee.
		local bounds = createPartWithDefaults({
			Name = "Bounds",
			Parent = targetContainer,
			Transparency = 1,
			Size = size,
		})

		-- A recessed platform with a border outline underneath it.
		local base = createPartWithDefaults({
			Name = "PlatformBase",
			Parent = targetContainer,
			Color = baseColor,
			CFrame = CFrame.new(0, (-size.Y + 1) / 2, 0),
			Size = Vector3.new(
				size.X - 2 * borderThickness,
				1.01,
				size.Z - 2 * borderThickness
			),
		})
		local outline = createPartWithDefaults({
			Name = "PlatformOutline",
			Parent = targetContainer,
			Color = outlineColor,
			Position = Vector3.yAxis * (-size.Y + 1) / 2,
			Size = Vector3.new(size.X, 1, size.Z),
		})

		-- "Hello World!" billboard. Generators can create any instance type, not just parts.
		local billboard = createInstance("BillboardGui", {
			Name = "Text",
			Parent = targetContainer,
			Adornee = bounds,
			LightInfluence = 0,
			Size = UDim2.fromScale(minSize, minSize),
		})
		local textLabel = createInstance("TextLabel", {
			Name = "HelloWorld",
			Parent = billboard,
			AnchorPoint = Vector2.new(0.5, 0.5),
			BackgroundTransparency = 1,
			Position = UDim2.fromScale(0.5, 0.5),
			Size = UDim2.fromScale(1, 1),
			Text = "Hello World!",
			TextColor3 = baseColor,
			TextScaled = true,
			TextStrokeTransparency = 0,
		})
		local textStroke = createInstance("UIStroke", {
			Parent = textLabel,
			Color = outlineColor,
			Thickness = borderThickness * 3,
		})
	end,
}

-- Returning the module definition is what makes this ModuleScript usable as a `Generator`.
return Generator

-- A generator module is a ModuleScript that returns a table with `Attributes` and `OnGenerate`.
-- Assigning this ModuleScript to a ProceduralModel's `Generator` property runs `OnGenerate`
-- whenever the model's Size, attributes, or the module source changes.
-- See https://create.roblox.com/docs/reference/engine/classes/ProceduralModel.

local ClassicRobloxLadderGenerator = {}

-- Default attribute values. Each key becomes an editable attribute on any ProceduralModel that
-- uses this generator, and shows up in the Studio Properties panel under Attributes. Editing any
-- of them re-runs `OnGenerate` with the new values.
ClassicRobloxLadderGenerator.Attributes = {
	RungSpacing = 2,
	RungThickness = 1,
	PostSize = 1,
	Color = Color3.new(0.5, 0.3, 0),
}

-- `OnGenerate` is called by the engine to build the model's contents.
-- Contract:
--   * `parameters.Size`       - the bounding box (from `ProceduralModel.Size`) to build within.
--   * `parameters.Attributes` - current attribute values on the ProceduralModel.
--   * `parameters:Pause()`    - cooperative yield; call inside long loops so large generations
--                               don't stall the thread.
--   * `targetContainer`       - anything parented here (or to its descendants) becomes the output.
--   * Do not return a value from `OnGenerate`; outputs are communicated via `targetContainer`.
ClassicRobloxLadderGenerator.OnGenerate = function(parameters, targetContainer)
	local size = parameters.Size
	local rungThickness = parameters.Attributes.RungThickness
	local postSize = parameters.Attributes.PostSize
	local count = (size.Y - rungThickness) // parameters.Attributes.RungSpacing + 1

	local function createPart(position, size)
		local part = Instance.new("Part")
		part.Size = size
		part.Position = position
		part.Anchored = true
		part.Color = parameters.Attributes.Color
		part.TopSurface = Enum.SurfaceType.Smooth
		part.BottomSurface = Enum.SurfaceType.Smooth
		-- Parenting into `targetContainer` is what adds the part to the generated output.
		part.Parent = targetContainer
	end

	-- Rungs, stacked from the bottom of the bounding box upward.
	local position = Vector3.new(0, -size.Y / 2 + rungThickness / 2, 0)
	for i = 1, count do
		-- Yield between rungs so a ladder with many rungs doesn't block the thread.
		parameters:Pause()
		createPart(position, Vector3.new(size.X - 2 * postSize, rungThickness, size.Z))
		position += Vector3.new(0, parameters.Attributes.RungSpacing, 0)
	end

	-- Left and right side posts spanning the full height.
	createPart(Vector3.new(-0.5 * size.X + postSize / 2, 0, 0), Vector3.new(postSize, size.Y, size.Z))
	createPart(Vector3.new(0.5 * size.X - postSize / 2, 0, 0), Vector3.new(postSize, size.Y, size.Z))
end

-- Returning the module definition is what makes this ModuleScript usable as a `Generator`.
return ClassicRobloxLadderGenerator

local proceduralModel = ...
proceduralModel:SetAttribute("ThrowAnError", true) --> Deliberately fail
print(proceduralModel:WaitForGenerationAsync()) --> false