--!strict

--[[
	Applies a table of properties to an instance, including binding to any
	given state objects and applying any special keys.

	No strong reference is kept by default - special keys should take care not
	to accidentally hold strong references to instances forever.

	If a key is used twice, an error will be thrown. This is done to avoid
	double assignments or double bindings. However, some special keys may want
	to enable such assignments - in which case unique keys should be used for
	each occurence.
]]

local PubTypes = require "../PubTypes"
local External = require "../External"
local cleanup = require "../Utility/cleanup"
local xtypeof = require "../Utility/xtypeof"
local logError = require "../Logging/logError"
local Observer = require "../State/Observer"
local peek = require "../State/peek"
local typeof = require "../../../Modules/Polyfill/typeof"

local function setProperty_unsafe(
	instance: Instance,
	property: string,
	value: any
)
	(instance :: any)[property] = value
end

local function testPropertyAssignable(instance: Instance, property: string)
	(instance :: any)[property] = (instance :: any)[property]
end

local function setProperty(instance: Instance, property: string, value: any)
	if not pcall(setProperty_unsafe, instance, property, value) then
		if not pcall(testPropertyAssignable, instance, property) then
			if instance == nil then
				-- reference has been lost
				logError("setPropertyNilRef", nil, property, tostring(value))
			else
				-- property is not assignable
				logError(
					"cannotAssignProperty",
					nil,
					instance.ClassName,
					property
				)
			end
		else
			-- property is assignable, but this specific assignment failed
			-- this typically implies the wrong type was received
			local givenType = typeof(value)
			local expectedType = typeof((instance :: any)[property])
			logError(
				"invalidPropertyType",
				nil,
				instance.ClassName,
				property,
				expectedType,
				givenType
			)
		end
	end
end

local function bindProperty(
	instance: Instance,
	property: string,
	value: PubTypes.CanBeState<any>,
	cleanupTasks: { PubTypes.Task }
)
	if xtypeof(value) == "State" then
		-- value is a state object - assign and observe for changes
		local willUpdate = false
		local function updateLater()
			if not willUpdate then
				willUpdate = true
				External.doTaskDeferred(function()
					willUpdate = false
					setProperty(instance, property, peek(value))
				end)
			end
		end

		setProperty(instance, property, peek(value))
		table.insert(cleanupTasks, Observer(value :: any):onChange(updateLater))
	else
		-- value is a constant - assign once only
		setProperty(instance, property, value)
	end
end

local function applyInstanceProps(
	props: PubTypes.PropertyTable,
	applyTo: Instance
)
	local specialKeys = {
		self = {} :: { [PubTypes.SpecialKey]: any },
		descendants = {} :: { [PubTypes.SpecialKey]: any },
		ancestor = {} :: { [PubTypes.SpecialKey]: any },
		observer = {} :: { [PubTypes.SpecialKey]: any },
	}
	local cleanupTasks = {}

	for key, value in pairs(props) do
		local keyType = xtypeof(key)

		if keyType == "string" then
			if key ~= "Parent" then
				bindProperty(applyTo, key :: string, value, cleanupTasks)
			end
		elseif keyType == "SpecialKey" then
			local stage = (key :: PubTypes.SpecialKey).stage
			local keys = specialKeys[stage]
			if keys == nil then
				logError("unrecognisedPropertyStage", nil, stage)
			else
				keys[key] = value
			end
		else
			-- we don't recognise what this key is supposed to be
			logError("unrecognisedPropertyKey", nil, xtypeof(key))
		end
	end

	for key, value in pairs(specialKeys.self) do
		key:apply(value, applyTo, cleanupTasks)
	end
	for key, value in pairs(specialKeys.descendants) do
		key:apply(value, applyTo, cleanupTasks)
	end

	if props.Parent ~= nil then
		bindProperty(applyTo, "Parent", props.Parent, cleanupTasks)
	end

	for key, value in pairs(specialKeys.ancestor) do
		key:apply(value, applyTo, cleanupTasks)
	end
	for key, value in pairs(specialKeys.observer) do
		key:apply(value, applyTo, cleanupTasks)
	end

	-- applyTo.Destroying:connect(function()
	-- 	cleanup(cleanupTasks)
	-- end)

	if applyTo.Parent then -- close enough?
		game.DescendantRemoving:connect(function(descendant)
			if descendant == applyTo then
				cleanup(cleanupTasks)
			end
		end)
	end
end

return applyInstanceProps