--[[
	A method called by consumers of Roact to create a new component class.
	Components can not be extended beyond this point, with the exception of
	PureComponent.
]]
function Component:extend(name)
	if config.typeChecks then
		assert(Type.of(self) == Type.StatefulComponentClass, "Invalid `self` argument to `extend`.")
		assert(typeof(name) == "string", "Component class name must be a string")
	end

	local class = {}

	for key, value in pairs(self) do
		-- Roact opts to make consumers use composition over inheritance, which
		-- lines up with React.
		-- https://reactjs.org/docs/composition-vs-inheritance.html
		if key ~= "extend" then
			class[key] = value
		end
	end

	class[Type] = Type.StatefulComponentClass
	class.__index = class
	class.__componentName = name

	setmetatable(class, componentClassMetatable)

	return class
end

function Component:__getDerivedState(incomingProps, incomingState)
	if config.internalTypeChecks then
		internalAssert(Type.of(self) == Type.StatefulComponentInstance, "Invalid use of `__getDerivedState`")
	end

	local internalData = self[InternalData]
	local componentClass = internalData.componentClass

	if componentClass.getDerivedStateFromProps ~= nil then
		local derivedState = componentClass.getDerivedStateFromProps(incomingProps, incomingState)

		if derivedState ~= nil then
			if config.typeChecks then
				assert(typeof(derivedState) == "table", "getDerivedStateFromProps must return a table!")
			end

			return derivedState
		end
	end

	return nil
end

function Component:setState(mapState)
	if config.typeChecks then
		assert(Type.of(self) == Type.StatefulComponentInstance, "Invalid `self` argument to `extend`.")
	end

	local internalData = self[InternalData]
	local lifecyclePhase = internalData.lifecyclePhase

	--[[
		When preparing to update, rendering, or unmounting, it is not safe
		to call `setState` as it will interfere with in-flight updates. It's
		also disallowed during unmounting
	]]
	if lifecyclePhase == ComponentLifecyclePhase.ShouldUpdate or
		lifecyclePhase == ComponentLifecyclePhase.WillUpdate or
		lifecyclePhase == ComponentLifecyclePhase.Render or
		lifecyclePhase == ComponentLifecyclePhase.WillUnmount
	then
		local messageTemplate = invalidSetStateMessages[internalData.lifecyclePhase]

		local message = messageTemplate:format(tostring(internalData.componentClass))

		error(message, 2)
	end

	local pendingState = internalData.pendingState

	local partialState
	if typeof(mapState) == "function" then
		partialState = mapState(pendingState or self.state, self.props)

		-- Abort the state update if the given state updater function returns nil
		if partialState == nil then
			return
		end
	elseif typeof(mapState) == "table" then
		partialState = mapState
	else
		error("Invalid argument to setState, expected function or table", 2)
	end

	local newState
	if pendingState ~= nil then
		newState = assign(pendingState, partialState)
	else
		newState = assign({}, self.state, partialState)
	end

	if lifecyclePhase == ComponentLifecyclePhase.Init then
		-- If `setState` is called in `init`, we can skip triggering an update!
		local derivedState = self:__getDerivedState(self.props, newState)
		self.state = assign(newState, derivedState)

	elseif lifecyclePhase == ComponentLifecyclePhase.DidMount or
		lifecyclePhase == ComponentLifecyclePhase.DidUpdate or
		lifecyclePhase == ComponentLifecyclePhase.ReconcileChildren
	then
		--[[
			During certain phases of the component lifecycle, it's acceptable to
			allow `setState` but defer the update until we're done with ones in flight.
			We do this by collapsing it into any pending updates we have.
		]]
		local derivedState = self:__getDerivedState(self.props, newState)
		internalData.pendingState = assign(newState, derivedState)

	elseif lifecyclePhase == ComponentLifecyclePhase.Idle then
		-- Outside of our lifecycle, the state update is safe to make immediately
		self:__update(nil, newState)

	else
		local messageTemplate = invalidSetStateMessages.default

		local message = messageTemplate:format(tostring(internalData.componentClass))

		error(message, 2)
	end
end