local utils = require(script.Parent.utils)
local getConnectFunction = utils.getConnectFunction

type GenericTable = utils.GenericTable
type SignalLike<U...> = utils.SignalLike<U...>
type ConnectionLike = utils.ConnectionLike
type ConnectFn<T, U...> = utils.ConnectFn<T, U...>
type Callback<U...> = utils.Callback<U...>

type Condition = () -> boolean

--- @class Conditions
---
--- Conditions can be used in systems or as Run Conditions.

--- @within Conditions
--- @param time number -- Time in seconds
--- @return hasTimePassed () -> boolean
---
--- A Throttle condition which checks whether the amount of
--- time given has passed or not.
local function timePassed(time: number): Condition
	local storedTime

	return function()
		if storedTime == nil or os.clock() - storedTime >= time then
			storedTime = os.clock()
			return true
		end

		return false
	end
end

--- @within Conditions
--- @return hasRanOnce () -> boolean
---
--- Checks whether the condition has been called once before
local function runOnce(): Condition
	local hasRan = false

	return function()
		if not hasRan then
			hasRan = true
			return true
		end

		return false
	end
end

type CollectEvents<U...> = () -> () -> (number, U...)

local conditionToCleanupFn = {}

local function cleanupCondition(condition: Condition)
	local cleanup = conditionToCleanupFn[condition]
	if cleanup then
		cleanup()
		conditionToCleanupFn[condition] = nil
	end
end

type GetDisconnectFn = () -> () -> ()

type OnEventFn =
	-- RBXScriptSignal & nil
	(<U...>(
		RBXScriptSignal<U...>
	) -> (Condition, CollectEvents<U...>, GetDisconnectFn))
	-- Instance & RBXScriptSignal
	-- Instance & string
	& (<U...>(
		Instance,
		RBXScriptSignal<U...> | string
	) -> (Condition, CollectEvents<U...>, GetDisconnectFn))
	-- SignalLike & nil
	& (<U...>(
		SignalLike<U...>
	) -> (Condition, CollectEvents<U...>, GetDisconnectFn))
	-- table & string
	& (<U...>(
		GenericTable,
		string
	) -> (Condition, CollectEvents<U...>, GetDisconnectFn))
	-- table & connectable method
	& (<T, U...>(
		GenericTable,
		(GenericTable, Callback<U...>, ...any) -> T?
	) -> (Condition, CollectEvents<U...>, GetDisconnectFn))
	-- connectable function
	& (<T, U...>(
		(Callback<U...>, ...any) -> T?
	) -> (Condition, CollectEvents<U...>, GetDisconnectFn))

--- @within Conditions
--- @param instance RBXScriptSignal | Instance | SignalLike<...any> | GenericTable | ((Callback<U...>,...any) -> ...any)
--- @param event (RBXScriptSignal | string | (...any) -> ())?
--- @return hasNewEvent () -> boolean
--- @return collectEvents () -> () -> (number, U...)
--- @return getDisconnectFn () -> () -> ()
---
--- Checks for any new events and allows for the collection of
--- those events.\
--- \
--- Read [OnEvent](../docs/design/conditions#on-event) for more information.
local function onEvent<U...>(
	instance,
	event
): (Condition, CollectEvents<U...>, () -> () -> ())
	local connect = getConnectFunction(instance, event)
	assert(connect, "Event passed to .onEvent is not valid")

	local newEvent = false
	local queue = {}

	local connection: ConnectionLike?

	local function disconnect()
		if not connection then
			return
		end

		utils.disconnectEvent(connection)
		connection = nil
	end

	local function callback(...)
		newEvent = true
		table.insert(queue, { ... })
	end

	connection = connect(callback)

	local function hasNewEvent()
		if newEvent then
			newEvent = false
			return true
		end

		table.clear(queue)
		return false
	end

	local function collectEvents()
		local n = 0
		return function(): (number, U...)
			n += 1

			local args = table.remove(queue, 1)

			if args then
				return n, table.unpack(args)
			end

			return nil :: any
		end
	end

	local function getDisconnectFn()
		return disconnect
	end

	conditionToCleanupFn[hasNewEvent] = disconnect

	return hasNewEvent, collectEvents, getDisconnectFn
end

--- @within Conditions
--- @param condition () -> boolean
--- @return inverseCondition () -> boolean
---
--- Inverses a given condition.

-- selene: allow(unused_variable)
local function isNot(condition: Condition, ...: any): Condition
	return function()
		return not condition()
	end
end

return {
	timePassed = timePassed,
	runOnce = runOnce,
	onEvent = onEvent :: OnEventFn,
	isNot = isNot,

	cleanupCondition = cleanupCondition,
}