--- ubiquitousse.signal

let registry_mt = {
	--- Map of signals to list of listeners.
	signals = {},

	--- Bind one or several functions to a signal name.
	bind = :(name, fn, ...)
		if not @signals[name] then
			@signals[name] = {}
		end
		table.insert(@signals[name], fn)
		if ... then
			return @bind(name, ...)
		end
	end,

	--- Unbind one or several functions to a signal name.
	unbind = :(name, fn, ...)
		if not @signals[name] then
			return
		end
		for i=#@signals[name], 1, -1 do
			if @signals[name] == fn then
				table.remove(@signals[name], i)
			end
		end
		if ... then
			return @unbind(name, ...)
		end
	end,

	--- Remove every bound function to a signal name.
	unbindAll = :(name)
		@signals[name] = nil
	end,

	--- Replace a bound function with another function.
	replace = :(name, sourceFn, destFn)
		if not @signals[name] then
			@signals[name] = {}
		end
		for i, fn in ipairs(@signals[name]) do
			if fn == sourceFn then
				@signals[name][i] = destFn
				break
			end
		end
	end,

	--- Remove every bound function to every signal.
	clear = :()
		@signals = {}
	end,

	--- Emit a signal, i.e. call every function bound to it, with the given arguments.
	emit = :(name, ...)
		if @signals[name] then
			for _, fn in ipairs(@signals[name]) do
				fn(...)
			end
		end
	end
}
registry_mt.__index = registry_mt

let signal = {
	--- Creates and return a new SignalRegistry.
	-- A SignalRegistry is a separate ubiquitousse.signal instance: its signals will be independant from other registries.
	new = ()
		return setmetatable({ signals = {} }, registry_mt)
	end,

	--- Global SignalRegistry.
	signals = {},
	bind = (...)
		return registry_mt.bind(signal, ...)
	end,
	unbind = (...)
		return registry_mt.unbind(signal, ...)
	end,
	clear = (...)
		return registry_mt.clear(signal, ...)
	end,
	emit = (...)
		return registry_mt.emit(signal, ...)
	end,

	--- SignalRegistry which will be used to bind signals that need to be called on game engine event.
	-- For example, every ubiquitousse module with a "update" function will bind it to the "update" signal in the registry;
	-- you can then call this signal on each game update to update every ubiquitousse module easily.
	-- Provided signals:
	-- * update(dt), should be called on every game update
	-- * draw, should be called on every game draw
	-- * for LÖVE, there are callbacks for every LÖVE callback function that need to be called on their corresponding LÖVE callback
	event = nil,

	--- Call this function to hook signal.event signals to the current backend.
	-- For LÖVE, this means overriding every existing LÖVE callback. If a callback is already defined, the new one will call the old function along with the signal:emit.
	-- @require love
	registerEvents = ()
		local callbacks = { -- everything except run, errorhandler, threaderror
			"displayrotated", "draw", "load", "lowmemory", "quit", "update",
			"directorydropped", "filedropped", "focus", "mousefocus", "resize", "visible",
			"keypressed", "keyreleased", "textedited", "textinput",
			"mousemoved", "mousepressed", "mousereleased", "wheelmoved",
			"gamepadaxis", "gamepadpressed", "gamepadreleased",
			"joystickadded", "joystickaxis", "joystickhat", "joystickpressed", "joystickreleased", "joystickremoved",
			"touchmoved", "touchpressed", "touchreleased"
		}
		local event = signal.event
		for _, callback in ipairs(callbacks) do
			if callback == "update" then
				if love[callback] then
					local old = love[callback]
					love[callback] = function(dt)
						old(dt)
						event:emit(callback, dt)
					end
				else
					love[callback] = function(dt)
						event:emit(callback, dt)
					end
				end
			else
				if love[callback] then
					local old = love[callback]
					love[callback] = function(...)
						old(...)
						event:emit(callback, ...)
					end
				else
					love[callback] = function(...)
						event:emit(callback, ...)
					end
				end
			end
		end
	end
}

signal.event = signal.new()

return signal