--- Signal management for Lua.
--
-- No dependency.
-- Optional dependency: LÖVE to hook into LÖVE events.
-- @module signal
-- @usage
-- TODO

--- Signal registry.
--
-- A SignalRegistry is a separate ubiquitousse.signal instance: its signals will be independant from other registries.
-- @type SignalRegistry
let registry_mt = {
	--- Map of signals to list of listeners.
	-- @ftype {["name"]={fn,...}}
	signals = {},

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

	--- Unbind one or several functions to a signal name.
	-- @tparam string name the name of the signal
	-- @tparam function fn the function to unbind to the signal
	-- @tparam function,... ... other function to unbind to the signal
	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
			@unbind(name, ...)
		end
	end,

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

	--- Replace a bound function with another function.
	-- @tparam string name the name of the signal
	-- @tparam function sourceFn the function currently bound to the signal
	-- @tparam function destFn the function that will replace the previous one
	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.
	-- @tparam string name the name of the signal
	-- @param ... arguments to pass to the functions bound to this signal
	emit = :(name, ...)
		if @signals[name] then
			for _, fn in ipairs(@signals[name]) do
				fn(...)
			end
		end
	end
}
registry_mt.__index = registry_mt

--- Module.
--
-- This module also acts as a global `SignalRegistry`, so you can call the `:bind`, `:emit`, etc. methods directly on the module
-- if you don't need to isolate your signals in separate registries.
-- @section module

let signal = {
	--- Creates and return a new SignalRegistry.
	-- @treturn SignalRegistry
	new = ()
		return setmetatable({ signals = {} }, registry_mt)
	end,

	-- Global SignalRegistry.
	signals = {},
	bind = (...)
		return registry_mt.bind(signal, ...)
	end,
	unbind = (...)
		return registry_mt.unbind(signal, ...)
	end,
	unbindAll = (...)
		return registry_mt.unbindAll(signal, ...)
	end,
	replace = (...)
		return registry_mt.replace(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; other ubiquitousse modules may bind to this registry
	-- if avaible.
	--
	-- 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
	-- @ftype SignalRegistry
	event = nil,

	--- Call this function to hook `signal.event` signals to LÖVE events.
	-- 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