# Simple service keeping track of which keys are currently pressed
#
# This service revolves around `app.pressed_keys`, a `Set` of the names of currently pressed keys.
# As a `Set`, `app.pressed_keys` can be iterated and queried with `has`.
#
# Limitations: The keys names are platform dependent.
#
# ~~~nitish
# redef class App
#     redef fun accept_event(event)
#     do
#         # First, pass the event to `super`, `pressed_keys` must see all
#         # events but it doesn't intercept any of them.
#         if super then return true
#         return false
#     end
#
#     redef fun update(dt)
#     do
#         for key in pressed_keys do
#             if k == "left" or k == "a" then
#                 # Act on key pressed down
#                 print "left or a is pressed down"
#             end
#         end
#     end
# end
# ~~~
module keys

import mnit::input
import gamnit

redef class App
	# Currently pressed keys
	var pressed_keys = new Set[String] is lazy

	# Register `event` to update `app.pressed_keys`
	private fun register_key_event(event: KeyEvent)
	do
		var key = event.name
		if event.is_down then
			app.pressed_keys.add key
		else if app.pressed_keys.has(key) then
			app.pressed_keys.remove key
		end
	end

	redef fun accept_event(event)
	do
		if event isa KeyEvent then register_key_event event

		return super
	end
end