-- state
local context = {maxid = 0}
local draw_items = {n = 0}
local NO_WIDGET = function()end

local function generateID()
	context.maxid = context.maxid + 1
	return context.maxid
end

local function setHot(id) context.hot = id end
local function isHot(id)  return context.hot == id end

local function setActive(id) context.active = id end
local function isActive(id)  return context.active == id end

local function setKeyFocus(id) context.keyfocus = id end
local function hasKeyFocus(id) return context.keyfocus == id end

-- input
local mouse = {x = 0, y = 0, down = false}
local keyboard = {key = nil, code = -1}
keyboard.cycle = {
	-- binding = {key = key, modifier1, modifier2, ...} XXX: modifiers are OR-ed!
	prev = {key = 'tab', 'lshift', 'rshift'},
	next = {key = 'tab'},
}

function mouse.inRect(x,y,w,h)
	return mouse.x >= x and mouse.x <= x+w and mouse.y >= y and mouse.y <= y+h
end

function mouse.updateState(id, x,y,w,h)
	if mouse.inRect(x,y,w,h) then
		setHot(id)
		if not context.active and mouse.down then
			setActive(id)
		end
	end
end

function mouse.releasedOn(id)
	return not mouse.down and isHot(id) and isActive(id)
end

function keyboard.pressed(key, code)
	keyboard.key = key
	keyboard.code = code
end

function keyboard.tryGrab(id)
	if not context.keyfocus then
		context.keyfocus = id
	end
end

function keyboard.isBindingDown(bind)
	local modifiersDown = #bind == 0 or love.keyboard.isDown(unpack(bind))
	return keyboard.key == bind.key and modifiersDown
end

local function makeTabable(id)
	keyboard.tryGrab(id)
	if hasKeyFocus(id) then
		if keyboard.isBindingDown(keyboard.cycle.prev) then
			setKeyFocus(context.lastwidget)
			keyboard.key = nil
		elseif keyboard.isBindingDown(keyboard.cycle.next) then
			setKeyFocus(nil)
			keyboard.key = nil
		end
	end
	context.lastwidget = id
end

-- helper functions
local function strictAnd(...)
	local n = select("#", ...)
	local ret = true
	for i = 1,n do ret = select(i, ...) and ret end
	return ret
end

local function strictOr(...)
	local n = select("#", ...)
	local ret = false
	for i = 1,n do ret = select(i, ...) or ret end
	return ret
end

-- allow packed nil
local function save_pack(...)
	return {n = select('#', ...), ...}
end

local function save_unpack(t, i)
	i = i or 1
	if i >= t.n then return t[i] end
	return t[i], save_unpack(t, i+1)
end

local function registerDraw(id, f, ...)
	assert(type(f) == 'function' or (getmetatable(f) or {}).__call,
	       'Drawing function is not a callable type!')

	local state = 'normal'
	if isHot(id) or hasKeyFocus(id) then
		state = isActive(id) and 'active' or 'hot'
	end
	local rest = save_pack(...)
	draw_items.n = draw_items.n + 1
	draw_items[draw_items.n] = function() f(state, save_unpack(rest)) end
end

-- actually update-and-draw
local function draw()
	-- close frame state
	if not mouse.down then -- released
		setActive(nil)
	elseif not context.active then -- clicked outside
		setActive(NO_WIDGET)
	end

	for i = 1,draw_items.n do draw_items[i]() end

	-- prepare for next frame
	draw_items.n = 0
	context.maxid = 0

	-- update mouse status
	setHot(nil)
	mouse.x, mouse.y = love.mouse.getPosition()
	mouse.down = love.mouse.isDown('l')

	keyboard.key, keyboard.code = nil, -1
end

return {
	mouse        = mouse,
	keyboard     = keyboard,

	generateID   = generateID,
	setHot       = setHot,
	setActive    = setActive,
	setKeyFocus  = setKeyFocus,
	isHot        = isHot,
	isActive     = isActive,
	hasKeyFocus  = hasKeyFocus,
	makeTabable  = makeTabable,

	style        = require((...):match("(.-)[^%.]+$") .. '.style-default'),
	color        = color,
	registerDraw = registerDraw,
	draw         = draw,

	strictAnd    = strictAnd,
	strictOr     = strictOr,
	save_pack    = save_pack,
	save_unpack  = save_unpack,
}