local syscalls = require("syscalls")

local systemColors = syscalls.GetSystemColors()
local skinHeight = syscalls.GetSkinHeight()

local display = "0"
local ans = "0"

local buttons = {
	{"1", "2", "3", "+", "-"},
	{"4", "5", "6", "*", "/"},
	{"7", "8", "9", "%", ""},
	{"0", ".", "Ans", "="}
}

local function DrawDisplay()
	syscalls.DrawText(
    	display,
    	20,
    	20 + skinHeight,
    	systemColors.workText
    )
end

local function redraw()
    syscalls.StartRedraw()

    syscalls.CreateWindow(
    	100,
    	100,
    	200,
    	256,
    	"lua example Calc",
    	systemColors.workArea,
    	syscalls.windowStyle.WithSkinFixSizes
    )

    DrawDisplay()

    --local t = syscalls.ThreadInfo()

    local i = 2
    local h = math.floor(150 / #buttons)

    for rowN, row in pairs(buttons) do

    	local w = math.floor(200 / #row)

       	for col, v in pairs(row) do

    		local x = math.floor((col-1) * w)
    		local y = math.floor((rowN-1) * h + 50 + skinHeight)

    		syscalls.DefineButton(
    			x,
    			y,
    			w,
    			h,
    			i,
    			systemColors.workButton
    		)

    		syscalls.DrawText(
    			v,
    			x,
    			y,
    			systemColors.workButtonText
    		)

    		i=i+1
    	end
    end


    syscalls.EndRedraw()
end

local function CheckButton(ButtonID)
	local i = 2
	for k, v in pairs(buttons) do
		for j, s in pairs(v) do
			if ButtonID ~= i then
				i = i + 1
			else
    			return s
			end
		end
	end

	return nil
end

local function checkInput(s)
	if s == "=" then
		display = assert(load( "return " .. display))()
		ans = display
	elseif s == "Ans" then
       	display = display .. ans
    elseif s then
      	if display == "0" then
       		display = s
       	else
       		display = display .. s
       	end
	end

	syscalls.DrawRectangle(20, 20 + skinHeight, 200, 30, systemColors.workArea)
	DrawDisplay()
end

-- main

redraw()
 
local exit = false
while not exit do
    local event = syscalls.WaitEvent()

    if event == syscalls.Event.Redraw then
        redraw()
    elseif event == syscalls.Event.Button then
        local ButtonID = syscalls.GetButton()

        if ButtonID == syscalls.buttons.close then
            exit = true
        else
        	local s = CheckButton(ButtonID)

			checkInput(s)
        end
    elseif event == syscalls.Event.Key then
    	local key, a = syscalls.GetKey()

    	key = key:sub(1, 1)

    	for _, row in pairs(buttons) do
    		for _, v in pairs(row) do
    			if v == key then
    				checkInput(key)
					break
    			end
    		end
    	end
    end
end