local scr_x, scr_y = term.getSize()

local grid = {
	x1 = -80,
	y1 = -80,
	x2 = 80,
	y2 = 80,
	border = "#",
	voidcol = "f",
	forecol = "8",
	backcol = "7",
	edgecol = "0"
}

local scrollX = 0
local scrollY = 0

local player = {
	x = 0,
	y = 0,
	color = colors.blue
}

local gridFore = {
	"+-------",
	"|       ",
	"|       ",
	"|       ",
	"|       "

}
local gridBack = {
	"+------------",
	"|            ",
	"|            ",
	"|            ",
	"|            ",
	"|            ",
	"|            ",
	"|            "
}
for y = 1, #gridFore do
	gridFore[y] = gridFore[y]:gsub("#","\127")
end

--draws grid and background at scroll 'x' and 'y'
local drawGrid = function(x, y)
	x, y = math.floor(x + 0.5), math.floor(y + 0.5)
	local bg = {{},{},{}}
	local foreX, foreY
	local backX, backY
	local adjX, adjY
	for sy = 1, scr_y do
		bg[1][sy] = ""
		bg[2][sy] = ""
		bg[3][sy] = ""
		for sx = 1, scr_x do
			adjX = (sx - x)
			adjY = (sy - y)
			foreX = 1 + (sx - x) % #gridFore[1]
			foreY = 1 + (sy - y) % #gridFore
			backX = 1 + math.floor(sx - (x / 3)) % #gridBack[1]
			backY = 1 + math.floor(sy - (y / 3)) % #gridBack
			if adjX < grid.x1 or adjX > grid.x2 or adjY < grid.y1 or adjY > grid.y2 then
				bg[1][sy] = bg[1][sy] .. " "
				bg[2][sy] = bg[2][sy] .. grid.voidcol
				bg[3][sy] = bg[3][sy] .. grid.voidcol
			elseif adjX == grid.x1 or adjX == grid.x2 or adjY == grid.y1 or adjY == grid.y2 then
				bg[1][sy] = bg[1][sy] .. grid.border
				bg[2][sy] = bg[2][sy] .. grid.voidcol
				bg[3][sy] = bg[3][sy] .. grid.edgecol
			else
				if gridFore[foreY]:sub(foreX,foreX) ~= " " then
					bg[1][sy] = bg[1][sy] .. gridFore[foreY]:sub(foreX,foreX)
					bg[2][sy] = bg[2][sy] .. grid.forecol
					bg[3][sy] = bg[3][sy] .. grid.voidcol
				elseif gridBack[backY]:sub(backX,backX) ~= " " then
					bg[1][sy] = bg[1][sy] .. gridBack[backY]:sub(backX,backX)
					bg[2][sy] = bg[2][sy] .. grid.backcol
					bg[3][sy] = bg[3][sy] .. grid.voidcol
				else
					bg[1][sy] = bg[1][sy] .. " "
					bg[2][sy] = bg[2][sy] .. grid.voidcol
					bg[3][sy] = bg[3][sy] .. grid.voidcol
				end
			end
		end
	end
	for sy = 1, scr_y do
		term.setCursorPos(1,sy)
		term.blit(bg[1][sy], bg[2][sy], bg[3][sy])
	end
end

-- test background drawing

local evt
local keysDown = {}
local getInput = function()
	while true do
		evt = {os.pullEvent()}
		if evt[1] == "key" then
			keysDown[evt[2]] = true
		elseif evt[1] == "key_up" then
			keysDown[evt[2]] = false
		end
	end
end
local gridDemo = function()
	while true do
		if keysDown[keys.left] then
			scrollX = scrollX + 1
		end
		if keysDown[keys.right] then
			scrollX = scrollX - 1
		end
		if keysDown[keys.up] then
			scrollY = scrollY + 1
		end
		if keysDown[keys.down] then
			scrollY = scrollY - 1
		end
		drawGrid(scrollX, scrollY)
		sleep(0.05)
	end
end
parallel.waitForAny(getInput, gridDemo)