function love.load()
    love.graphics.setBackgroundColor(1, 1, 1)

    cellSize = 5

    gridXCount = 70
    gridYCount = 50

    grid = {}
    for y = 1, gridYCount do
        grid[y] = {}
        for x = 1, gridXCount do
            grid[y][x] = false
        end
    end

    love.keyboard.setKeyRepeat(true)
end

function love.update()
    selectedX = math.min(math.floor(love.mouse.getX() / cellSize) + 1, gridXCount)
    selectedY = math.min(math.floor(love.mouse.getY() / cellSize) + 1, gridYCount)

    if love.mouse.isDown(1) then
        grid[selectedY][selectedX] = true
    elseif love.mouse.isDown(2) then
        grid[selectedY][selectedX] = false
    end
end

function love.keypressed()
    local nextGrid = {}

    for y = 1, gridYCount do
        nextGrid[y] = {}
        for x = 1, gridXCount do
            local neighborCount = 0

            for dy = -1, 1 do
                for dx = -1, 1 do
                    if not (dy == 0 and dx == 0)
                    and grid[y + dy]
                    and grid[y + dy][x + dx] then
                        neighborCount = neighborCount + 1
                    end
                end
            end

            nextGrid[y][x] = neighborCount == 3
                or (grid[y][x] and neighborCount == 2)
        end
    end

    grid = nextGrid
end

function love.draw()
    for y = 1, gridYCount do
        for x = 1, gridXCount do
            local cellDrawSize = cellSize - 1

            if x == selectedX and y == selectedY then
                love.graphics.setColor(0, 1, 1)
            elseif grid[y][x] then
                love.graphics.setColor(1, 0, 1)
            else
                love.graphics.setColor(.86, .86, .86)
            end

            love.graphics.rectangle(
                'fill',
                (x - 1) * cellSize,
                (y - 1) * cellSize,
                cellDrawSize,
                cellDrawSize
            )
        end
    end
end