local playerx = 10
local playery = 10
local angle = 1

local playerspeed = 0
local playerswspeed = 0
local playermaxspeed = 100

local sin = {0, 0.707, 1, 0.707, 0, -0.707, -1, -0.707}
local cos = {1, 0.707, 0, -0.707, -1, -0.707, 0, 0.707}

function love.update(dt)
	playerx = playerx + sin[angle] * playerspeed * dt
	playerx = playerx + cos[angle] * playerswspeed * dt
	playery = playery + cos[angle] * playerspeed * dt
	playery = playery - sin[angle] * playerswspeed * dt
end

function love.keypressed(key)
	if key == 'w' then
		playerspeed = playerspeed + playermaxspeed
	elseif key == 's' then
		playerspeed = playerspeed - playermaxspeed
	elseif key == 'a' then
		playerswspeed = playerswspeed + playermaxspeed
	elseif key == 'd' then
		playerswspeed = playerswspeed - playermaxspeed
	elseif key == 'q' then
		angle = angle + 1
		if angle > 8 then angle = 1 end
	elseif key == 'e' then
		angle = angle - 1
		if angle < 1 then angle = 8 end
	elseif key == 'escape' then
		love.event.quit()
	end
end

function love.keyreleased(key)
	if key == 'w' then
		playerspeed = playerspeed - playermaxspeed
	elseif key == 's' then
		playerspeed = playerspeed + playermaxspeed
	elseif key == 'a' then
		playerswspeed = playerswspeed - playermaxspeed
	elseif key == 'd' then
		playerswspeed = playerswspeed + playermaxspeed
	end
end

function transform(wx, wy)
	-- Player-relative space (translation)
	local tx = wx - playerx
	local ty = wy - playery

	-- Player-relative space (rotation)
	local rx = cos[angle] * tx - sin[angle] * ty
	local ry = cos[angle] * ty + sin[angle] * tx

	-- -1.0 to +1.0 abstract screen space (perspective)
	-- Player-relative x maps to *-x*
	-- Player-relative y maps to *z*
	local px = -rx / ry

	-- Screen space (scaling and translation)
	local hwidth = love.graphics.getWidth() / 2
	local x = px * hwidth + hwidth
	local z = ry

	return x, z
end

function drawWall(wx1, wy1, wx2, wy2)
	local hwidth = love.graphics.getWidth() / 2
	local hheight = love.graphics.getHeight() / 2
	local x1, z1 = transform(wx1, wy1)
	local x2, z2 = transform(wx2, wy2)

	if z1 < 0 and z2 < 0 then
		-- Fully outside of viewport, don't bother
		return
	end

	if z1 < 0 or z2 < 0 then
		local clippingx = playerx + 0.001*sin[angle]
		local clippingy = playery + 0.001*cos[angle]

		local x = nil
		local y = nil

		if angle == 1 or angle == 5 then
			y = clippingy
			if wx1 == wx2 then x = wx1
			elseif (wx1 < wx2) == (wy1 < wy2) then x = wx1 - wy1 + y
			else x = wx1 + wy1 - y
			end
		elseif angle == 3 or angle == 7 then
			x = clippingx
			if wy1 == wy2 then y = wy1
			elseif (wx1 < wx2) == (wy1 < wy2) then y = wy1 - wx1 + x
			else y = wy1 + wx1 - x
			end
		elseif angle == 2 or angle == 6 then
			if wy1 == wy2 then
				x = clippingx + clippingy - wy1
				y = wy1
			elseif wx1 == wx2 then
				x = wx1
				y = clippingx + clippingy - wx1
			else
				x = (wx1 + clippingx + clippingy - wy1) / 2
				y = (wy1 + clippingy + clippingx - wx1) / 2
			end
		elseif angle == 4 or angle == 8 then
			if wy1 == wy2 then
				x = clippingx - clippingy + wy1
				y = wy1
			elseif wx1 == wx2 then
				x = wx1
				y = clippingy - clippingx + wx1
			else
				x = (wx1 + clippingx - clippingy + wy1) / 2
				y = (wy1 + clippingy - clippingx + wx1) / 2
			end
		end

		if z1 < 0 then x1, z1 = transform(x, y)
		else x2, z2 = transform(x, y)
		end
	end

	local wall1 = hwidth * 60 / z1
	local wall2 = hwidth * 60 / z2

	love.graphics.setColor(1, 1, 1)
	love.graphics.line(x1, hheight - wall1, x2, hheight - wall2)
	love.graphics.line(x1, hheight + wall1, x2, hheight + wall2)
	love.graphics.line(x1, hheight - wall1, x1, hheight + wall1)
	love.graphics.line(x2, hheight - wall2, x2, hheight + wall2)
end

function love.draw()
	local hwidth = love.graphics.getWidth() / 2
	local hheight = love.graphics.getHeight() / 2

	drawWall(-300, -200, -100, 0)
	drawWall(-100, 0, -300, 200)
	drawWall(-150, 200, 300, 200)
	drawWall(300, 200, 300, -200)
	drawWall(300, -200, -300, -200)

	love.graphics.setColor(1, 1, 1)
	anglecw = angle - 1
	if anglecw < 1 then anglecw = 8 end
	anglecc = angle + 1
	if anglecc > 8 then anglecc = 1 end
	love.graphics.line(hwidth, hheight, hwidth + sin[anglecw] * 5, hheight + cos[anglecw] * 5)
	love.graphics.line(hwidth, hheight, hwidth + sin[anglecc] * 5, hheight + cos[anglecc] * 5)
end