-- Open Road:  a road-racing game of the arcade kind, drawn a screen row at a time.  There is no 3D
-- here at all.  The track is a list of short segments, each with how sharply it bends and how high
-- it is.  Every frame projects the segments ahead with one division each, and fills the screen rows
-- between one segment and the next with a cut-out row of road stretched to the road's width there
-- (spriteDrawGrid's stretched form).  Bends move each row sideways a little more than the last;
-- hills move rows up or down, and a crest hides what is beyond it, scenery included.
--
-- Cars and scenery are flat pictures scaled to their distance.  The player's car is one picture,
-- leaned into a turn and spun in a crash by turning it.
--
-- Left and right steer, button 1 (or up) accelerates, button 2 (or down) brakes.  Reach the arch
-- before the time runs out for more time.
dofile("Singe/Framework.singe")

local W             = 320
local H             = 240
local HORIZON_Y     = 110           -- Where the horizon sits on a level road;  the sky art assumes it
local FOCAL         = 160           -- Screen offset = world offset * FOCAL / distance ahead
local CAM_HEIGHT    = 60            -- The camera's height over the road under the car
local SEG           = 20            -- World units of track in a segment
local DRAW          = 150           -- Segments drawn ahead
local NEAR          = 1             -- Closer than this, a point is behind the camera
local ROAD_HALF     = 100           -- Half a road row in world units, rumble to rumble
local STRIP_W       = 256           -- The strip art's width;  the art script sets these four
local HAZE          = 8
local ROW_ROAD      = 0             -- Row kinds in the strip, each HAZE rows deep
local ROW_GRASS     = 2
local RUMBLE_SEGS   = 3             -- Segments from one light band to the next dark one
local LANE          = 58            -- World units from one lane's centre to the next
local PLAYER_AHEAD  = 80            -- The car is this far ahead of the camera;  it is drawn there at its own size
local PLAYER_W      = 36            -- And this wide in the world, for hitting things
local PLAYER_BOTTOM = 230           -- Its bottom row on screen:  HORIZON_Y + CAM_HEIGHT * FOCAL / PLAYER_AHEAD
local MAX_SPEED     = 420           -- World units a second
local ACCEL         = 120
local BRAKE         = 320
local COAST         = 50
local OFFROAD_SPEED = MAX_SPEED / 3 -- Off the road the car slows to this
local OFFROAD_DRAG  = 260
local STEER         = 170           -- World units a second across, at full speed
local CENTRIFUGAL   = 150           -- How hard a sharp bend at full speed pushes the car out
local CURVE_EASY    = 0.2           -- A bend's sharpness:  how much each segment turns from the last
local CURVE_MEDIUM  = 0.4
local CURVE_HARD    = 0.6
local HILL_LOW      = 120
local HILL_MEDIUM   = 260
local HILL_HIGH     = 420
local HILLS_SCROLL  = 4             -- Pixels the far hills move for each segment of a bend at full sharpness
local LEAN          = 6             -- Degrees the car leans into a full turn
local SPIN_SECONDS  = 1.2
local SPIN_TURNS    = 2
local TRAFFIC       = 24
local CAR_LENGTH    = 30            -- How close behind a car the player can be before hitting it
local TIME_START    = 85
local TIME_BONUS    = 75
local ARCH_SEGMENT  = 8             -- Where the start arch stands, just ahead of the car

-- What each kind of thing is:  its picture, its width in the world (its height follows from the
-- picture), and whether the car hits it.
local KINDS = {}

local track      = {}
local trackLen   = 0
local traffic    = {}
local drawn      = {}
local held       = {}
local strip      = nil
local sky        = nil
local hills      = nil
local hillsW     = 0
local position   = 0                -- The camera's distance along the track
local playerX    = 0                -- The car's distance across from the road's centre
local speed      = 0
local spin       = nil              -- Seconds into a crash's spin, or nil
local hillsAt    = 0
local timeLeft   = TIME_START
local distance   = 0
local nextLap    = 0
local lap        = 1
local score      = 0
local message    = nil
local messageEnd = 0
local clock      = 0
local lastTicks  = nil


local function addSegment(curve, y)
	local last = track[#track]

	track[#track + 1] = { index = #track, curve = curve, y1 = last and last.y2 or 0, y2 = y, scenery = {}, cars = {} }
end


local function easeIn(a, b, t)
	return a + (b - a) * t * t
end


local function easeInOut(a, b, t)
	return a + (b - a) * (0.5 - math.cos(t * math.pi) / 2)
end


-- A piece of road:  it eases into its bend, holds it, and eases out, climbing or falling by rise
-- over its whole length.
local function addRoad(enter, hold, leave, curve, rise)
	local startY = track[#track] and track[#track].y2 or 0
	local endY   = startY + rise
	local total  = enter + hold + leave

	for n = 0, enter - 1 do
		addSegment(easeIn(0, curve, n / enter), easeInOut(startY, endY, n / total))
	end
	for n = 0, hold - 1 do
		addSegment(curve, easeInOut(startY, endY, (enter + n) / total))
	end
	for n = 0, leave - 1 do
		addSegment(easeInOut(curve, 0, n / leave), easeInOut(startY, endY, (enter + hold + n) / total))
	end
end


local function addScenery(index, kind, x)
	local segment = track[(index % #track) + 1]

	segment.scenery[#segment.scenery + 1] = { kind = kind, x = x }
end


local function buildTrack()
	track = {}
	addRoad(0, 40, 0, 0, 0)
	addRoad(25, 50, 25, CURVE_MEDIUM, 0)
	addRoad(30, 40, 30, 0, HILL_MEDIUM)
	addRoad(25, 40, 25, -CURVE_EASY, 0)
	addRoad(20, 30, 20, -CURVE_MEDIUM, -HILL_LOW)
	addRoad(20, 30, 20, CURVE_MEDIUM, HILL_LOW)
	addRoad(30, 60, 30, 0, -HILL_HIGH)
	addRoad(30, 60, 30, CURVE_HARD, 0)
	for _ = 1, 4 do
		addRoad(15, 10, 15, 0, HILL_LOW)
		addRoad(15, 10, 15, 0, -HILL_LOW)
	end
	addRoad(25, 50, 25, -CURVE_MEDIUM, HILL_MEDIUM)
	addRoad(20, 20, 20, CURVE_EASY, 0)
	addRoad(20, 20, 20, -CURVE_EASY, 0)
	addRoad(30, 40, 30, -CURVE_HARD, 0)
	addRoad(40, 60, 40, CURVE_EASY, -track[#track].y2)
	addRoad(0, 30, 0, 0, 0)
	trackLen = #track * SEG

	-- Palms along both sides, bushes farther out, a warning board on the outside before each bend
	-- (where the car goes if it is taken too fast), and the arch, with nothing hiding it.
	for i = 0, #track - 1 do
		local segment = track[i + 1]
		local nearArch = math.abs(i - ARCH_SEGMENT) < 6

		if i % 6 == 0 and not nearArch then
			addScenery(i, KINDS.palm, -(ROAD_HALF + 35 + math.random(0, 60)))
			addScenery(i, KINDS.palm, ROAD_HALF + 35 + math.random(0, 60))
		end
		if math.random() < 0.25 then
			local side = (math.random() < 0.5) and -1 or 1

			addScenery(i, KINDS.bush, side * (ROAD_HALF + 90 + math.random(0, 260)))
		end
		local previous = track[((i - 1) % #track) + 1]

		if previous.curve == 0 and segment.curve ~= 0 then
			local outside = (segment.curve > 0) and -1 or 1

			for back = 25, 5, -5 do
				addScenery(i - back, KINDS.sign, outside * (ROAD_HALF + 22))
			end
		end
	end
	addScenery(ARCH_SEGMENT, KINDS.arch, 0)
end


local function loadKind(name, width, solid)
	local sprite = spriteLoad(DIR .. "art/" .. name .. ".png")
	local w      = spriteGetWidth(sprite)
	local h      = spriteGetHeight(sprite)

	return { sprite = sprite, width = width, height = width * h / w, naturalW = w, naturalH = h, solid = solid }
end


local function segmentAt(z)
	return track[(math.floor(z / SEG) % #track) + 1]
end


local function showMessage(text, seconds)
	message    = text
	messageEnd = clock + seconds
end


local function reset()
	position = 0
	playerX  = 0
	speed    = 0
	spin     = nil
	timeLeft = TIME_START
	distance = 0
	nextLap  = ARCH_SEGMENT * SEG - PLAYER_AHEAD + trackLen
	lap      = 1
	score    = 0
	traffic  = {}
	for _ = 1, TRAFFIC do
		local kind = (math.random() < 0.75) and KINDS.traffic or KINDS.truck

		traffic[#traffic + 1] = { kind = kind, z = math.random(ARCH_SEGMENT + 20, #track - 10) * SEG, x = math.random(-1, 1) * LANE, speed = math.random(120, 260) }
	end
	showMessage("GO!", 2)
end


local function crash()
	spin  = 0
	speed = 0
end


local function step(dt)
	local steer   = (held[SWITCH_RIGHT] and 1 or 0) - (held[SWITCH_LEFT] and 1 or 0)
	local gas     = held[SWITCH_BUTTON1] or held[SWITCH_UP]
	local brake   = held[SWITCH_BUTTON2] or held[SWITCH_DOWN]
	local playerZ = position + PLAYER_AHEAD
	local segment = segmentAt(playerZ)
	local pace    = speed / MAX_SPEED
	local offRoad = math.abs(playerX) > ROAD_HALF

	clock = clock + dt
	if timeLeft > 0 then
		timeLeft = math.max(0, timeLeft - dt)
		if timeLeft == 0 then
			showMessage("TIME UP", 1000)
		end
	end

	-- A spin takes the controls away until it is over, and leaves the car on the road's edge.
	if spin then
		spin = spin + dt
		if spin >= SPIN_SECONDS then
			spin    = nil
			playerX = (playerX < 0 and -1 or 1) * (ROAD_HALF - PLAYER_W)
		end
		steer = 0
		gas   = false
	end
	if timeLeft == 0 then
		gas = false
	end

	if gas then
		speed = speed + ACCEL * dt
	elseif brake then
		speed = speed - BRAKE * dt
	else
		speed = speed - COAST * dt
	end
	if offRoad and speed > OFFROAD_SPEED then
		speed = speed - OFFROAD_DRAG * dt
	end
	speed = math.max(0, math.min(MAX_SPEED, speed))

	-- Steering moves the car across in proportion to its speed;  a bend pushes it outward by the
	-- square of it.
	playerX = playerX + steer * STEER * pace * dt
	playerX = playerX - segment.curve / CURVE_HARD * pace * pace * CENTRIFUGAL * dt
	playerX = math.max(-ROAD_HALF * 3, math.min(ROAD_HALF * 3, playerX))

	position = (position + speed * dt) % trackLen
	distance = distance + speed * dt
	score    = score + math.floor(speed * dt)
	hillsAt  = (hillsAt + segment.curve / CURVE_HARD * HILLS_SCROLL * speed * dt / SEG) % hillsW
	if distance >= nextLap then
		nextLap  = nextLap + trackLen
		lap      = lap + 1
		timeLeft = timeLeft + TIME_BONUS
		showMessage("EXTENDED TIME", 2)
	end

	-- Off the road, anything solid in the car's segment stops it dead.
	playerZ = position + PLAYER_AHEAD
	segment = segmentAt(playerZ)
	if not spin and math.abs(playerX) > ROAD_HALF then
		for _, thing in ipairs(segment.scenery) do
			if thing.kind.solid and math.abs(thing.x - playerX) < (PLAYER_W + thing.kind.width) * 0.35 then
				crash()
				break
			end
		end
	end

	-- Traffic keeps its lane at its own speed.  Running into the back of a car drops the player to
	-- that car's speed, behind it.
	for _, car in ipairs(traffic) do
		car.z = (car.z + car.speed * dt) % trackLen
		local gap = (car.z - playerZ) % trackLen

		if gap < CAR_LENGTH and speed > car.speed and math.abs(car.x - playerX) < (PLAYER_W + car.kind.width) * 0.4 then
			speed    = car.speed * 0.7
			position = (car.z - CAR_LENGTH - PLAYER_AHEAD) % trackLen
		end
	end
end


-- The far hills, twice the screen's width, drawn round from wherever they have scrolled to.
local function drawHills()
	local from  = math.floor(hillsAt)
	local first = math.min(W, hillsW - from)
	local top   = HORIZON_Y - spriteGetHeight(hills) + 1

	spriteDrawGrid(hills, 0, top, from, 0, first, spriteGetHeight(hills))
	if first < W then
		spriteDrawGrid(hills, first, top, 0, 0, W - first, spriteGetHeight(hills))
	end
end


-- A picture standing on the road at its distance, centred across on x, its foot at bottom.  Rows at
-- clip and below are hidden by nearer road, so a thing beyond a crest shows only what is above it:
-- the picture's top part, cut out and stretched to what is left.
local function drawStanding(kind, x, bottom, perUnit, clip)
	local w = kind.width * perUnit
	local h = kind.height * perUnit

	if w < 1 or x + w / 2 < 0 or x - w / 2 >= W or bottom - h >= clip then
		return
	end
	local left  = math.floor(x - w / 2)
	local right = math.floor(x + w / 2)
	local top   = math.floor(bottom - h)

	if bottom <= clip then
		spriteDraw(kind.sprite, left, top, right, math.floor(bottom) - 1)
	else
		local shown = math.min(kind.naturalH, math.max(1, math.floor(kind.naturalH * (clip - (bottom - h)) / h)))

		spriteDrawGrid(kind.sprite, left, top, 0, 0, kind.naturalW, shown, right, clip - 1)
	end
end


-- The road, nearest segment first.  Each segment fills the rows between where its near edge and its
-- far edge land, as far up as the nearest road drawn so far reaches (clip).  Each row is one cut-out
-- row of the strip stretched to the road's width there, over one stretched row of grass.
local function drawRoad(camX, camY)
	local base     = math.floor(position / SEG)
	local within   = position - base * SEG
	local first    = track[(base % #track) + 1]
	local x        = 0
	local dx       = -first.curve * within / SEG
	local clip     = H
	local hazeFar  = DRAW * SEG

	drawn = {}
	for n = 0, DRAW - 1 do
		local index   = base + n
		local segment = track[(index % #track) + 1]
		local z1      = math.max(NEAR, n * SEG - within)
		local z2      = n * SEG - within + SEG
		local scale1  = FOCAL / z1
		local scale2  = FOCAL / z2

		segment.sx1    = W / 2 + (x - camX) * scale1
		segment.sy1    = HORIZON_Y - (segment.y1 - camY) * scale1
		segment.scale1 = scale1
		segment.sx2    = W / 2 + (x + dx - camX) * scale2
		segment.sy2    = HORIZON_Y - (segment.y2 - camY) * scale2
		segment.scale2 = scale2
		segment.clip   = clip
		segment.z1     = z1
		x  = x + dx
		dx = dx + segment.curve
		drawn[#drawn + 1] = segment

		if segment.sy2 < clip and segment.sy1 > segment.sy2 then
			local top    = math.max(0, math.ceil(segment.sy2))
			local bottom = math.min(clip - 1, math.floor(segment.sy1))
			local light  = (index // RUMBLE_SEGS) % 2
			local haze   = math.min(HAZE - 1, math.floor(z1 / hazeFar * HAZE))
			local road   = (ROW_ROAD + light) * HAZE + haze
			local grass  = (ROW_GRASS + light) * HAZE + haze
			local height = segment.sy1 - segment.sy2

			if top <= bottom then
				spriteDrawGrid(strip, 0, top, 0, grass, STRIP_W, 1, W - 1, bottom)
				for row = bottom, top, -1 do
					local t    = (segment.sy1 - row) / height
					local cx   = segment.sx1 + (segment.sx2 - segment.sx1) * t
					local half = ROAD_HALF * (scale1 + (scale2 - scale1) * t)

					spriteDrawGrid(strip, math.floor(cx - half), row, 0, road, STRIP_W, 1, math.floor(cx + half), row)
				end
				clip = top
			end
		end
	end
end


-- Scenery and traffic, farthest first, each clipped by the road nearer than it.
local function drawThings()
	for _, car in ipairs(traffic) do
		local segment = segmentAt(car.z)

		segment.cars[#segment.cars + 1] = car
	end
	for i = #drawn, 2, -1 do
		local segment = drawn[i]

		for _, thing in ipairs(segment.scenery) do
			drawStanding(thing.kind, segment.sx1 + thing.x * segment.scale1, segment.sy1, segment.scale1, segment.clip)
		end
		for _, car in ipairs(segment.cars) do
			local t       = (car.z % SEG) / SEG
			local perUnit = segment.scale1 + (segment.scale2 - segment.scale1) * t
			local sx      = segment.sx1 + (segment.sx2 - segment.sx1) * t + car.x * perUnit
			local sy      = segment.sy1 + (segment.sy2 - segment.sy1) * t

			drawStanding(car.kind, sx, sy, perUnit, segment.clip)
		end
	end
	for _, segment in ipairs(drawn) do
		segment.cars = {}
	end
end


-- The player's car:  one picture at its own size, leaned into the turn, shaken on the grass, and
-- spun right round in a crash.
local function drawCar(steer)
	local pace  = speed / MAX_SPEED
	local angle = math.floor(steer * LEAN * pace + 0.5)
	local shake = 0

	if spin then
		local t = spin / SPIN_SECONDS

		angle = math.floor(360 * SPIN_TURNS * (1 - (1 - t) * (1 - t)))
	end
	if math.abs(playerX) > ROAD_HALF and speed > 0 then
		shake = math.random(0, 2)
	end
	-- Turned, the picture grows, so it is drawn by its centre, which stays where the upright one's was.
	spriteRotate(KINDS.car.sprite, angle % 360)
	spriteDraw(KINDS.car.sprite, W // 2, PLAYER_BOTTOM - KINDS.car.naturalH // 2 - shake, true)
end


function onInputPressed(what)
	held[what] = true
	if what == SWITCH_BUTTON1 and timeLeft == 0 and speed == 0 then
		reset()
	end
end


function onInputReleased(what)
	held[what] = false
end


function onOverlayUpdate()
	local now = singeGetTicks()
	local dt  = lastTicks and math.min(0.05, (now - lastTicks) / 1000) or 0

	lastTicks = now
	step(dt)

	local playerZ = position + PLAYER_AHEAD
	local segment = segmentAt(playerZ)
	local t       = (playerZ % SEG) / SEG
	local camY    = segment.y1 + (segment.y2 - segment.y1) * t + CAM_HEIGHT
	local steer   = (held[SWITCH_RIGHT] and 1 or 0) - (held[SWITCH_LEFT] and 1 or 0)

	spriteDraw(sky, 0, 0)
	drawHills()
	drawRoad(playerX, camY)
	drawThings()
	drawCar(steer)

	overlayPrint(1, 0, string.format("TIME %2d", math.ceil(timeLeft)))
	overlayPrint(15, 0, string.format("LAP %d", lap))
	overlayPrint(26, 0, string.format("%06d", score // 10))
	overlayPrint(1, 14, string.format("%3d km/h", math.floor(speed * 0.7)))
	if message and clock < messageEnd then
		overlayPrint(20 - #message // 2, 5, message)
	end
	if timeLeft == 0 and speed == 0 then
		overlayPrint(9, 7, "Button 1 drives again")
	end

	return OVERLAY_UPDATED
end


overlaySetResolution(W, H)
strip         = spriteLoad(DIR .. "art/strip.png")
sky           = spriteLoad(DIR .. "art/sky.png")
hills         = spriteLoad(DIR .. "art/hills.png")
hillsW        = spriteGetWidth(hills)
KINDS.car     = loadKind("car", 40, false)
KINDS.traffic = loadKind("traffic", 42, true)
KINDS.truck   = loadKind("truck", 46, true)
KINDS.palm    = loadKind("palm", 50, true)
KINDS.bush    = loadKind("bush", 50, false)
KINDS.sign    = loadKind("sign", 40, true)
KINDS.arch    = loadKind("arch", ROAD_HALF * 2.3, false)
buildTrack()
reset()