-- title:  asteroids
-- author: Bob Grant
-- desc:   
-- script: lua

-- game state control
STATE_START = 0
STATE_PLAY = 10
STATE_END = 20

gameState = STATE_START

SCREEN_MAX_X = 240
SCREEN_MAX_Y = 136

playerShip = {
	position = {
		x = 100,
		y = 60
	},
	velocity = {
		speed = 0,
		direction = 0
	},
	acceleration = 0.05,
	deceleration = 0.01,
	rotation = 0,
	rotationSpeed = 0.07,
	points = {
		{x=8,y=0},
		{x=-8,y=6},
		{x=-4,y=0},
		{x=-8,y=-6},
		{x=8,y=0}
	}
}

function TIC()

	if gameState == STATE_START then
		doStartScreen()
	elseif gameState == STATE_PLAY then
		doPlayGame()
	elseif gameState == STATE_END then
		doEndScreen()
	end

end

function doStartScreen()

	cls()
	print ("ASTEROIDS", 80,40)
	print ("press Z to start", 60,60)
	if btnp(4) then
		gameState = STATE_PLAY
	end

end -- doStartScreen()

function doEndScreen()

	cls()
	print ("GAME OVER", 80,40)
	print ("press Z to start", 60,60)
	if btnp(4) then
		gameState = STATE_PLAY
	end

end -- doEndScreen()

function doPlayGame()

	cls()
	
	-- update
	checkPlayerButtons()
	movePlayerShip()
	
	-- draw
	drawVectorShape(playerShip)
	print(playerShip.rotation, 0,0)
	
	if btnp(4) then
		gameState = STATE_END
	end

end -- doPlayGame()

function drawVectorShape(shape)

	local firstPoint = true
	local lastPoint = 0
	local rotatedPoint = 0
	for index, point in ipairs(shape.points) do
	
		rotatedPoint = rotatePoint(point,shape.rotation)
	
		if firstPoint then
			lastPoint = rotatedPoint
			firstPoint = false
		else
			line(lastPoint.x + shape.position.x,
			 lastPoint.y + shape.position.y,
				rotatedPoint.x + shape.position.x,
				rotatedPoint.y + shape.position.y,
				8)
				lastPoint = rotatedPoint
		end
	
	end -- for

end -- drawVectorShape

function rotatePoint(point, rotation)

	local rotatedX =
		(point.x * math.cos(rotation))
		- (point.y * math.sin(rotation))
		
	local rotatedY =
		(point.y * math.cos(rotation))
		+ (point.x * math.sin(rotation))
		
	return {x=rotatedX, y=rotatedY}

end -- rotatePoint

function checkPlayerButtons()
	
	if btn(2) then -- left
		playerShip.rotation = playerShip.rotation
			- playerShip.rotationSpeed
	end
	if  btn(3) then -- right
		playerShip.rotation = playerShip.rotation
			+ playerShip.rotationSpeed
	end
	
	playerShip.rotation = 
		keepAngleInRange(playerShip.rotation)

end -- checkPlayerButtons

function keepAngleInRange(angle)

	if angle < 0 then
		while angle < 0 do
			angle = angle + (2 * math.pi)
		end
	end
	if angle > (2 * math.pi) then
		while angle > (2 * math.pi) do
			angle = angle - (2 * math.pi)
		end
	end
	
	return angle

end -- keepAngleInRange

function movePointByVelocity(object)

	components =
		getVectorComponents(object.velocity)
	
	local newPosition = {
		x = object.position.x 
						+ components.xComp,
		y = object.position.y 
						+ components.yComp
	}
	
	return newPosition

end -- movePointByVelocity

function 	movePlayerShip()

	-- thrust
	if btn(0) then -- up key
		playerShipThrust()
	end -- if
	
	playerShip.velocity.speed = 
		playerShip.velocity.speed - 
			playerShip.deceleration
	
	if playerShip.velocity.speed < 0 then
		playerShip.velocity.speed = 0
	end

	playerShip.position = 
		movePointByVelocity(playerShip)
		
	playerShip.position = 
		wrapPosition(playerShip.position)

end -- movePlayerShip

function playerShipThrust()

	local acceleration = {
		speed = playerShip.acceleration,
		direction = playerShip.rotation
	}
	
	playerShip.velocity = 
		addVectors(playerShip.velocity,
			acceleration)

end -- playerShipThrust

function addVectors(vector1, vector2)

	v1Comp = getVectorComponents(vector1)
	v2Comp = getVectorComponents(vector2)
	resultantX = v1Comp.xComp + v2Comp.xComp
	resultantY = v1Comp.yComp + v2Comp.yComp

	local resVector =
		compToVector(resultantX, resultantY) 

	return resVector
	
end -- addVectors

function getVectorComponents(vector)

	local xComp = vector.speed
		* math.cos(vector.direction)
	
	local yComp = vector.speed
		* math.sin(vector.direction)
		
	local components = {
		xComp = xComp,
		yComp = yComp
	}
	
	return components

end -- getVectorComponents

function compToVector(x, y)

	local magnitude = 
		math.sqrt( (x * x) + (y * y))
	local direction = 
		math.atan2(y, x)
	direction = keepAngleInRange(direction)
		
	local vector = {
		speed = magnitude,
		direction = direction
	}
	
	return vector

end -- compToVector

function wrapPosition(position)

	if (position.x >= SCREEN_MAX_X) then
		position.x = 0
	elseif (position.x < 0) then
		position.x = SCREEN_MAX_X - 1
	end
	
	if (position.y >= SCREEN_MAX_Y) then
		position.y = 0
	elseif (position.y < 0) then
		position.y = SCREEN_MAX_Y - 1
	end
	
	return position

end -- wrapPosition