to snake
    ; written by David Costanzo
    ;
    ; The author disclaims all copyrights associated with this code (hereafter
    ; referred to as the "Work").
    ;
    ; The author makes this dedication for the benefit of the public at large
    ; and to the detriment of the author's heirs and successors. The author
    ; intends this dedication to be an overt act of relinquishment in
    ; perpetuity of all present and future rights under copyright law,
    ; whether vested or contingent, in the Work. The author understands that
    ; such relinquishment of all rights includes the relinquishment of all
    ; rights to enforce (by lawsuit or otherwise) those copyrights in the
    ; Work.
    ;
    ; The author recognizes that, once placed in the public domain, the
    ; Work may be freely reproduced, distributed, transmitted, used,
    ; modified, built upon, or otherwise exploited by anyone for any
    ; purpose, commercial or non-commercial, and in any way, including by
    ; methods that have not yet been invented or conceived.
	clearscreen
	hideturtle
	ConsoleSetfocus
	GameLoop
end

to GetBoardSquare x y
	output item x (item y GameBoard)
end

to SetBoardSquare x y value
	setitem x (item y GameBoard) value
end

to BoardSquareIsBlocked x y
	local "square
	square=GetBoardSquare x y
	output (or (:square == "X) (:square == "S) )
end

to MoveToGrid_LowerLeft X Y
	penup
	setxy 	GridSize * (X - GameBoardWidth  / 2)
			GridSize * (Y - GameBoardHeight / 2)
	pendown
end

to MoveToGrid_LowerRight X Y
	penup
	setxy 	GridSize * (X + 1 - GameBoardWidth  / 2) - 1
			GridSize * (Y     - GameBoardHeight / 2)
	pendown
end

to MoveToGrid_UpperLeft X Y
	penup
	setxy 	GridSize * (X     - GameBoardWidth  / 2)
			GridSize * (Y + 1 - GameBoardHeight / 2) - 1
	pendown
end

to fillBlock X Y
	MoveToGrid_LowerLeft X Y
	setHeading 0
	fillRect [0 0] list GridSize GridSize
	setPenColor FloodColor
	repeat 4 [forward GridSize-1 right 90]
end

to EraseGrid X Y
	setfloodcolor screencolor
	fillBlock X Y
end

to DrawWall X Y
	setfloodcolor 0
	fillBlock X Y
end

to DrawApple X Y
	setfloodcolor RGB 1 0 0
	fillBlock X Y
end

to PlaceApple
	; places an apple randomly in an open space.
	local [applex appley appleisplaced foundopenspace]
	; randomly select places on the game board
	; until we find an open one
	foundopenspace=false
	while [not foundopenspace]
	[	AppleX=(random GameBoardWidth  - 2) + 2
		AppleY=(random GameBoardHeight - 2) + 2

		if (GetBoardSquare AppleX AppleY) == ".
		[	foundopenspace=true
		]
	]
	; place the apple
	SetBoardSquare AppleX AppleY "A
	TotalApples= TotalApples + 1
	DrawApple AppleX AppleY
end

to InitGameBoard
	local [row boardsquare]
	; copy the game board template to the live game board
	GameBoardWidth=40
	GameBoardHeight=40

	GameBoard=Array GameBoardHeight
	for [j 1 GameBoardHeight ]
	[	; add a new array for this row
		row=Array GameBoardWidth

		for [i 1 GameBoardWidth]
		[	; the game board starts off as an empty space
			boardsquare=".

			; put a border around the game board
			if (or (j == 1)
			(j == GameBoardHeight)
			(i == 1)
			(i == GameBoardWidth))
			[	boardsquare="X
			]
			setitem i row boardsquare
		]
		; set this row in the game board
		setitem j GameBoard row
	]
end

to DrawGameBoard
	local [gameboard_row boardsquare]
	; now draw the game board
	for [j 1 GameBoardHeight ]
	[	gameboard_row=Item j GameBoard
		for [i 1 GameBoardWidth ]
		[	boardsquare=Item i gameboard_row
			if boardsquare == "X
			[	DrawWall i j
			]
			if boardsquare == "A
			[	DrawApple i j
			]
		]
	]
end

to UpKey
	if not Direction == "down [NextDirection="up]
end

to DownKey
	if not Direction == "up [NextDirection="down]
end

to LeftKey
	if not Direction == "right [NextDirection="left]
end

to RightKey
	if not Direction == "left [NextDirection="right ]
end

to ProcessKeyEvent Key
	if Key==WXK_UP     [UpKey    ]
	if Key==WXK_LEFT   [LeftKey  ]
	if Key==WXK_RIGHT  [RightKey ]
	if Key==WXK_DOWN   [DownKey  ]
	if Key==WXK_ESCAPE [IsDone=true]
end

to StartKeyboardCapture
	OnKeyDown [ProcessKeyEvent keyboardvalue]
	OnChar [ch=readChar]
end

to EndKeyboardCapture
	OnKeyDown []
	OnChar []
end

to Move
	; push the current position onto the list
	queue "SnakeBody (list SnakeX SnakeY)
	; mark the space as filled
	SetBoardSquare SnakeX SnakeY "S

	if MaxSnakeLength < count SnakeBody
	[	local [tail]
		tail=dequeue "SnakeBody
		EraseGrid (item 1 tail) (item 2 tail)

		; mark the space as empty
		SetBoardSquare  (item 1 tail) (item 2 tail) ".
	]
	; move the snake
	Direction=NextDirection

	if Direction == "left  [SnakeX=SnakeX - 1 ]
	if Direction == "right [SnakeX=SnakeX + 1 ]
	if Direction == "down  [SnakeY=SnakeY - 1 ]
	if Direction == "up    [SnakeY=SnakeY + 1 ]

	; eat the apple, if we're over it
	if (GetBoardSquare SnakeX SnakeY) == "A
	[	Score=Score + 1
		MaxSnakeLength=MaxSnakeLength + 5
		TotalApples=TotalApples    - 1
	]
end

to CheckIfDead
	; if the square is blocked by something other than this player's head
	if BoardSquareIsBlocked SnakeX SnakeY
	[	; just died
		IsAlive=false
		stop
		; remove the player's trail from the board
		for [j 1 GameBoardHeight ]
		[	gameboard_row=Item j GameBoard
			for [i 1 GameBoardWidth ]
			[	boardsquare=item i gameboard_row
				if boardsquare == "S
				[	; this is the dead player's trail.
					; remove it by setting it to an empty space
					setitem i gameboard_row ".
					EraseGrid i j
				]
			]
		]
	]
end

to PrintGameBoard
	; prints the game board to the commander console
	for [j GameBoardHeight 1 ]
	[	print item j GameBoard
	]
end

to DrawBody
	if IsAlive
	[	setPenColor BoardColor
		DrawHead
		setfloodcolor SnakeColor
		fillBlock SnakeX SnakeY
	]
end

to DrawHead
	if Direction == "right
	[	MoveToGrid_LowerLeft SnakeX SnakeY
		setheading 0
		repeat 3 [forward GridSize - 1 right 120]
	]
	if Direction == "left
	[	MoveToGrid_LowerRight SnakeX SnakeY
		setheading 0
		repeat 3 [forward GridSize - 1 left 120]
	]
	if Direction == "up
	[	MoveToGrid_LowerLeft SnakeX SnakeY
		setheading 90
		repeat 3 [forward GridSize - 1 left 120]
	]
	if Direction == "down
	[	MoveToGrid_UpperLeft SnakeX SnakeY
		setheading 90
		repeat 3 [forward GridSize - 1 right 120]
	]
end

to UpdateNextFrame ; handles a single game tick
	if TotalApples == 0
	[	repeat 5 [PlaceApple]
	]
	DrawBody	; replace the old head with the color of the body
	Move		; move the snake
	setpencolor SnakeColor
	DrawHead	; draw the snake
	CheckIfDead	; remove the dead snakes
	if not IsAlive
	[	IsDone=true
	]
	updateGraph
end

to GameLoop
	local [GameBoard GridSize GameBoardWidth GameBoardHeight
		BoardColor SnakeColor]
	GridSize=14
	GameBoardWidth=40
	GameBoardHeight=40
	BoardColor=RGB 1 1 1
	SnakeColor=RGB 0 .8 0
	disableLineSmooth

	InitGameBoard
	local [IsAlive IsDone
		SnakeBody MaxSnakeLength
		SnakeX SnakeY
		Score TotalApples
		Direction NextDirection]
	IsAlive=true
	SnakeBody=[]
	MaxSnakeLength=10
	SnakeX=10
	SnakeY=10
	Score=0
	TotalApples=0

	Direction="right
	NextDirection="right

	DrawHead
	DrawGameBoard
	StartKeyboardCapture

	IsDone=false
	while [ not IsDone ]
	[	UpdateNextFrame
		waitMS 150
		DispatchMessages
	]
	EndKeyboardCapture
	(print "|Game Over.  Score =| Score)
end