Snake

term.setBackgroundColor(32768)
-- Display the start screen
local w,h = term.getSize()

local headingColour, textColour, wormColour, fruitColour
if term.isColour() then
        headingColour = colours.yellow
        textColour = colours.white
        wormColour = colours.lime
        fruitColour = colours.red
else
        headingColour = colours.white
        textColour = colours.white
        wormColour = colours.white
        fruitColour = colours.white
end

function printCentred( y, s )
        local x = math.floor((w - string.len(s)) / 2)
        term.setCursorPos(x,y)
        --term.clearLine()
        term.write( s )
end

local xVel,yVel = 1,0
local xPos, yPos = math.floor(w/2), math.floor(h/2)
local pxVel, pyVel = nil, nil

local nLength = 1
local nExtraLength = 6
local bRunning = true

local tailX,tailY = xPos,yPos
local nScore = 0
local nDifficulty = 2
local nSpeed, nInterval

-- Setup the screen
local screen = {}
for x=1,w do
        screen[x] = {}
        for y=1,h do
                screen[x][y] = {}
        end
end
screen[xPos][yPos] = { snake = true }

local nFruit = 1
local tFruits = {
        "A", "B", "C", "D", "E", "F", "G", "H",
        "I", "J", "K", "L", "M", "N", "O", "P",
        "Q", "R", "S", "T", "U", "V", "W", "X",
        "Y", "Z",
        "a", "b", "c", "d", "e", "f", "g", "h",
        "i", "j", "k", "l", "m", "n", "o", "p",
        "q", "r", "s", "t", "u", "v", "w", "x",
        "y", "z",
        "1", "2", "3", "4", "5", "6", "7", "8", "9", "0",
        "@", "$", "%", "#", "&", "!", "?", "+", "*", "~"
}

local function addFruit()
        while true do
                local x = math.random(1,w)
                local y = math.random(2,h)
                local fruit = screen[x][y]
                if fruit.snake == nil and fruit.wall == nil and fruit.fruit == nil then
                        screen[x][y] = { fruit = true }
                        term.setCursorPos(x,y)
                        term.setBackgroundColour( fruitColour )
                        term.write(" ")
                        term.setBackgroundColour( colours.black )
                        break
                end
        end

        nFruit = nFruit + 1
        if nFruit > #tFruits then
                nFruit = 1
        end
end

local function drawMenu()
        term.setTextColour( headingColour )
        term.setCursorPos(1,1)
        term.write( "SCORE " )

        term.setTextColour( textColour )
        term.setCursorPos(7,1)
        term.write( tostring(nScore) )

        term.setTextColour( headingColour )
        term.setCursorPos(w-11,1)
        term.write( "DIFFICULTY ")

        term.setTextColour( textColour )
        term.setCursorPos(w,1)
        term.write( tostring(nDifficulty or "?") )

        term.setTextColour( colours.white )
end

local function update( )
        local x,y = xPos,yPos
        if pxVel and pyVel then
                xVel, yVel = pxVel, pyVel
                pxVel, pyVel = nil, nil
        end

        -- Remove the tail
        if nExtraLength == 0 then
                local tail = screen[tailX][tailY]
                screen[tailX][tailY] = {}
                term.setCursorPos(tailX,tailY)
                term.write(" ")
                tailX = tail.nextX
                tailY = tail.nextY
        else
                nExtraLength = nExtraLength - 1
        end

        -- Update the head
        local head = screen[xPos][yPos]
        local newXPos = xPos + xVel
        local newYPos = yPos + yVel
        if newXPos < 1 then
                newXPos = w
        elseif newXPos > w then
                newXPos = 1
        end
        if newYPos < 2 then
                newYPos = h
        elseif newYPos > h then
                newYPos = 2
        end

        local newHead = screen[newXPos][newYPos]
        term.setCursorPos(1,1);
        print( newHead.snake )
        if newHead.snake == true or newHead.wall == true then
                bRunning = false

        else
                if newHead.fruit == true then
                        nScore = nScore + 10
                        nExtraLength = nExtraLength + 1
                        addFruit()
                end
                xPos = newXPos
                yPos = newYPos
                head.nextX = newXPos
                head.nextY = newYPos
                screen[newXPos][newYPos] = { snake = true }

        end

        term.setCursorPos(xPos,yPos)
        term.setBackgroundColour( wormColour )
        term.write(" ")
        term.setBackgroundColour( colours.black )

        drawMenu()
end

-- Display the frontend
term.clear()
local function drawFrontend()
        term.setTextColour( headingColour )
        printCentred( math.floor(h/2) - 3, "APERTURE SNAKE(R)" )
        printCentred( math.floor(h/2) - 2, " SELECT DIFFICULTY " )
        printCentred( math.floor(h/2) - 1, "" )

        printCentred( math.floor(h/2) + 0, "            " )
        printCentred( math.floor(h/2) + 1, "            " )
        printCentred( math.floor(h/2) + 2, "            " )
        printCentred( math.floor(h/2) - 1 + nDifficulty, " [        ] " )

        term.setTextColour( textColour )
        printCentred( math.floor(h/2) + 0, "EASY" )
        printCentred( math.floor(h/2) + 1, "MEDIUM" )
        printCentred( math.floor(h/2) + 2, "HARD" )
        printCentred( math.floor(h/2) + 3, "" )

        term.setTextColour( colours.white )
end

drawMenu()
drawFrontend()
while true do
        local e,key = os.pullEvent( "key" )
        if key == keys.up or key == keys.w then
                -- Up
                if nDifficulty > 1 then
                        nDifficulty = nDifficulty - 1
                        drawMenu()
                        drawFrontend()
                end
        elseif key == keys.down or key == keys.s then
                -- Down
                if nDifficulty < 3 then
                        nDifficulty = nDifficulty + 1
                        drawMenu()
                        drawFrontend()
                end
        elseif key == keys.enter then
                -- Enter
                break
        end
end

local tSpeeds = { 5, 10, 25 }
nSpeed = tSpeeds[nDifficulty]
nInterval = 1 / nSpeed

-- Grow the snake to its intended size
term.clear()
drawMenu()
screen[tailX][tailY].snake = true
while nExtraLength > 0 do
        update()
end
addFruit()
addFruit()

-- Play the game
local timer = os.startTimer(0)
while bRunning do
        local event, p1, p2 = os.pullEvent()
        if event == "timer" and p1 == timer then
                timer = os.startTimer(nInterval)
                update( false )

        elseif event == "key" then
                local key = p1
                if key == keys.up or key == keys.w then
                        -- Up
                        if yVel == 0 then
                                pxVel,pyVel = 0,-1
                        end
                elseif key == keys.down or key == keys.s then
                        -- Down
                        if yVel == 0 then
                                pxVel,pyVel = 0,1
                        end
                elseif key == keys.left or key == keys.a then
                        -- Left
                        if xVel == 0 then
                                pxVel,pyVel = -1,0
                        end

                elseif key == keys.right or key == keys.d then
                        -- Right
                        if xVel == 0 then
                                pxVel,pyVel = 1,0
                        end

                end
        end
end

-- Display the gameover screen
term.setTextColour( headingColour )
printCentred( math.floor(h/2) - 2, "                   " )
printCentred( math.floor(h/2) - 1, " G A M E   O V E R " )

term.setTextColour( textColour )
printCentred( math.floor(h/2) + 0, "                 " )
printCentred( math.floor(h/2) + 1, " FINAL SCORE "..nScore.." " )
printCentred( math.floor(h/2) + 2, "                 " )
term.setTextColour( colours.white )

local timer = os.startTimer(2.5)
repeat
        local e,p = os.pullEvent()
        if e == "timer" and p == timer then
                term.setTextColour( textColour )
                printCentred( math.floor(h/2) + 2, " PRESS ANY KEY " )
                printCentred( math.floor(h/2) + 3, "               " )
                term.setTextColour( colours.white )
        end
until e == "char"

term.clear()
term.setCursorPos(1,1)