' ================================
' SIMPLE SNAKE GAME - Liberty BASIC
' ================================

' Graphics constants
global cellSize, gridWidth, gridHeight
global snakeLength, foodX, foodY, gamespeed
global gridOffsetY, score

cellSize = 20
gridWidth = 20
gridHeight = 20
gridOffsetY = 20
foodX = 0
foodY = 0
gamespeed = 333
score = 0

' Movement directions
global dirX, dirY
dirX = 1 : dirY = 0   ' start moving right

' Snake body array
dim snakeX(400)
dim snakeY(400)
snakeLength = 5

' Initialize snake position in center
for i = 1 to snakeLength
    snakeX(i) = 10 - i
    snakeY(i) = 10
next

' Create first food position
call newFood

' Open graphics window
WindowWidth = cellSize * gridWidth + 10
WindowHeight = cellSize * gridHeight + 60
open "SNAKE GAME - WASD to Move" for graphics_nsb_nf as #g
#g "trapclose [quit]"
#g "down; fill white; flush"

' Force focus
#g "setfocus"

' Enable character input
#g "when characterInput [keypress]"

' Start game timer
[startGame]
timer gamespeed, [gameTick]

wait

[gameTick]

    ' Move snake segments
    for i = snakeLength to 2 step -1
        snakeX(i) = snakeX(i-1)
        snakeY(i) = snakeY(i-1)
    next

    ' Head moves in current direction
    snakeX(1) = snakeX(1) + dirX
    snakeY(1) = snakeY(1) + dirY

    ' Wall collision ends game
    if snakeX(1) < 0 or snakeX(1) >= gridWidth _
        or snakeY(1) < 0 or snakeY(1) >= gridHeight then
        call gameOver
        wait
    end if

    ' Check self collision
    for i = 2 to snakeLength
        if snakeX(1) = snakeX(i) and snakeY(1) = snakeY(i) then
            call gameOver
            wait
        end if
    next

    ' Check food collision
    if snakeX(1) = foodX and snakeY(1) = foodY then
        snakeLength = snakeLength + 1
        score = score + 10

        ' Initialize new tail segment at same spot as previous tail
        snakeX(snakeLength) = snakeX(snakeLength - 1)
        snakeY(snakeLength) = snakeY(snakeLength - 1)

        ' Speed up the game
        timer 0
        gamespeed = max(gamespeed - 5, 150)
        timer gamespeed, [gameTick]

        call newFood
    end if

    call redraw
wait

[keypress]
    key$ = Inkey$
    key$ = lower$(key$)
    select case key$
        case "w"
            if dirY <> 1 then dirX = 0 : dirY = -1
        case "a"
            if dirX <> 1 then dirX = -1 : dirY = 0
        case "s"
            if dirY <> -1 then dirX = 0 : dirY = 1
        case "d"
            if dirX <> -1 then dirX = 1 : dirY = 0
        case chr$(27)    ' ESC
            call gameOver
            wait
    end select
wait

[quit]
  close #g
  end

sub redraw
    ' Clear screen
    #g "cls"

    ' Draw top banner background
    #g "color lightgray"
    #g, "backcolor lightgray"
    #g "place 0 0"
    #g "boxfilled "; (gridWidth * cellSize); " "; gridOffsetY

    ' Draw banner text
    #g "color black"
    #g "font Courier_New 10"
    #g "place 5 15"
    #g "\"; "Score: "; score; "        Speed: "; gamespeed; "ms"

    ' Draw food
    call drawBlock foodX, foodY, "red"

    ' Draw snake
    for i = 1 to snakeLength
        call drawBlock snakeX(i), snakeY(i), "green"
    next

    #g "flush"
end sub

sub drawBlock x, y, color$
    x1 = x * cellSize
    y1 = gridOffsetY + y * cellSize
    x2 = x1 + cellSize
    y2 = y1 + cellSize

    #g "color "; color$
    #g, "backcolor "; color$
    #g "place "; x1; " "; y1
    #g "boxfilled "; x2; " "; y2
end sub

sub newFood
    overlap = 1
    while overlap = 1
        foodX = int(rnd(0) * gridWidth)
        foodY = int(rnd(0) * gridHeight)
        overlap = 0
        for i = 1 to snakeLength
            if foodX = snakeX(i) and foodY = snakeY(i) then
                overlap = 1
                exit for
            end if
        next
    wend
end sub

sub gameOver
    timer 0
    #g "cls"
    #g "color black"
    #g, "backcolor white"
    #g "place 110 200"
    #g "font Courier_New 24 bold"
    #g "\"; "GAME OVER!"
    #g "place 110 250"
    #g "font Courier_New 16"
    #g "\"; "Score: "; score
    #g "flush"
end sub