# Main Command: Go
# Knight's Tour by Guy Walker
# www.logoarts.co.uk

To New
  # set default screen, pen and turtle
  ResetAll SetScreenSize [400 400] HideTurtle
  SetSC Black SetPC Green SetPS 1 PenUp
End

To Init
  Make "Moves [1 2 2 1 -1 -2 -2 -1 1 2]
  Make "Free [ ] Repeat 64 [Make "Free LPut 0 :Free]
End

To Title
  # write header
  SetPC White
  SetPos [-190 180] Label [Knight's Tour]
End

To Gridd :Xc :Yc
  # return X Y screen position
  Make "X (38*:Xc) - 132
  Make "Y (38*:Yc) - 132
  Output List :X :Y
End

To DrawBoard
  SetPC Brown Square 334 SetPC [96 57 19] Fill
  SetPC Brown Square 310 SetPC [199 178 153] Fill
  SetPC Brown Repeat 4 [
  SetH (Repcount*90)-45 Forward 220 PenDown Forward 15 PenUp Home]
  # label grid numbers 
  SetPC [64 64 64] Repeat 8 [
    SetPos Gridd RepCount-1 Minus 1.25
    Label Character 96+RepCount
    SetPos Gridd 8.15 RepCount-1
    Label RepCount]
  # draw 64 alt colored squares 
  For (List "N 0 7) [
    For (List "M 0 7) [
    SetPos Gridd :M :N 
    SetPC Brown Square 32 
    If Even (:M+:N) [SetPC [117 76 36] ] [SetPC [198 156 109] ] Fill ] ]
End

To Empty :X :Y
  # Output True if Cell is empty and within board 
  If And And And (:X>-1) (:X<8) (:Y>-1) (:Y<8) [
    If ( 0=Item (1+:X+8*:Y) :Free) [Output "True] ]
  Output "False
End

To Step :Xc :Yc :Count
  # move to next square and update 'free' list 
  SetPos Gridd :Xc :Yc PenUp
  If :Count=0 [SetPC Green Square 32]
  SetPC Black Label :Count
  Make "Free Replace :Free (1+:Xc+8*:Yc) 1
  Write (Word :Xc :Yc "\ )
  Make "Poss NextPos :Xc :Yc
  # choose a random next move 
  If 0<Count :Poss [
    SetPC Red PenDown 
    Make "NextPos (Pick :Poss) Wait 20 
    Step First :NextPos Last :NextPos :Count+1] 
End

To NextPos :Xc :Yc
  # return list of possible next moves 
  Make "Poss [ ]
  Repeat 8 [
    Make "Xn :Xc + Item RepCount :Moves
    Make "Yn :Yc + Item RepCount+2 :Moves
    If Empty :Xn :Yn [
    Make "Poss LPut List :Xn :Yn :Poss] ] 
  Output :Poss
End

To Even :Num
  # Output True if Num even, else output False 
  If (Mod :Num 2) = 0 [Output "True] [Output "False]
End

To Square :Side
  # square (side x side) drawn from centre (tp)
  Back :Side/2 Right 90 Back :Side/2 PenDown
  Repeat 4 [
    Forward :Side Left 90]
  PenUp Forward :Side/2 Left 90 Forward :Side/2     # return to centre
End

To Go
  New Init Title
  Home DrawBoard Wait 40 
  SetPW 2 Step Random 8 Random 8 0
  SetPC Yellow Square 32
End

to nextpos2 :xc :yc
  # return best list of possible next moves 
Make "Poss [ ] Make "High 8
Repeat 8 [
Make "Xn :Xc + Item RepCount :Moves
Make "Yn :Yc + Item RepCount+2 :Moves
If Empty :Xn :Yn [

  Make "PossNo 0
  Repeat 8 [
  Make "Xt :Xn + Item RepCount :Moves
  Make "Yt :Yn + Item RepCount+2 :Moves
  If Empty :Xt :Yt [
  Make "PossNo :PossNo + 1] ] 

  If :PossNo < :High [ 
    Make "Poss [ ] Make "High :PossNo 
    Make "Poss LPut List :Xn :Yn :Poss ] [
  If :PossNo = :High [ Make "Poss LPut List :Xn :Yn :Poss ] ] ] ] 
Output :Poss
end

to gox
  New DrawBoard Title Wait 40 SetPW 2
Make "Tour [00 21 40 61 73 65 77 56 75 63 71 50 31 10 02 14 06 27 46 67 55 76 64 52 33 54 35 47 26 07 15 03 11 30 51 70 62 74 66 45 57 36 17 05 13 01 20 41 60 72 53 32 24 43 22 34 42 23 44 25 37 16 04 12 00]
Repeat Count :Tour [
  Make "Cell Item RepCount :Tour
  SetPC Red SetPos Gridd First :Cell Last :Cell
  SetPC Black cLabel RepCount-1 PenDown Wait 20]
  # return to first cell and border in yellow 
SetPC Red Make "Cell Item 1 :Tour 
SetPos Gridd First :Cell Last :Cell
SetPC Yellow PenUp Square 32
end