var black = -1; // computer is black
var red = 1; // visitor is red
var piece_toggled = false;
var my_turn = false;
var double_jump = false;
var comp_move = false;
var game_is_over = false;
var safe_from = safe_to = null;
var toggler = null;
var togglers = 0;
var g_wait = false;

var board;
Board(1,0,1,0,1,0,1,0,
      0,1,0,1,0,1,0,1,
      1,0,1,0,1,0,1,0,
      0,0,0,0,0,0,0,0,
      0,0,0,0,0,0,0,0,
      0,-1,0,-1,0,-1,0,-1,
      -1,0,-1,0,-1,0,-1,0,
      0,-1,0,-1,0,-1,0,-1);

// the higher the jump_priority, the more often the computer will take the jump over the safe move
var jump_priority = 10;


function init()
{
    message("Select an orange piece to move.");
    my_turn = true;
}

function Board()
{
    board = new Array();
    for (var i=0;i<8; i++) {
         board[i] = new Array();
         for (var j=0;j<8;j++)
            board[i][j] = Board.arguments[8*j+i];
    }
    board[-2] = new Array(); // prevents errors
    board[-1] = new Array();
    board[8] = new Array();
    board[9] = new Array();
}

function message(s)
{
    if (!game_is_over) {
        var elm = document.getElementById("message");
        elm.innerHTML = s;
    }
}

function moveable_space(i, j)
{
    // Calculates whether it is a gray (moveable) or black (non-moveable) space
    return ( ((i%2)+j)%2 == 0 );
}

function Coord(x, y)
{
    this.x = x;
    this.y = y;
}

function coord(x, y)
{
    c = new Coord(x,y);
    return c;
}

function didClick(i, j)
{
    if (!g_wait)
    {
        if (my_turn)
        {
            if ( integ(board[i][j]) == 1 ) {
                toggle(i,j);
            }
            else if (piece_toggled) {
                g_wait = true;
                move( selected,coord(i,j) );
                setTimeout("stopWait()", 2000);
            }
            else {
                message("Click on your orange piece, then click where you want to move it.");
            }
        }
        else
        {
             message("Please wait.");
        }
    }
    else
    {
        message("Please wait.");
    }
}

function stopWait()
{
    g_wait = false;
}

function toggle(x, y)
{
    if (my_turn) {
         if (piece_toggled)
            draw(selected.x,selected.y,"you1"+((board[selected.x][selected.y]==1.1)?"k":"")+".gif");
         if (piece_toggled && (selected.x == x) && (selected.y == y)) {
            piece_toggled = false;
            if (double_jump) { my_turn = double_jump = false; computer(); }
         } else {
            piece_toggled = true;
            draw(x,y,"you2"+((board[x][y]==1.1)?"k":"")+".gif");
         }
         selected = coord(x,y);
    } else {
         if ((piece_toggled) && (integ(board[selected_c.x][selected_c.y])==-1))
            draw(selected_c.x,selected_c.y,"me1"+((board[selected_c.x][selected_c.y]==-1.1)?"k":"")+".gif");
         if (piece_toggled && (selected_c.x == x) && (selected_c.y == y)) {
            piece_toggled = false;
         } else {
            piece_toggled = true;
            draw(x,y,"me2"+((board[x][y]==-1.1)?"k":"")+".gif");
         }
         selected_c = coord(x,y);
    }
}

function draw(x, y, name)
{
    document.images["space"+x+""+y].src = name;
}

function integ(num)
{
    if (num != null)
         return Math.round(num);
    else
         return null;
}

function abs(num)
{
    return Math.abs(num);
}

function sign(num)
{
    if (num < 0) return -1;
    else return 1;
}

function concatenate(arr1, arr2)
{
    // function tacks the second array onto the end of the first and returns result
    for(var i=0;i<arr2.length;i++)
         arr1[arr1.length+i] = arr2[i];
    return arr1;
}

function legal_move(from, to)
{
    if ((to.x < 0) || (to.y < 0) || (to.x > 7) || (to.y > 7)) return false;
    piece = board[from.x][from.y];
    distance = coord(to.x-from.x,to.y-from.y);
    if ((distance.x == 0) || (distance.y == 0)) {
         message("Move diagonally only.");
         return false;
    }
    if (abs(distance.x) != abs(distance.y)) {
         message("This is an invalid move.");
         return false;
    }
    if (abs(distance.x) > 2) {
         message("This is an invalid move.");
         return false;
    }
    if ((abs(distance.x) == 1) && double_jump) {
         return false;
    }
    if ((board[to.x][to.y] != 0) || (piece == 0)) {
         return false;
    }
    if ((abs(distance.x) == 2)
    && (integ(piece) != -integ(board[from.x+sign(distance.x)][from.y+sign(distance.y)]))) {
         return false;
    }
    if ((integ(piece) == piece) && (sign(piece) != sign(distance.y))) {
         return false;
    }
    
    return true;
}

function move(from, to)
{
    my_turn = true;
    if (legal_move(from,to)) {
         piece = board[from.x][from.y];
         distance = coord(to.x-from.x,to.y-from.y);
         if ((abs(distance.x) == 1) && (board[to.x][to.y] == 0)) {
            swap(from,to);
         } else if ((abs(distance.x) == 2)
         && (integ(piece) != integ(board[from.x+sign(distance.x)][from.y+sign(distance.y)]))) {
            double_jump = false;
            swap(from,to);
            remove(from.x+sign(distance.x),from.y+sign(distance.y));
            if ((legal_move(to,coord(to.x+2,to.y+2)))
            || (legal_move(to,coord(to.x+2,to.y-2)))
            || (legal_move(to,coord(to.x-2,to.y-2)))
            || (legal_move(to,coord(to.x-2,to.y+2)))) {
             double_jump = true;
             message("Complete the double jump or click on your piece to stay still.");
            }
         }
         if ((board[to.x][to.y] == 1) && (to.y == 7)) king_me(to.x,to.y);
         selected = to;
         if (game_over() && !double_jump) {
            setTimeout("toggle("+to.x+","+to.y+");my_turn = double_jump = false;computer();",1000);
         }
    }
    return true;
}

function king_me(x, y)
{
    if (board[x][y] == 1) {
         board[x][y] = 1.1; // king you
         draw(x,y,"you2k.gif");
    } else if (board[x][y] == -1) {
         board[x][y] = -1.1; // king me
         draw(x,y,"me2k.gif");
    }
}

function swap(from, to)
{
    if (my_turn || comp_move) {
         dummy_src = document.images["space"+to.x+""+to.y].src;
         document.images["space"+to.x+""+to.y].src = document.images["space"+from.x+""+from.y].src;
         document.images["space"+from.x+""+from.y].src = dummy_src;
    }
    dummy_num = board[from.x][from.y];
    board[from.x][from.y] = board[to.x][to.y];
    board[to.x][to.y] = dummy_num;
}

function remove(x, y)
{
    if (my_turn || comp_move)
         draw(x,y,"gray.gif");
    board[x][y] = 0;
}

function Result(val)
{
    this.high = val;
    this.dir = new Array();
}

function move_comp(from, to)
{
    toggle(from.x,from.y);
    comp_move = true;
    swap(from,to);
    if (abs(from.x-to.x) == 2) {
         remove(from.x+sign(to.x-from.x),from.y+sign(to.y-from.y));
    }
    if ((board[to.x][to.y] == -1) && (to.y == 0)) king_me(to.x,to.y);
    setTimeout("selected_c = coord("+to.x+","+to.y+");piece_toggled = true;",900);
    setTimeout("bak=my_turn;my_turn=false;toggle("+to.x+","+to.y+");my_turn=bak;",1000);
    if (game_over()) {
         setTimeout("comp_move = false;my_turn = true;togglers=0;",600);
         message("Make a move.");
    }
    return true;
}

function game_over()
{
    // make sure game is not over (return false if game is over)
    comp = you = false;
    for(var i=0;i<8;i++) {
         for(var j=0;j<8;j++) {
            if(integ(board[i][j]) == -1) comp = true;
            if(integ(board[i][j]) == 1) you = true;
         }
    }
    if (!comp) message("You won the game, congratulations!");
    if (!you) message("You lose. Game over.");
    game_is_over = (!comp || !you)

    return (!game_is_over);
}

function computer()
{
    // step one - prevent any jumps
    for (var j=0;j<8;j++) {
         for(var i=0;i<8;i++) {
            if (integ(board[i][j]) == 1) {
             if ((legal_move(coord(i,j),coord(i+2,j+2))) && (prevent(coord(i+2,j+2),coord(i+1,j+1)))) {
              return true;
             } if ((legal_move(coord(i,j),coord(i-2,j+2))) && (prevent(coord(i-2,j+2),coord(i-1,j+1)))) {
              return true;
             }
            } if (board[i][j] == 1.1) {
             if ((legal_move(coord(i,j),coord(i-2,j-2))) && (prevent(coord(i-2,j-2),coord(i-1,j-1)))) {
              return true;
             } if ((legal_move(coord(i,j),coord(i+2,j-2))) && (prevent(coord(i+2,j-2),coord(i+1,j-1)))) {
              return true;
             }
            }
         }
    }

    // step two - if step one not taken, look for jumps
    for (var j=7;j>=0;j--) {
         for(var i=0;i<8;i++) {
            if (jump(i,j))
             return true;
         }
    }
    safe_from = null;

    // step three - if step two not taken, look for safe single space moves
    for (var j=0;j<8;j++) {
         for(var i=0;i<8;i++) {
            if (single(i,j))
             return true;
         }
    }

    // if no safe moves, just take whatever you can get
    if (safe_from != null) {
         move_comp(safe_from,safe_to);
    } else {
         message("You have won!");
         game_is_over = true;
    }
    safe_from = safe_to = null;
    return false;
}

function jump(i, j)
{
    if (board[i][j] == -1.1) {  
         if (legal_move(coord(i,j),coord(i+2,j+2))) {
            move_comp(coord(i,j),coord(i+2,j+2));
            setTimeout("jump("+(i+2)+","+(j+2)+");",500);
            return true;
         } if (legal_move(coord(i,j),coord(i-2,j+2))) {
            move_comp(coord(i,j),coord(i-2,j+2));
            setTimeout("jump("+(i-2)+","+(j+2)+");",500);
            return true;
         }
    } if (integ(board[i][j]) == -1) {
         if (legal_move(coord(i,j),coord(i-2,j-2))) {
            move_comp(coord(i,j),coord(i-2,j-2));
            setTimeout("jump("+(i-2)+","+(j-2)+");",500);
            return true;
         } if (legal_move(coord(i,j),coord(i+2,j-2))) {
            move_comp(coord(i,j),coord(i+2,j-2));
            setTimeout("jump("+(i+2)+","+(j-2)+");",500);
            return true;
         }
    }
    return false;
}

function single(i, j)
{
    if (board[i][j] == -1.1) {
         if (legal_move(coord(i,j),coord(i+1,j+1))) {
            safe_from = coord(i,j);
            safe_to = coord(i+1,j+1);
            if (wise(coord(i,j),coord(i+1,j+1))) {
             move_comp(coord(i,j),coord(i+1,j+1));
             return true;
            }
         } if (legal_move(coord(i,j),coord(i-1,j+1))) {
            safe_from = coord(i,j);
            safe_to = coord(i-1,j+1);
            if (wise(coord(i,j),coord(i-1,j+1))) {
             move_comp(coord(i,j),coord(i-1,j+1));
             return true;
            }
         }
    } if (integ(board[i][j]) == -1) {
         if (legal_move(coord(i,j),coord(i+1,j-1))) {
            safe_from = coord(i,j);
            safe_to = coord(i+1,j-1);
            if (wise(coord(i,j),coord(i+1,j-1))) {
             move_comp(coord(i,j),coord(i+1,j-1));
             return true;
            }
         } if (legal_move(coord(i,j),coord(i-1,j-1))) {
            safe_from = coord(i,j);
            safe_to = coord(i-1,j-1);
            if (wise(coord(i,j),coord(i-1,j-1))) {
             move_comp(coord(i,j),coord(i-1,j-1));
             return true;
            }
         }
    }
    return false;
}

function possibilities(x, y)
{
    if (!jump(x,y))
         if (!single(x,y))
            return true;
         else
            return false;
    else
         return false;
}

function prevent(end, s)
{
    i = end.x;
    j = end.y;
    if (!possibilities(s.x,s.y))
         return true;
    else if ((integ(board[i-1][j+1])==-1) && (legal_move(coord(i-1,j+1),coord(i,j)))) {
            return move_comp(coord(i-1,j+1),coord(i,j));
    } else if ((integ(board[i+1][j+1])==-1) && (legal_move(coord(i+1,j+1),coord(i,j)))) {
            return move_comp(coord(i+1,j+1),coord(i,j));
    } else if ((board[i-1][j-1]==-1.1) && (legal_move(coord(i-1,j-1),coord(i,j)))) {
            return move_comp(coord(i-1,j-1),coord(i,j));
    } else if ((board[i+1][j-1]==-1.1) && (legal_move(coord(i+1,j-1),coord(i,j)))) {
            return move_comp(coord(i+1,j-1),coord(i,j));
    } else {
         return false;
    }
}

function wise(from, to)
{
    i = to.x;
    j = to.y;
    n = (j>0);
    s = (j<7);
    e = (i<7);
    w = (i>0);
    if (n&&e) ne = board[i+1][j-1]; else ne = null;
    if (n&&w) nw = board[i-1][j-1]; else nw = null;
    if (s&&e) se = board[i+1][j+1]; else se = null;
    if (s&&w) sw = board[i-1][j+1]; else sw = null;
    eval(((j-from.y != 1)?"s":"n")+((i-from.x != 1)?"e":"w")+"=0;");
    if ((sw==0) && (integ(ne)==1)) return false;
    if ((se==0) && (integ(nw)==1)) return false;
    if ((nw==0) && (se==1.1)) return false;
    if ((ne==0) && (sw==1.1)) return false;
    return true;
}