/**

        0

    1   ╬   3

        2

**/


var c = [       //  0   1   2   3
    '╝',        //  x   x               0b0011  3
    '║',        //  x       x           0b0101  5
    '╗',        //      x   x           0b0110  6
    '╣',        //  x   x   x           0b0111  7
    '╚',        //  x           x       0b1001  9
    '═',        //      x       x       0b1010  10
    '╩',        //  x   x       x       0b1011  11
    '╔',        //          x   x       0b1100  12
    '╠',        //  x       x   x       0b1101  13
    '╦',        //      x   x   x       0b1110  14
    '╬'         //  x   x   x   x       0b1111  15

                // RDLU
];

var e = [       // ENUM
    0b0011,
    0b0101,
    0b0110,
    0b0111,
    0b1001,
    0b1010,
    0b1011,
    0b1100,
    0b1101,
    0b1110,
    0b1111,
];

var boxgen_poll = function( u,l,d,r ){
    var sel = e, z = false;
    if( u != undefined )
    {
        u = !u == false; z=true;
        sel = sel.filter( (x)=> (!(x&0b0001) == !u)  );
    }
    if( l != undefined )
    {
        l = !l == false; z=true;
        sel = sel.filter( (x)=> (!(x&0b0010) == !l)  );
    }
    if( d != undefined )
    {
        d = !d == false; z=true;
        sel = sel.filter( (x)=> (!(x&0b0100) == !d)  );
    }
    if( r != undefined )
    {
        r = !r == false; z=true;
        sel = sel.filter( (x)=> (!(x&0b1000) == !r)  );
    }
    if( !z )
    {
        sel = Array(2000).fill(0).concat(e);
    }
    return sel[ Math.floor(Math.random()*sel.length) ];
}

var boxgen_plot = function( _x, _y ){

    var o = Array(_x*_y)
        .fill(0)
        .map( (x,i)=>i )
        .sort( (x)=>.5-Math.random() ),
    m = Array(_y)
        .fill(null)
        .map( (x)=>Array(_x).fill(null) )
    for( let z = 0, x, y; z<o.length; z++ )
    {
        y = Math.floor( o[z] / _x );
        x = o[z] % _x;
        m[y][x] = boxgen_poll(
            y>0  && m[y-1][x] && (m[y-1][x] & 0b0100),
            x>0  && m[y][x-1] && (m[y][x-1] & 0b1000),
            y<(_y-1) && m[y+1][x] && (m[y+1][x] & 0b0001),
            x<(_x-1) && m[y][x+1] && (m[y][x+1] & 0b0010), ) || 0;
    }
    return m;
}

var boxgen_draw = function( x, y )
{
    return boxgen_plot(x,y).map( (r)=>{
        return r.map(
            (x)=>c[ e.indexOf(x) ] || ' '
        ).join('');
    }).join('\n');
}