export const Region = 
{
    I(inX, inY, inZ)
    {
        return inX + inY*16 + inZ*256;
    },
    XYZ(inI)
    {
        let zWhole = Math.floor(inI / 256);
        let zPart = inI % 256;
        let yWhole = Math.floor(zPart / 16);
        let yPart = zPart % 16;
        return [yPart, yWhole, zWhole];
    },
    Surface(inVoxels)
    {
        function Vert(a)
        {
            var vertPointer = voxPointVert[a]
            if(vertPointer === undefined)
            {
                let vert = Region.XYZ(a);
                vertPointer = vertices.length;
                voxPointVert[a] = vertPointer;
                vertPointNeighbors.push([]);
                vertices.push(vert);
            }
            return vertPointer;
        }
        function Face(a, b, c, d)
        {
            let p1 = Vert(a);
            let p2 = Vert(b);
            let p3 = Vert(c);
            let p4 = Vert(d);

            triPointVert.push(p1, p2, p3, p3, p4, p1);

            vertPointNeighbors[p1].push(p2);
            vertPointNeighbors[p2].push(p1);

            vertPointNeighbors[p2].push(p3);
            vertPointNeighbors[p3].push(p2);

            vertPointNeighbors[p3].push(p4);
            vertPointNeighbors[p4].push(p3);

            vertPointNeighbors[p4].push(p1);
            vertPointNeighbors[p1].push(p2);
        }

        var vertices = [];
        var voxPointVert = [];
        var triPointVert = [];
        var vertPointNeighbors = [];

        var i;
        var BA, BU, BC, BR,  TA, TU, TC, TR,  CL, CD, CB;
        for(i=0; i<inVoxels.length; i++)
        {
            if(inVoxels[i])
            {
                let [x, y, z] = Region.XYZ(i);

                console.log("at", x, y, z);

                // bottom: at, "up", corner, right
                BA = i;
                BU = Region.I(x,   y+1, z  );
                BC = Region.I(x+1, y+1, z  );
                BR = Region.I(x+1, y,   z  );

                // top: at, "up" corner, right
                TA = Region.I(x,   y,   z+1);
                TU = Region.I(x,   y+1, z+1);
                TC = Region.I(x+1, y+1, z+1);
                TR = Region.I(x+1, y,   z+1);

                // check: left, "down", below
                CL = Region.I(x-1, y,   z  );
                CD = Region.I(x,   y-1, z  );
                CB = Region.I(x,   y,   z-1);

                if(!inVoxels[BU]){ Face(BU, BC, TC, TU); }
                if(!inVoxels[BR]){ Face(BC, BR, TR, TC); }
                if(!inVoxels[TA]){ Face(TA, TU, TC, TR); }

                if(!inVoxels[CL]){ Face(BA, BU, TU, TA); }
                if(!inVoxels[CD]){ Face(BR, BA, TA, TR); }
                if(!inVoxels[CB]){ Face(BA, BU, BC, BR); }
            }
        }

        return {vert:new Float32Array(vertices.flat()), voxPointVert, triPointVert, vertPointNeighbors};
    }
};