'use strict';

// Transforms the coordinates of each feature in the given tile from
// mercator-projected space into (extent x extent) tile space.
function transformTile(tile, extent) {
    if (tile.transformed) return tile;

    var z2 = tile.z2,
        tx = tile.x,
        ty = tile.y,
        i, j, k;

    for (i = 0; i < tile.features.length; i++) {
        var feature = tile.features[i],
            geom = feature.geometry,
            type = feature.type;

        if (type === 1) {
            for (j = 0; j < geom.length; j++) geom[j] = transformPoint(geom[j], extent, z2, tx, ty);

        } else {
            for (j = 0; j < geom.length; j++) {
                var ring = geom[j];
                for (k = 0; k < ring.length; k++) ring[k] = transformPoint(ring[k], extent, z2, tx, ty);
            }
        }
    }

    tile.transformed = true;

    return tile;
}

function transformPoint(p, extent, z2, tx, ty) {
    var x = Math.round(extent * (p[0] * z2 - tx)),
        y = Math.round(extent * (p[1] * z2 - ty));
    return [x, y];
}
