@mapbox/mapbox-gl-style-spec/deref.ts

a specification for mapbox gl styles

import refProperties from './util/ref_properties';

import type {LayerSpecification} from './types';

function deref(layer: LayerSpecification, parent: LayerSpecification): LayerSpecification {
    const result = {} as LayerSpecification;

    for (const k in layer) {
        if (k !== 'ref') {
            result[k] = layer[k];
        }
    }

    refProperties.forEach((k) => {
        if (k in parent) {
            result[k] = parent[k];
        }
    });

    return result;
}

/**
 * Given an array of layers, some of which may contain `ref` properties
 * whose value is the `id` of another property, return a new array where
 * such layers have been augmented with the 'type', 'source', etc. properties
 * from the parent layer, and the `ref` property has been removed.
 *
 * The input is not modified. The output may contain references to portions
 * of the input.
 *
 * @private
 * @param {Array<Layer>} layers
 * @returns {Array<Layer>}
 */
export default function derefLayers(layers: Array<LayerSpecification>): Array<LayerSpecification> {
    layers = layers.slice();

    const map: Record<string, LayerSpecification> = Object.create(null);
    for (let i = 0; i < layers.length; i++) {
        map[layers[i].id] = layers[i];
    }

    for (let i = 0; i < layers.length; i++) {
        if ('ref' in layers[i]) {
            layers[i] = deref(layers[i], map[(layers[i] as LayerSpecification & {ref: string}).ref]);
        }
    }

    return layers;
}