mapcomplete/Logic/FeatureSource/FeatureSourceMerger.ts

import FeatureSource from "./FeatureSource";
import {UIEventSource} from "../UIEventSource";

export default class FeatureSourceMerger implements FeatureSource {

    public features: UIEventSource<{ feature: any; freshness: Date }[]> = new UIEventSource<{feature: any; freshness: Date}[]>([]);
    private readonly _sources: FeatureSource[];

    constructor(sources: FeatureSource[]) {
        this._sources = sources;
        const self = this;
        for (const source of sources) {
            source.features.addCallback(() => self.Update());
        }
    }

    private Update() {
        let all = {}; // Mapping 'id' -> {feature, freshness}
        for (const source of this._sources) {
            if(source?.features?.data === undefined){
                continue;
            }
            for (const f of source.features.data) {
                const id = f.feature.properties.id+f.feature.geometry.type+f.feature._matching_layer_id;
                const oldV = all[id];
                if(oldV === undefined){
                    all[id] = f;
                }else{
                    if(oldV.freshness < f.freshness){
                        all[id]=f;
                    }
                }
            }
        }
        const newList = [];
        for (const id in all) {
            newList.push(all[id]);
        }
        this.features.setData(newList);
    }


}