import { FeatureSource } from "../FeatureSource"
import { Feature } from "geojson"
import { Store, UIEventSource } from "../../UIEventSource"

export class IfVisibleFeatureSource<T extends Feature> implements FeatureSource<T> {

    private readonly _features: UIEventSource<T[]> = new UIEventSource<T[]>([])
    public readonly features: Store<T[]> = this._features

    constructor(upstream: FeatureSource<T>, visible: Store<boolean>) {

        let dirty = false
        upstream.features.addCallbackAndRun(features => {
            if (!visible.data) {
                dirty = true
                this._features.set([])
                return
            }
            this._features.set(features)
            dirty = false
        })

        visible.addCallbackAndRun(isVisible => {
            if (isVisible && dirty) {
                this._features.set(upstream.features.data)
                dirty = false
            }
            if (!visible) {
                this._features.set([])
            }

        })


    }


}