MapComplete/src/Logic/Actors/InitialMapPositioning.ts

import { ImmutableStore, Store, UIEventSource } from "../UIEventSource"
import LayoutConfig from "../../Models/ThemeConfig/LayoutConfig"
import { LocalStorageSource } from "../Web/LocalStorageSource"
import { QueryParameters } from "../Web/QueryParameters"
import Hash from "../Web/Hash"
import OsmObjectDownloader from "../Osm/OsmObjectDownloader"
import { OsmObject } from "../Osm/OsmObject"
import Constants from "../../Models/Constants"

/**
 * This actor is responsible to set the map location.
 * It will attempt to
 * - Set the map to the position of the selected element
 * - Set the map to the position as passed in by the query parameters (if available)
 * - Set the map to the position remembered in LocalStorage (if available)
 * - Set the map to the layout default
 *
 * Additionally, it will save the map location to local storage
 */
export default class InitialMapPositioning {
    public zoom: UIEventSource<number>
    public location: UIEventSource<{ lon: number; lat: number }>
    public useTerrain: Store<boolean>

    constructor(layoutToUse: LayoutConfig) {
        function localStorageSynced(
            key: string,
            deflt: number,
            docs: string
        ): UIEventSource<number> {
            const localStorage = LocalStorageSource.Get(key)
            const previousValue = localStorage.data
            const src = UIEventSource.asFloat(
                QueryParameters.GetQueryParameter(key, "" + deflt, docs).syncWith(localStorage)
            )

            if (src.data === deflt) {
                const prev = Number(previousValue)
                if (!isNaN(prev)) {
                    src.setData(prev)
                }
            }

            return src
        }

        const initialHash = Hash.hash.data

        // -- Location control initialization
        this.zoom = localStorageSynced(
            "z",
            layoutToUse?.startZoom ?? 1,
            "The initial/current zoom level"
        )
        const lat = localStorageSynced(
            "lat",
            layoutToUse?.startLat ?? 0,
            "The initial/current latitude"
        )
        const lon = localStorageSynced(
            "lon",
            layoutToUse?.startLon ?? 0,
            "The initial/current longitude of the app"
        )

        this.location = new UIEventSource({ lon: lon.data, lat: lat.data })
        // Note: this syncs only in one direction
        this.location.addCallbackD((loc) => {
            lat.setData(loc.lat)
            lon.setData(loc.lon)
        })
        this.useTerrain = new ImmutableStore<boolean>(layoutToUse.enableTerrain)

        if (initialHash?.match(/^(node|way|relation)\/[0-9]+$/)) {
            const [type, id] = initialHash.split("/")
            OsmObjectDownloader.RawDownloadObjectAsync(type, Number(id), Constants.osmAuthConfig.url + "/").then(osmObject => {
                if (osmObject === "deleted") {
                    return
                }
                const targetLayer = layoutToUse.getMatchingLayer(osmObject.tags)
                this.zoom.setData(Math.max(this.zoom.data, targetLayer.minzoom))
                const [lat, lon] = osmObject.centerpoint()
                this.location.setData({ lon, lat })
            })
        }

    }
}