MapComplete/src/Logic/State/GeoLocationState.ts

import { Store, UIEventSource } from "../UIEventSource"
import { LocalStorageSource } from "../Web/LocalStorageSource"
import { QueryParameters } from "../Web/QueryParameters"

export type GeolocationPermissionState = "prompt" | "requested" | "granted" | "denied"

export interface GeoLocationPointProperties extends GeolocationCoordinates {
    id: "gps"
    "user:location": "yes"
    date: string
}

/**
 * An abstract representation of the current state of the geolocation.
 */
export class GeoLocationState {
    /**
     * What do we know about the current state of having access to the GPS?
     * If 'prompt', then we just started and didn't request access yet
     * 'requested' means the user tapped the 'locate me' button at least once
     * 'granted' means that it is granted
     * 'denied' means that we don't have access
     */
    public readonly permission: UIEventSource<GeolocationPermissionState> = new UIEventSource(
        "prompt"
    )

    /**
     * If an error occurs with a code indicating "gps unavailable", this will be set to "false".
     * This is about the physical availability of the GPS-signal; this might e.g. become false if the user is in a tunnel
     */
    private readonly _gpsAvailable: UIEventSource<boolean> = new UIEventSource<boolean>(true)
    public readonly gpsAvailable: Store<boolean> = this._gpsAvailable

    /**
     * Important to determine e.g. if we move automatically on fix or not
     */
    public readonly requestMoment: UIEventSource<Date | undefined> = new UIEventSource(undefined)
    /**
     * If true: the map will center (and re-center) to the current GPS-location
     */
    public readonly allowMoving: UIEventSource<boolean> = new UIEventSource<boolean>(true)

    /**
     * The latest GeoLocationCoordinates, as given by the WebAPI
     */
    public readonly currentGPSLocation: UIEventSource<GeolocationCoordinates | undefined> =
        new UIEventSource<GeolocationCoordinates | undefined>(undefined)

    /**
     * A small flag on localstorage. If the user previously granted the geolocation, it will be set.
     * On firefox, the permissions api is broken (probably fingerprint resistiance) and "granted + don't ask again" doesn't stick between sessions.
     *
     * Instead, we set this flag. If this flag is set upon loading the page, we start geolocating immediately.
     * If the user denies the geolocation this time, we unset this flag
     * @private
     */
    private readonly _previousLocationGrant: UIEventSource<boolean> = LocalStorageSource.GetParsed<boolean>("geolocation-permissions", false)

    /**
     * Used to detect a permission retraction
     */
    private readonly _grantedThisSession: UIEventSource<boolean> = new UIEventSource<boolean>(false)

    constructor() {
        const self = this

        this.permission.addCallbackAndRunD(async (state) => {
            if (state === "granted") {
                self._previousLocationGrant.setData(true)
                self._grantedThisSession.setData(true)
            }
            if (state === "prompt" && self._grantedThisSession.data) {
                // This is _really_ weird: we had a grant earlier, but it's 'prompt' now?
                // This means that the rights have been revoked again!
                self._previousLocationGrant.setData(false)
                self.permission.setData("denied")
                self.currentGPSLocation.setData(undefined)
                console.warn("Detected a downgrade in permissions!")
            }
            if (state === "denied") {
                self._previousLocationGrant.setData(false)
            }
        })
        console.log("Previous location grant:", this._previousLocationGrant.data)
        if (this._previousLocationGrant.data) {
            // A previous visit successfully granted permission. Chance is high that we are allowed to use it again!

            // We set the flag to false again. If the user only wanted to share their location once, we are not gonna keep bothering them
            this._previousLocationGrant.setData(false)
            console.log("Requesting access to GPS as this was previously granted")
            const latLonGivenViaUrl =
                QueryParameters.wasInitialized("lat") || QueryParameters.wasInitialized("lon")
            if (!latLonGivenViaUrl) {
                this.requestMoment.setData(new Date())
            }
            this.requestPermission()
        }
    }

    /**
     * Requests the user to allow access to their position.
     * When granted, will be written to the 'geolocationState'.
     * This class will start watching
     */
    public requestPermission() {
        this.requestPermissionAsync()
    }

    public static isSafari(): boolean {
        return navigator.permissions === undefined && navigator.geolocation !== undefined
    }

    /**
     * Requests the user to allow access to their position.
     * When granted, will be written to the 'geolocationState'.
     * This class will start watching
     */
    public async requestPermissionAsync() {
        if (typeof navigator === "undefined") {
            // Not compatible with this browser
            this.permission.setData("denied")
            return
        }
        if (this.permission.data !== "prompt" && this.permission.data !== "requested") {
            // If the user denies the first prompt, revokes the deny and then tries again, we have to run the flow as well
            // Hence that we continue the flow if it is "requested"
            return
        }

        if (GeoLocationState.isSafari()) {
            /*
             This is probably safari
             Safari does not support the 'permissions'-API for geolocation,
             so we just start watching right away
            */

            this.permission.setData("requested")
            this.startWatching()
            return
        }

        this.permission.setData("requested")
        try {
            const status = await navigator?.permissions?.query({ name: "geolocation" })
            const self = this
            console.log("Got geolocation state", status.state)
            if (status.state === "granted" || status.state === "denied") {
                self.permission.setData(status.state)
                self.startWatching()
                return
            }
            status.addEventListener("change", () => {
                self.permission.setData(status.state)
            })
            // The code above might have reset it to 'prompt', but we _did_ request permission!
            this.permission.setData("requested")
            // We _must_ call 'startWatching', as that is the actual trigger for the popup...
            self.startWatching()
        } catch (e) {
            console.error("Could not get permission:", e)
        }
    }

    /**
     * Installs the listener for updates
     * @private
     */
    private async startWatching() {
        const self = this
        navigator.geolocation.watchPosition(
            function (position) {
                self._gpsAvailable.set(true)
                self.currentGPSLocation.setData(position.coords)
                self._previousLocationGrant.setData(true)
            },
            function (e) {
                if(e.code === 2 || e.code === 3){
                    self._gpsAvailable.set(false)
                    return
                }
                self._gpsAvailable.set(true) // We go back to the default assumption that the location is physically available
                if(e.code === 1) {
                    self.permission.set("denied")
                    self._grantedThisSession.setData(false)
                    return
                }
                console.warn("Could not get location with navigator.geolocation due to", e)
            },
            {
                enableHighAccuracy: true,
            }
        )
    }
}