angular_software_update.service.ts

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

import { interval } from 'rxjs';
import { MatSnackBar } from '@angular/material';
import { environment } from '@environments/environment';

@Injectable({ providedIn: 'root' })
export class ThisSoftwareUpdateService {
    constructor(
        private http: HttpClient,
        private _snackBar: MatSnackBar) { }

    // this will be replaced by actual timestamp post-build.js
    private currentTimestamp = '{{POST_BUILD_ENTERS_TIMESTAMP_HERE}}'
    private appJsonFile = 'software.json'

    public initApplicationUpdating() {
        console.debug("SoftwareUpdateService.initApplicationUpdating()")
        let frequency = environment.applicationVersionCheckDelayMs
        console.debug("SoftwareUpdateService.initApplicationUpdating()", frequency)
        let frequencyNumber = Number(frequency);
        if (isNaN(frequencyNumber) || 0 >= frequencyNumber) {
            console.warn("SoftwareUpdateService.initApplicationUpdating() no frequency : runApplicationUpdating is skipped")
        } else {
            // on application init, force reload if necessary
            this.runApplicationCheck(true)
            // check will be done to reload on user validation
            interval(frequencyNumber).subscribe(val => this.runApplicationCheck(false))
        }
    }

    /**
    * Will get new application timestamp and launch application update if needed
    * @param forceReload
    */
    private runApplicationCheck(forceReload: boolean = false): void {
        console.debug("SoftwareUpdateService.runApplicationCheck()", forceReload)
        let url = environment.applicationUrl + '/' + this.appJsonFile
        // get file plus timestamp in request to invalidate caches
        this.http.get(url + '?t=' + new Date().getTime())
            .subscribe(
                (response: any) => {
                    // get timestamp in json
                    const newTimestamp = response.timestamp;
                    const applicationNeedsToBeUpdated = this.isApplicationHasBeenUpdatedOnServer(newTimestamp);
                    // If application needs to be updated
                    if (applicationNeedsToBeUpdated) {
                        this.updateApplication(forceReload);
                    } else {
                        console.debug("SoftwareUpdateService.runApplicationCheck() application does not need to be updated")
                    }
                },
                (err) => {
                    console.error(err, `SoftwareUpdateService.runApplicationCheck() : could not get ${this.appJsonFile}`);
                }
            );

    }

    /**
     * Reload application, user may be asked for validation
     * if forceReload is false then user will be asked for application refresh
     * if foceTeload is true then application will be refreshed
     * @param forceReload 
     */
    private updateApplication(forceReload: boolean): void {
        console.debug("SoftwareUpdateService.updateApplication() application has to be updated")
        if (forceReload) {
            // Force reload
            console.debug("SoftwareUpdateService.updateApplication() refresh forced")
            window.location.reload();
        } else {
            // ask for user's validation to reload
            let snackBarRef = this._snackBar.open("Application has been updated ! OK to get refreshed ?", "Update application", {});
            snackBarRef.onAction().subscribe(() => {
                // Refresh application when user asks for...
                console.debug("SoftwareUpdateService.updateApplication() refresh asked")
                window.location.reload()
            });
        }
    }

    /**
    * Checks if application timestamp has changed
    * @param newTimestamp
    * @returns {boolean}
    */
    private isApplicationHasBeenUpdatedOnServer(newTimestamp: string): boolean {
        console.debug("SoftwareUpdateService.isApplicationHasBeenUpdatedOnServer()", this.currentTimestamp, newTimestamp)
        if (!this.currentTimestamp || !newTimestamp) {
            console.debug("SoftwareUpdateService.isApplicationHasBeenUpdatedOnServer() : missing input : false")
            return false
        }
        let result = this.currentTimestamp !== newTimestamp
        console.debug(`SoftwareUpdateService.isApplicationHasBeenUpdatedOnServer() : ${result}`)
        return result
    }
}