import {
    Inject,
    Injectable,
} from '@angular/core';

import {
    PopStateEvent,
} from '@angular/common';
import {
    NavigationEnd,
    NavigationStart,
    Router,
} from '@angular/router';

interface RouteTrailInterface {
    url: string;
    scroll: {
        x: number;
        y: number;
    };
}

@Injectable()
export class ScrollToTopOnRouteChangeService {
    public routeTrail: RouteTrailInterface[] = [];
    public backRouteTrail: RouteTrailInterface;

    constructor(
        private _router: Router,
        @Inject('window')
        private _window: Window,
    ) { }

    public scrollToTopOnRouteChange() {
        this._router.events.subscribe((ev) => {
            if (ev instanceof NavigationStart) {
                const lastRoute = this.routeTrail[this.routeTrail.length - 2];
                if (lastRoute && lastRoute.url === ev.url) {
                    this.backRouteTrail = this.routeTrail.pop();
                } else {
                    this.routeTrail.push({
                        scroll: {
                            x: this._window.scrollX,
                            y: this._window.scrollY,
                        },
                        url: ev.url,
                    });
                }
            } else if (ev instanceof NavigationEnd) {
                if (this.backRouteTrail) {
                    setTimeout(() => {
                        // Give time angular view to render
                        this._window.scrollTo(
                            this.backRouteTrail.scroll.x,
                            this.backRouteTrail.scroll.y,
                        );
                        this.backRouteTrail = null;
                    });
                } else {
                    this._window.scrollTo(0, 0);
                }
            }
        });
    }
}