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

@Injectable()
export class DomElementLocationService {
    constructor(
        @Inject('window')
        private _window: Window,
    ) {}

    public getCenterPointOfElement(
        elementRef: ElementRef,
    ) {
        const boundingRect = elementRef.nativeElement
            .getBoundingClientRect();
        return boundingRect.top + boundingRect.height / 2;
    }

    public getMostCentralElement(
        elementRefs: ElementRef[],
    ) {
        const centerPoint = this._window
            .innerHeight / 2;
        let mostCentral = elementRefs[0];
        let mostCentralIndex = 0;

        elementRefs.forEach((prodViewEl, index) => {
            const newElDistance =
                this.getCenterPointOfElement(prodViewEl) -
                centerPoint;
            const oldElDistance =
                this.getCenterPointOfElement(mostCentral) -
                centerPoint;
            if (Math.abs(newElDistance) < Math.abs(oldElDistance)) {
                mostCentral = prodViewEl;
                mostCentralIndex = index;
            }
        });

        return {
            mostCentral,
            mostCentralIndex,
        };
    }
}