// (C) Copyright 2015 Moodle Pty Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import { Directive, ElementRef, EventEmitter, OnDestroy, OnInit, Output } from '@angular/core';
import { CoreDomUtils } from '@services/utils/dom';

/**
 * Directive to listen when an element becomes visible.
 */
@Directive({
    selector: '[onAppear]',
})
export class CoreOnAppearDirective implements OnInit, OnDestroy {

    @Output() onAppear = new EventEmitter();

    private element: HTMLElement;
    private interval?: number;

    constructor(element: ElementRef) {
        this.element = element.nativeElement;
    }

    /**
     * @inheritdoc
     */
    ngOnInit(): void {
        this.interval = window.setInterval(() => {
            if (!CoreDomUtils.isElementVisible(this.element)) {
                return;
            }

            this.onAppear.emit();
            window.clearInterval(this.interval);

            delete this.interval;
        }, 50);
    }

    /**
     * @inheritdoc
     */
    ngOnDestroy(): void {
        this.interval && window.clearInterval(this.interval);
    }

}