// (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 { Component, ElementRef, Input, OnChanges } from '@angular/core';

/**
 * Component to add a <style> tag.
 *
 * @description
 * This component will include a <style> tag with some CSS rules that can optionally be pefixed.
 *
 * Example:
 *
 * <core-style [css]="'p { color: red; }'" prefix=".custom-rules"></core-style>
 */
@Component({
    selector: 'core-style',
    template: '',
})
export class CoreStyleComponent implements OnChanges {

    @Input() css = ''; // CSS rules.
    @Input() prefix = ''; // Prefix to add to CSS rules.

    constructor(private element: ElementRef) {}

    /**
     * @inheritdoc
     */
    ngOnChanges(): void {
        if (this.element && this.element.nativeElement) {
            const style = document.createElement('style');
            style.innerText = this.prefixCSS(this.css, this.prefix);

            this.element.nativeElement.innerHTML = '';
            this.element.nativeElement.appendChild(style);
        }
    }

    /**
     * Add a prefix to all rules in a CSS string.
     *
     * @param css CSS code to be prefixed.
     * @param prefix Prefix css selector.
     * @return Prefixed CSS.
     */
    protected prefixCSS(css: string, prefix: string): string {
        if (!css) {
            return '';
        }

        if (!prefix) {
            return css;
        }

        // Remove comments first.
        let regExp = /\/\*[\s\S]*?\*\/|([^:]|^)\/\/.*$/gm;
        css = css.replace(regExp, '');

        // Add prefix.
        regExp = /([^]*?)({[^]*?}|,)/g;

        return css.replace(regExp, prefix + ' $1 $2');
    }

}
