import { InjectionToken, Inject, Injectable, Optional } from '@angular/core';
import { DOCUMENT } from '@angular/common';
import { of } from 'rxjs';
import { MatIconRegistry } from '@angular/material/icon';
import { HttpClient } from '@angular/common/http';
import { DomSanitizer } from '@angular/platform-browser';

/**
 * Use SVG_ICONS (and SvgIconInfo) as "multi" providers to provide the SVG source
 * code for the icons that you wish to have preloaded in the `CustomIconRegistry`
 * For compatibility with the MdIconComponent, please ensure that the SVG source has
 * the following attributes:
 *
 * * `xmlns="http://www.w3.org/2000/svg"`
 * * `focusable="false"` (disable IE11 default behavior to make SVGs focusable)
 * * `height="100%"` (the default)
 * * `width="100%"` (the default)
 * * `preserveAspectRatio="xMidYMid meet"` (the default)
 *
 */
export const SVG_ICONS = new InjectionToken<Array<SvgIconInfo>>('SvgIcons');
export interface SvgIconInfo {
  namespace?: string;
  name: string;
  svgSource: string;
}

interface SvgIconMap {
  [namespace: string]: {
    [iconName: string]: SVGElement;
  };
}

const DEFAULT_NS = '$$default';

/**
 * A custom replacement for Angular Material's `MdIconRegistry`, which allows
 * us to provide preloaded icon SVG sources.
 */
@Injectable()
export class CustomIconRegistry extends MatIconRegistry {
  private preloadedSvgElements: SvgIconMap = {[DEFAULT_NS]: {}};

  constructor(http: HttpClient, sanitizer: DomSanitizer, @Optional() @Inject(DOCUMENT) document,
              @Inject(SVG_ICONS) svgIcons: SvgIconInfo[]) {
    super(http, sanitizer, document);
    this.loadSvgElements(svgIcons);
  }

  getNamedSvgIcon(iconName: string, namespace?: string) {
    const nsIconMap = this.preloadedSvgElements[namespace || DEFAULT_NS];
    const preloadedElement = nsIconMap && nsIconMap[iconName];

    return preloadedElement
        ? of(preloadedElement.cloneNode(true) as SVGElement)
        : super.getNamedSvgIcon(iconName, namespace);
  }

  private loadSvgElements(svgIcons: SvgIconInfo[]) {
    const div = document.createElement('DIV');
    svgIcons.forEach(icon => {
      const ns = icon.namespace || DEFAULT_NS;
      const nsIconMap = this.preloadedSvgElements[ns] || (this.preloadedSvgElements[ns] = {});

      // SECURITY: the source for the SVG icons is provided in code by trusted developers
      div.innerHTML = icon.svgSource;

      nsIconMap[icon.name] = div.querySelector('svg')!;
    });
  }
}
