import { Injectable } from '@angular/core';
import { BehaviorSubject } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';

export type ContentRenderSourceKey = symbol;

/**
 * Bridges page content render-readiness to the frame so it paints the surrounding sections
 * (footer, actions, small print) only once content has rendered, avoiding Cumulative Layout
 * Shift (CLS).
 *
 * Several Building Block pages can be alive at the same time — the routed page plus the
 * projected `frame-header-actions` and `frame-global-sidebar-content` pages — so readiness
 * is tracked per source and only reported as ready once every registered source is ready.
 *
 * Provided by `FrameComponent`, so the frame and the Building Block pages projected into it
 * (routed page, header-actions, global-sidebar) resolve the same instance via the element
 * injector. Pages rendered outside a frame inject it optionally and simply skip reporting.
 */
@Injectable()
export class TalyContentRenderService {
  private _sourceReadiness = new Map<ContentRenderSourceKey, boolean>();
  private _contentRenderReady$ = new BehaviorSubject<boolean>(true);

  contentRenderReady$ = this._contentRenderReady$.pipe(distinctUntilChanged());

  /**
   * Register a content source. It starts as not-ready, so registering holds back the frame
   * until the source reports otherwise. Returns a key used to update or remove it.
   */
  registerSource(): ContentRenderSourceKey {
    const key = Symbol('content-render-source');
    this._sourceReadiness.set(key, false);
    this._emitReadiness();
    return key;
  }

  setSourceReady(key: ContentRenderSourceKey, ready: boolean): void {
    if (!this._sourceReadiness.has(key)) {
      return;
    }
    this._sourceReadiness.set(key, ready);
    this._emitReadiness();
  }

  unregisterSource(key: ContentRenderSourceKey): void {
    if (this._sourceReadiness.delete(key)) {
      this._emitReadiness();
    }
  }

  private _emitReadiness(): void {
    const allReady = Array.from(this._sourceReadiness.values()).every(Boolean);
    this._contentRenderReady$.next(allReady);
  }
}