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

const SHOW_DELAY_MS = 180;
const MIN_VISIBLE_MS = 360;

/** Coordinates one unobtrusive loading indicator for all admin HttpClient requests. */
@Injectable({ providedIn: 'root' })
export class AdminRequestActivityService {
  private readonly pendingState = signal(0);
  private readonly visibleState = signal(false);
  private showTimer: ReturnType<typeof setTimeout> | undefined;
  private hideTimer: ReturnType<typeof setTimeout> | undefined;
  private shownAt = 0;

  readonly pending = this.pendingState.asReadonly();
  readonly visible = this.visibleState.asReadonly();

  begin(): () => void {
    if (this.hideTimer) {
      clearTimeout(this.hideTimer);
      this.hideTimer = undefined;
    }
    this.pendingState.update(count => count + 1);
    if (!this.visibleState() && !this.showTimer) {
      this.showTimer = setTimeout(() => {
        this.showTimer = undefined;
        if (this.pendingState() > 0) {
          this.shownAt = Date.now();
          this.visibleState.set(true);
        }
      }, SHOW_DELAY_MS);
    }

    let completed = false;
    return () => {
      if (completed) return;
      completed = true;
      this.pendingState.update(count => Math.max(0, count - 1));
      if (this.pendingState() > 0) return;

      if (this.showTimer) {
        clearTimeout(this.showTimer);
        this.showTimer = undefined;
      }
      if (!this.visibleState()) return;

      const delay = Math.max(0, MIN_VISIBLE_MS - (Date.now() - this.shownAt));
      this.hideTimer = setTimeout(() => {
        this.hideTimer = undefined;
        if (this.pendingState() === 0) this.visibleState.set(false);
      }, delay);
    };
  }
}