import {
  DestroyRef,
  ENVIRONMENT_INITIALIZER,
  Injectable,
  inject,
} from '@angular/core';
import { CanDeactivateFn } from '@angular/router';

/**
 * A source of debounced, not-yet-flushed writes (autosave). The two autosave owners in
 * this app have different lifetimes — root singleton stores (`BriefStore`,
 * `OrgTemplateStore`) and per-wizard `createDraftSync` controllers living inside child
 * organisms — so both register here instead of the guard/unload handler needing to know
 * which page or store owns the pending write.
 */
export interface PendingSave {
  /** True while a debounced edit hasn't been written to the backend yet. */
  hasPendingSave(): boolean;
  /** Flush that pending write now and await it. No-op when nothing is pending. */
  flushPending(): Promise<void>;
}

/** Registry of every active autosave owner. The `CanDeactivate` guard and the
    `beforeunload` handler flush through this — one seam, both callers. */
@Injectable({ providedIn: 'root' })
export class PendingSaves {
  private readonly owners = new Set<PendingSave>();

  /** Register an owner; returns an unregister function. */
  register(owner: PendingSave): () => void {
    this.owners.add(owner);
    return () => this.owners.delete(owner);
  }

  hasPending(): boolean {
    return [...this.owners].some((o) => o.hasPendingSave());
  }

  /** Flush every owner that has a pending write, awaiting all. Best-effort: a rejected
      flush is swallowed (a failed autosave surfaces its own error state; navigation must
      not be blocked by it). */
  async flushAll(): Promise<void> {
    await Promise.allSettled(
      [...this.owners].filter((o) => o.hasPendingSave()).map((o) => o.flushPending()),
    );
  }
}

/** Register the current injection context's owner for the life of its `DestroyRef`.
    Call from a constructor or field initializer (root store, or `createDraftSync`). */
export function registerPendingSave(owner: PendingSave): void {
  const unregister = inject(PendingSaves).register(owner);
  inject(DestroyRef).onDestroy(unregister);
}

/** `CanDeactivate` guard: flush any pending debounced write before an in-app route change,
    then allow navigation. Awaitable, so the write lands before the page tears down (which
    would otherwise drop a sub-debounce edit). We never block leaving — the flush is a
    guarantee of effort, not a gate. */
export const flushPendingGuard: CanDeactivateFn<unknown> = () => {
  const pending = inject(PendingSaves);
  return pending.hasPending() ? pending.flushAll().then(() => true) : true;
};

/** Wire a `beforeunload` handler that guards the last-mile save on a hard tab-close/reload.
    ponytail: the HTTP seam is Angular `HttpClient` (no `keepalive`/`sendBeacon`), so an
    async flush can't be guaranteed to finish as the page tears down — we fire it best-effort
    AND trigger the browser's native "unsaved changes" prompt, which lets the ~600ms debounce
    land if the user stays. Upgrade path: a `sendBeacon`/keepalive last-mile if this ever
    needs to be guaranteed. */
export function provideUnloadFlush() {
  return {
    provide: ENVIRONMENT_INITIALIZER,
    multi: true,
    useValue: () => {
      const pending = inject(PendingSaves);
      window.addEventListener('beforeunload', (e) => {
        if (!pending.hasPending()) return;
        void pending.flushAll();
        e.preventDefault();
        e.returnValue = '';
      });
    },
  };
}