bookhoard/web/src/library-switcher.ts

import { Alpine } from "./alpine";
import { ALL_LIBRARIES, setSelectedLibrary } from "./storage";
import { showToast } from "./toast";

export async function switchWithTransition(
  containerId: string,
  fetchFn: () => Promise<void>,
): Promise<void> {
  const container = document.getElementById(containerId);
  const loading = document.getElementById("loading-spinner");

  if (!container || !loading) return;

  // View Transitions (native, where supported): the browser snapshots the
  // old shelves, fetchFn swaps the DOM, and the two snapshots crossfade —
  // no blank phase, no manual opacity choreography. The dim + spinner is
  // shown before the snapshot and hidden inside the update, so the dim
  // blends away as part of the crossfade. Browsers without the API fall
  // through to the dim + fade sequence below.
  const doc = document as Document & {
    startViewTransition?: (updateCallback: () => void | Promise<void>) => {
      finished: Promise<void>;
    };
  };
  if (doc.startViewTransition) {
    try {
      loading.classList.remove("hidden");
      const transition = doc.startViewTransition(async () => {
        await fetchFn();
        loading.classList.add("hidden");
      });
      await transition.finished;
    } catch (error) {
      loading.classList.add("hidden");
      showToast("Failed to load library", "error");
      console.error("Switch library error:", error);
    }
    return;
  }

  try {
    container.classList.add("opacity-0", "transition-opacity", "duration-150");
    await new Promise((resolve) => setTimeout(resolve, 150));

    loading.classList.remove("hidden");

    await fetchFn();

    // Lift the dim BEFORE the fade-in starts, so the new content's fade
    // plays fully visible instead of being hard-cut by the overlay
    // disappearing mid-transition.
    loading.classList.add("hidden");

    container.classList.remove("duration-150");
    container.classList.add("duration-300");
    void container.offsetHeight;
    container.classList.remove("opacity-0");

    setTimeout(() => {
      container.classList.remove("transition-opacity", "duration-300");
    }, 300);
  } catch (error) {
    container.classList.remove("opacity-0", "transition-opacity", "duration-150", "duration-300");
    showToast("Failed to load library", "error");
    console.error("Switch library error:", error);
  } finally {
    loading.classList.add("hidden");
  }
}

export interface LibrarySwitcherOptions {
  // Async switchers (SSR navigation awaits nothing, API-backed switchers
  // await their fetch) — hence void | Promise<void>.
  onSwitch: (libraryId: string) => void | Promise<void>;
}

export function initLibrarySwitcher(options: LibrarySwitcherOptions): void {
  const librarySelect = document.getElementById("library-select") as HTMLSelectElement;
  if (!librarySelect) return;

  const stored = localStorage.getItem("selectedLibrary");
  if (stored === ALL_LIBRARIES) {
    librarySelect.value = "";
  } else if (stored) {
    const option = librarySelect.querySelector(`option[value="${stored}"]`);
    if (option) {
      librarySelect.value = stored;
    }
  }

  librarySelect.addEventListener("change", async (e) => {
    const target = e.target as HTMLSelectElement;
    const libraryId = target.value;

    setSelectedLibrary(libraryId);
    await options.onSwitch(libraryId);
  });
}

Alpine.data("librarySwitcher", () => ({}));