feat: wire guide data source and POI focus UI

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/usecases/explainUseCase.ts

@@ -0,0 +1,75 @@
+import type {
+  ExplainTrack,
+  MediaAsset,
+  MuseumExhibit,
+  MuseumHall,
+  SearchIndexItem
+} from '@/domain/museum'
+import {
+  explainRepository,
+  type ExplainRepository
+} from '@/repositories/ExplainRepository'
+import {
+  mediaRepository,
+  type MediaRepository
+} from '@/repositories/MediaRepository'
+
+export interface ExplainAudioSelection {
+  exhibit: MuseumExhibit
+  track: ExplainTrack | null
+  media: MediaAsset | null
+  playable: boolean
+  unavailableMessage?: string
+}
+
+export class ExplainUseCase {
+  constructor(
+    private readonly explain: ExplainRepository = explainRepository,
+    private readonly media: MediaRepository = mediaRepository
+  ) {}
+
+  listExhibits() {
+    return this.explain.listExhibits()
+  }
+
+  getExhibitById(id: string) {
+    return this.explain.getExhibitById(id)
+  }
+
+  listHalls(): Promise<MuseumHall[]> {
+    return this.explain.listHalls()
+  }
+
+  getHallById(id: string) {
+    return this.explain.getHallById(id)
+  }
+
+  async listExhibitsByHallId(hallId: string) {
+    const exhibits = await this.explain.listExhibits()
+    return exhibits.filter((exhibit) => exhibit.hallId === hallId)
+  }
+
+  searchExplain(keyword?: string): Promise<SearchIndexItem[]> {
+    return this.explain.searchExplain(keyword)
+  }
+
+  async selectAudioForExhibit(exhibitId: string): Promise<ExplainAudioSelection | null> {
+    const exhibit = await this.explain.getExhibitById(exhibitId)
+    if (!exhibit) return null
+
+    const track = await this.explain.getTrackByExhibitId(exhibitId)
+    const media = track?.mediaId
+      ? await this.media.getMediaById(track.mediaId)
+      : null
+
+    return {
+      exhibit,
+      track,
+      media,
+      playable: media?.available === true && Boolean(media.url),
+      unavailableMessage: media?.unavailableReason || '该展项暂无讲解音频'
+    }
+  }
+}
+
+export const explainUseCase = new ExplainUseCase()