Refactor song selection to a service

src/app/core/services/selection.service.ts

@@ -0,0 +1,96 @@
+import { Injectable, EventEmitter } from '@angular/core'
+import { SongResult } from 'src/electron/shared/interfaces/search.interface'
+import { SearchService } from './search.service'
+
+// Note: this class prevents event cycles by only emitting events if the checkbox changes
+
+@Injectable({
+  providedIn: 'root'
+})
+export class SelectionService {
+
+  private searchResults: SongResult[] = []
+
+  private selectAllChangedEmitter = new EventEmitter<boolean>()
+  private selectionChangedEmitters: { [songID: number]: EventEmitter<boolean> } = {}
+
+  private allSelected = false
+  private selections: { [songID: number]: boolean | undefined } = {}
+
+  constructor(searchService: SearchService) {
+    searchService.onSearchChanged((results) => {
+      this.searchResults = results
+      this.removeOldListeners(results.map(result => result.id))
+
+      if (this.allSelected) {
+        this.selectAll() // Select newly added rows if allSelected
+      }
+    })
+
+    searchService.onNewSearch((results) => {
+      this.searchResults = results
+      this.removeOldListeners(results.map(result => result.id))
+
+      this.deselectAll()
+    })
+  }
+
+  private removeOldListeners(songIDs: number[]) {
+    for (const oldSongID in this.selectionChangedEmitters) {
+      if (!songIDs.find(newSongID => newSongID == Number(oldSongID))) {
+        delete this.selectionChangedEmitters[oldSongID]
+        delete this.selections[oldSongID]
+      }
+    }
+  }
+
+  getSelectedResults() {
+    return this.searchResults.filter(result => this.selections[result.id] == true)
+  }
+
+  onSelectAllChanged(callback: (selected: boolean) => void) {
+    this.selectAllChangedEmitter.subscribe(callback)
+  }
+
+  /**
+   * Emits an event when the selection for `songID` needs to change.
+   * (note: only one emitter can be registered per `songID`)
+   */
+  onSelectionChanged(songID: number, callback: (selection: boolean) => void) {
+    this.selectionChangedEmitters[songID] = new EventEmitter()
+    this.selectionChangedEmitters[songID].subscribe(callback)
+  }
+
+
+  deselectAll() {
+    if (this.allSelected) {
+      this.allSelected = false
+      this.selectAllChangedEmitter.emit(false)
+    }
+
+    setTimeout(() => this.searchResults.forEach(result => this.deselectSong(result.id)), 0)
+  }
+
+  selectAll() {
+    if (!this.allSelected) {
+      this.allSelected = true
+      this.selectAllChangedEmitter.emit(true)
+    }
+
+    setTimeout(() => this.searchResults.forEach(result => this.selectSong(result.id)), 0)
+  }
+
+  deselectSong(songID: number) {
+    if (this.selections[songID]) {
+      this.selections[songID] = false
+      this.selectionChangedEmitters[songID].emit(false)
+    }
+  }
+
+  selectSong(songID: number) {
+    if (!this.selections[songID] && this.selectionChangedEmitters[songID] != undefined) {
+      this.selections[songID] = true
+      this.selectionChangedEmitters[songID].emit(true)
+    }
+  }
+}