More core audio work

src/app/lib/IndexedArray.ts

@@ -0,0 +1,73 @@
+import {computed, effect, Signal, signal, WritableSignal} from '@angular/core';
+
+export class IndexedArray<T> {
+  protected list: WritableSignal<T[]> = signal([]);
+  protected currentIndex: WritableSignal<number> = signal(0);
+
+  public playlist: Signal<T[]> = this.list.asReadonly();
+  public index: Signal<number> = this.currentIndex.asReadonly();
+  public current: Signal<T|null>;
+
+  constructor() {
+    this.current = computed(() : T | null => {
+      if (this.currentIndex() > -1 && this.list().length === 0) return null;
+      return this.list()[this.currentIndex()];
+    });
+  }
+
+  next(): T | null {
+    const length = this.list().length;
+    if (length === 0) return null;
+    if (length === 1) return this.list()[0];
+
+    if (this.currentIndex() === length - 1) {
+      this.currentIndex.set(0);
+    } else {
+      this.currentIndex.set(this.currentIndex() + 1);
+    }
+
+    return this.current();
+  }
+
+  prev(): T | null {
+    const length = this.list().length;
+    if (length === 0) return null;
+    if (length === 1) return this.list()[0];
+
+    if (this.currentIndex() === 0) {
+      this.currentIndex.set(length - 1);
+    } else {
+      this.currentIndex.set(this.currentIndex() - 1);
+    }
+
+    return this.current();
+  }
+
+  add(item: T) {
+    this.list.update((list: T[]) => {
+      return [...list, item];
+    });
+  }
+
+  remove(item: T) {
+    // Check item is actually in the list, and find its index
+    const index = this.list().indexOf(item);
+    if (index > -1) {
+      // If we deleted an item before the current index pointer, then shift the index back one to maintain current item
+      if (index < this.currentIndex()) {
+        this.currentIndex.update((index) => index - 1);
+      }
+
+      // If we are at the end of the list (and the list won't become empty) shift index back to maintain pointer at end of list
+      if (index === this.list().length - 1 && index > 0) {
+        this.currentIndex.update((index) => index - 1);
+      }
+
+      // Remove the item
+      this.list.update((list: T[]) => {
+        list.splice(index, 1);
+        return [...list];
+      });
+    }
+  }
+}