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];
      });
    }
  }
}