import {IQueueConfiguration} from './IQueueConfiguration';

/**
 * Each node corresponds to an entry within the queue. This helps with
 * storage and removal from local storage.
 */
export class Node<T> {
  private _key: string;
  private _serializedNode: string;

  /**
   * Constructs a node representing an entry in the queue.
   * @param config The queue configuration. This is used to provide the prefix for the key.
   * @param index The index within the queue
   * @param value The value of the entry
   */
  constructor(config: IQueueConfiguration, index: number, public value: T) {
    this._key = Node.createKey(config, index);
    this._serializedNode = JSON.stringify(value);
  }

  /**
   * Returns an estimate of the size this will take up in local storage.
   */
  estimatedSize() {
    return this._serializedNode.length + this._key.length;
  }

  /**
   * Stores the serialized entry in local storage.
   */
  store() {
    localStorage.setItem(this._key, this._serializedNode);
  }

  /**
   * Removes the entry from local storage if it exists.
   */
  remove() {
    localStorage.removeItem(this._key);
  }

  /**
   * Creates a key for an entry.
   * @param config The configuration containing the key prefix
   * @param index The index of the entry in the queue
   */
  static createKey(config: IQueueConfiguration, index: number) {
    return `${config.keyPrefix}-item-${index}`;
  }

  /**
   * Loads an entry from local storage and deserializes it. Returns the associated node.
   * @param config The configuration containing the key prefix
   * @param index The index of the entry in the queue
   */
  static fromLocalStorage<T>(config: IQueueConfiguration, index: number) {
    const serializedNode = localStorage.getItem(Node.createKey(config, index));
    const value = JSON.parse(serializedNode);
    return new Node<T>(config, index, value);
  }
}