/**
   * @fileoverview Define the abstract class about cursors which iterate tokens.
   * @author Toru Nagashima
   */
  "use strict";
  
  //------------------------------------------------------------------------------
  // Exports
  //------------------------------------------------------------------------------
  
  /**
   * The abstract class about cursors which iterate tokens.
   *
   * This class has 2 abstract methods.
   *
   * - `current: Token | Comment | null` ... The current token.
   * - `moveNext(): boolean` ... Moves this cursor to the next token. If the next token didn't exist, it returns `false`.
   *
   * This is similar to ES2015 Iterators.
   * However, Iterators were slow (at 2017-01), so I created this class as similar to C# IEnumerable.
   *
   * There are the following known sub classes.
   *
   * - ForwardTokenCursor .......... The cursor which iterates tokens only.
   * - BackwardTokenCursor ......... The cursor which iterates tokens only in reverse.
   * - ForwardTokenCommentCursor ... The cursor which iterates tokens and comments.
   * - BackwardTokenCommentCursor .. The cursor which iterates tokens and comments in reverse.
   * - DecorativeCursor
   *     - FilterCursor ............ The cursor which ignores the specified tokens.
   *     - SkipCursor .............. The cursor which ignores the first few tokens.
   *     - LimitCursor ............. The cursor which limits the count of tokens.
   *
   */
  module.exports = class Cursor {
  
      /**
       * Initializes this cursor.
       */
      constructor() {
          this.current = null;
      }
  
      /**
       * Gets the first token.
       * This consumes this cursor.
       * @returns {Token|Comment} The first token or null.
       */
      getOneToken() {
          return this.moveNext() ? this.current : null;
      }
  
      /**
       * Gets the first tokens.
       * This consumes this cursor.
       * @returns {(Token|Comment)[]} All tokens.
       */
      getAllTokens() {
          const tokens = [];
  
          while (this.moveNext()) {
              tokens.push(this.current);
          }
  
          return tokens;
      }
  
      /**
       * Moves this cursor to the next token.
       * @returns {boolean} `true` if the next token exists.
       * @abstract
       */
      /* istanbul ignore next */
      moveNext() { // eslint-disable-line class-methods-use-this
          throw new Error("Not implemented.");
      }
  };