/**
   * @fileoverview Rule to flag the generator functions that does not have yield.
   * @author Toru Nagashima
   * @copyright 2015 Toru Nagashima. All rights reserved.
   */
  
  "use strict";
  
  //------------------------------------------------------------------------------
  // Rule Definition
  //------------------------------------------------------------------------------
  
  module.exports = function(context) {
      var stack = [];
  
      /**
       * If the node is a generator function, start counting `yield` keywords.
       * @param {Node} node - A function node to check.
       * @returns {void}
       */
      function beginChecking(node) {
          if (node.generator) {
              stack.push(0);
          }
      }
  
      /**
       * If the node is a generator function, end counting `yield` keywords, then
       * reports result.
       * @param {Node} node - A function node to check.
       * @returns {void}
       */
      function endChecking(node) {
          if (!node.generator) {
              return;
          }
  
          var countYield = stack.pop();
          if (countYield === 0 && node.body.body.length > 0) {
              context.report(
                  node,
                  "This generator function does not have `yield`.");
          }
      }
  
      return {
          "FunctionDeclaration": beginChecking,
          "FunctionDeclaration:exit": endChecking,
          "FunctionExpression": beginChecking,
          "FunctionExpression:exit": endChecking,
  
          // Increases the count of `yield` keyword.
          "YieldExpression": function() {
              /* istanbul ignore else */
              if (stack.length > 0) {
                  stack[stack.length - 1] += 1;
              }
          }
      };
  };
  
  module.exports.schema = [];