/**
   * @fileoverview Rule to flag duplicate arguments
   * @author Jamund Ferguson
   * @copyright 2015 Jamund Ferguson. All rights reserved.
   * @copyright 2015 Toru Nagashima. All rights reserved.
   * See LICENSE file in root directory for full license.
   */
  
  "use strict";
  
  //------------------------------------------------------------------------------
  // Rule Definition
  //------------------------------------------------------------------------------
  
  module.exports = function(context) {
  
      //--------------------------------------------------------------------------
      // Helpers
      //--------------------------------------------------------------------------
  
      /**
       * Checks whether or not a given definition is a parameter's.
       * @param {escope.DefEntry} def - A definition to check.
       * @returns {boolean} `true` if the definition is a parameter's.
       */
      function isParameter(def) {
          return def.type === "Parameter";
      }
  
      /**
       * Determines if a given node has duplicate parameters.
       * @param {ASTNode} node The node to check.
       * @returns {void}
       * @private
       */
      function checkParams(node) {
          var variables = context.getDeclaredVariables(node);
          var keyMap = Object.create(null);
  
          for (var i = 0; i < variables.length; ++i) {
              var variable = variables[i];
  
              // TODO(nagashima): Remove this duplication check after https://github.com/estools/escope/pull/79
              var key = "$" + variable.name; // to avoid __proto__.
              if (!isParameter(variable.defs[0]) || keyMap[key]) {
                  continue;
              }
              keyMap[key] = true;
  
              // Checks and reports duplications.
              var defs = variable.defs.filter(isParameter);
              if (defs.length >= 2) {
                  context.report({
                      node: node,
                      message: "Duplicate param '{{name}}'.",
                      data: {name: variable.name}
                  });
              }
          }
      }
  
      //--------------------------------------------------------------------------
      // Public API
      //--------------------------------------------------------------------------
  
      return {
          "FunctionDeclaration": checkParams,
          "FunctionExpression": checkParams
      };
  
  };
  
  module.exports.schema = [];