/**
   * @fileoverview Rule to flag duplicate arguments
   * @author Jamund Ferguson
   */
  
  "use strict";
  
  //------------------------------------------------------------------------------
  // Rule Definition
  //------------------------------------------------------------------------------
  
  module.exports = {
      meta: {
          docs: {
              description: "disallow duplicate arguments in `function` definitions",
              category: "Possible Errors",
              recommended: true
          },
  
          schema: []
      },
  
      create(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) {
              const variables = context.getDeclaredVariables(node);
  
              for (let i = 0; i < variables.length; ++i) {
                  const variable = variables[i];
  
                  // Checks and reports duplications.
                  const defs = variable.defs.filter(isParameter);
  
                  if (defs.length >= 2) {
                      context.report({
                          node,
                          message: "Duplicate param '{{name}}'.",
                          data: { name: variable.name }
                      });
                  }
              }
          }
  
          //--------------------------------------------------------------------------
          // Public API
          //--------------------------------------------------------------------------
  
          return {
              FunctionDeclaration: checkParams,
              FunctionExpression: checkParams
          };
  
      }
  };