/**
   * @fileoverview Ensure handling of errors when we know they exist.
   * @author Jamund Ferguson
   */
  
  "use strict";
  
  //------------------------------------------------------------------------------
  // Rule Definition
  //------------------------------------------------------------------------------
  
  module.exports = {
      meta: {
          docs: {
              description: "require error handling in callbacks",
              category: "Node.js and CommonJS",
              recommended: false
          },
  
          schema: [
              {
                  type: "string"
              }
          ]
      },
  
      create(context) {
  
          const errorArgument = context.options[0] || "err";
  
          /**
           * Checks if the given argument should be interpreted as a regexp pattern.
           * @param {string} stringToCheck The string which should be checked.
           * @returns {boolean} Whether or not the string should be interpreted as a pattern.
           */
          function isPattern(stringToCheck) {
              const firstChar = stringToCheck[0];
  
              return firstChar === "^";
          }
  
          /**
           * Checks if the given name matches the configured error argument.
           * @param {string} name The name which should be compared.
           * @returns {boolean} Whether or not the given name matches the configured error variable name.
           */
          function matchesConfiguredErrorName(name) {
              if (isPattern(errorArgument)) {
                  const regexp = new RegExp(errorArgument);
  
                  return regexp.test(name);
              }
              return name === errorArgument;
          }
  
          /**
           * Get the parameters of a given function scope.
           * @param {Object} scope The function scope.
           * @returns {array} All parameters of the given scope.
           */
          function getParameters(scope) {
              return scope.variables.filter(variable => variable.defs[0] && variable.defs[0].type === "Parameter");
          }
  
          /**
           * Check to see if we're handling the error object properly.
           * @param {ASTNode} node The AST node to check.
           * @returns {void}
           */
          function checkForError(node) {
              const scope = context.getScope(),
                  parameters = getParameters(scope),
                  firstParameter = parameters[0];
  
              if (firstParameter && matchesConfiguredErrorName(firstParameter.name)) {
                  if (firstParameter.references.length === 0) {
                      context.report({ node, message: "Expected error to be handled." });
                  }
              }
          }
  
          return {
              FunctionDeclaration: checkForError,
              FunctionExpression: checkForError,
              ArrowFunctionExpression: checkForError
          };
  
      }
  };