/**
 * @fileoverview Rule to flag references to the undefined variable.
 * @author Michael Ficarra
 */
'use strict';

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

/** @type {import('../types').Rule.RuleModule} */
module.exports = {
  meta: {
    type: 'suggestion',

    docs: {
      description: 'Disallow the use of `undefined` as an identifier',
      recommended: false,
      frozen: true,
      url: 'https://eslint.org/docs/latest/rules/no-undefined',
    },

    schema: [],

    messages: {
      unexpectedUndefined: 'Unexpected use of undefined.',
    },
  },

  create(context) {
    const sourceCode = context.sourceCode;

    /**
     * Report an invalid "undefined" identifier node.
     * @param {ASTNode} node The node to report.
     * @returns {void}
     */
    function report(node) {
      context.report({
        node,
        messageId: 'unexpectedUndefined',
      });
    }

    /**
     * Checks the given scope for references to `undefined` and reports
     * all references found.
     * @param {eslint-scope.Scope} scope The scope to check.
     * @returns {void}
     */
    function checkScope(scope) {
      const undefinedVar = scope.set.get('undefined');

      if (!undefinedVar) {
        return;
      }

      const references = undefinedVar.references;

      const defs = undefinedVar.defs;

      // Report non-initializing references (those are covered in defs below)
      references
        .filter((ref) => !ref.init)
        .forEach((ref) => report(ref.identifier));

      defs.forEach((def) => report(def.name));
    }

    return {
      'Program:exit'(node) {
        const globalScope = sourceCode.getScope(node);

        const stack = [globalScope];

        while (stack.length) {
          const scope = stack.pop();

          stack.push(...scope.childScopes);
          checkScope(scope);
        }
      },
    };
  },
};