/**
 * @fileoverview Disallow sparse arrays
 * @author Nicholas C. Zakas
 */
'use strict';

const astUtils = require('./utils/ast-utils');

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

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

    docs: {
      description: 'Disallow sparse arrays',
      recommended: true,
      url: 'https://eslint.org/docs/latest/rules/no-sparse-arrays',
    },

    schema: [],

    messages: {
      unexpectedSparseArray: 'Unexpected comma in middle of array.',
    },
  },

  create(context) {
    //--------------------------------------------------------------------------
    // Public
    //--------------------------------------------------------------------------

    return {
      ArrayExpression(node) {
        if (!node.elements.includes(null)) {
          return;
        }

        const { sourceCode } = context;
        let commaToken;

        for (const [index, element] of node.elements.entries()) {
          if (index === node.elements.length - 1 && element) {
            return;
          }

          commaToken = sourceCode.getTokenAfter(
            element ?? commaToken ?? sourceCode.getFirstToken(node),
            astUtils.isCommaToken
          );

          if (element) {
            continue;
          }

          context.report({
            node,
            loc: commaToken.loc,
            messageId: 'unexpectedSparseArray',
          });
        }
      },
    };
  },
};