/**
 * @fileoverview Rule to flag comparison where left part is the same as the right
 * part.
 * @author Ilya Volodin
 */

'use strict';

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

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

    docs: {
      description: 'Disallow comparisons where both sides are exactly the same',
      recommended: false,
      url: 'https://eslint.org/docs/latest/rules/no-self-compare',
    },

    schema: [],

    messages: {
      comparingToSelf: 'Comparing to itself is potentially pointless.',
    },
  },

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

    /**
     * Determines whether two nodes are composed of the same tokens.
     * @param {ASTNode} nodeA The first node
     * @param {ASTNode} nodeB The second node
     * @returns {boolean} true if the nodes have identical token representations
     */
    function hasSameTokens(nodeA, nodeB) {
      const tokensA = sourceCode.getTokens(nodeA);
      const tokensB = sourceCode.getTokens(nodeB);

      return (
        tokensA.length === tokensB.length &&
        tokensA.every(
          (token, index) =>
            token.type === tokensB[index].type &&
            token.value === tokensB[index].value
        )
      );
    }

    return {
      BinaryExpression(node) {
        const operators = new Set([
          '===',
          '==',
          '!==',
          '!=',
          '>',
          '<',
          '>=',
          '<=',
        ]);

        if (
          operators.has(node.operator) &&
          hasSameTokens(node.left, node.right)
        ) {
          context.report({ node, messageId: 'comparingToSelf' });
        }
      },
    };
  },
};