/**
   * @fileoverview Rule to flag assignment in a conditional statement's test expression
   * @author Stephen Murray <spmurrayzzz>
   */
  "use strict";
  
  const astUtils = require("../ast-utils");
  
  const NODE_DESCRIPTIONS = {
      DoWhileStatement: "a 'do...while' statement",
      ForStatement: "a 'for' statement",
      IfStatement: "an 'if' statement",
      WhileStatement: "a 'while' statement"
  };
  
  //------------------------------------------------------------------------------
  // Rule Definition
  //------------------------------------------------------------------------------
  
  module.exports = {
      meta: {
          docs: {
              description: "disallow assignment operators in conditional expressions",
              category: "Possible Errors",
              recommended: true
          },
  
          schema: [
              {
                  enum: ["except-parens", "always"]
              }
          ]
      },
  
      create(context) {
  
          const prohibitAssign = (context.options[0] || "except-parens");
  
          const sourceCode = context.getSourceCode();
  
          /**
           * Check whether an AST node is the test expression for a conditional statement.
           * @param {!Object} node The node to test.
           * @returns {boolean} `true` if the node is the text expression for a conditional statement; otherwise, `false`.
           */
          function isConditionalTestExpression(node) {
              return node.parent &&
                  node.parent.test &&
                  node === node.parent.test;
          }
  
          /**
           * Given an AST node, perform a bottom-up search for the first ancestor that represents a conditional statement.
           * @param {!Object} node The node to use at the start of the search.
           * @returns {?Object} The closest ancestor node that represents a conditional statement.
           */
          function findConditionalAncestor(node) {
              let currentAncestor = node;
  
              do {
                  if (isConditionalTestExpression(currentAncestor)) {
                      return currentAncestor.parent;
                  }
              } while ((currentAncestor = currentAncestor.parent) && !astUtils.isFunction(currentAncestor));
  
              return null;
          }
  
          /**
           * Check whether the code represented by an AST node is enclosed in two sets of parentheses.
           * @param {!Object} node The node to test.
           * @returns {boolean} `true` if the code is enclosed in two sets of parentheses; otherwise, `false`.
           */
          function isParenthesisedTwice(node) {
              const previousToken = sourceCode.getTokenBefore(node, 1),
                  nextToken = sourceCode.getTokenAfter(node, 1);
  
              return astUtils.isParenthesised(sourceCode, node) &&
                  astUtils.isOpeningParenToken(previousToken) && previousToken.range[1] <= node.range[0] &&
                  astUtils.isClosingParenToken(nextToken) && nextToken.range[0] >= node.range[1];
          }
  
          /**
           * Check a conditional statement's test expression for top-level assignments that are not enclosed in parentheses.
           * @param {!Object} node The node for the conditional statement.
           * @returns {void}
           */
          function testForAssign(node) {
              if (node.test &&
                  (node.test.type === "AssignmentExpression") &&
                  (node.type === "ForStatement"
                      ? !astUtils.isParenthesised(sourceCode, node.test)
                      : !isParenthesisedTwice(node.test)
                  )
              ) {
  
                  // must match JSHint's error message
                  context.report({
                      node,
                      loc: node.test.loc.start,
                      message: "Expected a conditional expression and instead saw an assignment."
                  });
              }
          }
  
          /**
           * Check whether an assignment expression is descended from a conditional statement's test expression.
           * @param {!Object} node The node for the assignment expression.
           * @returns {void}
           */
          function testForConditionalAncestor(node) {
              const ancestor = findConditionalAncestor(node);
  
              if (ancestor) {
                  context.report({ node: ancestor, message: "Unexpected assignment within {{type}}.", data: {
                      type: NODE_DESCRIPTIONS[ancestor.type] || ancestor.type
                  } });
              }
          }
  
          if (prohibitAssign === "always") {
              return {
                  AssignmentExpression: testForConditionalAncestor
              };
          }
  
          return {
              DoWhileStatement: testForAssign,
              ForStatement: testForAssign,
              IfStatement: testForAssign,
              WhileStatement: testForAssign
          };
  
      }
  };