/**
 * @fileoverview Rule to flag the generator functions that does not have yield.
 * @author Toru Nagashima
 * @copyright 2015 Toru Nagashima. All rights reserved.
 */

"use strict";

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

module.exports = function(context) {
    var stack = [];

    /**
     * If the node is a generator function, start counting `yield` keywords.
     * @param {Node} node - A function node to check.
     * @returns {void}
     */
    function beginChecking(node) {
        if (node.generator) {
            stack.push(0);
        }
    }

    /**
     * If the node is a generator function, end counting `yield` keywords, then
     * reports result.
     * @param {Node} node - A function node to check.
     * @returns {void}
     */
    function endChecking(node) {
        if (!node.generator) {
            return;
        }

        var countYield = stack.pop();
        if (countYield === 0 && node.body.body.length > 0) {
            context.report(
                node,
                "This generator function does not have `yield`.");
        }
    }

    return {
        "FunctionDeclaration": beginChecking,
        "FunctionDeclaration:exit": endChecking,
        "FunctionExpression": beginChecking,
        "FunctionExpression:exit": endChecking,

        // Increases the count of `yield` keyword.
        "YieldExpression": function() {
            /* istanbul ignore else */
            if (stack.length > 0) {
                stack[stack.length - 1] += 1;
            }
        }
    };
};

module.exports.schema = [];