/**
 * @fileoverview Rule for disallowing require() outside of the top-level module context
 * @author Jamund Ferguson
 * @copyright 2015 Jamund Ferguson. All rights reserved.
 */

"use strict";

var ACCEPTABLE_PARENTS = [
    "AssignmentExpression",
    "VariableDeclarator",
    "MemberExpression",
    "ExpressionStatement",
    "CallExpression",
    "ConditionalExpression",
    "Program",
    "VariableDeclaration"
];

/**
 * Finds the escope reference in the given scope.
 * @param {Object} scope The scope to search.
 * @param {ASTNode} node The identifier node.
 * @returns {Reference|null} Returns the found reference or null if none were found.
 */
function findReference(scope, node) {
    var references = scope.references.filter(function(reference) {
        return reference.identifier.range[0] === node.range[0] &&
            reference.identifier.range[1] === node.range[1];
    });

    /* istanbul ignore else: correctly returns null */
    if (references.length === 1) {
        return references[0];
    } else {
        return null;
    }
}

/**
 * Checks if the given identifier node is shadowed in the given scope.
 * @param {Object} scope The current scope.
 * @param {ASTNode} node The identifier node to check.
 * @returns {boolean} Whether or not the name is shadowed.
 */
function isShadowed(scope, node) {
    var reference = findReference(scope, node);

    return reference && reference.resolved && reference.resolved.defs.length > 0;
}

module.exports = function(context) {
    return {
        "CallExpression": function(node) {
            var currentScope = context.getScope(),
                isGoodRequire;

            if (node.callee.name === "require" && !isShadowed(currentScope, node.callee)) {
                isGoodRequire = context.getAncestors().every(function(parent) {
                    return ACCEPTABLE_PARENTS.indexOf(parent.type) > -1;
                });
                if (!isGoodRequire) {
                    context.report(node, "Unexpected require().");
                }
            }
        }
    };
};

module.exports.schema = [];
