checkFileForModifiedImports

# grunt-newer: 
# Check for newer @import .less files example
# See: https://github.com/tschaub/grunt-newer/issues/29

newer: {
    options: {
        /**
         * when changing a less file, we run an addional check on all the *.less files to see if they are @importing a modified *.less file, and if so we include it in the files which less task should execute.
         */
        override: function(details, shouldIncludeCallback) {
            var fs = require('fs');
            var path = require('path'); 
            var async = require('async');

            var checkFileForModifiedImports = async.memoize(function(filepath, fileCheckCallback) {
                fs.readFile(filepath, 'utf8', function(error, data) {
                    var directoryPath = path.dirname(filepath);
                    var regex = /@import (?:\([^)]+\) )?"(.+?)(\.less)?"/g
                    var match;

                    function checkNextImport() {
                        if ((match = regex.exec(data)) === null) {
                            return fileCheckCallback(false); // all @import files has been checked.
                        }

                        var importFilePath = path.join(directoryPath, match[1] + '.less');
                        fs.exists(importFilePath, function(exists) {
                            if (!exists) { // @import file does not exists.
                                return checkNextImport(); // skip to next
                            }

                            fs.stat(importFilePath, function(error, stats) {
                                if (stats.mtime > details.time) { // @import file has been modified, -> include it.
                                    fileCheckCallback(true);
                                }
                                else { // @import file has not been modified but, lets check the @import's of this file.
                                    checkFileForModifiedImports(importFilePath, function(hasModifiedImport) {
                                        if (hasModifiedImport) {
                                            fileCheckCallback(true);
                                        }
                                        else {
                                            checkNextImport();
                                        }
                                    });
                                }
                            });
                        });
                    };

                    checkNextImport();
                });
            });

            // only add override behavior to less tasks.
            if (details.task == 'less') {
                checkFileForModifiedImports(details.path, function(found) {
                    shouldIncludeCallback(found);
                });
            }
            else {
                shouldIncludeCallback(false);
            }
        }
    }
}