Invalidate Cloudfront Cache from aws_s3 output in Grunt

invalidate-cache.js

// Pulls in the changed files from aws_s3 at run time and pass them
// into cloudfront invalidation

grunt.registerTask('invalidate_cache', 'Invalidate Cloudfront from aws_s3 output', function (subtask) {

    var aws_changed = grunt.config.get('aws_s3_changed'),
        task = 'cloudfront',
        changed_files;

    if ( !Array.isArray(aws_changed) ) {
        console.log('Changed files is not an array');
        return;
    }

    changed_files = aws_changed.map(function(file) {
        return '/' + file;
    });

    if ( subtask ) {
        task = task + ':' + subtask;
    }

    grunt.config.set('cloudfront.options.invalidations', changed_files);

    if ( !Array.isArray(changed_files) || changed_files.length === 0 ) {
        console.log('No files changed');
        return;
    }

    grunt.task.run(task);

});