document.body.addEventListener('drop', function(e) {
    e.preventDefault();
    upload(e, '/tmp').then(() => console.log('DONE!'));
});
document.body.addEventListener('dragover', function(e) {
    e.preventDefault();
});
document.body.addEventListener('dragenter', function(e) {
    e.preventDefault();
});


function upload_file(file, path) {
    return new Promise(function(resolve) {
        console.log('UPLOAD TO ' + path);
        console.log(file);
        resolve();
    });
}
function upload(e, path) {
    const files = Array.from(event.dataTransfer.files || event.target.files || []);
    const items = Array.from(event.dataTransfer.items);
    return new Promise(function(resolve, reject) {
        if (items && items.length) {
            if (items[0].webkitGetAsEntry) {
                var entries = [];
                items.forEach(function(item) {
                    var entry = item.webkitGetAsEntry();
                    if (entry) {
                        entries.push(entry);
                    }
                });
                (function recur() {
                    var entry = entries.shift();
                    if (entry) {
                        process_tree(entry, upload_file, path).then(recur);
                    } else {
                        resolve();
                    }
                })();
            }
        } else if (files && files.length) {
            (function recur() {
                var file = files.shift();
                if (entry) {
                    upload_file(file).then(recur);
                } else {
                    resolve();
                }
            })();
        } else if (event.dataTransfer.getFilesAndDirectories) {
            event.dataTransfer.getFilesAndDirectories().then(function(items) {
                (function recur() {
                    var item = items.shift();
                    if (entry) {
                        process_tree(item, upload_file, path).then(recur);
                    } else {
                        resolve();
                    }
                })();
            });
        } else {
            resolve();
        }
    });
}
function process_tree(tree, process_file, path) {
    return new Promise(function(resolve, reject) {
        function process(entries, callback) {
            entries = entries.slice();
            (function recur() {
                var entry = entries.shift();
                if (entry) {
                    callback(entry).then(recur).catch(reject);
                } else {
                    resolve();
                }
            })();
        }
        function process_and_resolve(file) {
            process_file(file, path).then(resolve).catch(reject);
        }
        function process_entries(entries) {
            process(entries, function(entry) {
                return process_tree(entry, process_file, path + "/" + tree.name);
            });
        }
        if (typeof Directory != 'undefined' && tree instanceof Directory) { // firefox
            tree.getFilesAndDirectories().then(process_entries);
        } else if (typeof File != 'undefined' && tree instanceof File) { // firefox
            process_and_resolve(tree);
        } else if (tree.isFile) { // chrome
            tree.file(process_and_resolve);
        } else if (tree.isDirectory) { // chrome
            var dirReader = tree.createReader();
            dirReader.readEntries(process_entries);
        }
    });
}