var readFirstNLines = (fileelement, count, process_content_fns) => {
    var thefile = fileelement.files[0];
    var reader = new FileReader();
    if(typeof thefile !== "undefined" && thefile !== null) {
        reader.addEventListener("load", (event) => {
            var content = event
                .target
                .result
                .split("\n")
                .slice(0, count)
                .map((line) => {return line.trim("\r");});
            process_content_fns.forEach((fn) => {fn(content);});
        });
        reader.readAsText(thefile);
    }
};
var read_first_n_lines = readFirstNLines;


var readBinaryFile = (file) => {
    return new Promise((resolve, reject) => {
        var _reader = new FileReader();
        _reader.onload = (event) => {resolve(_reader.result);};
        _reader.readAsArrayBuffer(file);
    });
};


var Uint8ArrayToHex = (arr) => {
    var toHex = (val) => {
        _hex = val.toString(16);
        if(_hex.length < 2) {
            return "0" + val;
        }
        return _hex;
    };
    _hexstr = ""
    arr.forEach((val) => {_hexstr += toHex(val)});
    return _hexstr
};


var computeFileChecksum = (file) => {
    return readBinaryFile(file)
        .then((content) => {
            return window.crypto.subtle.digest(
                "SHA-256", new Uint8Array(content));
        }).then((digest) => {
            return Uint8ArrayToHex(new Uint8Array(digest))
        });
};


var defaultResumableHandler = (event) => {
    throw new Error("Please provide a valid event handler!");
};

var addHandler = (resumable, handlername, handler) => {
    if(resumable.support) {
        resumable.on(handlername, (handler || defaultResumableHandler));
    }
    return resumable;
};


var makeResumableHandler = (handlername) => {
    return (resumable, handler) => {
        return addHandler(resumable, handlername, handler);
    };
};


var fileSuccessHandler = makeResumableHandler("fileSuccess");
var fileProgressHandler = makeResumableHandler("fileProgress");
var fileAddedHandler = makeResumableHandler("fileAdded");
var filesAddedHandler = makeResumableHandler("filesAdded");
var filesRetryHandler = makeResumableHandler("filesRetry");
var filesErrorHandler = makeResumableHandler("filesError");
var uploadStartHandler = makeResumableHandler("uploadStart");
var completeHandler = makeResumableHandler("complete");
var progressHandler = makeResumableHandler("progress");
var errorHandler = makeResumableHandler("error");


var markResumableDragAndDropElement = (resumable, fileinput, droparea, browsebutton) => {
    if(resumable.support) {
        //Hide file input element and display drag&drop UI
        add_class(fileinput, "hidden");
        remove_class(droparea, "hidden");

        // Define UI elements for browse and drag&drop
        resumable.assignDrop(droparea);
        resumable.assignBrowse(browsebutton);
    }

    return resumable;
};


var makeResumableElement = (targeturi, fileinput, droparea, uploadbutton, filetype) => {
    var resumable = Resumable({
        target: targeturi,
        fileType: filetype,
        maxFiles: 1,
        forceChunkSize: true,
        generateUniqueIdentifier: (file, event) => {
            return computeFileChecksum(file).then((checksum) => {
                var _relativePath = (file.webkitRelativePath
                                     || file.relativePath
                                     || file.fileName
                                     || file.name);
                return checksum + "-" + _relativePath.replace(
                    /[^a-zA-Z0-9_-]/img, "");
            });
        }
    });

    return resumable;
};