algorithm for creating file tree structure from flat file paths (for kendo table)

fileTreeStructure.js

// algorithm for creating file tree structure from flat file paths (for kendo table)
function createFileTreeStructure(filePaths){

    var prefix;
    var items = {
        "root" : []
    };

    if(typeof filePaths === 'undefined' && filePaths.length == 0) {
        return null;
    }

    var pathArray = filePaths[0].split('/');

    // base path with orgId/proId/tmp...
    var basePath = pathArray.splice(0,3).join('/');

    for (var i = filePaths.length - 1; i >= 0; i--) {

        var path = filePaths[i].substring(basePath.length);

        var index = path.lastIndexOf('/');

        var node = {
            id: filePaths[i],
            text: path.substring(index + 1),
            spriteCssClass: 'file'
        };

        if (index <= 0) {
            items.root.unshift(node);
        } else {

            prefix = path.substring(0, index);


            while ((i>0 && !filePaths[i-1].startsWith(prefix, basePath.length)) || i==0) {

                index = prefix.lastIndexOf('/');

                if (typeof items[prefix] === 'undefined'){
                    items[prefix] = [];
                }

                items[prefix].unshift(node);

                node = {
                    id: basePath + prefix,
                    text: prefix.substring(index + 1),
                    spriteCssClass: 'folder',
                    items: items[prefix]
                };

                if (index == 0) {
                    prefix = "root";
                } else {
                    prefix = prefix.substring(0, index);
                }

            }
            if (typeof items[prefix] === 'undefined'){
                items[prefix] = [];
            }
            items[prefix].unshift(node);
        }
    }


    var fileTreeData = [{
        id: '',
        text: 'TEST-TRANSFER',
        expanded: true,
        spriteCssClass: 'rootfolder',
        items: items.root
    }];

    return fileTreeData;
}

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