How we built dynamic reports at SSRS 2014

[BasicAuthentication]
public class ReportProxyController : ApiController
{
    [HttpGet()]
    public List<ReportItem> Get(string rootPath)
    {
        //  ...
    }

    public HttpResponseMessage Post([FromBody]ReportRequest request)
    {
        //  ...
    }
}

public class BasicAuthenticationAttribute : AuthorizationFilterAttribute
{
    public override void OnAuthorization(HttpActionContext actionContext)
    {
        var authHeader = actionContext.Request.Headers.Authorization;

        if (authHeader != null)
        {
            var authenticationToken = actionContext.Request.Headers.Authorization.Parameter;
            var tokenFromBase64 = Convert.FromBase64String(authenticationToken);
            var decodedAuthenticationToken = Encoding.UTF8.GetString(tokenFromBase64);
            var usernamePasswordArray = decodedAuthenticationToken.Split(':');
            var userName = usernamePasswordArray[0];
            var password = usernamePasswordArray[1];

            var isValid = userName == BasiAuthConf.Login && password == BasiAuthConf.Password;

            if (isValid)
            {
                var principal = new GenericPrincipal(new GenericIdentity(userName), null);
                Thread.CurrentPrincipal = principal;

                return;
            }
        }

        HandleUnathorized(actionContext);
    }

    private static void HandleUnathorized(HttpActionContext actionContext)
    {
        actionContext.Response = actionContext.Request.CreateResponse(
            HttpStatusCode.Unauthorized
        );

        actionContext.Response.Headers.Add(
            "WWW-Authenticate", "Basic Scheme='Data' location = 'http://localhost:"
        );
    }
}

type FixationType = 'row' | 'column' | 'both';

init(reportHTML: HTMLElement) {
    //    

    // -  
    const rowsFixed: NodeList = reportHTML.querySelectorAll('[title^="RowFixed"]');
    // -  
    const columnFixed: NodeList = reportHTML.querySelectorAll('[title^="ColumnFixed"]');
    // -    
    const bothFixed: NodeList = reportHTML.querySelectorAll('[title^="BothFixed"]');

    this.prepare(rowsFixed, 'row');
    this.prepare(columnFixed, 'column');
    this.prepare(bothFixed, 'both');
}

//    
prepare(nodeList: NodeList, fixingType: FixationType) {
    for (let i = 0; i < nodeList.length; i++) {
        const element: HTMLElement = nodeList[i];
        //   -
        element.classList.add(fixingType + '-fixed');

        element.removeAttribute('title');
        element.removeAttribute('alt'); //   SSRS

        element.parentElement.classList.add(fixingType  + '-fixed-parent');

        //     ,     
        element.style.width = element.getBoundingClientRect().width  + 'px';
        //     ,     
        element.style.height = element.getBoundingClientRect().height  + 'px';

        //  
        this.calculateCellCascadeParams(element, fixingType);
    }
}

//      
calculateCellCascadeParams(cell: HTMLElement, fixationType: FixationType) {
    const currentTD: HTMLTableCellElement = cell.parentElement;
    const currentCellIndex = currentTD.cellIndex;

    //   
    currentTD.style.left = '';
    currentTD.style.top = '';

    const currentTDStyles = getComputedStyle(currentTD);

    //  
    if (fixationType === 'row' || fixationType === 'both') {
        const parentRow: HTMLTableRowElement = currentTD.parentElement;

        //        
        //    .
        //   ,    .
        let previousRow: HTMLTableRowElement = parentRow;
        let topOffset = 0;

        while (previousRow = previousRow.previousElementSibling) {
            let previousCellIndex = 0;
            let cellIndexBulk = 0;

            for (let i = 0; i < previousRow.cells.length; i++) {
                if (previousRow.cells[i].colSpan > 1) {
                    cellIndexBulk += previousRow.cells[i].colSpan;
                } else {
                    cellIndexBulk += 1;
                }

                if ((cellIndexBulk - 1) >= currentCellIndex) {
                    previousCellIndex = i;
                    break;
                }
            }

            const previousCell = previousRow.cells[previousCellIndex];

            if (previousCell.classList.contains(fixationType + '_fixed_parent')) {
                topOffset += previousCell.getBoundingClientRect().height;
            }
        }

        if (topOffset > 0) {
            if (currentTDStyles.top) {
                topOffset += <any>currentTDStyles.top.replace('px', '') - 0;
            }

            currentTD.style.top = topOffset + 'px';
        }
    }

    //  
    if (fixationType === 'column' || fixationType === 'both') {
        //       
        //     .
        //   ,    .
        let previousCell: HTMLTableCellElement = currentTD;
        let leftOffset = 0;

        while (previousCell = previousCell.previousElementSibling) {
            if (previousCell.classList.contains(fixationType + '_fixed_parent')) {
                leftOffset += previousCell.getBoundingClientRect().width;
            }
        }

        if (leftOffset > 0) {
            if (currentTDStyles.left) {
                leftOffset += <any>currentTDStyles.left.replace('px', '') - 0;
            }

            currentTD.style.left = leftOffset + 'px';
        }
    }
}