OData PageLink Header Builder

ODataPageLinkBuilder.cs

using System.Collections.Generic;
using System.Web.Http;
using System.Web.Http.Routing;

namespace System.Net.Http {
  /// <summary>
  /// OData PageLink Header Builder 
  /// </summary>
  //http://www.jerriepelser.com/blog/paging-in-aspnet-webapi-pagination-links
  public class ODataPageLinkBuilder {
    public const string TOTAL_COUNT_HEADER = "X-Total-Count";
    public const string SKIP = "$skip";
    public const string TOP = "$top";
    private const string FIRST = "first";
    private const string LAST = "last";
    private const string PREV = "prev";
    private const string NEXT = "next";
    private const string LINK = "Link";
    private const string LINK_TEMPLATE = "<{0}>; rel=\"{1}\"";
    public Uri FirstPage { get; private set; }
    public Uri LastPage { get; private set; }
    public Uri NextPage { get; private set; }
    public Uri PreviousPage { get; private set; }

    public ODataPageLinkBuilder(UrlHelper urlHelper,
      string routeName, object routeValues,
      int skip, int top, long totalItemCount) {
      // Determine total number of pages
      var pageCount = totalItemCount > 0
          ? (int)Math.Ceiling(totalItemCount / (double)top)
          : 0;
      var pageNumber = skip > 0
          ? (int)Math.Ceiling(skip / (double)top) + 1
          : 1;

      // Create them page links
      FirstPage = new Uri(
        urlHelper.Link(
          routeName,
          new HttpRouteValueDictionary(routeValues) {
            { SKIP, 0 },
            { TOP, top }
            }));
      LastPage = new Uri(
        urlHelper.Link(
          routeName,
          new HttpRouteValueDictionary(routeValues) {
            { SKIP, (pageCount - 1) * top },
            { TOP, top }
            }));
      if (pageNumber > 1) {
        PreviousPage = new Uri(
          urlHelper.Link(
            routeName,
            new HttpRouteValueDictionary(routeValues) {
              { SKIP, skip - top > 0 ? skip - top : 0 },
              { TOP, top }
              }));
      }
      if (pageNumber < pageCount) {
        NextPage = new Uri(
          urlHelper.Link(
            routeName,
            new HttpRouteValueDictionary(routeValues) {
              { SKIP, skip + top },
              { TOP, top }
              }));
      }
    }

    public string GetLink(Uri pageUri, string relName) {
      return string.Format(LINK_TEMPLATE, pageUri, relName);
    }

    public string GetLinks() {
      var links = new List<string>();
      if (FirstPage != null) {
        links.Add(GetLink(FirstPage, FIRST));
      }
      if (PreviousPage != null) {
        links.Add(GetLink(PreviousPage, PREV));
      }
      if (NextPage != null) {
        links.Add(GetLink(NextPage, NEXT));
      }
      if (LastPage != null) {
        links.Add(GetLink(LastPage, LAST));
      }
      return string.Join(", ", links);
    }

    public static HttpResponseMessage Build(ApiController control,
      string routeName,
      HttpResponseMessage response,
      int skip,int top,int totalItemCount) {
      response.Headers.TryAddWithoutValidation(TOTAL_COUNT_HEADER, totalItemCount.ToString());
      if (top > 0) {
        var linkBuilder = new ODataPageLinkBuilder(control.Url, routeName, control.Request.GetRouteData().Values, skip, top, totalItemCount);
        response.Headers.Add(LINK, linkBuilder.GetLinks());
      }
      return response;
    }
  }
}