namespace GMap.NET.Projections
{
   using System;

   /// <summary>
   /// The Mercator projection
   /// PROJCS["World_Mercator",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Mercator"],PARAMETER["False_Easting",0],PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",0],PARAMETER["standard_parallel_1",0],UNIT["Meter",1]]
   /// </summary>
   public class MercatorProjection : PureProjection
   {
      public static readonly MercatorProjection Instance = new MercatorProjection();

      static readonly double MinLatitude = -85.05112878;
      static readonly double MaxLatitude = 85.05112878;
      static readonly double MinLongitude = -180;
      static readonly double MaxLongitude = 180;

      public override RectLatLng Bounds
      {
         get
         {
            return RectLatLng.FromLTRB(MinLongitude, MaxLatitude, MaxLongitude, MinLatitude);
         }
      }

      readonly GSize tileSize = new GSize(256, 256);
      public override GSize TileSize
      {
         get
         {
            return tileSize;
         }
      }

      public override double Axis
      {
         get
         {
            return 6378137;
         }
      }

      public override double Flattening
      {
         get
         {
            return (1.0 / 298.257223563);
         }
      }

      public override GPoint FromLatLngToPixel(double lat, double lng, int zoom)
      {
         GPoint ret = GPoint.Empty;

         lat = Clip(lat, MinLatitude, MaxLatitude);
         lng = Clip(lng, MinLongitude, MaxLongitude);

         double x = (lng + 180) / 360;
         double sinLatitude = Math.Sin(lat * Math.PI / 180);
         double y = 0.5 - Math.Log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI);

         GSize s = GetTileMatrixSizePixel(zoom);
         long mapSizeX = s.Width;
         long mapSizeY = s.Height;

         ret.X = (long)Clip(x * mapSizeX + 0.5, 0, mapSizeX - 1);
         ret.Y = (long)Clip(y * mapSizeY + 0.5, 0, mapSizeY - 1);

         return ret;
      }

      public override PointLatLng FromPixelToLatLng(long x, long y, int zoom)
      {
         PointLatLng ret = PointLatLng.Empty;

         GSize s = GetTileMatrixSizePixel(zoom);
         double mapSizeX = s.Width;
         double mapSizeY = s.Height;

         double xx = (Clip(x, 0, mapSizeX - 1) / mapSizeX) - 0.5;
         double yy = 0.5 - (Clip(y, 0, mapSizeY - 1) / mapSizeY);

         ret.Lat = 90 - 360 * Math.Atan(Math.Exp(-yy * 2 * Math.PI)) / Math.PI;
         ret.Lng = 360 * xx;

         return ret;
      }

      public override GSize GetTileMatrixMinXY(int zoom)
      {
         return new GSize(0, 0);
      }

      public override GSize GetTileMatrixMaxXY(int zoom)
      {
         long xy = (1 << zoom);
         return new GSize(xy - 1, xy - 1);
      }
   }
}