Added DirectoryInfo.FreeDiskSpace to get the free disk space of any directory.

NzbDrone.Core.Test/FluentTest.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Linq;
 using System.Net;
 using System.ServiceModel.Syndication;
 using AutoMoq;
@@ -91,5 +92,13 @@ namespace NzbDrone.Core.Test
             Console.WriteLine(dateTime.DayOfWeek);
             dateTime.ToBestDateString().Should().Be(dateTime.ToShortDateString());
         }
+
+        [Test]
+        public void FreeDiskSpace()
+        {
+            //Checks to ensure that the free space on the first is greater than 0 (It should be in 99.99999999999999% of cases... I hope)
+            var di = DriveInfo.GetDrives().First().RootDirectory;
+            di.FreeDiskSpace().Should().BeGreaterThan(0);
+        }
     }
 }

NzbDrone.Core/Fluent.cs

@@ -1,11 +1,20 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
+using System.Runtime.InteropServices;
 using System.Text;
 
 namespace NzbDrone.Core
 {
     public static class Fluent
     {
+        [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        static extern bool GetDiskFreeSpaceEx(string lpDirectoryName,
+        out ulong lpFreeBytesAvailable,
+        out ulong lpTotalNumberOfBytes,
+        out ulong lpTotalNumberOfFreeBytes);
+
         public static string WithDefault(this string actual, object defaultValue)
         {
             if (defaultValue == null)
@@ -18,7 +27,6 @@ namespace NzbDrone.Core
             return actual;
         }
 
-
         public static Int64 Megabytes(this int megabytes)
         {
             return megabytes * 1048576L;
@@ -45,5 +53,19 @@ namespace NzbDrone.Core
 
             return dateTime.ToShortDateString();
         }
+
+        public static ulong FreeDiskSpace(this DirectoryInfo directoryInfo)
+        {
+            ulong freeBytesAvailable;
+            ulong totalNumberOfBytes;
+            ulong totalNumberOfFreeBytes;
+
+            bool success = GetDiskFreeSpaceEx(directoryInfo.FullName, out freeBytesAvailable, out totalNumberOfBytes,
+                               out totalNumberOfFreeBytes);
+            if (!success)
+                throw new System.ComponentModel.Win32Exception();
+
+            return freeBytesAvailable;
+        }
     }
 }