Fix broken paging (#136)

* Add unit tests
* Use calculated page size instead of page

Co-authored-by: ITDancer139 <kevinitdancersommer@gmail.com>

Sieve/Models/SieveOptions.cs

@@ -10,6 +10,7 @@
         /// <summary>
         /// Fallback value of no page size is specified in the request.
         /// </summary>
+        /// <remarks>Values less or equal to 0 disable paging.</remarks>
         public int DefaultPageSize { get; set; } = 0;
 
         /// <summary>

Sieve/Services/SieveProcessor.cs

@@ -389,7 +389,7 @@ namespace Sieve.Services
             }
 
             result = result.Skip((page - 1) * pageSize);
-            result = result.Take(page);
+            result = result.Take(pageSize);
 
             return result;
         }

SieveUnitTests/General.cs

@@ -613,5 +613,44 @@ namespace SieveUnitTests
             Assert.Equal(1,posts[2].Id);
             Assert.Equal(0,posts[3].Id);
         }
+        
+        [Theory]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        [InlineData(4)]
+        public void Paging_DifferentPages(int page)
+        {
+            var model = new SieveModel
+            {
+                Page = page,
+                PageSize = 1,
+            };
+
+            var result = _processor.Apply(model, _posts);
+            var posts = result.ToList();
+            
+            Assert.Single(posts);
+            var expectedId = page - 1;
+            Assert.Equal(expectedId, posts.First().Id);
+        }
+        
+        [Theory]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        [InlineData(4)]
+        public void Paging_DifferentPageSizes(int pageSize)
+        {
+            var model = new SieveModel
+            {
+                Page = 1,
+                PageSize = pageSize,
+            };
+
+            var result = _processor.Apply(model, _posts);
+
+            Assert.Equal(pageSize, result.Count());
+        }
     }
 }