Fixed page preview caching

Author: Albert Kapitanov

src/ITGlobal.MarkDocs.Core/Impl/PagePreview.cs

@@ -1,4 +1,4 @@
-using ITGlobal.MarkDocs.Cache;
+using ITGlobal.MarkDocs.Cache;
 using ITGlobal.MarkDocs.Cache.Model;
 using System.IO;
 
@@ -20,7 +20,7 @@ public PagePreview(ICacheReader cache, IDocumentation documentation, PagePreview
         public string Id => _model.Id;
         public IDocumentation Documentation { get; }
         public string RelativePath => _model.RelativePath;
-        public ResourceType Type => ResourceType.Page;
+        public ResourceType Type => ResourceType.PagePreview;
         public IPage Page { get; }
 
         public Stream OpenRead() => _cache.Read(this);

src/ITGlobal.MarkDocs.Markdown/Format/Impl/Extensions/LaTeX/CodecogsGeneratedAsset.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.IO;
 using System.Net.Http;
 using ITGlobal.MarkDocs.Source;
@@ -37,7 +37,7 @@ public void Write(Stream stream)
             }
             catch (HttpRequestException e)
             {
-                MarkdownPageRenderContext.Current?.Error($"Failed to render math markup. {e.Message}", _lineNumber);
+                MarkdownPageRenderContext.CurrentNullable?.Error($"Failed to render math markup. {e.Message}", _lineNumber);
             }
         }
     }

src/ITGlobal.MarkDocs.Markdown/Format/Impl/Extensions/PlantUml/PlantUmlGeneratedContent.cs

@@ -33,7 +33,7 @@ public void Write(Stream stream)
             }
             catch (HttpRequestException e)
             {
-                MarkdownPageRenderContext.Current?.Error($"Failed to render PlantUML markup. {e.Message}", _lineNumber);
+                MarkdownPageRenderContext.CurrentNullable?.Error($"Failed to render PlantUML markup. {e.Message}", _lineNumber);
             }
         }
     }

src/ITGlobal.MarkDocs.Markdown/Format/Impl/MarkdownPageRenderContext.cs

@@ -1,17 +1,21 @@
-using System;
+using System;
 using System.Threading;
 
 namespace ITGlobal.MarkDocs.Format.Impl
 {
     internal static class MarkdownPageRenderContext
     {
+
         public static bool IsPresent => CurrentState.Value != null;
 
-        public static IPageRenderContext Current => Get(_ => _);
+        public static IPageRenderContext Current => Get(_ => _, canBeNull: false);
+        public static IPageRenderContext CurrentNullable => Get(_ => _, canBeNull: true);
 
         public struct ScopeToken : IDisposable
         {
+
             public void Dispose() => ClearContext();
+
         }
 
         public static ScopeToken Use(IPageRenderContext context)
@@ -24,15 +28,22 @@ public static ScopeToken Use(IPageRenderContext context)
 
         private static readonly ThreadLocal<IPageRenderContext> CurrentState = new ThreadLocal<IPageRenderContext>();
 
-        private static T Get<T>(Func<IPageRenderContext, T> f)
+        private static T Get<T>(Func<IPageRenderContext, T> f, bool canBeNull)
+            where T : class
         {
             var state = CurrentState.Value;
             if (state == null)
             {
+                if (canBeNull)
+                {
+                    return null;
+                }
+
                 throw new InvalidOperationException("No active MarkdownRenderingContext");
             }
 
             return f(state);
         }
+
     }
 }