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QuickLook.Plugin/QuickLook.Plugin.TextViewer/Plugin.cs

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+using System.IO;
+using System.Windows;
+using ICSharpCode.AvalonEdit.Highlighting;
+
+namespace QuickLook.Plugin.TextViewer
+{
+    public class Plugin : IViewer
+    {
+        private TextViewerPanel _tvp;
+
+        public int Priority => 0;
+
+        public bool CanHandle(string path)
+        {
+            if (Directory.Exists(path))
+                return false;
+
+            const long MAX_SIZE = 20 * 1024 * 1024;
+
+            // if there is a possible highlighting scheme (by file extension), treat it as a plain text file
+            if (HighlightingManager.Instance.GetDefinitionByExtension(Path.GetExtension(path)) != null)
+                return new FileInfo(path).Length <= MAX_SIZE;
+
+            // otherwise, read the first 512 bytes as string (StreamReader handles encoding automatically),
+            // check whether they are all printable chars. 
+            using (var sr = new StreamReader(new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)))
+            {
+                var buffer = new char[512];
+                var len = sr.Read(buffer, 0, 512);
+
+                for (var i = 0; i < len; i++)
+                {
+                    if (!char.IsControl(buffer[i])) continue;
+
+                    if (buffer[i] != '\r' && buffer[i] != '\n' && buffer[i] != '\t')
+                        return false;
+                }
+
+                return new FileInfo(path).Length <= MAX_SIZE;
+            }
+        }
+
+        public void Prepare(string path, ViewContentContainer container)
+        {
+            container.PreferedSize = new Size {Width = 800, Height = 600};
+        }
+
+        public void View(string path, ViewContentContainer container)
+        {
+            _tvp = new TextViewerPanel(path);
+
+            container.SetContent(_tvp);
+            container.Title = $"{Path.GetFileName(path)}";
+        }
+
+        public void Close()
+        {
+        }
+    }
+}