Refactor partitioning, don't create empty files

Closes #246

DiscordChatExporter.Cli/Commands/ExportDirectMessagesCommand.cs

@@ -3,6 +3,7 @@ using System.Net;
 using System.Threading.Tasks;
 using CliFx.Attributes;
 using CliFx.Services;
+using DiscordChatExporter.Core.Models.Exceptions;
 using DiscordChatExporter.Core.Services;
 using DiscordChatExporter.Core.Services.Exceptions;
 
@@ -39,6 +40,10 @@ namespace DiscordChatExporter.Cli.Commands
                 {
                     console.Error.WriteLine("This channel doesn't exist.");
                 }
+                catch (DomainException ex)
+                {
+                    console.Error.WriteLine(ex.Message);
+                }
             }
         }
     }

DiscordChatExporter.Cli/Commands/ExportGuildCommand.cs

@@ -4,6 +4,7 @@ using System.Threading.Tasks;
 using CliFx.Attributes;
 using CliFx.Services;
 using DiscordChatExporter.Core.Models;
+using DiscordChatExporter.Core.Models.Exceptions;
 using DiscordChatExporter.Core.Services;
 using DiscordChatExporter.Core.Services.Exceptions;
 
@@ -43,6 +44,10 @@ namespace DiscordChatExporter.Cli.Commands
                 {
                     console.Error.WriteLine("This channel doesn't exist.");
                 }
+                catch (DomainException ex)
+                {
+                    console.Error.WriteLine(ex.Message);
+                }
             }
         }
     }

DiscordChatExporter.Core.Models/Exceptions/DomainException.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace DiscordChatExporter.Core.Models.Exceptions
+{
+    public class DomainException : Exception
+    {
+        public DomainException(string message)
+            : base(message)
+        {
+        }
+    }
+}

DiscordChatExporter.Core.Rendering/CsvMessageRenderer.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System.IO;
+using System.Threading.Tasks;
 using DiscordChatExporter.Core.Models;
 using DiscordChatExporter.Core.Rendering.Logic;
 
@@ -8,8 +9,8 @@ namespace DiscordChatExporter.Core.Rendering
     {
         private bool _isHeaderRendered;
 
-        public CsvMessageRenderer(string filePath, RenderContext context)
-            : base(filePath, context)
+        public CsvMessageRenderer(TextWriter writer, RenderContext context)
+            : base(writer, context)
         {
         }
 

DiscordChatExporter.Core.Rendering/FacadeMessageRenderer.cs

@@ -0,0 +1,112 @@
+using System;
+using System.IO;
+using System.Threading.Tasks;
+using DiscordChatExporter.Core.Models;
+
+namespace DiscordChatExporter.Core.Rendering
+{
+    public partial class FacadeMessageRenderer : IMessageRenderer
+    {
+        private readonly string _baseFilePath;
+        private readonly ExportFormat _format;
+        private readonly RenderContext _context;
+
+        private int _partitionIndex;
+        private TextWriter _writer;
+        private IMessageRenderer _innerRenderer;
+
+        public FacadeMessageRenderer(string baseFilePath, ExportFormat format, RenderContext context)
+        {
+            _baseFilePath = baseFilePath;
+            _format = format;
+            _context = context;
+        }
+
+        private void EnsureInnerRendererInitialized()
+        {
+            if (_writer != null && _innerRenderer != null)
+                return;
+
+            // Get partition file path
+            var filePath = GetPartitionFilePath(_baseFilePath, _partitionIndex);
+
+            // Create output directory
+            var dirPath = Path.GetDirectoryName(_baseFilePath);
+            if (!string.IsNullOrWhiteSpace(dirPath))
+                Directory.CreateDirectory(dirPath);
+
+            // Create writer (will be disposed by renderer)
+            _writer = File.CreateText(filePath);
+
+            // Create inner renderer
+            if (_format == ExportFormat.PlainText)
+            {
+                _innerRenderer = new PlainTextMessageRenderer(_writer, _context);
+            }
+            else if (_format == ExportFormat.Csv)
+            {
+                _innerRenderer = new CsvMessageRenderer(_writer, _context);
+            }
+            else if (_format == ExportFormat.HtmlDark)
+            {
+                _innerRenderer = new HtmlMessageRenderer(_writer, _context, "Dark");
+            }
+            else if (_format == ExportFormat.HtmlLight)
+            {
+                _innerRenderer = new HtmlMessageRenderer(_writer, _context, "Light");
+            }
+            else
+            {
+                throw new InvalidOperationException($"Unknown export format [{_format}].");
+            }
+        }
+
+        public async Task NextPartitionAsync()
+        {
+            // Dispose writer and inner renderer
+            await DisposeAsync();
+            _writer = null;
+            _innerRenderer = null;
+
+            // Increment partition index
+            _partitionIndex++;
+        }
+
+        public async Task RenderMessageAsync(Message message)
+        {
+            EnsureInnerRendererInitialized();
+            await _innerRenderer.RenderMessageAsync(message);
+        }
+
+        public async ValueTask DisposeAsync()
+        {
+            if (_innerRenderer != null)
+                await _innerRenderer.DisposeAsync();
+
+            if (_writer != null)
+                await _writer.DisposeAsync();
+        }
+    }
+
+    public partial class FacadeMessageRenderer
+    {
+        private static string GetPartitionFilePath(string baseFilePath, int partitionIndex)
+        {
+            // First partition - no changes
+            if (partitionIndex <= 0)
+                return baseFilePath;
+
+            // Inject partition index into file name
+            var fileNameWithoutExt = Path.GetFileNameWithoutExtension(baseFilePath);
+            var fileExt = Path.GetExtension(baseFilePath);
+            var fileName = $"{fileNameWithoutExt} [part {partitionIndex + 1}]{fileExt}";
+
+            // Generate new path
+            var dirPath = Path.GetDirectoryName(baseFilePath);
+            if (!string.IsNullOrWhiteSpace(dirPath))
+                return Path.Combine(dirPath, fileName);
+
+            return fileName;
+        }
+    }
+}

DiscordChatExporter.Core.Rendering/HtmlMessageRenderer.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Reflection;
 using System.Threading.Tasks;
@@ -22,8 +23,8 @@ namespace DiscordChatExporter.Core.Rendering
 
         private bool _isLeadingBlockRendered;
 
-        public HtmlMessageRenderer(string filePath, RenderContext context, string themeName)
-            : base(filePath, context)
+        public HtmlMessageRenderer(TextWriter writer, RenderContext context, string themeName)
+            : base(writer, context)
         {
             _themeName = themeName;
 

DiscordChatExporter.Core.Rendering/MessageRendererBase.cs

@@ -10,14 +10,14 @@ namespace DiscordChatExporter.Core.Rendering
 
         protected RenderContext Context { get; }
 
-        protected MessageRendererBase(string filePath, RenderContext context)
+        protected MessageRendererBase(TextWriter writer, RenderContext context)
         {
-            Writer = File.CreateText(filePath);
+            Writer = writer;
             Context = context;
         }
 
         public abstract Task RenderMessageAsync(Message message);
 
-        public virtual ValueTask DisposeAsync() => Writer.DisposeAsync();
+        public virtual ValueTask DisposeAsync() => default;
     }
 }

DiscordChatExporter.Core.Rendering/PlainTextMessageRenderer.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System.IO;
+using System.Threading.Tasks;
 using DiscordChatExporter.Core.Models;
 using DiscordChatExporter.Core.Rendering.Logic;
 
@@ -8,8 +9,8 @@ namespace DiscordChatExporter.Core.Rendering
     {
         private bool _isPreambleRendered;
 
-        public PlainTextMessageRenderer(string filePath, RenderContext context)
-            : base(filePath, context)
+        public PlainTextMessageRenderer(TextWriter writer, RenderContext context)
+            : base(writer, context)
         {
         }
 

DiscordChatExporter.Core.Services/ExportService.cs

@@ -3,13 +3,14 @@ using System.Collections.Generic;
 using System.IO;
 using System.Threading.Tasks;
 using DiscordChatExporter.Core.Models;
+using DiscordChatExporter.Core.Models.Exceptions;
 using DiscordChatExporter.Core.Rendering;
 using DiscordChatExporter.Core.Services.Logic;
 using Tyrrrz.Extensions;
 
 namespace DiscordChatExporter.Core.Services
 {
-    public class ExportService
+    public partial class ExportService
     {
         private readonly SettingsService _settingsService;
         private readonly DataService _dataService;
@@ -20,47 +21,6 @@ namespace DiscordChatExporter.Core.Services
             _dataService = dataService;
         }
 
-        private string GetFilePathFromOutputPath(string outputPath, ExportFormat format, RenderContext context)
-        {
-            // Output is a directory
-            if (Directory.Exists(outputPath) || string.IsNullOrWhiteSpace(Path.GetExtension(outputPath)))
-            {
-                var fileName = ExportLogic.GetDefaultExportFileName(format, context.Guild, context.Channel, context.After, context.Before);
-                return Path.Combine(outputPath, fileName);
-            }
-
-            // Output is a file
-            return outputPath;
-        }
-
-        private IMessageRenderer CreateRenderer(string outputPath, int partitionIndex, ExportFormat format, RenderContext context)
-        {
-            var filePath = ExportLogic.GetExportPartitionFilePath(
-                GetFilePathFromOutputPath(outputPath, format, context),
-                partitionIndex);
-
-            // Create output directory
-            var dirPath = Path.GetDirectoryName(filePath);
-            if (!string.IsNullOrWhiteSpace(dirPath))
-                Directory.CreateDirectory(dirPath);
-
-            // Create renderer
-
-            if (format == ExportFormat.PlainText)
-                return new PlainTextMessageRenderer(filePath, context);
-
-            if (format == ExportFormat.Csv)
-                return new CsvMessageRenderer(filePath, context);
-
-            if (format == ExportFormat.HtmlDark)
-                return new HtmlMessageRenderer(filePath, context, "Dark");
-
-            if (format == ExportFormat.HtmlLight)
-                return new HtmlMessageRenderer(filePath, context, "Light");
-
-            throw new InvalidOperationException($"Unknown export format [{format}].");
-        }
-
         public async Task ExportChatLogAsync(AuthToken token, Guild guild, Channel channel,
             string outputPath, ExportFormat format, int? partitionLimit,
             DateTimeOffset? after = null, DateTimeOffset? before = null, IProgress<double>? progress = null)
@@ -76,35 +36,50 @@ namespace DiscordChatExporter.Core.Services
                 mentionableUsers, mentionableChannels, mentionableRoles
             );
 
-            // Render messages
-            var partitionIndex = 0;
-            var partitionMessageCount = 0;
-            var renderer = CreateRenderer(outputPath, partitionIndex, format, context);
+            // Create renderer
+            var baseFilePath = GetFilePathFromOutputPath(outputPath, format, context);
+            await using var renderer = new FacadeMessageRenderer(baseFilePath, format, context);
 
+            // Render messages
+            var messageCount = 0L;
             await foreach (var message in _dataService.GetMessagesAsync(token, channel.Id, after, before, progress))
             {
                 // Add encountered users to the list of mentionable users
                 mentionableUsers.Add(message.Author);
                 mentionableUsers.AddRange(message.MentionedUsers);
 
-                // If new partition is required, reset renderer
-                if (partitionLimit != null && partitionLimit > 0 && partitionMessageCount >= partitionLimit)
-                {
-                    partitionIndex++;
-                    partitionMessageCount = 0;
-
-                    // Flush old renderer and create a new one
-                    await renderer.DisposeAsync();
-                    renderer = CreateRenderer(outputPath, partitionIndex, format, context);
-                }
-
                 // Render message
                 await renderer.RenderMessageAsync(message);
-                partitionMessageCount++;
+                messageCount++;
+
+                // Trigger next partition when needed
+                if (partitionLimit != null &&
+                    partitionLimit != 0 &&
+                    messageCount % partitionLimit.Value == 0)
+                {
+                    await renderer.NextPartitionAsync();
+                }
             }
 
-            // Flush last renderer
-            await renderer.DisposeAsync();
+            // Throw if no messages were rendered
+            if (messageCount == 0)
+                throw new DomainException($"Channel [{channel.Name}] contains no messages for specified period");
+        }
+    }
+
+    public partial class ExportService
+    {
+        private static string GetFilePathFromOutputPath(string outputPath, ExportFormat format, RenderContext context)
+        {
+            // Output is a directory
+            if (Directory.Exists(outputPath) || string.IsNullOrWhiteSpace(Path.GetExtension(outputPath)))
+            {
+                var fileName = ExportLogic.GetDefaultExportFileName(format, context.Guild, context.Channel, context.After, context.Before);
+                return Path.Combine(outputPath, fileName);
+            }
+
+            // Output is a file
+            return outputPath;
         }
     }
 }

DiscordChatExporter.Core.Services/Logic/ExportLogic.cs

@@ -49,24 +49,5 @@ namespace DiscordChatExporter.Core.Services.Logic
 
             return buffer.ToString();
         }
-
-        public static string GetExportPartitionFilePath(string baseFilePath, int partitionIndex)
-        {
-            // First partition - no changes
-            if (partitionIndex <= 0)
-                return baseFilePath;
-
-            // Inject partition index into file name
-            var fileNameWithoutExt = Path.GetFileNameWithoutExtension(baseFilePath);
-            var fileExt = Path.GetExtension(baseFilePath);
-            var fileName = $"{fileNameWithoutExt} [part {partitionIndex + 1}]{fileExt}";
-
-            // Generate new path
-            var dirPath = Path.GetDirectoryName(baseFilePath);
-            if (!string.IsNullOrWhiteSpace(dirPath))
-                return Path.Combine(dirPath, fileName);
-
-            return fileName;
-        }
     }
 }

DiscordChatExporter.Gui/ViewModels/RootViewModel.cs

@@ -4,6 +4,7 @@ using System.Linq;
 using System.Net;
 using System.Threading.Tasks;
 using DiscordChatExporter.Core.Models;
+using DiscordChatExporter.Core.Models.Exceptions;
 using DiscordChatExporter.Core.Services;
 using DiscordChatExporter.Core.Services.Exceptions;
 using DiscordChatExporter.Gui.Services;
@@ -230,6 +231,10 @@ namespace DiscordChatExporter.Gui.ViewModels
             {
                 Notifications.Enqueue("Forbidden – account may be locked by 2FA");
             }
+            catch (DomainException ex)
+            {
+                Notifications.Enqueue(ex.Message);
+            }
             finally
             {
                 operation.Dispose();
@@ -276,6 +281,10 @@ namespace DiscordChatExporter.Gui.ViewModels
                 {
                     Notifications.Enqueue($"Channel [{channel.Model.Name}] doesn't exist");
                 }
+                catch (DomainException ex)
+                {
+                    Notifications.Enqueue(ex.Message);
+                }
                 finally
                 {
                     operation.Dispose();
@@ -283,6 +292,7 @@ namespace DiscordChatExporter.Gui.ViewModels
             }
 
             // Notify of overall completion
+            if (successfulExportCount > 0)
                 Notifications.Enqueue($"Successfully exported {successfulExportCount} channel(s)");
         }
     }