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Fix #58: add autosave backup rotation and atomic write #59

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Fix #58: add autosave backup rotation and atomic write #59

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58 changes: 57 additions & 1 deletion grzyClothTool/Helpers/SaveHelper.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -150,7 +150,7 @@ public static async Task SaveAsync()

var saveFileName = GetSaveFileName(isExternalProject);
var autoSavePath = Path.Combine(projectFolder, saveFileName);
await File.WriteAllTextAsync(autoSavePath, json);
await WriteAutoSaveWithBackupAsync(autoSavePath, json);

LogHelper.Log($"Auto-saved to {autoSavePath} in {timer.ElapsedMilliseconds}ms");
}
Expand All @@ -173,6 +173,62 @@ public static async Task SaveAsync()
}
}

private static async Task WriteAutoSaveWithBackupAsync(string autoSavePath, string json)
{
var directory = Path.GetDirectoryName(autoSavePath);
if (string.IsNullOrWhiteSpace(directory))
{
throw new InvalidOperationException("Auto-save path directory is invalid.");
}

var fileName = Path.GetFileName(autoSavePath);
var tempPath = Path.Combine(directory, $"{fileName}.{Guid.NewGuid():N}.tmp");
var backupPath = $"{autoSavePath}.bak";
var hadOriginal = false;

try
{
await File.WriteAllTextAsync(tempPath, json);

if (File.Exists(autoSavePath))
{
hadOriginal = true;

if (File.Exists(backupPath))
{
File.Delete(backupPath);
}

File.Move(autoSavePath, backupPath);
}

// Atomic rename in same directory.
File.Move(tempPath, autoSavePath, overwrite: true);
}
catch
{
if (File.Exists(tempPath))
{
File.Delete(tempPath);
}

// If rotation already happened and new write failed, restore the previous autosave.
if (hadOriginal && !File.Exists(autoSavePath) && File.Exists(backupPath))
{
File.Move(backupPath, autoSavePath, overwrite: true);
}

throw;
}
finally
{
if (File.Exists(tempPath))
{
File.Delete(tempPath);
}
}
}

public static void SetUnsavedChanges(bool status)
{
HasUnsavedChanges = status;
Expand Down