feat(diff): add helper function to create synthetic diffs for new files

This update introduces a new function, createNewFileDiff, to streamline the generation of synthetic diffs for untracked files. The function reduces code duplication by handling the diff formatting for new files, including directories and large files, improving overall maintainability.

libs/git-utils/src/diff.ts

@@ -24,6 +24,24 @@ function isBinaryFile(filePath: string): boolean {
   return BINARY_EXTENSIONS.has(ext);
 }
 
+/**
+ * Create a synthetic diff for a new file with the given content lines
+ * This helper reduces duplication in diff generation logic
+ */
+function createNewFileDiff(relativePath: string, mode: string, contentLines: string[]): string {
+  const lineCount = contentLines.length;
+  const addedLines = contentLines.map((line) => `+${line}`).join('\n');
+
+  return `diff --git a/${relativePath} b/${relativePath}
+new file mode ${mode}
+index 0000000..0000000
+--- /dev/null
++++ b/${relativePath}
+@@ -0,0 +${lineCount === 1 ? '1' : `1,${lineCount}`} @@
+${addedLines}
+`;
+}
+
 /**
  * Generate a synthetic unified diff for an untracked (new) file
  * This is needed because `git diff HEAD` doesn't include untracked files
@@ -49,26 +67,14 @@ Binary file ${relativePath} added
 
     // Check if it's a directory (can happen with untracked directories from git status)
     if (stats.isDirectory()) {
-      return `diff --git a/${relativePath} b/${relativePath}
+      return createNewFileDiff(relativePath, '040000', ['[Directory]']);
-new file mode 040000
-index 0000000..0000000
---- /dev/null
-+++ b/${relativePath}
-@@ -0,0 +1 @@
-+[Directory]
-`;
     }
 
     if (stats.size > MAX_SYNTHETIC_DIFF_SIZE) {
       const sizeKB = Math.round(stats.size / 1024);
-      return `diff --git a/${relativePath} b/${relativePath}
+      return createNewFileDiff(relativePath, '100644', [
-new file mode 100644
+        `[File too large to display: ${sizeKB}KB]`,
-index 0000000..0000000
+      ]);
---- /dev/null
-+++ b/${relativePath}
-@@ -0,0 +1 @@
-+[File too large to display: ${sizeKB}KB]
-`;
     }
 
     // Read file content
@@ -103,14 +109,7 @@ ${addedLines}`;
     // Log the error for debugging
     logger.error(`Failed to generate synthetic diff for ${fullPath}:`, error);
     // Return a placeholder diff
-    return `diff --git a/${relativePath} b/${relativePath}
+    return createNewFileDiff(relativePath, '100644', ['[Unable to read file content]']);
-new file mode 100644
-index 0000000..0000000
---- /dev/null
-+++ b/${relativePath}
-@@ -0,0 +1 @@
-+[Unable to read file content]
-`;
   }
 }