feat: phase 3 for git integration

src/main/engine/GitEngine.ts

@@ -36,6 +36,11 @@ export interface GitStatusDto {
   counts: GitStatusCounts;
 }
 
+export interface GitDiffDto {
+  filePath: string;
+  patch: string;
+}
+
 export type GitInitPhase =
   | 'checking-git'
   | 'initializing-repo'
@@ -217,6 +222,16 @@ export class GitEngine {
     };
   }
 
+  async getDiff(projectPath: string, filePath: string): Promise<GitDiffDto> {
+    const git = simpleGit(projectPath);
+    const patch = await git.diff(['--', filePath]);
+
+    return {
+      filePath,
+      patch,
+    };
+  }
+
   async ensureGitignore(projectPath: string): Promise<GitIgnoreEnsureResult> {
     const gitignorePath = path.join(projectPath, '.gitignore');