unify diff generation before and after an edit

packages/core/src/tools/edit.ts

@@ -298,62 +298,26 @@ Expectation for required parameters:
       );
       return false;
     }
-    let currentContent: string | null = null;
-    let fileExists = false;
-    let finalNewString = params.new_string;
-    let finalOldString = params.old_string;
-    let occurrences = 0;
 
+    let editData: CalculatedEdit;
     try {
-      currentContent = fs.readFileSync(params.file_path, 'utf8');
-      // Normalize line endings to LF for consistent processing.
-      currentContent = currentContent.replace(/\r\n/g, '\n');
-      fileExists = true;
-    } catch (err: unknown) {
-      if (isNodeError(err) && err.code === 'ENOENT') {
-        fileExists = false;
-      } else {
-        console.error(`Error reading file for confirmation diff: ${err}`);
-        return false;
-      }
+      editData = await this.calculateEdit(params, abortSignal);
+    } catch (error) {
+      const errorMsg = error instanceof Error ? error.message : String(error);
+      console.log(`Error preparing edit: ${errorMsg}`);
+      return false;
     }
 
-    if (params.old_string === '' && !fileExists) {
-      // Creating new file, newContent is just params.new_string
-    } else if (!fileExists) {
-      return false; // Cannot edit non-existent file if old_string is not empty
-    } else if (currentContent !== null) {
-      const correctedEdit = await ensureCorrectEdit(
-        currentContent,
-        params,
-        this.client,
-        abortSignal,
-      );
-      finalOldString = correctedEdit.params.old_string;
-      finalNewString = correctedEdit.params.new_string;
-      occurrences = correctedEdit.occurrences;
-
-      const expectedReplacements = params.expected_replacements ?? 1;
-      if (occurrences === 0 || occurrences !== expectedReplacements) {
-        return false;
-      }
-    } else {
-      return false; // Should not happen
+    if (editData.error) {
+      console.log(`Error: ${editData.error.display}`);
+      return false;
     }
 
-    const isNewFileScenario = params.old_string === '' && !fileExists;
-    const newContent = this._applyReplacement(
-      currentContent,
-      finalOldString,
-      finalNewString,
-      isNewFileScenario,
-    );
-
     const fileName = path.basename(params.file_path);
     const fileDiff = Diff.createPatch(
       fileName,
-      currentContent ?? '',
-      newContent,
+      editData.currentContent ?? '',
+      editData.newContent,
       'Current',
       'Proposed',
       DEFAULT_DIFF_OPTIONS,