private async calculateEdit()

in packages/core/src/tools/edit.ts [201:290]
77 lines of code
14 McCabe index (conditional complexity)

  private async calculateEdit(
    params: EditToolParams,
    abortSignal: AbortSignal,
  ): Promise<CalculatedEdit> {
    const expectedReplacements = params.expected_replacements ?? 1;
    let currentContent: string | null = null;
    let fileExists = false;
    let isNewFile = false;
    let finalNewString = params.new_string;
    let finalOldString = params.old_string;
    let occurrences = 0;
    let error: { display: string; raw: string } | undefined = undefined;

    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') {
        // Rethrow unexpected FS errors (permissions, etc.)
        throw err;
      }
      fileExists = false;
    }

    if (params.old_string === '' && !fileExists) {
      // Creating a new file
      isNewFile = true;
    } else if (!fileExists) {
      // Trying to edit a non-existent file (and old_string is not empty)
      error = {
        display: `File not found. Cannot apply edit. Use an empty old_string to create a new file.`,
        raw: `File not found: ${params.file_path}`,
      };
    } else if (currentContent !== null) {
      // Editing an existing file
      const correctedEdit = await ensureCorrectEdit(
        currentContent,
        params,
        this.client,
        abortSignal,
      );
      finalOldString = correctedEdit.params.old_string;
      finalNewString = correctedEdit.params.new_string;
      occurrences = correctedEdit.occurrences;

      if (params.old_string === '') {
        // Error: Trying to create a file that already exists
        error = {
          display: `Failed to edit. Attempted to create a file that already exists.`,
          raw: `File already exists, cannot create: ${params.file_path}`,
        };
      } else if (occurrences === 0) {
        error = {
          display: `Failed to edit, could not find the string to replace.`,
          raw: `Failed to edit, 0 occurrences found for old_string in ${params.file_path}. No edits made. The exact text in old_string was not found. Ensure you're not escaping content incorrectly and check whitespace, indentation, and context. Use ${ReadFileTool.Name} tool to verify.`,
        };
      } else if (occurrences !== expectedReplacements) {
        const occurenceTerm =
          expectedReplacements === 1 ? 'occurrence' : 'occurrences';

        error = {
          display: `Failed to edit, expected ${expectedReplacements} ${occurenceTerm} but found ${occurrences}.`,
          raw: `Failed to edit, Expected ${expectedReplacements} ${occurenceTerm} but found ${occurrences} for old_string in file: ${params.file_path}`,
        };
      }
    } else {
      // Should not happen if fileExists and no exception was thrown, but defensively:
      error = {
        display: `Failed to read content of file.`,
        raw: `Failed to read content of existing file: ${params.file_path}`,
      };
    }

    const newContent = this._applyReplacement(
      currentContent,
      finalOldString,
      finalNewString,
      isNewFile,
    );

    return {
      currentContent,
      newContent,
      occurrences,
      error,
      isNewFile,
    };
  }