Summary

This PR fixes critical issues with the text editor tool's diff generation and string replacement functionality, particularly for large files. The changes significantly improve the user experience by showing only relevant context in diffs and enabling robust multi-line string replacements.

Problem

Users reported that "the edit tool doesn't apply diffs correctly for larger files" (#12). Investigation revealed two major issues:

1. Excessive diff output: For a single line change in a 336-line file, the tool displayed all 336 lines in the confirmation dialog, making it impossible to review changes effectively
2. Failed multi-line replacements: Multi-line string replacements failed due to formatting differences (quotes, whitespace, indentation)

Before

• Single line change showed entire file: @@ -1,336 +1,336 @@
• Incorrect change count: "272 additions and 272 removals" for a 1-line change
• Multi-line replacements failed with "String not found in file"

After

• Single line change shows only context: @@ -62,7 +62,7 @@
• Accurate change count: "1 addition and 1 removal"
• Multi-line replacements work with intelligent fuzzy matching

Changes

1. Rewrote generateDiff method with proper unified diff algorithm

• Implements two-pass algorithm: first finds changes, then generates contextual hunks
• Shows only 3 lines of context before/after changes (configurable via CONTEXT_LINES)
• Merges nearby changes into single hunks for better readability
• Correctly calculates line numbers and change counts

2. Added fuzzy matching for multi-line string replacements

• New findFuzzyMatch method intelligently matches code blocks (especially functions)
• Uses structural matching based on brace counting and token analysis
• Handles differences in quotes, whitespace, and formatting
• Returns the actual content from the file for accurate replacement

3. Additional improvements

• Added replaceAll parameter to replace all occurrences (not just first)
• Added replaceLines method for line-based editing when string matching isn't suitable
• Improved user feedback with occurrence counts
• Better error messages guiding users to appropriate tools

Testing

Tested with:

• Large files (300+ lines) with single line changes
• Multi-line function replacements with formatting differences
• Multiple scattered changes throughout a file
• Adjacent changes that should merge into single hunks

Breaking Changes

None. The changes are backward compatible and improve existing functionality.

Screenshots

Before

After

Checklist

• Self-review completed
• No new warnings introduced
• Documentation updated if needed

Related Issues

Fixes #12 - Edit tool doesn't apply diffs correctly for larger files