Core & Buffer Management #6

Buffer structure

• Create the Buffer struct
• Store file contents using Vec<String>
• Add cursor position tracking (row and column)
• Define cursor position invariants
• Prevent invalid cursor positions
• Handle empty lines correctly

File loading

• Implement fetch() to load file contents
• Handle missing files
• Handle empty files
• Handle file reading errors
• Preserve trailing empty lines
• Support large files

Buffer operations

• Implement line access helpers
• Implement character access helpers
• Implement line insertion
• Implement line deletion
• Implement character insertion
• Implement character deletion
• Implement buffer modification tracking

Cursor management

• Implement cursor boundary validation
• Handle cursor movement across empty lines
• Handle cursor movement across different line lengths
• Handle UTF-8 text correctly
• Add cursor position tests

Definition of Done

• Buffer operations never access invalid indexes.
• Empty buffers and empty lines are handled safely.
• Cursor coordinates remain consistent after modifications.
• Core operations are covered by unit tests.