edit_core

A small, dependency-free text editing core for building a terminal or GUI editor. It models a buffer of lines, a cursor, and a viewport, and applies editing actions (movement, insertion, deletion) while keeping the cursor visible.

Features

• Line-oriented buffer with UTF-8 safe, character-based indexing.
• Cursor movement across lines with automatic clamping.
• UTF-8-aware word movement (MoveWordLeft, MoveWordRight) with consistent token jumps.
• Insert, delete, and newline actions.
• Viewport scrolling with visible line slicing.
• Dirty flag tracking for mutations only.

Usage

use edit_core::{Action, Buffer, Editor, Viewport};

let buffer = Buffer::from_text("hello\nworld");
let viewport = Viewport::new(5, 40);
let mut editor = Editor::new(buffer, viewport);

editor.apply(Action::MoveRight);
editor.apply(Action::Insert('!'));

assert_eq!(editor.buffer().as_text(), "h!ello\nworld");

Public API

Types

• Buffer: Stores the text as a vector of lines.
• Cursor: Row and column position (character-based).
• Viewport: Visible window with row/column offsets and size.
• Action: Editing actions (character movement, word movement, insertion, deletion, newline).
• Editor: Applies actions to a buffer while managing cursor, viewport, and dirty state.

Buffer

• Buffer::new() -> Buffer
• Buffer::from_text(text: &str) -> Buffer
• Buffer::as_text(&self) -> String
• Buffer::line(&self, row: usize) -> Option<&str>
• Buffer::line_count(&self) -> usize

Cursor

• Cursor::new(row: usize, col: usize) -> Cursor
• Fields: row, col

Viewport

• Viewport::new(height: usize, width: usize) -> Viewport
• Fields: row_offset, col_offset, height, width

Action

• MoveLeft, MoveRight, MoveWordLeft, MoveWordRight, MoveUp, MoveDown
• Insert(char)
• DeleteBackward, DeleteForward
• Newline

Word movement behavior:

• Skip leading whitespace first.
• Jump an identifier run [A-Za-z0-9_]+ as one token.
• Treat punctuation/symbol characters as single-token jumps.
• Cross line boundaries when needed.

Editor

• Editor::new(buffer: Buffer, viewport: Viewport) -> Editor
• Editor::buffer(&self) -> &Buffer
• Editor::cursor(&self) -> Cursor
• Editor::viewport(&self) -> Viewport
• Editor::set_viewport(&mut self, viewport: Viewport)
• Editor::is_dirty(&self) -> bool
• Editor::reset_dirty(&mut self)
• Editor::apply(&mut self, action: Action)
• Editor::visible_lines(&self) -> Vec<String>
• Editor::cursor_screen_pos(&self) -> (usize, usize)

Notes

• Rows and columns are character indices, not byte offsets.
• visible_lines returns slices based on the current viewport offsets and size.

Internal Layout

• src/lib.rs: Crate wiring and re-exports.
• src/types.rs: Public types (Action, Cursor, Viewport).
• src/buffer.rs: Line-based text storage.
• src/editor.rs: Editing engine and cursor/viewport behavior.
• src/text.rs: UTF-8 helper routines for character-safe slicing/indexing.