tui-textarea 0.3.1

tui-textarea is a simple yet powerful text editor widget for ratatui and tui-rs. Multi-line text editor can be easily put as part of your TUI application.
Documentation 
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use std::collections::VecDeque;

#[derive(Clone, Debug)]
pub enum EditKind {
    InsertChar(char, usize),
    DeleteChar(char, usize),
    InsertNewline(usize),
    DeleteNewline(usize),
    Insert(String, usize),
    Remove(String, usize),
}

impl EditKind {
    fn apply(&self, row: usize, lines: &mut Vec<String>) {
        match self {
            EditKind::InsertChar(c, i) => {
                lines[row].insert(*i, *c);
            }
            EditKind::DeleteChar(_, i) => {
                lines[row].remove(*i);
            }
            EditKind::InsertNewline(i) => {
                let line = &mut lines[row];
                let next_line = line[*i..].to_string();
                line.truncate(*i);
                lines.insert(row + 1, next_line);
            }
            EditKind::DeleteNewline(_) => {
                if row > 0 {
                    let line = lines.remove(row);
                    lines[row - 1].push_str(&line);
                }
            }
            EditKind::Insert(s, i) => {
                lines[row].insert_str(*i, s.as_str());
            }
            EditKind::Remove(s, i) => {
                let end = *i + s.len();
                lines[row].replace_range(*i..end, "");
            }
        }
    }

    fn invert(&self) -> Self {
        use EditKind::*;
        match self.clone() {
            InsertChar(c, i) => DeleteChar(c, i),
            DeleteChar(c, i) => InsertChar(c, i),
            InsertNewline(i) => DeleteNewline(i),
            DeleteNewline(i) => InsertNewline(i),
            Insert(s, i) => Remove(s, i),
            Remove(s, i) => Insert(s, i),
        }
    }
}

#[derive(Clone, Debug)]
pub struct Edit {
    kind: EditKind,
    cursor_before: (usize, usize),
    cursor_after: (usize, usize),
}

impl Edit {
    pub fn new(
        kind: EditKind,
        cursor_before: (usize, usize),
        cursor_after: (usize, usize),
    ) -> Self {
        Self {
            kind,
            cursor_before,
            cursor_after,
        }
    }

    pub fn redo(&self, lines: &mut Vec<String>) {
        let (row, _) = self.cursor_before;
        self.kind.apply(row, lines);
    }

    pub fn undo(&self, lines: &mut Vec<String>) {
        let (row, _) = self.cursor_after;
        self.kind.invert().apply(row, lines); // Undo is redo of inverted edit
    }

    pub fn cursor_before(&self) -> (usize, usize) {
        self.cursor_before
    }

    pub fn cursor_after(&self) -> (usize, usize) {
        self.cursor_after
    }
}

#[derive(Clone, Debug)]
pub struct History {
    index: usize,
    max_items: usize,
    edits: VecDeque<Edit>,
}

impl History {
    pub fn new(max_items: usize) -> Self {
        Self {
            index: 0,
            max_items,
            edits: VecDeque::new(),
        }
    }

    pub fn push(&mut self, edit: Edit) {
        if self.max_items == 0 {
            return;
        }

        if self.edits.len() == self.max_items {
            self.edits.pop_front();
            self.index = self.index.saturating_sub(1);
        }

        if self.index < self.edits.len() {
            self.edits.truncate(self.index);
        }

        self.index += 1;
        self.edits.push_back(edit);
    }

    pub fn redo(&mut self, lines: &mut Vec<String>) -> Option<(usize, usize)> {
        if self.index == self.edits.len() {
            return None;
        }
        let edit = &self.edits[self.index];
        edit.redo(lines);
        self.index += 1;
        Some(edit.cursor_after())
    }

    pub fn undo(&mut self, lines: &mut Vec<String>) -> Option<(usize, usize)> {
        self.index = self.index.checked_sub(1)?;
        let edit = &self.edits[self.index];
        edit.undo(lines);
        Some(edit.cursor_before())
    }

    pub fn max_items(&self) -> usize {
        self.max_items
    }
}