Module undo 

Undo/Redo command history framework.

This module provides infrastructure for reversible operations in FrankenTUI applications. It implements the Command Pattern with support for:

• Reversibility: Every command can be undone and redone
• Merging: Consecutive similar commands batch together (e.g., typing)
• Memory management: Commands report size for bounded history
• Batching: Multiple commands group into atomic operations

Architecture

┌─────────────────────────────────────────────────────────────────┐
│                        UndoStack                                  │
│  ┌──────────────────┐          ┌──────────────────┐             │
│  │   Undo Stack     │          │   Redo Stack     │             │
│  │  ┌────────────┐  │          │  ┌────────────┐  │             │
│  │  │ CommandN   │  │  undo()  │  │ Command1   │  │             │
│  │  ├────────────┤  │ ──────►  │  ├────────────┤  │             │
│  │  │ Command2   │  │          │  │ Command2   │  │             │
│  │  ├────────────┤  │  ◄────── │  ├────────────┤  │             │
│  │  │ Command1   │  │  redo()  │  │ CommandN   │  │             │
│  │  └────────────┘  │          │  └────────────┘  │             │
│  └──────────────────┘          └──────────────────┘             │
└─────────────────────────────────────────────────────────────────┘

Quick Start

use ftui_runtime::undo::{UndoableCmd, CommandMetadata, TextInsertCmd, WidgetId};

// Create a command
let cmd = TextInsertCmd::new(WidgetId::new(1), 0, "Hello")
    .with_apply(|id, pos, text| {
        // Apply the insertion
        Ok(())
    })
    .with_remove(|id, pos, len| {
        // Remove the insertion
        Ok(())
    });

// Execute the command
cmd.execute()?;

// Later, undo it
cmd.undo()?;

Module Structure

• command: Core UndoableCmd trait and built-in commands

Design Notes

Why Commands Store Callbacks

Commands need to interact with widget state, but we can’t store references to widgets (lifetime issues). Instead, commands store callbacks that are set by the widget when the command is created. This allows:

1. Commands to be stored in history (owned, not borrowed)
2. Widgets to control how operations are applied
3. Commands to work with any widget implementation

Merge Strategy

Command merging reduces memory usage and makes undo more natural:

• Typing “hello” creates 5 insert commands
• Merged, they become 1 command that inserts “hello”
• Undo removes “hello” in one step (more intuitive)

Merge decisions use:

• Time window (500ms default)
• Word boundaries (optional)
• Size limits (prevent unbounded growth)

Memory Budget

Every command reports its size via size_bytes(). The undo stack uses this to enforce memory limits:

• Default: 10MB history
• Oldest commands evicted when limit exceeded
• Commands can estimate or measure their size

Re-exports

pub use command::CommandBatch;

pub use command::CommandError;

pub use command::CommandMetadata;

pub use command::CommandResult;

pub use command::CommandSource;

pub use command::MergeConfig;

pub use command::TextDeleteCmd;

pub use command::TextInsertCmd;

pub use command::TextReplaceCmd;

pub use command::UndoableCmd;

pub use command::WidgetId;

pub use history::HistoryConfig;

pub use history::HistoryManager;

pub use transaction::Transaction;

pub use transaction::TransactionScope;

Modules

command

Undoable command infrastructure for the undo/redo system.

history

History stack for undo/redo operations.

transaction

Transaction support for grouping multiple commands atomically.