1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101

//! An undo/redo library with dynamic dispatch and automatic command merging.
//! It uses the [Command Pattern](https://en.wikipedia.org/wiki/Command_pattern)
//! where the user modifies a receiver by applying `Command`s on it.
//!
//! The library has currently two data structures that can be used to modify the receiver:
//!
//! * A simple `Stack` that pushes and pops commands to modify the receiver.
//! * A `Record` that can roll the state of the receiver forwards and backwards.

#![forbid(unstable_features, bad_style)]
#![deny(missing_debug_implementations,
        unused_import_braces,
        unused_qualifications)]

// TODO: serde? groups?

extern crate fnv;

mod record;
mod stack;

pub use record::Record;
pub use stack::Stack;

use std::fmt::{self, Debug, Formatter};
use std::error::Error;

/// Base functionality for all commands.
pub trait Command<T> {
    /// Executes the desired command and returns `Ok` if everything went fine, and `Err` if
    /// something went wrong.
    fn redo(&mut self, receiver: &mut T) -> Result<(), Box<Error>>;

    /// Restores the state as it was before [`redo`] was called and returns `Ok` if everything
    /// went fine, and `Err` if something went wrong.
    ///
    /// [`redo`]: trait.Command.html#tymethod.redo
    fn undo(&mut self, receiver: &mut T) -> Result<(), Box<Error>>;

    /// Used for automatic merging of `Command`s.
    ///
    /// Two commands are merged together when a command is pushed, and it has
    /// the same id as the top command already on the stack. When commands are merged together,
    /// undoing and redoing them are done in one step. An example where this is useful is a text
    /// editor where you might want to undo a whole word instead of each character.
    #[inline]
    fn id(&self) -> Option<u64> {
        None
    }
}

impl<T> Command<T> for Box<Command<T>> {
    #[inline]
    fn redo(&mut self, receiver: &mut T) -> Result<(), Box<Error>> {
        (**self).redo(receiver)
    }

    #[inline]
    fn undo(&mut self, receiver: &mut T) -> Result<(), Box<Error>> {
        (**self).undo(receiver)
    }

    #[inline]
    fn id(&self) -> Option<u64> {
        (**self).id()
    }
}

impl<T> Debug for Command<T> {
    #[inline]
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        match self.id() {
            Some(id) => write!(f, "{}", id),
            None => write!(f, "_"),
        }
    }
}

struct Merger<T> {
    cmd1: Box<Command<T>>,
    cmd2: Box<Command<T>>,
}

impl<T> Command<T> for Merger<T> {
    #[inline]
    fn redo(&mut self, receiver: &mut T) -> Result<(), Box<Error>> {
        self.cmd1.redo(receiver)?;
        self.cmd2.redo(receiver)
    }

    #[inline]
    fn undo(&mut self, receiver: &mut T) -> Result<(), Box<Error>> {
        self.cmd2.undo(receiver)?;
        self.cmd1.undo(receiver)
    }

    #[inline]
    fn id(&self) -> Option<u64> {
        self.cmd1.id()
    }
}