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
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152

//! Implementation of transactional Vec which tracks all changes before committing, and allows
//! rollbacks
use crate::util::transactional_hashmap::Transactional;

#[derive(Debug, Eq, PartialEq, Clone)]
enum Reversible<T> {
	Add { index: usize },
	Remove { index: usize, value: T },
}

#[derive(Debug, PartialEq, Clone)]
pub struct TransactionalVec<T>
where
	T: Clone,
{
	inner: Vec<T>,
	rollback_operations: Vec<Reversible<T>>,
}

impl<T> TransactionalVec<T>
where
	T: Clone,
{
	pub fn new() -> Self {
		Self { inner: Vec::new(), rollback_operations: vec![] }
	}

	/// This is creating a new TransactionalVec from iterator and since it is initializing
	/// a new instance there is no need to track the initial items inside
	pub fn from(inner: Vec<T>) -> Self {
		Self { inner, rollback_operations: vec![] }
	}

	pub fn inner(&self) -> &Vec<T> {
		&self.inner
	}

	#[inline]
	pub fn len(&self) -> usize {
		self.inner.len()
	}

	#[inline]
	pub fn clear(&mut self) {
		for (index, val) in self.inner.iter().enumerate().rev() {
			self.rollback_operations.push(Reversible::Remove { index, value: val.clone() });
		}

		self.inner.clear()
	}

	#[inline]
	pub fn push(&mut self, value: T) {
		self.rollback_operations.push(Reversible::Add { index: self.inner.len() });
		self.inner.push(value)
	}

	pub fn retain<F>(&mut self, mut f: F)
	where
		F: FnMut(&T) -> bool,
	{
		for (index, val) in self.inner.iter().enumerate().rev() {
			if !f(val) {
				self.rollback_operations.push(Reversible::Remove { index, value: val.clone() });
			}
		}
		self.inner.retain(f);
	}

	pub fn extend_from_slice(&mut self, other: &[T]) {
		let mut index = self.inner.len();
		for _ in other {
			self.rollback_operations.push(Reversible::Add { index });
			index += 1;
		}
		self.inner.extend_from_slice(other)
	}
}

impl<T> Transactional for TransactionalVec<T>
where
	T: Clone,
{
	fn commit(&mut self) {
		self.rollback_operations = vec![];
	}

	fn rollback(&mut self) {
		while !self.rollback_operations.is_empty() {
			let op = self.rollback_operations.pop().unwrap();
			match op {
				Reversible::Add { index } => {
					self.inner.remove(index);
				},
				Reversible::Remove { index, value } => {
					self.inner.insert(index, value);
				},
			};
		}
	}
}

#[cfg(test)]
mod tests {
	use super::*;

	#[test]
	fn transactional_vec_should_revert_the_state_as_before_using_clean_and_extend() {
		let arr = vec![1, 2, 3, 4, 5, 6, 7, 8, 9];
		let mut transactional = TransactionalVec::from(arr.clone());

		let arr2 = vec![10, 11, 12, 13];
		transactional.extend_from_slice(&arr2);
		assert_eq!(transactional.inner, vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]);

		transactional.rollback();
		assert_eq!(transactional.inner, arr);

		transactional.clear();
		assert_eq!(transactional.inner, Vec::<i32>::new());
		transactional.extend_from_slice(&vec![100, 89, 8]);

		transactional.rollback();
		assert_eq!(transactional.inner, arr);

		let arr3 = vec![9, 3, 5, 6];
		transactional.clear();
		transactional.extend_from_slice(&arr3);
		transactional.commit();
		assert_eq!(transactional.inner, arr3);
	}

	#[test]
	fn transactional_vec_should_revert_the_state_as_before_using_push_and_retain() {
		let arr = vec![1, 2, 3, 4, 5, 6, 7, 8, 9];
		let mut transactional = TransactionalVec::from(arr.clone());

		let arr2 = vec![10, 11, 12, 13];
		arr2.iter().for_each(|i| transactional.push(*i));
		assert_eq!(transactional.inner, vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]);

		transactional.rollback();
		assert_eq!(transactional.inner, arr);

		transactional.retain(|i| *i < 5);
		assert_eq!(transactional.inner, vec![1, 2, 3, 4]);
		transactional.push(1000);

		transactional.rollback();
		assert_eq!(transactional.inner, arr);
	}
}