```  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
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
```
```use std::sync::{Arc, Mutex, Weak};
use std::clone::Clone;

#[derive(Debug, Clone)]
struct GraphInner<T> {
nodes: Vec<(Option<Arc<Mutex<NodeInner<T>>>>, usize)>,
next: usize,
}

#[derive(Debug, Clone, PartialEq)]
pub enum GraphError {
InvalidNode,
LockFailure,
}

#[derive(Debug, Clone)]
pub struct Graph<T>(Arc<Mutex<GraphInner<T>>>);

impl<T> Graph<T> {
pub fn new() -> Self {
let inner = GraphInner {
nodes: Vec::new(),
next: 0,
};
Self(Arc::new(Mutex::new(inner)))
}

pub fn new_node(&self, value: T) -> Node<T> {
let mut lock = self.0.lock().unwrap();
let next = lock.next;
let inner = NodeInner {
value,
neighbors: Vec::new(),
id: next,
};

let node = Arc::new(Mutex::new(inner));
if next < lock.nodes.len() {
lock.nodes[next].0.replace(node.clone());
lock.next = lock.nodes[next].1;
node_weak
} else {
lock.nodes.push((Some(node.clone()), next + 1));
lock.next += 1;
node_weak
}
}

pub fn remove_node(&self, node: &Node<T>) -> Result<(), GraphError> {
let mut lock = self.0.lock().or(Err(GraphError::LockFailure))?;
let id = rc.lock().unwrap().id;
if id < lock.nodes.len() {
let tar_node = lock.nodes[id].0.take();
if tar_node.is_none() {
Err(GraphError::InvalidNode)
} else {
lock.nodes[id].1 = lock.next;
lock.next = id;
Ok(())
}
} else {
Err(GraphError::InvalidNode)
}
}
}

#[derive(Debug, Clone)]
pub struct Node<T>(Weak<Mutex<NodeInner<T>>>);

impl<T> Node<T> {
pub fn push(&self, neighbor: &Node<T>) -> Result<(), GraphError> {
let mut lock = rc.lock().or(Err(GraphError::LockFailure))?;
lock.neighbors.push(Node(neighbor.0.clone()));
Ok(())
}

pub fn read<V, F>(&self, f: F) -> Result<V, GraphError> where F: Fn(&T) -> V {
let lock = rc.lock().or(Err(GraphError::LockFailure))?;
let result = f(&lock.value);
Ok(result)
}

pub fn write(&self, val: T) -> Result<(), GraphError> {
let mut lock = rc.lock().or(Err(GraphError::LockFailure))?;
lock.value = val;
Ok(())
}

pub fn modify<F>(&self, f: F) -> Result<(), GraphError> where F: Fn(&mut T) {
let mut lock = rc.lock().or(Err(GraphError::LockFailure))?;
f(&mut lock.value);
Ok(())
}

pub fn get_neighbors(&self) -> Result<Vec<Node<T>>, GraphError> {
self.gc()?;
let lock = rc.lock().or(Err(GraphError::LockFailure))?;
let mut result = Vec::new();
for n in lock.neighbors.iter().filter(|n| n.is_lived()) {
result.push(Node(n.0.clone()))
}
Ok(result)
}

fn gc(&self) -> Result<(), GraphError> {
let mut lock = rc.lock().or(Err(GraphError::LockFailure))?;
let mut cleaned = Vec::new();
for n in lock.neighbors.iter().filter(|n| n.is_lived()) {
cleaned.push(Node(n.0.clone()))
}
lock.neighbors = cleaned;
Ok(())
}

fn is_lived(&self) -> bool {
self.0.strong_count() > 0
}
}

#[derive(Debug)]
struct NodeInner<T> {
value: T,
neighbors: Vec<Node<T>>,
id: usize,
}

#[cfg(test)]
mod tests {
use crate::{Graph, GraphError};

#[test]
fn test_push_and_remove() {
let graph = Graph::new();
let node1 = graph.new_node(1);
assert!(node1.is_lived());
let node2 = graph.new_node(2);
assert!(node2.is_lived());
let node3 = graph.new_node(3);
assert!(node3.is_lived());
assert!(node1.push(&node2).is_ok());
assert!(node2.push(&node3).is_ok());
assert!(node3.push(&node1).is_ok());

assert!(graph.remove_node(&node2).is_ok());
assert!(graph.remove_node(&node2).is_err());
assert!(node2.push(&node1).is_err());
let node4 = graph.new_node(4);
let node5 = graph.new_node(5);
assert!(node4.is_lived());
assert!(node5.is_lived());
assert!(!node2.is_lived());
assert!(node4.push(&node1).is_ok());
assert!(node4.push(&node5).is_ok());
assert!(node1.push(&node5).is_ok());

assert_eq!(1, node1.get_neighbors().unwrap().len());
assert_eq!(1, node3.get_neighbors().unwrap().len());
assert_eq!(2, node4.get_neighbors().unwrap().len());
assert_eq!(0, node5.get_neighbors().unwrap().len());
}

#[test]
let graph = Graph::new();
let node = graph.new_node("Hello".to_owned());

let length = node.read(|value: &String| {
value.len()
}).unwrap();
assert_eq!(5, length);
node.modify(|value: &mut String| {
*value = "World".to_owned();
}).unwrap();