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

use shape_core::{Line, Point};
use std::vec::IntoIter;

/// A vector backed tree implementation used to essentially cache the user's tree.
use crate::NodeInfo;

#[cfg(test)]
mod test;

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct TreeNode<D> {
    /// Data needed by the actual algorithm.
    pub data: D,

    /// The position of this node among it's siblings.
    ///
    /// Can also be thought of as the number of left-siblings this node has.
    pub order: usize,
    /// The depth of this node.
    ///
    /// Can be thought of as the number of edges between this node and the root node.
    pub depth: usize,

    /// The index into `Tree` of this node's parent.
    pub parent: Option<usize>,
    /// The indices into `Tree` of this node's children.
    pub children: Vec<usize>,
}

impl<D> TreeNode<D> {
    pub fn is_leaf(&self) -> bool {
        self.children.is_empty()
    }

    pub fn is_root(&self) -> bool {
        self.parent.is_none()
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct TreeLayout<D> {
    arena: Vec<TreeNode<D>>,
}

impl<D> Default for TreeLayout<D> {
    fn default() -> Self {
        Self { arena: vec![] }
    }
}

impl<D> TreeLayout<D> {
    pub fn new<F, N, T>(user_tree: &T, root: N, data: F) -> Self
    where
        F: Fn(&T, N) -> D,
        N: Clone,
        T: NodeInfo<N>,
    {
        let mut tree = Vec::new();
        tree.push(TreeNode { data: data(user_tree, root.clone()), order: 0, depth: 0, parent: None, children: Vec::new() });

        let mut queue = std::collections::VecDeque::new();
        queue.push_back((0, root));

        while let Some((parent, node)) = queue.pop_front() {
            let index = tree.len();

            for (i, child) in user_tree.children(node).into_iter().enumerate() {
                let index = index + i;
                let depth = tree[parent].depth + 1;

                tree[parent].children.push(index);

                tree.push(TreeNode {
                    data: data(user_tree, child.clone()),

                    order: i,
                    depth,

                    parent: Some(parent),
                    children: Vec::new(),
                });

                queue.push_back((index, child));
            }
        }

        TreeLayout { arena: tree }
    }

    pub fn root(&self) -> Option<usize> {
        if self.arena.is_empty() { None } else { Some(0) }
    }

    pub fn breadth_first(&self, node: usize) -> Vec<usize> {
        let mut breadth_first = vec![node];
        let mut index = 0;

        while index < breadth_first.len() {
            let node = breadth_first[index];
            breadth_first.extend_from_slice(&self[node].children);
            index += 1;
        }

        breadth_first
    }

    pub fn post_order(&self, node: usize) -> Vec<usize> {
        let mut breadth_first = vec![node];
        let mut post_order = Vec::new();

        while let Some(node) = breadth_first.pop() {
            breadth_first.extend_from_slice(&self[node].children);
            post_order.push(node);
        }

        post_order.reverse();
        post_order
    }

    pub fn left_siblings(&self, node: usize) -> Vec<usize> {
        let order = self[node].order;

        if let Some(parent) = self[node].parent { self[parent].children[0..order].into() } else { Vec::new() }
    }

    pub fn siblings_between(&self, left: usize, right: usize) -> Vec<usize> {
        let left_order = self[left].order;
        let right_order = self[right].order;

        if self[left].is_root() || self[right].is_root() {
            assert!(self[left].is_root(), "If one node is the root then both nodes must be.");
            assert!(self[right].is_root(), "If one node is the root then both nodes must be.");

            return Vec::new();
        }

        let left_parent = self[left].parent.expect("`is_none` has already been checked.");

        let right_parent = self[right].parent.expect("`is_none` has already been checked.");

        assert_eq!(left_parent, right_parent, "Nodes must actually be siblings.");

        let parent = left_parent;

        self[parent].children[left_order + 1..right_order].into()
    }

    pub fn previous_sibling(&self, node: usize) -> Option<usize> {
        let order = self[node].order;
        if order == 0 {
            return None;
        }

        let parent = self[node].parent.expect("Nodes where `order != 0` always have parents.");

        Some(self[parent].children[order - 1])
    }

    pub fn find_parent(&self, node: &TreeNode<D>) -> Option<&TreeNode<D>> {
        self.arena.get(node.parent?)
    }
}

impl<D> IntoIterator for TreeLayout<D> {
    type Item = TreeNode<D>;
    type IntoIter = IntoIter<TreeNode<D>>;

    fn into_iter(self) -> Self::IntoIter {
        self.arena.into_iter()
    }
}

impl<D> std::ops::Index<usize> for TreeLayout<D> {
    type Output = TreeNode<D>;

    fn index(&self, index: usize) -> &Self::Output {
        &self.arena[index]
    }
}

impl<D> std::ops::IndexMut<usize> for TreeLayout<D> {
    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
        &mut self.arena[index]
    }
}