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

use std::ops::{Index, IndexMut};

/// This struct represents a two-dimensional window into a one-dimensional slice. This is
/// accomplished through taking either a `columns` parameter, and dividing the size of the slice
/// evenly into `rows` based on its length, or by taking `rows` and `columns` directly, trusting
/// that the caller provided correct values. The latter option provides a zero-cost abstraction.
///
/// # Example
/// ```
/// # use ilyvion_util::multi_dimensional::Window2D;
/// let mut values = [0u32; 8];
/// let mut window = Window2D::new_mut(&mut values, 2);
/// window[0][1] = 1;
/// window[1][1] = 2;
/// window[2][1] = 3;
/// window[3][1] = 4;
///
/// assert_eq!(values, [0, 1, 0, 2, 0, 3, 0, 4]);
/// ```
#[derive(Debug)]
pub struct Window2D<T> {
    raw: T,
    rows: usize,
    columns: usize,
}

impl<'b, T> Window2D<&'b mut [T]> {
    /// Creates a new `Window2D` with rows divided into `columns` length. (I.e., `w[rows][columns]`)
    ///
    /// # Panics
    ///
    /// If the length of `raw` cannot be divided evenly into `column`s
    pub fn new_mut(raw: &'b mut [T], columns: usize) -> Self {
        let rows = raw.len() / columns;
        if raw.len() % columns != 0 {
            panic!("The length of raw must divide evenly into columns.");
        }

        Self { raw, rows, columns }
    }

    /// Creates a new `Window2D` divided into `rows` number of slices with `columns` entries each.
    ///
    /// Providing incorrect values for `rows` and `columns` will most likely lead to run-time panics
    /// due to indexing outside the range of the slice.
    ///
    /// Using this constructor gives you an essentially zero-cost abstraction.  
    pub fn new_mut_unchecked(raw: &'b mut [T], rows: usize, columns: usize) -> Self {
        Self { raw, rows, columns }
    }
}

impl<'b, T> Window2D<&'b [T]> {
    /// Creates a new `Window2D` with rows divided into `columns` length. (I.e., `w[rows][columns]`)
    ///
    /// # Panics
    ///
    /// If the length of `raw` cannot be divided evenly into `column`s
    pub fn new_ref(raw: &'b [T], columns: usize) -> Self {
        let rows = raw.len() / columns;
        if raw.len() % columns != 0 {
            panic!("The length of raw must divide evenly into columns.");
        }

        Self { raw, rows, columns }
    }

    /// Creates a new `Window2D` divided into `rows` number of slices with `columns` entries each.
    ///
    /// Providing incorrect values for `rows` and `columns` will most likely lead to run-time panics
    /// due to indexing outside the range of the slice.
    ///
    /// Using this constructor gives you an essentially zero-cost abstraction.
    pub fn new_ref_unchecked(raw: &'b [T], rows: usize, columns: usize) -> Self {
        Self { raw, rows, columns }
    }
}

impl<T> Index<usize> for Window2D<&'_ [T]> {
    type Output = [T];

    fn index(&self, row: usize) -> &Self::Output {
        assert!(row < self.rows);
        &self.raw[row * self.columns..][..self.columns]
    }
}

impl<T> Index<(usize, usize)> for Window2D<&'_ [T]> {
    type Output = T;

    fn index(&self, index: (usize, usize)) -> &Self::Output {
        &self[index.0][index.1]
    }
}

impl<T> Index<usize> for Window2D<&'_ mut [T]> {
    type Output = [T];

    fn index(&self, row: usize) -> &Self::Output {
        assert!(row < self.rows);
        &self.raw[row * self.columns..][..self.columns]
    }
}

impl<T> IndexMut<usize> for Window2D<&'_ mut [T]> {
    fn index_mut(&mut self, row: usize) -> &mut Self::Output {
        assert!(row < self.rows);
        &mut self.raw[row * self.columns..][..self.columns]
    }
}

impl<T> Index<(usize, usize)> for Window2D<&'_ mut [T]> {
    type Output = T;

    fn index(&self, index: (usize, usize)) -> &Self::Output {
        &self[index.0][index.1]
    }
}

impl<T> IndexMut<(usize, usize)> for Window2D<&'_ mut [T]> {
    fn index_mut(&mut self, index: (usize, usize)) -> &mut Self::Output {
        &mut self[index.0][index.1]
    }
}

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

    #[test]
    fn indexing_works_correctly() {
        let mut values = [0, 1, 2, 3, 4, 5, 6, 7];
        let window = Window2D::new_ref(&values, 2);

        assert_eq!(window[0], [0, 1]);
        assert_eq!(window[1], [2, 3]);
        assert_eq!(window[2], [4, 5]);
        assert_eq!(window[3], [6, 7]);

        assert_eq!(window[(0, 0)], 0);
        assert_eq!(window[(0, 1)], 1);
        assert_eq!(window[(1, 0)], 2);
        assert_eq!(window[(1, 1)], 3);
        assert_eq!(window[(2, 0)], 4);
        assert_eq!(window[(2, 1)], 5);
        assert_eq!(window[(3, 0)], 6);
        assert_eq!(window[(3, 1)], 7);

        let mut window_mut = Window2D::new_mut(&mut values, 2);
        for y in 0..4 {
            for x in 0..2 {
                window_mut[y][x] = 2 * (3 - y) + (1 - x);
            }
        }
        assert_eq!(window_mut[0], [7, 6]);
        assert_eq!(window_mut[1], [5, 4]);
        assert_eq!(window_mut[2], [3, 2]);
        assert_eq!(window_mut[3], [1, 0]);

        for y in 0..4 {
            for x in 0..2 {
                window_mut[(y, x)] *= 2;
            }
        }

        assert_eq!(window_mut[(0, 0)], 14);
        assert_eq!(window_mut[(0, 1)], 12);
        assert_eq!(window_mut[(1, 0)], 10);
        assert_eq!(window_mut[(1, 1)], 8);
        assert_eq!(window_mut[(2, 0)], 6);
        assert_eq!(window_mut[(2, 1)], 4);
        assert_eq!(window_mut[(3, 0)], 2);
        assert_eq!(window_mut[(3, 1)], 0);
    }
}