From 76c978ae1fccd5ff49b8a2591b8e9aca3585816a Mon Sep 17 00:00:00 2001
From: Rob Watson <rob@netflux.io>
Date: Wed, 9 Sep 2020 00:46:05 +0200
Subject: [PATCH] Add ChunksFixed iterator

---
 src/lib.rs   |   1 +
 src/utils.rs | 129 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 130 insertions(+)
 create mode 100644 src/utils.rs

diff --git a/src/lib.rs b/src/lib.rs
index edd41a2..a2d70af 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,6 +10,7 @@ mod app;
 mod canvas;
 mod controls;
 mod home;
+mod utils;
 
 #[wasm_bindgen(start)]
 pub fn run_app() {
diff --git a/src/utils.rs b/src/utils.rs
new file mode 100644
index 0000000..128695e
--- /dev/null
+++ b/src/utils.rs
@@ -0,0 +1,129 @@
+/// Utils: general utilities.
+
+/// An iterator over a slice in a fixed number of non-overlapping
+/// chunks, starting at the beginning of the slice.
+///
+/// When the slice len is not evenly divisible by the number of
+/// chunks, the length of individual chunks may vary, with each chunk
+/// being augmented by a single element until the remainder is
+/// evenly distributed.
+///
+/// TODO:
+/// - implement size_hint, count, etc as appropriate
+/// - improve test coverage
+/// - extract to own crate
+#[derive(Debug, Clone)]
+pub struct ChunksFixed<'a, T: 'a> {
+    v: &'a [T],
+    size: usize,
+    rem: usize,
+}
+
+pub fn chunks_fixed<T>(slice: &[T], num_chunks: usize) -> ChunksFixed<T> {
+    ChunksFixed {
+        v: slice,
+        size: slice.len() / num_chunks,
+        rem: slice.len() % num_chunks,
+    }
+}
+
+impl<'a, T> Iterator for ChunksFixed<'a, T> {
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        if self.v.is_empty() {
+            return None;
+        }
+
+        let s = if self.rem > 0 {
+            self.rem -= 1;
+            self.size + 1
+        } else {
+            self.size
+        };
+
+        let (fst, snd) = self.v.split_at(s);
+        self.v = snd;
+        Some(fst)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_chunks_fixed_10_into_10() {
+        let v = vec![0; 10];
+        let chunks = chunks_fixed(&v, 10).collect::<Vec<_>>();
+
+        assert_eq!(chunks.len(), 10);
+        chunks.iter().for_each(|chunk| assert_eq!(chunk.len(), 1));
+    }
+
+    #[test]
+    fn test_chunks_fixed_100_into_10() {
+        let v = vec![0; 100];
+        let chunks = chunks_fixed(&v, 10).collect::<Vec<_>>();
+
+        assert_eq!(chunks.len(), 10);
+        chunks.iter().for_each(|chunk| assert_eq!(chunk.len(), 10));
+    }
+
+    #[test]
+    fn test_chunks_fixed_101_into_10() {
+        let v = vec![0; 101];
+        let chunks = chunks_fixed(&v, 10).collect::<Vec<_>>();
+
+        assert_eq!(chunks.len(), 10);
+        chunks.iter().enumerate().for_each(|(i, chunk)| {
+            if i == 0 {
+                assert_eq!(chunk.len(), 11);
+            } else {
+                assert_eq!(chunk.len(), 10);
+            }
+        });
+    }
+
+    #[test]
+    fn test_chunks_fixed_10399_into_800() {
+        let v = vec![0; 10399];
+        let chunks = chunks_fixed(&v, 800).collect::<Vec<_>>();
+
+        assert_eq!(chunks.len(), 800);
+        chunks.iter().enumerate().for_each(|(i, chunk)| {
+            if i < 799 {
+                assert_eq!(chunk.len(), 13);
+            } else {
+                assert_eq!(chunk.len(), 12);
+            }
+        });
+    }
+
+    #[test]
+    fn test_chunks_fixed_10400_into_800() {
+        let v = vec![0; 10400];
+        let chunks = chunks_fixed(&v, 800).collect::<Vec<_>>();
+
+        assert_eq!(chunks.len(), 800);
+        chunks.iter().for_each(|chunk| {
+            assert_eq!(chunk.len(), 13);
+        });
+    }
+
+    #[test]
+    fn test_chunks_fixed_10401_into_800() {
+        let v = vec![0; 10401];
+        let chunks = chunks_fixed(&v, 800).collect::<Vec<_>>();
+
+        assert_eq!(chunks.len(), 800);
+        chunks.iter().enumerate().for_each(|(i, chunk)| {
+            if i == 0 {
+                assert_eq!(chunk.len(), 14);
+            } else {
+                assert_eq!(chunk.len(), 13);
+            }
+        });
+    }
+}