1 files changed, 132 insertions, 0 deletions
diff --git a/src/split_producer.rs b/src/split_producer.rs
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--- /dev/null
+++ b/src/split_producer.rs
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+//! Common splitter for strings and slices
+//!
+//! This module is private, so these items are effectively `pub(super)`
+
+use crate::iter::plumbing::{Folder, UnindexedProducer};
+
+/// Common producer for splitting on a predicate.
+pub(super) struct SplitProducer<'p, P, V> {
+    data: V,
+    separator: &'p P,
+
+    /// Marks the endpoint beyond which we've already found no separators.
+    tail: usize,
+}
+
+/// Helper trait so `&str`, `&[T]`, and `&mut [T]` can share `SplitProducer`.
+pub(super) trait Fissile<P>: Sized {
+    fn length(&self) -> usize;
+    fn midpoint(&self, end: usize) -> usize;
+    fn find(&self, separator: &P, start: usize, end: usize) -> Option<usize>;
+    fn rfind(&self, separator: &P, end: usize) -> Option<usize>;
+    fn split_once(self, index: usize) -> (Self, Self);
+    fn fold_splits<F>(self, separator: &P, folder: F, skip_last: bool) -> F
+    where
+        F: Folder<Self>,
+        Self: Send;
+}
+
+impl<'p, P, V> SplitProducer<'p, P, V>
+where
+    V: Fissile<P> + Send,
+{
+    pub(super) fn new(data: V, separator: &'p P) -> Self {
+        SplitProducer {
+            tail: data.length(),
+            data,
+            separator,
+        }
+    }
+
+    /// Common `fold_with` implementation, integrating `SplitTerminator`'s
+    /// need to sometimes skip its final empty item.
+    pub(super) fn fold_with<F>(self, folder: F, skip_last: bool) -> F
+    where
+        F: Folder<V>,
+    {
+        let SplitProducer {
+            data,
+            separator,
+            tail,
+        } = self;
+
+        if tail == data.length() {
+            // No tail section, so just let `fold_splits` handle it.
+            data.fold_splits(separator, folder, skip_last)
+        } else if let Some(index) = data.rfind(separator, tail) {
+            // We found the last separator to complete the tail, so
+            // end with that slice after `fold_splits` finds the rest.
+            let (left, right) = data.split_once(index);
+            let folder = left.fold_splits(separator, folder, false);
+            if skip_last || folder.full() {
+                folder
+            } else {
+                folder.consume(right)
+            }
+        } else {
+            // We know there are no separators at all.  Return our whole data.
+            if skip_last {
+                folder
+            } else {
+                folder.consume(data)
+            }
+        }
+    }
+}
+
+impl<'p, P, V> UnindexedProducer for SplitProducer<'p, P, V>
+where
+    V: Fissile<P> + Send,
+    P: Sync,
+{
+    type Item = V;
+
+    fn split(self) -> (Self, Option<Self>) {
+        // Look forward for the separator, and failing that look backward.
+        let mid = self.data.midpoint(self.tail);
+        let index = match self.data.find(self.separator, mid, self.tail) {
+            Some(i) => Some(mid + i),
+            None => self.data.rfind(self.separator, mid),
+        };
+
+        if let Some(index) = index {
+            let len = self.data.length();
+            let (left, right) = self.data.split_once(index);
+
+            let (left_tail, right_tail) = if index < mid {
+                // If we scanned backwards to find the separator, everything in
+                // the right side is exhausted, with no separators left to find.
+                (index, 0)
+            } else {
+                let right_index = len - right.length();
+                (mid, self.tail - right_index)
+            };
+
+            // Create the left split before the separator.
+            let left = SplitProducer {
+                data: left,
+                tail: left_tail,
+                ..self
+            };
+
+            // Create the right split following the separator.
+            let right = SplitProducer {
+                data: right,
+                tail: right_tail,
+                ..self
+            };
+
+            (left, Some(right))
+        } else {
+            // The search is exhausted, no more separators...
+            (SplitProducer { tail: 0, ..self }, None)
+        }
+    }
+
+    fn fold_with<F>(self, folder: F) -> F
+    where
+        F: Folder<Self::Item>,
+    {
+        self.fold_with(folder, false)
+    }
+}