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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)
}
}