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use std::cmp::Ordering;
use std::iter::Fuse;
use std::fmt;
use super::adaptors::{PutBack, put_back};
use crate::either_or_both::EitherOrBoth;
#[cfg(doc)]
use crate::Itertools;
/// Return an iterator adaptor that merge-joins items from the two base iterators in ascending order.
///
/// [`IntoIterator`] enabled version of [`Itertools::merge_join_by`].
pub fn merge_join_by<I, J, F>(left: I, right: J, cmp_fn: F)
-> MergeJoinBy<I::IntoIter, J::IntoIter, F>
where I: IntoIterator,
J: IntoIterator,
F: FnMut(&I::Item, &J::Item) -> Ordering
{
MergeJoinBy {
left: put_back(left.into_iter().fuse()),
right: put_back(right.into_iter().fuse()),
cmp_fn,
}
}
/// An iterator adaptor that merge-joins items from the two base iterators in ascending order.
///
/// See [`.merge_join_by()`](crate::Itertools::merge_join_by) for more information.
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct MergeJoinBy<I: Iterator, J: Iterator, F> {
left: PutBack<Fuse<I>>,
right: PutBack<Fuse<J>>,
cmp_fn: F
}
impl<I, J, F> Clone for MergeJoinBy<I, J, F>
where I: Iterator,
J: Iterator,
PutBack<Fuse<I>>: Clone,
PutBack<Fuse<J>>: Clone,
F: Clone,
{
clone_fields!(left, right, cmp_fn);
}
impl<I, J, F> fmt::Debug for MergeJoinBy<I, J, F>
where I: Iterator + fmt::Debug,
I::Item: fmt::Debug,
J: Iterator + fmt::Debug,
J::Item: fmt::Debug,
{
debug_fmt_fields!(MergeJoinBy, left, right);
}
impl<I, J, F> Iterator for MergeJoinBy<I, J, F>
where I: Iterator,
J: Iterator,
F: FnMut(&I::Item, &J::Item) -> Ordering
{
type Item = EitherOrBoth<I::Item, J::Item>;
fn next(&mut self) -> Option<Self::Item> {
match (self.left.next(), self.right.next()) {
(None, None) => None,
(Some(left), None) =>
Some(EitherOrBoth::Left(left)),
(None, Some(right)) =>
Some(EitherOrBoth::Right(right)),
(Some(left), Some(right)) => {
match (self.cmp_fn)(&left, &right) {
Ordering::Equal =>
Some(EitherOrBoth::Both(left, right)),
Ordering::Less => {
self.right.put_back(right);
Some(EitherOrBoth::Left(left))
},
Ordering::Greater => {
self.left.put_back(left);
Some(EitherOrBoth::Right(right))
}
}
}
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
let (a_lower, a_upper) = self.left.size_hint();
let (b_lower, b_upper) = self.right.size_hint();
let lower = ::std::cmp::max(a_lower, b_lower);
let upper = match (a_upper, b_upper) {
(Some(x), Some(y)) => x.checked_add(y),
_ => None,
};
(lower, upper)
}
fn count(mut self) -> usize {
let mut count = 0;
loop {
match (self.left.next(), self.right.next()) {
(None, None) => break count,
(Some(_left), None) => break count + 1 + self.left.into_parts().1.count(),
(None, Some(_right)) => break count + 1 + self.right.into_parts().1.count(),
(Some(left), Some(right)) => {
count += 1;
match (self.cmp_fn)(&left, &right) {
Ordering::Equal => {}
Ordering::Less => self.right.put_back(right),
Ordering::Greater => self.left.put_back(left),
}
}
}
}
}
fn last(mut self) -> Option<Self::Item> {
let mut previous_element = None;
loop {
match (self.left.next(), self.right.next()) {
(None, None) => break previous_element,
(Some(left), None) => {
break Some(EitherOrBoth::Left(
self.left.into_parts().1.last().unwrap_or(left),
))
}
(None, Some(right)) => {
break Some(EitherOrBoth::Right(
self.right.into_parts().1.last().unwrap_or(right),
))
}
(Some(left), Some(right)) => {
previous_element = match (self.cmp_fn)(&left, &right) {
Ordering::Equal => Some(EitherOrBoth::Both(left, right)),
Ordering::Less => {
self.right.put_back(right);
Some(EitherOrBoth::Left(left))
}
Ordering::Greater => {
self.left.put_back(left);
Some(EitherOrBoth::Right(right))
}
}
}
}
}
}
fn nth(&mut self, mut n: usize) -> Option<Self::Item> {
loop {
if n == 0 {
break self.next();
}
n -= 1;
match (self.left.next(), self.right.next()) {
(None, None) => break None,
(Some(_left), None) => break self.left.nth(n).map(EitherOrBoth::Left),
(None, Some(_right)) => break self.right.nth(n).map(EitherOrBoth::Right),
(Some(left), Some(right)) => match (self.cmp_fn)(&left, &right) {
Ordering::Equal => {}
Ordering::Less => self.right.put_back(right),
Ordering::Greater => self.left.put_back(left),
},
}
}
}
}