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use core::{
cmp::{self, min},
iter::FusedIterator,
ops::RangeInclusive,
};
use alloc::collections::BinaryHeap;
use crate::{
Integer, MergeMap, SortedDisjointMap, SymDiffKMergeMap, SymDiffMergeMap,
map::ValueRef,
merge_map::KMergeMap,
sorted_disjoint_map::{Priority, PrioritySortedStartsMap},
};
/// This `struct` is created by the [`symmetric_difference`] method on [`SortedDisjointMap`]. See [`symmetric_difference`]'s
/// documentation for more.
///
/// [`SortedDisjointMap`]: crate::SortedDisjointMap
/// [`symmetric_difference`]: crate::SortedDisjointMap::symmetric_difference
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
pub struct SymDiffIterMap<T, VR, I> {
iter: I,
next_item: Option<Priority<T, VR>>,
workspace: BinaryHeap<Priority<T, VR>>,
workspace_next_end: Option<T>,
gather: Option<(RangeInclusive<T>, VR)>,
ready_to_go: Option<(RangeInclusive<T>, VR)>,
}
#[expect(clippy::ref_option)]
fn min_next_end<T: Integer>(next_end: &Option<T>, next_item_end: T) -> T {
next_end.map_or_else(
|| next_item_end,
|current_end| cmp::min(current_end, next_item_end),
)
}
impl<T, VR, I> FusedIterator for SymDiffIterMap<T, VR, I>
where
T: Integer,
VR: ValueRef,
I: PrioritySortedStartsMap<T, VR>,
{
}
impl<T, VR, I> Iterator for SymDiffIterMap<T, VR, I>
where
T: Integer,
VR: ValueRef,
I: PrioritySortedStartsMap<T, VR>,
{
type Item = (RangeInclusive<T>, VR);
fn next(&mut self) -> Option<(RangeInclusive<T>, VR)> {
// Keep doing this until we have something to return.
loop {
if let Some(value) = self.ready_to_go.take() {
// If ready_to_go is Some, return the value immediately.
return Some(value);
}
// if self.next_item should go into the workspace, then put it there, get the next, next_item, and loop
if let Some(next_item) = self.next_item.take() {
let (next_start, next_end) = next_item.start_and_end();
// If workspace is empty, just push the next item
let Some(best) = self.workspace.peek() else {
self.workspace_next_end =
Some(min_next_end(&self.workspace_next_end, next_end));
self.workspace.push(next_item);
self.next_item = self.iter.next();
continue; // return to top of the main processing loop
};
let best = best.range_value();
if next_start == *best.0.start() {
// Always push (this differs from UnionIterMap)
self.workspace_next_end =
Some(min_next_end(&self.workspace_next_end, next_end));
self.workspace.push(next_item);
self.next_item = self.iter.next();
continue; // return to top of the main processing loop
}
// It does not go into the workspace, so just hold it and keep processing.
self.next_item = Some(next_item);
}
// If the workspace is empty, we are done.
let Some(best) = self.workspace.peek() else {
debug_assert!(self.next_item.is_none());
debug_assert!(self.ready_to_go.is_none());
return self.gather.take();
};
let best = best.range_value();
// We buffer for output the best item up to the start of the next item (if any).
// Find the start of the next item, if any.
let mut next_end = self
.workspace_next_end
.take()
.expect("Real Assert: safe because we know the workspace is not empty");
if let Some(next_item) = self.next_item.as_ref() {
next_end = min(next_item.start().sub_one(), next_end);
}
// Add the front of best to the gather buffer.
if let Some(mut gather) = self.gather.take() {
if gather.1.borrow() == best.1.borrow()
&& (*gather.0.end()).add_one() == *best.0.start()
{
if self.workspace.len().is_odd() {
// if the gather is contiguous with the best, then merge them
gather.0 = *gather.0.start()..=next_end;
self.gather = Some(gather);
} else {
// if an even number of items in the workspace, then flush the gather
self.ready_to_go = Some(gather);
debug_assert!(self.gather.is_none());
}
} else {
// if the gather is not contiguous with the best, then output the gather and set the gather to the best
self.ready_to_go = Some(gather);
// FYI: this code appear twice # 1 of 2
if self.workspace.len().is_odd() {
self.gather = Some((*best.0.start()..=next_end, best.1.clone()));
} else {
debug_assert!(self.gather.is_none());
}
}
} else {
// if there is no gather, then set the gather to the best
// FYI: this code appear twice # 2 of 2
if self.workspace.len().is_odd() {
self.gather = Some((*best.0.start()..=next_end, best.1.clone()));
} else {
debug_assert!(self.gather.is_none());
}
}
// We also update the workspace to removing any items that are completely covered by the new_start.
// (Unlike UnionIterMap, we must keep any items that have a lower priority and are shorter than the new best.)
self.workspace_next_end = None;
self.workspace = self
.workspace
.drain()
.filter(|item| item.end() > next_end)
.map(|mut item| {
item.set_range(next_end.add_one()..=item.end());
self.workspace_next_end =
Some(min_next_end(&self.workspace_next_end, item.end()));
item
})
.collect();
} // end of main loop
}
}
impl<T, VR, L, R> SymDiffMergeMap<T, VR, L, R>
where
T: Integer,
VR: ValueRef,
L: SortedDisjointMap<T, VR>,
R: SortedDisjointMap<T, VR>,
{
#[inline]
pub(crate) fn new2(left: L, right: R) -> Self {
let iter = MergeMap::new(left, right);
Self::new(iter)
}
}
impl<T, VR, J> SymDiffKMergeMap<T, VR, J>
where
T: Integer,
VR: ValueRef,
J: SortedDisjointMap<T, VR>,
{
#[inline]
pub(crate) fn new_k<K>(k: K) -> Self
where
K: IntoIterator<Item = J>,
{
let iter = KMergeMap::new(k);
Self::new(iter)
}
}
impl<T, VR, I> SymDiffIterMap<T, VR, I>
where
T: Integer,
VR: ValueRef,
I: PrioritySortedStartsMap<T, VR>,
{
#[inline]
pub(crate) fn new(mut iter: I) -> Self {
let item = iter.next();
Self {
iter,
next_item: item,
workspace: BinaryHeap::new(),
workspace_next_end: None,
gather: None,
ready_to_go: None,
}
}
}
#[allow(clippy::wrong_self_convention)]
#[allow(clippy::redundant_pub_crate)]
pub(crate) trait UsizeExtensions {
fn is_odd(self) -> bool;
}
impl UsizeExtensions for usize {
#[inline]
fn is_odd(self) -> bool {
self & 1 != 0
}
}