refactoring

gpx-rs/engine/src/core/gpx/chunked.rs

@@ -0,0 +1,328 @@
+use std::{ops::Index, rc::Rc};
+
+use crate::Chunk;
+
+/// A list of items, stored in [`Chunk`]s that are shared between its versions: editing it only
+/// copies the chunks around the change, so that a version costs little more than the change.
+///
+/// There are no empty chunks.
+#[derive(Debug, PartialEq)]
+pub struct Chunked<C: Chunk> {
+    chunks: Vec<Rc<C>>,
+    cumul_length: Vec<usize>,
+}
+
+impl<C: Chunk> Clone for Chunked<C> {
+    fn clone(&self) -> Self {
+        Self {
+            chunks: self.chunks.clone(),
+            cumul_length: self.cumul_length.clone(),
+        }
+    }
+}
+
+impl<C: Chunk> Default for Chunked<C> {
+    fn default() -> Self {
+        Self {
+            chunks: vec![],
+            cumul_length: vec![],
+        }
+    }
+}
+
+/// The position of an item: in which chunk, where in it, and among all the items.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, PartialOrd, Ord)]
+pub struct ChunkIndex {
+    pub chunk: usize,
+    pub pos: usize,
+    pub flat: usize,
+}
+
+impl<C: Chunk> Chunked<C> {
+    /// Adds a chunk at the end, which is dropped if it is empty.
+    pub fn push(&mut self, chunk: C) {
+        self.push_shared(Rc::new(chunk));
+    }
+
+    pub fn push_shared(&mut self, chunk: Rc<C>) {
+        if chunk.items().is_empty() {
+            return;
+        }
+        self.cumul_length
+            .push(self.cumul_length.last().copied().unwrap_or_default() + chunk.items().len());
+        self.chunks.push(chunk);
+    }
+
+    pub fn chunks(&self) -> &[Rc<C>] {
+        &self.chunks
+    }
+
+    /// Replaces the items in `start..end` by `items`. Panics if the range is out of bounds.
+    ///
+    /// Chunks that are not concerned are kept as they are (shared), only the chunks around the
+    /// range are copied and refilled.
+    pub fn splice(&mut self, start: usize, end: usize, items: Vec<C::Item>) {
+        assert!(
+            start <= end && end <= self.len(),
+            "splice range out of bounds"
+        );
+        let old = std::mem::take(&mut self.chunks);
+        self.cumul_length.clear();
+
+        let mut items = Some(items);
+        let mut pending = vec![];
+        let mut offset = 0;
+        for chunk in old {
+            let (lo, hi) = (offset, offset + chunk.items().len());
+            offset = hi;
+            // a chunk ending at `start` is extended unless it is full, to avoid tiny chunks
+            if hi < start || (hi == start && chunk.is_full()) {
+                self.push_shared(chunk);
+                continue;
+            }
+            if let Some(items) = items.take() {
+                self.fill(&mut pending, chunk.items()[..start - lo].iter().cloned());
+                self.fill(&mut pending, items);
+            }
+            if hi <= end {
+                continue;
+            }
+            if lo >= end {
+                self.flush(&mut pending);
+                self.push_shared(chunk);
+            } else {
+                self.fill(&mut pending, chunk.items()[end - lo..].iter().cloned());
+            }
+        }
+        if let Some(items) = items {
+            self.fill(&mut pending, items);
+        }
+        self.flush(&mut pending);
+    }
+
+    fn fill(&mut self, pending: &mut Vec<C::Item>, items: impl IntoIterator<Item = C::Item>) {
+        for item in items {
+            pending.push(item);
+            if pending.len() >= C::MAX_SIZE {
+                self.flush(pending);
+            }
+        }
+    }
+
+    fn flush(&mut self, pending: &mut Vec<C::Item>) {
+        self.push(C::new(std::mem::take(pending)));
+    }
+
+    /// Edits the items of the chunks that contain an item accepted by `filter`.
+    ///
+    /// `f` receives a copy of the items of such a chunk and returns whether it changed them. A
+    /// changed chunk is replaced by a new one (so that what is derived from it is computed
+    /// again) and the chunks left empty are dropped. The other chunks are kept. Returns whether
+    /// anything changed.
+    pub fn edit(
+        &mut self,
+        filter: impl Fn(&C::Item) -> bool,
+        mut f: impl FnMut(&mut Vec<C::Item>) -> bool,
+    ) -> bool {
+        let mut changed = false;
+        let old = std::mem::take(&mut self.chunks);
+        self.cumul_length.clear();
+        for chunk in old {
+            if !chunk.items().iter().any(&filter) {
+                self.push_shared(chunk);
+                continue;
+            }
+            let mut items = chunk.items().clone();
+            if !f(&mut items) {
+                self.push_shared(chunk);
+                continue;
+            }
+            changed = true;
+            self.push(C::new(items));
+        }
+        changed
+    }
+
+    /// Changes what is in the chunk `chunk`, but not how many items there are. A chunk that is
+    /// shared is copied first, so that the other versions do not change.
+    fn replace_chunk(&mut self, chunk: usize, f: impl FnOnce(&mut Vec<C::Item>)) {
+        let len = self.chunks[chunk].items().len();
+        match Rc::get_mut(&mut self.chunks[chunk]) {
+            Some(unique) => f(unique.items_mut()),
+            None => {
+                let mut items = self.chunks[chunk].items().clone();
+                f(&mut items);
+                self.chunks[chunk] = Rc::new(C::new(items));
+            }
+        }
+        debug_assert_eq!(self.chunks[chunk].items().len(), len);
+    }
+
+    /// Applies `f` to the item at `index`, which is copied in a new chunk. Panics if there is no
+    /// such item.
+    pub fn update(&mut self, index: usize, f: impl FnOnce(&mut C::Item)) {
+        let ChunkIndex { chunk, pos, .. } = self.locate(index).unwrap();
+        self.replace_chunk(chunk, |items| f(&mut items[pos]));
+    }
+
+    /// Applies `f` to every item, with its index, in new chunks.
+    pub fn update_all(&mut self, mut f: impl FnMut(usize, &mut C::Item)) {
+        let mut offset = 0;
+        for chunk in 0..self.chunks.len() {
+            let len = self.chunks[chunk].items().len();
+            self.replace_chunk(chunk, |items| {
+                for (i, item) in items.iter_mut().enumerate() {
+                    f(offset + i, item);
+                }
+            });
+            offset += len;
+        }
+    }
+
+    pub fn len(&self) -> usize {
+        self.cumul_length.last().copied().unwrap_or_default()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.chunks.is_empty()
+    }
+
+    pub fn iter(&self) -> ChunkedIter<'_, C> {
+        ChunkedIter::new(self)
+    }
+
+    pub fn first_index(&self) -> Option<ChunkIndex> {
+        self.next_index(None)
+    }
+
+    pub fn last_index(&self) -> Option<ChunkIndex> {
+        self.prev_index(None)
+    }
+
+    pub fn next_index(&self, cur: Option<ChunkIndex>) -> Option<ChunkIndex> {
+        let mut next = cur.map_or_default(|idx| ChunkIndex {
+            chunk: idx.chunk,
+            pos: idx.pos + 1,
+            flat: idx.flat + 1,
+        });
+        loop {
+            if next.chunk >= self.chunks.len() {
+                return None;
+            }
+            if next.pos == self.chunks[next.chunk].items().len() {
+                next.chunk += 1;
+                next.pos = 0;
+            } else {
+                return Some(next);
+            }
+        }
+    }
+
+    pub fn prev_index(&self, cur: Option<ChunkIndex>) -> Option<ChunkIndex> {
+        let mut prev = cur.unwrap_or(ChunkIndex {
+            chunk: self.chunks.len(),
+            pos: 0,
+            flat: self.cumul_length.last().copied().unwrap_or_default(),
+        });
+        if prev.pos == 0 {
+            while prev.chunk > 0 {
+                prev.chunk -= 1;
+                if !self.chunks[prev.chunk].items().is_empty() {
+                    prev.pos = self.chunks[prev.chunk].items().len() - 1;
+                    prev.flat -= 1;
+                    return Some(prev);
+                }
+            }
+            None
+        } else {
+            prev.pos -= 1;
+            prev.flat -= 1;
+            Some(prev)
+        }
+    }
+
+    /// The position of the item `idx` among all the items.
+    pub fn locate(&self, idx: usize) -> Option<ChunkIndex> {
+        let chunk = self.cumul_length.partition_point(|l| idx >= *l);
+        if chunk >= self.chunks.len() {
+            return None;
+        }
+        let pos = if chunk > 0 {
+            idx - self.cumul_length[chunk - 1]
+        } else {
+            idx
+        };
+        if pos >= self.chunks[chunk].items().len() {
+            None
+        } else {
+            Some(ChunkIndex {
+                chunk,
+                pos,
+                flat: idx,
+            })
+        }
+    }
+}
+
+impl<C: Chunk> Index<ChunkIndex> for Chunked<C> {
+    type Output = C::Item;
+
+    fn index(&self, idx: ChunkIndex) -> &Self::Output {
+        &self.chunks[idx.chunk].items()[idx.pos]
+    }
+}
+
+impl<C: Chunk> Index<usize> for Chunked<C> {
+    type Output = C::Item;
+
+    fn index(&self, idx: usize) -> &Self::Output {
+        &self[self.locate(idx).unwrap()]
+    }
+}
+
+impl<'a, C: Chunk> IntoIterator for &'a Chunked<C> {
+    type Item = &'a C::Item;
+    type IntoIter = ChunkedIter<'a, C>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+pub struct ChunkedIter<'a, C: Chunk> {
+    chunked: &'a Chunked<C>,
+    idx: Option<ChunkIndex>,
+}
+
+impl<C: Chunk> Clone for ChunkedIter<'_, C> {
+    fn clone(&self) -> Self {
+        Self {
+            chunked: self.chunked,
+            idx: self.idx,
+        }
+    }
+}
+
+impl<'a, C: Chunk> ChunkedIter<'a, C> {
+    pub fn new(chunked: &'a Chunked<C>) -> Self {
+        Self {
+            chunked,
+            idx: Default::default(),
+        }
+    }
+}
+
+impl<'a, C: Chunk> Iterator for ChunkedIter<'a, C> {
+    type Item = &'a C::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.idx = self.chunked.next_index(self.idx);
+        self.idx.map(|idx| &self.chunked[idx])
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let idx = self.idx.map_or_default(|idx| idx.flat) + n;
+        self.idx = self.chunked.locate(idx);
+        self.idx.map(|idx| &self.chunked[idx])
+    }
+}