Extensible ChunkStorage

Co-authored-by: sdwhw <191973436+sdwhw@users.noreply.github.com>

3 files changed, 793 insertions, 0 deletions

diff --git a/azalea-world/src/chunk/mod.rs b/azalea-world/src/chunk/mod.rs
new file mode 100644
index 00000000..cd52026a
--- /dev/null
+++ b/azalea-world/src/chunk/mod.rs
@@ -0,0 +1,305 @@
+pub mod partial;
+pub mod storage;
+
+use std::{
+    collections::HashMap,
+    fmt::Debug,
+    io,
+    io::{Cursor, Write},
+};
+
+use azalea_block::block_state::{BlockState, BlockStateIntegerRepr};
+use azalea_buf::{AzBuf, BufReadError};
+use azalea_core::{
+    heightmap_kind::HeightmapKind,
+    position::{ChunkBiomePos, ChunkBlockPos, ChunkSectionBiomePos, ChunkSectionBlockPos},
+};
+use azalea_registry::data::Biome;
+use tracing::warn;
+
+use crate::{heightmap::Heightmap, palette::PalettedContainer};
+
+const SECTION_HEIGHT: u32 = 16;
+
+/// A single chunk in a world (16*?*16 blocks).
+///
+/// This only contains blocks and biomes. You can derive the height of the chunk
+/// from the number of sections, but you need a [`ChunkStorage`] to get the
+/// minimum Y coordinate.
+#[derive(Debug)]
+pub struct Chunk {
+    pub sections: Box<[Section]>,
+    /// Heightmaps are used for identifying the surface blocks in a chunk.
+    /// Usually for clients only `WorldSurface` and `MotionBlocking` are
+    /// present.
+    pub heightmaps: HashMap<HeightmapKind, Heightmap>,
+}
+
+/// A section of a chunk, i.e. a 16*16*16 block area.
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct Section {
+    /// The number of non-empty blocks in the section, which is initialized
+    /// based on a value sent to us by the server.
+    ///
+    /// This may be updated every time [`Self::get_and_set_block_state`] is
+    /// called.
+    pub block_count: u16,
+    pub states: PalettedContainer<BlockState>,
+    pub biomes: PalettedContainer<Biome>,
+}
+
+/// Get the actual stored view distance for the selected view distance.
+///
+/// For some reason, Minecraft stores an extra 3 chunks.
+pub fn calculate_chunk_storage_range(view_distance: u32) -> u32 {
+    u32::max(view_distance, 2) + 3
+}
+
+impl Default for Chunk {
+    fn default() -> Self {
+        Chunk {
+            sections: vec![Section::default(); (384 / 16) as usize].into(),
+            heightmaps: HashMap::new(),
+        }
+    }
+}
+
+impl Chunk {
+    pub fn read_with_dimension_height(
+        buf: &mut Cursor<&[u8]>,
+        dimension_height: u32,
+        min_y: i32,
+        heightmaps_data: &[(HeightmapKind, Box<[u64]>)],
+    ) -> Result<Self, BufReadError> {
+        let section_count = dimension_height / SECTION_HEIGHT;
+        let mut sections = Vec::with_capacity(section_count as usize);
+        for _ in 0..section_count {
+            let section = Section::azalea_read(buf)?;
+            sections.push(section);
+        }
+        let sections = sections.into_boxed_slice();
+
+        let mut heightmaps = HashMap::new();
+        for (kind, data) in heightmaps_data {
+            let data = data.clone();
+            let heightmap = Heightmap::new(*kind, dimension_height, min_y, data);
+            heightmaps.insert(*kind, heightmap);
+        }
+
+        Ok(Chunk {
+            sections,
+            heightmaps,
+        })
+    }
+
+    pub fn get_block_state(&self, pos: &ChunkBlockPos, min_y: i32) -> Option<BlockState> {
+        get_block_state_from_sections(&self.sections, pos, min_y)
+    }
+
+    #[must_use = "Use Chunk::set_block_state instead if you don't need the previous state"]
+    pub fn get_and_set_block_state(
+        &mut self,
+        pos: &ChunkBlockPos,
+        state: BlockState,
+        min_y: i32,
+    ) -> BlockState {
+        let section_index = section_index(pos.y, min_y);
+        let Some(section) = self.sections.get_mut(section_index as usize) else {
+            warn!(
+                "Tried to get and set block state {state:?} at out-of-bounds relative chunk position {pos:?}",
+            );
+            return BlockState::AIR;
+        };
+        let chunk_section_pos = ChunkSectionBlockPos::from(pos);
+        let previous_state = section.get_and_set_block_state(chunk_section_pos, state);
+
+        for heightmap in self.heightmaps.values_mut() {
+            heightmap.update(pos, state, &self.sections);
+        }
+
+        previous_state
+    }
+
+    pub fn set_block_state(&mut self, pos: &ChunkBlockPos, state: BlockState, min_y: i32) {
+        let section_index = section_index(pos.y, min_y);
+        let Some(section) = self.sections.get_mut(section_index as usize) else {
+            warn!(
+                "Tried to set block state {state:?} at out-of-bounds relative chunk position {pos:?}",
+            );
+            return;
+        };
+        let chunk_section_pos = ChunkSectionBlockPos::from(pos);
+        section.get_and_set_block_state(chunk_section_pos, state);
+
+        for heightmap in self.heightmaps.values_mut() {
+            heightmap.update(pos, state, &self.sections);
+        }
+    }
+
+    /// Get the biome at the given position, or `None` if it's out of bounds.
+    pub fn get_biome(&self, pos: ChunkBiomePos, min_y: i32) -> Option<Biome> {
+        if pos.y < min_y {
+            // y position is out of bounds
+            return None;
+        }
+        let section_index = section_index(pos.y, min_y);
+        let Some(section) = self.sections.get(section_index as usize) else {
+            warn!("Tried to get biome at out-of-bounds relative chunk position {pos:?}",);
+            return None;
+        };
+        let chunk_section_pos = ChunkSectionBiomePos::from(pos);
+        Some(section.get_biome(chunk_section_pos))
+    }
+}
+
+/// Get the block state at the given position from a list of sections. Returns
+/// `None` if the position is out of bounds.
+#[inline]
+pub fn get_block_state_from_sections(
+    sections: &[Section],
+    pos: &ChunkBlockPos,
+    min_y: i32,
+) -> Option<BlockState> {
+    if pos.y < min_y {
+        // y position is out of bounds
+        return None;
+    }
+    let section_index = section_index(pos.y, min_y) as usize;
+    if section_index >= sections.len() {
+        // y position is out of bounds
+        return None;
+    };
+    let section = &sections[section_index];
+
+    let chunk_section_pos = ChunkSectionBlockPos::from(pos);
+    Some(section.get_block_state(chunk_section_pos))
+}
+
+impl AzBuf for Section {
+    fn azalea_read(buf: &mut Cursor<&[u8]>) -> Result<Self, BufReadError> {
+        let block_count = u16::azalea_read(buf)?;
+
+        // this is commented out because the vanilla server is wrong
+        // TODO: ^ this comment was written ages ago. needs more investigation.
+        // assert!(
+        //     block_count <= 16 * 16 * 16,
+        //     "A section has more blocks than what should be possible. This is a bug!"
+        // );
+
+        let states = PalettedContainer::<BlockState>::read(buf)?;
+
+        for i in 0..states.storage.size() {
+            if !BlockState::is_valid_state(states.storage.get(i) as BlockStateIntegerRepr) {
+                return Err(BufReadError::Custom(format!(
+                    "Invalid block state {} (index {i}) found in section.",
+                    states.storage.get(i)
+                )));
+            }
+        }
+
+        let biomes = PalettedContainer::<Biome>::read(buf)?;
+        Ok(Section {
+            block_count,
+            states,
+            biomes,
+        })
+    }
+    fn azalea_write(&self, buf: &mut impl Write) -> io::Result<()> {
+        self.block_count.azalea_write(buf)?;
+        self.states.write(buf)?;
+        self.biomes.write(buf)?;
+        Ok(())
+    }
+}
+
+impl Section {
+    pub fn get_block_state(&self, pos: ChunkSectionBlockPos) -> BlockState {
+        self.states.get(pos)
+    }
+    pub fn get_and_set_block_state(
+        &mut self,
+        pos: ChunkSectionBlockPos,
+        state: BlockState,
+    ) -> BlockState {
+        let previous_state = self.states.get_and_set(pos, state);
+
+        if previous_state.is_air() && !state.is_air() {
+            self.block_count += 1;
+        } else if !previous_state.is_air() && state.is_air() {
+            self.block_count -= 1;
+        }
+
+        previous_state
+    }
+
+    pub fn get_biome(&self, pos: ChunkSectionBiomePos) -> Biome {
+        self.biomes.get(pos)
+    }
+    pub fn set_biome(&mut self, pos: ChunkSectionBiomePos, biome: Biome) {
+        self.biomes.set(pos, biome);
+    }
+    pub fn get_and_set_biome(&mut self, pos: ChunkSectionBiomePos, biome: Biome) -> Biome {
+        self.biomes.get_and_set(pos, biome)
+    }
+}
+
+/// Get the index of where a section is in a chunk based on its y coordinate
+/// and the minimum y coordinate of the world.
+#[inline]
+pub fn section_index(y: i32, min_y: i32) -> u32 {
+    if y < min_y {
+        #[cfg(debug_assertions)]
+        tracing::warn!("y ({y}) must be at least {min_y}");
+        #[cfg(not(debug_assertions))]
+        tracing::trace!("y ({y}) must be at least {min_y}")
+    };
+    let min_section_index = min_y >> 4;
+    ((y >> 4) - min_section_index) as u32
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::palette::SectionPos;
+
+    #[test]
+    fn test_section_index() {
+        assert_eq!(section_index(0, 0), 0);
+        assert_eq!(section_index(128, 0), 8);
+        assert_eq!(section_index(127, 0), 7);
+        assert_eq!(section_index(0, -64), 4);
+        assert_eq!(section_index(-64, -64), 0);
+        assert_eq!(section_index(-49, -64), 0);
+        assert_eq!(section_index(-48, -64), 1);
+        assert_eq!(section_index(128, -64), 12);
+    }
+
+    #[test]
+    fn serialize_and_deserialize_section() {
+        let mut states = PalettedContainer::new();
+
+        states.set(
+            SectionPos::new(1, 2, 3),
+            BlockState::try_from(BlockState::MAX_STATE).unwrap(),
+        );
+        states.set(
+            SectionPos::new(4, 5, 6),
+            BlockState::try_from(BlockState::MAX_STATE).unwrap(),
+        );
+        let biomes = PalettedContainer::new();
+        let section = Section {
+            block_count: 2,
+            states,
+            biomes,
+        };
+
+        let mut buf = Vec::new();
+        section.azalea_write(&mut buf).unwrap();
+
+        let mut cur = Cursor::new(buf.as_slice());
+        let deserialized_section = Section::azalea_read(&mut cur).unwrap();
+        assert_eq!(cur.position(), buf.len() as u64);
+
+        assert_eq!(section, deserialized_section);
+    }
+}
diff --git a/azalea-world/src/chunk/partial.rs b/azalea-world/src/chunk/partial.rs
new file mode 100644
index 00000000..e0f4912b
--- /dev/null
+++ b/azalea-world/src/chunk/partial.rs
@@ -0,0 +1,246 @@
+use std::{
+    fmt::{self, Debug},
+    io::Cursor,
+    sync::Arc,
+};
+
+use azalea_block::BlockState;
+use azalea_buf::BufReadError;
+use azalea_core::{
+    heightmap_kind::HeightmapKind,
+    position::{BlockPos, ChunkBlockPos, ChunkPos},
+};
+use parking_lot::RwLock;
+use tracing::{debug, trace, warn};
+
+use crate::{Chunk, chunk::storage::ChunkStorage};
+
+/// An efficient storage of chunks for a client that has a limited render
+/// distance.
+///
+/// This has support for using a shared [`ChunkStorage`].
+pub struct PartialChunkStorage {
+    /// The center of the view, i.e. the chunk the player is currently in.
+    view_center: ChunkPos,
+    pub(crate) chunk_radius: u32,
+    view_range: u32,
+    // chunks is a list of size chunk_radius * chunk_radius
+    chunks: Box<[Option<Arc<RwLock<Chunk>>>]>,
+}
+
+impl PartialChunkStorage {
+    pub fn new(chunk_radius: u32) -> Self {
+        let view_range = chunk_radius * 2 + 1;
+        PartialChunkStorage {
+            view_center: ChunkPos::new(0, 0),
+            chunk_radius,
+            view_range,
+            chunks: vec![None; (view_range * view_range) as usize].into(),
+        }
+    }
+
+    /// Update the chunk to center the view on.
+    ///
+    /// This should be called when the client receives a `SetChunkCacheCenter`
+    /// packet.
+    pub fn update_view_center(&mut self, view_center: ChunkPos) {
+        // this code block makes it force unload the chunks that are out of range after
+        // updating the view center. it's usually fine without it but the commented code
+        // is there in case you want to temporarily uncomment to test something
+
+        // ```
+        // for index in 0..self.chunks.len() {
+        //     let chunk_pos = self.chunk_pos_from_index(index);
+        //     if !in_range_for_view_center_and_radius(&chunk_pos, view_center, self.chunk_radius) {
+        //         self.chunks[index] = None;
+        //     }
+        // }
+        // ```
+
+        self.view_center = view_center;
+    }
+
+    /// Get the center of the view. This is usually the chunk that the player is
+    /// in.
+    pub fn view_center(&self) -> ChunkPos {
+        self.view_center
+    }
+
+    pub fn view_range(&self) -> u32 {
+        self.view_range
+    }
+
+    pub fn index_from_chunk_pos(&self, chunk_pos: &ChunkPos) -> usize {
+        let view_range = self.view_range as i32;
+
+        let x = i32::rem_euclid(chunk_pos.x, view_range) * view_range;
+        let z = i32::rem_euclid(chunk_pos.z, view_range);
+        (x + z) as usize
+    }
+
+    pub fn chunk_pos_from_index(&self, index: usize) -> ChunkPos {
+        let view_range = self.view_range as i32;
+
+        // find the base from the view center
+        let base_x = self.view_center.x.div_euclid(view_range) * view_range;
+        let base_z = self.view_center.z.div_euclid(view_range) * view_range;
+
+        // add the offset from the base
+        let offset_x = index as i32 / view_range;
+        let offset_z = index as i32 % view_range;
+
+        ChunkPos::new(base_x + offset_x, base_z + offset_z)
+    }
+
+    pub fn in_range(&self, chunk_pos: &ChunkPos) -> bool {
+        in_range_for_view_center_and_radius(chunk_pos, self.view_center, self.chunk_radius)
+    }
+
+    pub fn set_block_state(
+        &self,
+        pos: BlockPos,
+        state: BlockState,
+        chunk_storage: &ChunkStorage,
+    ) -> Option<BlockState> {
+        if pos.y < chunk_storage.min_y()
+            || pos.y >= (chunk_storage.min_y() + chunk_storage.height() as i32)
+        {
+            return None;
+        }
+        let chunk_pos = ChunkPos::from(pos);
+        let chunk_lock = chunk_storage.get(&chunk_pos)?;
+        let mut chunk = chunk_lock.write();
+        Some(chunk.get_and_set_block_state(&ChunkBlockPos::from(pos), state, chunk_storage.min_y()))
+    }
+
+    pub fn replace_with_packet_data(
+        &mut self,
+        pos: &ChunkPos,
+        data: &mut Cursor<&[u8]>,
+        heightmaps: &[(HeightmapKind, Box<[u64]>)],
+        chunk_storage: &mut ChunkStorage,
+    ) -> Result<(), BufReadError> {
+        debug!("Replacing chunk at {:?}", pos);
+        if !self.in_range(pos) {
+            warn!("Ignoring chunk since it's not in the view range: {pos:?}");
+            return Ok(());
+        }
+
+        let chunk = Chunk::read_with_dimension_height(
+            data,
+            chunk_storage.height(),
+            chunk_storage.min_y(),
+            heightmaps,
+        )?;
+
+        self.set(pos, Some(chunk), chunk_storage);
+        trace!("Loaded chunk {pos:?}");
+
+        Ok(())
+    }
+
+    /// Get a [`Chunk`] within render distance, or `None` if it's not loaded.
+    /// Use [`ChunkStorage::get`] to get a chunk from the shared storage.
+    pub fn limited_get(&self, pos: &ChunkPos) -> Option<&Arc<RwLock<Chunk>>> {
+        if !self.in_range(pos) {
+            warn!(
+                "Chunk at {:?} is not in the render distance (center: {:?}, {} chunks)",
+                pos, self.view_center, self.chunk_radius,
+            );
+            return None;
+        }
+
+        let index = self.index_from_chunk_pos(pos);
+        self.chunks[index].as_ref()
+    }
+    /// Get a mutable reference to a [`Chunk`] within render distance, or
+    /// `None` if it's not loaded.
+    ///
+    /// Use [`ChunkStorage::get`] to get a chunk from the shared storage.
+    pub fn limited_get_mut(&mut self, pos: &ChunkPos) -> Option<&mut Option<Arc<RwLock<Chunk>>>> {
+        if !self.in_range(pos) {
+            return None;
+        }
+
+        let index = self.index_from_chunk_pos(pos);
+
+        Some(&mut self.chunks[index])
+    }
+
+    /// Set a chunk in the shared storage and reference it from the limited
+    /// storage.
+    ///
+    /// Use [`Self::limited_set`] if you already have an `Arc<RwLock<Chunk>>`.
+    ///
+    /// # Panics
+    /// If the chunk is not in the render distance.
+    pub fn set(&mut self, pos: &ChunkPos, chunk: Option<Chunk>, chunk_storage: &mut ChunkStorage) {
+        let new_chunk = chunk.map(|c| chunk_storage.upsert(*pos, c));
+        self.limited_set(pos, new_chunk);
+    }
+
+    /// Set a chunk in our limited storage, useful if your chunk is already
+    /// referenced somewhere else and you want to make it also be referenced by
+    /// this storage.
+    ///
+    /// Use [`Self::set`] if you don't already have an `Arc<RwLock<Chunk>>`.
+    ///
+    /// # Panics
+    /// If the chunk is not in the render distance.
+    pub fn limited_set(&mut self, pos: &ChunkPos, chunk: Option<Arc<RwLock<Chunk>>>) {
+        if let Some(chunk_mut) = self.limited_get_mut(pos) {
+            *chunk_mut = chunk;
+        }
+    }
+
+    /// Get an iterator over all the chunks in the storage.
+    pub fn chunks(&self) -> impl Iterator<Item = &Option<Arc<RwLock<Chunk>>>> {
+        self.chunks.iter()
+    }
+}
+
+impl Debug for PartialChunkStorage {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("PartialChunkStorage")
+            .field("view_center", &self.view_center)
+            .field("chunk_radius", &self.chunk_radius)
+            .field("view_range", &self.view_range)
+            // .field("chunks", &self.chunks)
+            .field("chunks", &format_args!("{} items", self.chunks.len()))
+            .finish()
+    }
+}
+
+impl Default for PartialChunkStorage {
+    fn default() -> Self {
+        Self::new(8)
+    }
+}
+
+pub fn in_range_for_view_center_and_radius(
+    chunk_pos: &ChunkPos,
+    view_center: ChunkPos,
+    chunk_radius: u32,
+) -> bool {
+    (chunk_pos.x - view_center.x).unsigned_abs() <= chunk_radius
+        && (chunk_pos.z - view_center.z).unsigned_abs() <= chunk_radius
+}
+
+#[cfg(test)]
+mod tests {
+    use azalea_core::position::ChunkPos;
+
+    use crate::chunk::partial::PartialChunkStorage;
+
+    #[test]
+    fn test_chunk_pos_from_index() {
+        let mut partial_chunk_storage = PartialChunkStorage::new(5);
+        partial_chunk_storage.update_view_center(ChunkPos::new(0, -1));
+        assert_eq!(
+            partial_chunk_storage.chunk_pos_from_index(
+                partial_chunk_storage.index_from_chunk_pos(&ChunkPos::new(2, -1))
+            ),
+            ChunkPos::new(2, -1),
+        );
+    }
+}
diff --git a/azalea-world/src/chunk/storage.rs b/azalea-world/src/chunk/storage.rs
new file mode 100644
index 00000000..926c0b44
--- /dev/null
+++ b/azalea-world/src/chunk/storage.rs
@@ -0,0 +1,242 @@
+use std::{
+    any::Any,
+    collections::hash_map::Entry,
+    fmt::{self, Debug},
+    ops::{Deref, DerefMut},
+    sync::{Arc, Weak},
+};
+
+use azalea_block::{BlockState, fluid_state::FluidState};
+use azalea_core::position::{BlockPos, ChunkBiomePos, ChunkBlockPos, ChunkPos};
+use azalea_registry::data::Biome;
+use nohash_hasher::IntMap;
+use parking_lot::RwLock;
+
+use crate::Chunk;
+
+/// An abstract chunk storage backed by a [`ChunkStorageTrait`] implementation.
+///
+/// By default, this wraps a [`WeakChunkStorage`].
+pub struct ChunkStorage(pub Box<dyn ChunkStorageTrait>);
+
+pub trait ChunkStorageTrait: Send + Sync + Any {
+    /// Return the lowest y coordinate in the world, usually `-64`.
+    fn min_y(&self) -> i32;
+    /// Return the height of the world in blocks, usually `384`.
+    fn height(&self) -> u32;
+    /// Return a reference to the chunk from the storage.
+    #[must_use]
+    fn get(&self, pos: &ChunkPos) -> Option<Arc<RwLock<Chunk>>>;
+    /// Insert the chunk into the storage and return a reference to it.
+    ///
+    /// Since the storage may be a [`WeakChunkStorage`], you must immediately
+    /// put the returned `Arc<RwLock<Chunk>>` somewhere (probably a
+    /// [`PartialChunkStorage`](crate::PartialChunkStorage)).
+    #[must_use]
+    fn upsert(&mut self, pos: ChunkPos, chunk: Chunk) -> Arc<RwLock<Chunk>>;
+    fn chunks(&self) -> Box<[&ChunkPos]>;
+    fn clone_box(&self) -> Box<dyn ChunkStorageTrait>;
+
+    // these impls are here instead of in the `impl ChunkStorage` so rust is able to
+    // inline more and thus optimize them a lot better.
+
+    /// Returns the [`BlockState`] at the given position.
+    ///
+    /// If the block is outside of the world, then `None` is returned.
+    fn get_block_state(&self, pos: BlockPos) -> Option<BlockState> {
+        let chunk = self.get(&ChunkPos::from(pos))?;
+        let chunk = chunk.read();
+        chunk.get_block_state(&ChunkBlockPos::from(pos), self.min_y())
+    }
+    /// Set a [`BlockState`] at the given position.
+    ///
+    /// Returns the block that was previously there, or `None` if the position
+    /// is outside of the world.
+    fn set_block_state(&self, pos: BlockPos, state: BlockState) -> Option<BlockState> {
+        if pos.y < self.min_y() || pos.y >= (self.min_y() + self.height() as i32) {
+            return None;
+        }
+        let chunk = self.get(&ChunkPos::from(pos))?;
+        let mut chunk = chunk.write();
+        Some(chunk.get_and_set_block_state(&ChunkBlockPos::from(pos), state, self.min_y()))
+    }
+    fn get_fluid_state(&self, pos: BlockPos) -> Option<FluidState> {
+        let block_state = self.get_block_state(pos)?;
+        Some(FluidState::from(block_state))
+    }
+    fn get_biome(&self, pos: BlockPos) -> Option<Biome> {
+        let chunk = self.get(&ChunkPos::from(pos))?;
+        let chunk = chunk.read();
+        chunk.get_biome(ChunkBiomePos::from(pos), self.min_y())
+    }
+}
+impl ChunkStorage {
+    /// Create a storage backed by a [`WeakChunkStorage`] with the given world
+    /// dimensions.
+    pub fn new(height: u32, min_y: i32) -> Self {
+        Self(Box::new(WeakChunkStorage::new(height, min_y)))
+    }
+
+    /// Create a storage backed by a custom [`ChunkStorageTrait`]
+    /// implementation.
+    pub fn new_with(inner: Box<dyn ChunkStorageTrait>) -> Self {
+        Self(inner)
+    }
+}
+
+impl Deref for ChunkStorage {
+    type Target = dyn ChunkStorageTrait;
+
+    fn deref(&self) -> &Self::Target {
+        &*self.0
+    }
+}
+impl DerefMut for ChunkStorage {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut *self.0
+    }
+}
+impl Clone for ChunkStorage {
+    fn clone(&self) -> Self {
+        Self(self.0.clone_box())
+    }
+}
+
+/// A storage for chunks where they're only stored weakly, so if they're not
+/// actively being used somewhere else they'll be forgotten.
+///
+/// This is used for shared worlds.
+///
+/// This is relatively cheap to clone since it's just an `IntMap` with `Weak`
+/// pointers.
+#[derive(Clone, Debug)]
+pub struct WeakChunkStorage {
+    /// The height of the world.
+    ///
+    /// To get the maximum y position (exclusive), you have to combine this with
+    /// [`Self::min_y`].
+    pub height: u32,
+    /// The lowest y position in the world that can still have blocks placed on
+    /// it.
+    ///
+    /// This exists because in modern Minecraft versions, worlds can extend
+    /// below y=0.
+    pub min_y: i32,
+    pub map: IntMap<ChunkPos, Weak<RwLock<Chunk>>>,
+}
+
+impl WeakChunkStorage {
+    pub fn new(height: u32, min_y: i32) -> Self {
+        WeakChunkStorage {
+            height,
+            min_y,
+            map: IntMap::default(),
+        }
+    }
+}
+impl ChunkStorageTrait for WeakChunkStorage {
+    fn min_y(&self) -> i32 {
+        self.min_y
+    }
+    fn height(&self) -> u32 {
+        self.height
+    }
+    fn get(&self, pos: &ChunkPos) -> Option<Arc<RwLock<Chunk>>> {
+        self.map.get(pos).and_then(|chunk| chunk.upgrade())
+    }
+
+    fn upsert(&mut self, pos: ChunkPos, chunk: Chunk) -> Arc<RwLock<Chunk>> {
+        match self.map.entry(pos) {
+            Entry::Occupied(mut e) => {
+                if let Some(existing) = e.get_mut().upgrade() {
+                    *existing.write() = chunk;
+                    existing
+                } else {
+                    let arc = Arc::new(RwLock::new(chunk));
+                    e.insert(Arc::downgrade(&arc));
+                    arc
+                }
+            }
+            Entry::Vacant(e) => {
+                let arc = Arc::new(RwLock::new(chunk));
+                e.insert(Arc::downgrade(&arc));
+                arc
+            }
+        }
+    }
+
+    fn chunks(&self) -> Box<[&ChunkPos]> {
+        self.map.keys().collect::<Vec<_>>().into_boxed_slice()
+    }
+
+    fn clone_box(&self) -> Box<dyn ChunkStorageTrait> {
+        Box::new(self.clone())
+    }
+}
+
+impl Default for WeakChunkStorage {
+    fn default() -> Self {
+        Self::new(384, -64)
+    }
+}
+impl Default for ChunkStorage {
+    fn default() -> Self {
+        Self::new(384, -64)
+    }
+}
+
+impl Debug for ChunkStorage {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ChunkStorage")
+            .field("min_y", &self.0.min_y())
+            .field("height", &self.0.height())
+            .field("chunk_count", &self.0.chunks().len())
+            .finish()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use azalea_core::position::{BlockPos, ChunkPos};
+
+    use crate::{
+        Chunk,
+        chunk::{partial::PartialChunkStorage, storage::ChunkStorage},
+    };
+
+    #[test]
+    fn test_out_of_bounds_y() {
+        let mut chunk_storage = ChunkStorage::default();
+        let mut partial_chunk_storage = PartialChunkStorage::default();
+        partial_chunk_storage.set(
+            &ChunkPos { x: 0, z: 0 },
+            Some(Chunk::default()),
+            &mut chunk_storage,
+        );
+        assert!(
+            chunk_storage
+                .get_block_state(BlockPos { x: 0, y: 319, z: 0 })
+                .is_some()
+        );
+        assert!(
+            chunk_storage
+                .get_block_state(BlockPos { x: 0, y: 320, z: 0 })
+                .is_none()
+        );
+        assert!(
+            chunk_storage
+                .get_block_state(BlockPos { x: 0, y: 338, z: 0 })
+                .is_none()
+        );
+        assert!(
+            chunk_storage
+                .get_block_state(BlockPos { x: 0, y: -64, z: 0 })
+                .is_some()
+        );
+        assert!(
+            chunk_storage
+                .get_block_state(BlockPos { x: 0, y: -65, z: 0 })
+                .is_none()
+        );
+    }
+}