From 4b155f4c9bb62e22e74eb6341bf567e4898a60ae Mon Sep 17 00:00:00 2001
From: Ryan Johnson <ryanj00a@gmail.com>
Date: Mon, 14 Nov 2022 01:01:28 -0800
Subject: [PATCH] Expand on the "encoded buf" idea in valence_protocol (#155)

Adds a `Cached<T>` type and renames some things.
---
 valence_protocol/src/cache.rs       | 143 ++++++++++++++++++++++++++++
 valence_protocol/src/encoded_buf.rs |  47 ---------
 valence_protocol/src/lib.rs         |   2 +-
 3 files changed, 144 insertions(+), 48 deletions(-)
 create mode 100644 valence_protocol/src/cache.rs
 delete mode 100644 valence_protocol/src/encoded_buf.rs

diff --git a/valence_protocol/src/cache.rs b/valence_protocol/src/cache.rs
new file mode 100644
index 0000000..04bc1a2
--- /dev/null
+++ b/valence_protocol/src/cache.rs
@@ -0,0 +1,143 @@
+use std::io::Write;
+use std::marker::PhantomData;
+use std::mem;
+
+use anyhow::anyhow;
+
+use crate::{Decode, Encode, Result};
+
+/// Contains both a value of `T` and an [`EncodedBuf<T>`] to ensure the
+/// buffer is updated when `T` is modified[^note].
+///
+/// The `Encode` implementation for `Cached<T>` encodes only the contained
+/// `EncodedBuf`.
+///
+/// Use this type when you want `Encode` to be cached but you also need to read
+/// from the value of `T`. If the value of `T` is write-only, consider using
+/// `EncodedBuf` instead.
+///
+/// [`EncodedBuf<T>`]: EncodedBuf
+/// [^note]: Assuming `T` does not use internal mutability.
+pub struct Cached<T> {
+    val: T,
+    buf: EncodedBuf<T>,
+}
+
+impl<T: Encode> Cached<T> {
+    pub fn new(val: T) -> Self {
+        let buf = EncodedBuf::new(&val);
+
+        Self { val, buf }
+    }
+
+    pub fn get(&self) -> &T {
+        &self.val
+    }
+
+    pub fn buf(&self) -> &EncodedBuf<T> {
+        &self.buf
+    }
+
+    /// Provides a mutable reference to the contained `T` for modification. The
+    /// buffer is re-encoded when the closure returns.
+    pub fn modify<U>(&mut self, f: impl FnOnce(&mut T) -> U) -> U {
+        let u = f(&mut self.val);
+        self.buf.set(&self.val);
+        u
+    }
+
+    pub fn replace(&mut self, new: T) -> T {
+        self.modify(|old| mem::replace(old, new))
+    }
+
+    pub fn into_inner(self) -> (T, EncodedBuf<T>) {
+        (self.val, self.buf)
+    }
+}
+
+impl<T> Encode for Cached<T>
+where
+    T: Encode,
+{
+    fn encode(&self, w: impl Write) -> Result<()> {
+        self.buf.encode(w)
+    }
+}
+
+/// The `Decode` implementation for `Cached` exists for the sake of
+/// completeness, but you probably shouldn't need to use it.
+impl<'a, T> Decode<'a> for Cached<T>
+where
+    T: Encode + Decode<'a>,
+{
+    fn decode(r: &mut &'a [u8]) -> Result<Self> {
+        let val = T::decode(r)?;
+        Ok(Self::new(val))
+    }
+}
+
+/// Caches the result of `T`'s [`Encode`] implementation into an owned buffer.
+///
+/// This is useful for types with expensive [`Encode`] implementations such as
+/// [`Text`] or [`Compound`]. It has little to no benefit for primitive types
+/// such as `i32`, `VarInt`, `&str`, `&[u8]`, etc.
+///
+/// # Examples
+///
+/// ```
+/// use valence_protocol::cache::EncodedBuf;
+/// use valence_protocol::Encode;
+///
+/// let mut buf1 = Vec::new();
+/// let mut buf2 = Vec::new();
+///
+/// "hello".encode(&mut buf1).unwrap();
+///
+/// let cache = EncodedBuf::new("hello");
+/// cache.encode(&mut buf2).unwrap();
+///
+/// assert_eq!(buf1, buf2);
+/// ```
+///
+/// [`Text`]: crate::text::Text
+/// [`Compound`]: valence_nbt::Compound
+pub struct EncodedBuf<T: ?Sized> {
+    buf: Vec<u8>,
+    res: Result<()>,
+    _marker: PhantomData<fn(T) -> T>,
+}
+
+impl<T: Encode + ?Sized> EncodedBuf<T> {
+    pub fn new(t: &T) -> Self {
+        let mut buf = Vec::new();
+        let res = t.encode(&mut buf);
+
+        Self {
+            buf,
+            res,
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn set(&mut self, t: &T) {
+        self.buf.clear();
+        self.res = t.encode(&mut self.buf);
+    }
+
+    pub fn into_inner(self) -> Result<Vec<u8>> {
+        self.res.map(|()| self.buf)
+    }
+}
+
+impl<T: ?Sized> Encode for EncodedBuf<T> {
+    fn encode(&self, mut w: impl Write) -> Result<()> {
+        match &self.res {
+            Ok(()) => Ok(w.write_all(&self.buf)?),
+            Err(e) => Err(anyhow!("{e:#}")),
+        }
+    }
+
+    fn encoded_len(&self) -> usize {
+        self.buf.len()
+    }
+}
diff --git a/valence_protocol/src/encoded_buf.rs b/valence_protocol/src/encoded_buf.rs
deleted file mode 100644
index 34d2778..0000000
--- a/valence_protocol/src/encoded_buf.rs
+++ /dev/null
@@ -1,47 +0,0 @@
-use std::io::Write;
-use std::marker::PhantomData;
-
-use anyhow::anyhow;
-
-use crate::{Encode, Result};
-
-pub struct CachedEncode<T: ?Sized> {
-    buf: Vec<u8>,
-    res: Result<()>,
-    _marker: PhantomData<fn(T) -> T>,
-}
-
-impl<T: Encode + ?Sized> CachedEncode<T> {
-    pub fn new(t: &T) -> Self {
-        let mut buf = Vec::new();
-        let res = t.encode(&mut buf);
-
-        Self {
-            buf,
-            res,
-            _marker: PhantomData,
-        }
-    }
-
-    pub fn set(&mut self, t: &T) {
-        self.buf.clear();
-        self.res = t.encode(&mut self.buf);
-    }
-
-    pub fn into_inner(self) -> Result<Vec<u8>> {
-        self.res.map(|()| self.buf)
-    }
-}
-
-impl<T: ?Sized> Encode for CachedEncode<T> {
-    fn encode(&self, mut w: impl Write) -> Result<()> {
-        match &self.res {
-            Ok(()) => Ok(w.write_all(&self.buf)?),
-            Err(e) => Err(anyhow!("{e:#}")),
-        }
-    }
-
-    fn encoded_len(&self) -> usize {
-        self.buf.len()
-    }
-}
diff --git a/valence_protocol/src/lib.rs b/valence_protocol/src/lib.rs
index 9756d7b..11cc9ae 100644
--- a/valence_protocol/src/lib.rs
+++ b/valence_protocol/src/lib.rs
@@ -91,9 +91,9 @@ pub mod block_pos;
 pub mod bounded;
 pub mod byte_angle;
 mod byte_counter;
+pub mod cache;
 pub mod codec;
 pub mod enchant;
-pub mod encoded_buf;
 pub mod entity_meta;
 pub mod ident;
 mod impls;