From 03d5baced87952a7091572ff09329b970eb9aed3 Mon Sep 17 00:00:00 2001
From: pantonshire <tom@tomandtally.co.uk>
Date: Sun, 17 Sep 2023 09:52:44 +0100
Subject: [PATCH] capped string type with Deserialize impl

---
 enumscribe/Cargo.toml                    |   7 +-
 enumscribe/src/internal/capped_string.rs | 102 +++++++++++++++++++++++
 enumscribe/src/internal/mod.rs           |   3 +
 enumscribe/src/lib.rs                    |   3 +-
 4 files changed, 112 insertions(+), 3 deletions(-)
 create mode 100644 enumscribe/src/internal/capped_string.rs
 create mode 100644 enumscribe/src/internal/mod.rs

diff --git a/enumscribe/Cargo.toml b/enumscribe/Cargo.toml
index 9c2378f..faddb11 100644
--- a/enumscribe/Cargo.toml
+++ b/enumscribe/Cargo.toml
@@ -12,13 +12,16 @@ keywords = ["enum", "derive", "serde"]
 
 [dependencies]
 enumscribe_derive = { version = "0.3.0", path = "../enumscribe_derive", default-features = false, optional = true }
+serde = { version = "1.0", default-features = false, optional = true }
 
 [dev-dependencies]
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 
 [features]
-default = ["std", "derive", "derive_serde"]
+# default = ["std", "derive", "derive_serde"]
+default = ["derive", "derive_serde"]
 std = ["enumscribe_derive/std"]
 derive = ["enumscribe_derive"]
-derive_serde = ["derive", "enumscribe_derive/serde"]
+derive_serde = ["derive", "serde", "enumscribe_derive/serde"]
+serde = ["derive_serde", "dep:serde"]
diff --git a/enumscribe/src/internal/capped_string.rs b/enumscribe/src/internal/capped_string.rs
new file mode 100644
index 0000000..0f4a165
--- /dev/null
+++ b/enumscribe/src/internal/capped_string.rs
@@ -0,0 +1,102 @@
+//! Module for the [`CappedString`](CappedString) type, which is a string type which always stores
+//! its data inline.
+
+use core::{str, convert::TryFrom, ops::Deref, borrow::Borrow, fmt};
+
+/// TODO: documentation
+pub struct CappedString<const N: usize> {
+    /// The string data. It is an invariant that this must always be valid UTF-8.
+    buf: [u8; N],
+}
+
+impl<const N: usize> CappedString<N> {
+    /// TODO: documentation
+    #[inline]
+    #[must_use]
+    pub fn new(s: &str) -> Option<Self> {
+        unsafe { Self::from_utf8_unchecked(s.as_bytes()) }
+    }
+
+    /// TODO: documentation
+    #[inline]
+    #[must_use]
+    pub unsafe fn from_utf8_unchecked(bs: &[u8]) -> Option<Self> {
+        let buf =  <[u8; N]>::try_from(bs).ok()?;
+        Some(Self { buf })
+    }
+
+    /// TODO: documentation
+    #[inline]
+    #[must_use]
+    pub fn as_str(&self) -> &str {
+        unsafe { str::from_utf8_unchecked(&self.buf) }
+    }
+
+    /// TODO: documentation
+    #[inline]
+    #[must_use]
+    pub fn to_uppercase<const M: usize>(&self) -> Option<CappedString<M>> {
+        todo!()
+    }
+}
+
+impl<const N: usize> Deref for CappedString<N> {
+    type Target = str;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        self.as_str()
+    }
+}
+
+impl<const N: usize> AsRef<str> for CappedString<N> {
+    #[inline]
+    fn as_ref(&self) -> &str {
+        self
+    }
+}
+
+impl<const N: usize> Borrow<str> for CappedString<N> {
+    #[inline]
+    fn borrow(&self) -> &str {
+        self
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de, const N: usize> serde::Deserialize<'de> for CappedString<N> {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>
+    {
+        deserializer.deserialize_str(CappedStringVisitor::<N>)
+    }
+}
+
+struct CappedStringVisitor<const N: usize>;
+
+impl<'de, const N: usize> serde::de::Visitor<'de> for CappedStringVisitor<N> {
+    type Value = CappedString<N>;
+
+    fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "a string up to {} bytes long", N)
+    }
+
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        CappedString::new(v)
+            .ok_or_else(|| E::invalid_length(v.len(), &self))
+    }
+
+    fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        str::from_utf8(v)
+            .map_err(|_| E::invalid_value(serde::de::Unexpected::Bytes(v), &self))
+            .and_then(|v| CappedString::new(v)
+                .ok_or_else(|| E::invalid_length(v.len(), &self)))
+    }
+}
diff --git a/enumscribe/src/internal/mod.rs b/enumscribe/src/internal/mod.rs
new file mode 100644
index 0000000..6a46570
--- /dev/null
+++ b/enumscribe/src/internal/mod.rs
@@ -0,0 +1,3 @@
+//! Utilities for use by code generated by `enumscribe_derive`.
+
+pub mod capped_string;
diff --git a/enumscribe/src/lib.rs b/enumscribe/src/lib.rs
index 438b39b..cfc4bf7 100644
--- a/enumscribe/src/lib.rs
+++ b/enumscribe/src/lib.rs
@@ -183,7 +183,8 @@
 #![deny(missing_docs)]
 #![cfg_attr(not(feature = "std"), no_std)]
 
-#[macro_use]
+pub mod internal;
+
 extern crate enumscribe_derive;
 
 pub use enumscribe_derive::*;