From 587addd513f48aa1b5782c946645ee5fbbb9b0c1 Mon Sep 17 00:00:00 2001
From: Christian Ivicevic <mail@christian-ivicevic.com>
Date: Wed, 6 Mar 2024 11:34:41 +0100
Subject: [PATCH] Add wasm support to `rust-decimal`

A new optional feature 'wasm' has been introduced in the codebase. This enables `wasm-bindgen` support, making `Decimal` compatible with the `wasm_bindgen` attribute macro, and exposes `fromNumber()` and `toNumber()` methods to convert between `Decimal` and the primitive `number` type.
---
 Cargo.toml     |  2 ++
 README.md      |  7 +++++++
 src/decimal.rs |  3 +++
 src/lib.rs     |  2 ++
 src/wasm.rs    | 26 ++++++++++++++++++++++++++
 5 files changed, 40 insertions(+)
 create mode 100644 src/wasm.rs

diff --git a/Cargo.toml b/Cargo.toml
index b99a14c..2c70c13 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -36,6 +36,7 @@ rocket = { default-features = false, optional = true, version = "0.5.0-rc.3" }
 serde = { default-features = false, optional = true, version = "1.0" }
 serde_json = { default-features = false, optional = true, version = "1.0" }
 tokio-postgres = { default-features = false, optional = true, version = "0.7" }
+wasm-bindgen = { default-features = false, optional = true, version = "0.2" }
 
 [dev-dependencies]
 bincode = { default-features = false, version = "1.0" }
@@ -85,6 +86,7 @@ serde-with-float = ["serde"]
 serde-with-str = ["serde"]
 std = ["arrayvec/std", "borsh?/std", "bytes?/std", "rand?/std", "rkyv?/std", "serde?/std", "serde_json?/std"]
 tokio-pg = ["db-tokio-postgres"] # Backwards compatability
+wasm = ["dep:wasm-bindgen"]
 
 [[bench]]
 harness = false
diff --git a/README.md b/README.md
index 1927044..e87015d 100644
--- a/README.md
+++ b/README.md
@@ -104,6 +104,7 @@ assert_eq!(total, dec!(27.26));
 * [rocket-traits](#rocket-traits)
 * [rust-fuzz](#rust-fuzz)
 * [std](#std)
+* [wasm](#wasm)
 
 **Database**
 
@@ -331,6 +332,12 @@ Please see the `examples` directory for more information regarding `serde_json`
 Enable `std` library support. This is enabled by default, however in the future will be opt in. For now, to support `no_std`
 libraries, this crate can be compiled with `--no-default-features`.
 
+### `wasm`
+
+Enable [`wasm-bindgen`](https://github.com/rustwasm/wasm-bindgen) support which makes `Decimal` compatible with the
+`wasm_bindgen` attribute macro and exposes `fromNumber()` and `toNumber()` methods to convert between `Decimal` and
+the primitive `number` type across boundaries.
+
 ## Building
 
 Please refer to the [Build document](BUILD.md) for more information on building and testing Rust Decimal.
diff --git a/src/decimal.rs b/src/decimal.rs
index 45f5661..4f1ddfe 100644
--- a/src/decimal.rs
+++ b/src/decimal.rs
@@ -27,6 +27,8 @@ use num_traits::float::FloatCore;
 use num_traits::{FromPrimitive, Num, One, Signed, ToPrimitive, Zero};
 #[cfg(feature = "rkyv")]
 use rkyv::{Archive, Deserialize, Serialize};
+#[cfg(feature = "wasm")]
+use wasm_bindgen::prelude::wasm_bindgen;
 
 /// The smallest value that can be represented by this decimal type.
 const MIN: Decimal = Decimal {
@@ -121,6 +123,7 @@ pub struct UnpackedDecimal {
     archive_attr(derive(Clone, Copy, Debug))
 )]
 #[cfg_attr(feature = "rkyv-safe", archive(check_bytes))]
+#[cfg_attr(feature = "wasm", wasm_bindgen)]
 pub struct Decimal {
     // Bits 0-15: unused
     // Bits 16-23: Contains "e", a value between 0-28 that indicates the scale
diff --git a/src/lib.rs b/src/lib.rs
index d49db64..2306695 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -52,6 +52,8 @@ mod serde;
     )
 ))]
 pub mod serde;
+#[cfg(feature = "wasm")]
+pub mod wasm;
 
 pub use decimal::{Decimal, RoundingStrategy};
 pub use error::Error;
diff --git a/src/wasm.rs b/src/wasm.rs
new file mode 100644
index 0000000..03ed619
--- /dev/null
+++ b/src/wasm.rs
@@ -0,0 +1,26 @@
+use num_traits::{FromPrimitive, ToPrimitive};
+use wasm_bindgen::prelude::wasm_bindgen;
+
+use crate::Decimal;
+
+#[wasm_bindgen]
+impl Decimal {
+    /// Returns a new `Decimal` object instance by converting a primitive number.
+    #[wasm_bindgen(js_name = fromNumber)]
+    #[must_use]
+    pub fn from_number(value: f64) -> Option<Decimal> {
+        Decimal::from_f64(value)
+    }
+
+    /// Returns the value of this `Decimal` converted to a primitive number.
+    ///
+    /// # Caution
+    /// At the time of writing this implementation the conversion from `Decimal` to `f64` cannot
+    /// fail. To prevent undefined behavior in case the underlying implementation changes `f64::NAN`
+    /// is returned as a stable fallback value.
+    #[wasm_bindgen(js_name = toNumber)]
+    #[must_use]
+    pub fn to_number(&self) -> f64 {
+        self.to_f64().unwrap_or(f64::NAN)
+    }
+}