//! JSON codec marker and optional [`serde_json`] integration.
//!
//! The [`Json`] marker type is always available and can be used in type
//! signatures without any feature flags. Enable the `serde_json` feature to
//! get [`Encode`](super::Encode)/[`Decode`](super::Decode) implementations
//! via [`serde_json`].
//!
//! > **Note:** The `serde_json` feature requires `std`.

/// JSON codec marker type.
///
/// This type is always available regardless of feature flags, so you can
/// reference it in type signatures from `no_std` crates. Enable the
/// `serde_json` feature for [`Encode`](super::Encode)/[`Decode`](super::Decode)
/// implementations.
///
/// This codec does **not** implement [`Canonical`](super::Canonical) because
/// JSON object key ordering is not guaranteed by `serde_json`.
///
/// # Example
///
/// ```
/// # #[cfg(all(feature = "serde_json", feature = "sha2"))]
/// # {
/// use evidence::digest::{Digest, sha2::Sha256};
/// use evidence::codec::json::Json;
/// use serde::{Serialize, Deserialize};
///
/// #[derive(Serialize, Deserialize)]
/// struct MyData {
///     id: u32,
///     name: String,
/// }
///
/// let data = MyData { id: 42, name: "test".into() };
/// let digest: Digest<MyData, Sha256, Json> = Digest::hash(&data);
/// # }
/// ```
#[derive(Debug, Clone, Copy)]
pub enum Json {}

/// Error returned when JSON encoding fails.
#[cfg(feature = "serde_json")]
#[derive(Debug, Clone)]
pub struct JsonEncodeError(alloc::string::String);

#[cfg(feature = "serde_json")]
impl core::fmt::Display for JsonEncodeError {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "JSON encode error: {}", self.0)
    }
}

#[cfg(feature = "serde_json")]
impl<T: serde::Serialize> super::Encode<T> for Json {
    type Error = JsonEncodeError;

    fn encode(value: &T) -> Result<alloc::vec::Vec<u8>, Self::Error> {
        serde_json::to_vec(value)
            .map_err(|e| JsonEncodeError(alloc::string::ToString::to_string(&e)))
    }
}

/// Error returned when JSON decoding fails.
#[cfg(feature = "serde_json")]
#[derive(Debug, Clone)]
pub struct JsonDecodeError(alloc::string::String);

#[cfg(feature = "serde_json")]
impl core::fmt::Display for JsonDecodeError {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "JSON decode error: {}", self.0)
    }
}

#[cfg(feature = "serde_json")]
impl<T: serde::de::DeserializeOwned> super::Decode<T> for Json {
    type Error = JsonDecodeError;

    fn decode(bytes: &[u8]) -> Result<T, Self::Error> {
        serde_json::from_slice(bytes)
            .map_err(|e| JsonDecodeError(alloc::string::ToString::to_string(&e)))
    }
}