rssn 0.2.9

//! Bincode-based FFI API for numerical elementary operations.

use std::collections::HashMap;

use serde::Deserialize;
use serde::Serialize;

use crate::ffi_apis::common::BincodeBuffer;
use crate::ffi_apis::ffi_api::FfiResult;
use crate::numerical::elementary;
use crate::symbolic::core::Expr;

#[derive(Deserialize)]
struct EvalRequest {
    expr: Expr,
    vars: HashMap<String, f64>,
}

pub(crate) fn decode<T: for<'de> Deserialize<'de>>(
    data: *const u8,
    len: usize,
) -> Option<T> {
    if data.is_null() {
        return None;
    }

    let slice = unsafe { std::slice::from_raw_parts(data, len) };

    bincode_next::serde::decode_from_slice(slice, bincode_next::config::standard())
        .ok()
        .map(|(v, _)| v)
}

fn encode<T: Serialize>(val: &T) -> BincodeBuffer {
    match bincode_next::serde::encode_to_vec(val, bincode_next::config::standard()) {
        | Ok(bytes) => BincodeBuffer::from_vec(bytes),
        | Err(_) => BincodeBuffer::empty(),
    }
}

/// Evaluates an expression from a Bincode buffer.
///
/// # Safety
///
/// This function is unsafe because it dereferences raw pointers as part of the FFI boundary.
/// The caller must ensure:
/// 1. All pointer arguments are valid and point to initialized memory.
/// 2. The memory layout of passed structures matches the expected C-ABI layout.
/// 3. Any pointers returned by this function are managed according to the API's ownership rules.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn rssn_num_eval_bincode(
    data: *const u8,
    len: usize,
) -> BincodeBuffer {
    let req: EvalRequest = match decode(data, len) {
        | Some(r) => r,
        | None => {
            let res: FfiResult<f64, String> = FfiResult {
                ok: None,
                err: Some(
                    "Bincode decode \
                     error"
                        .to_string(),
                ),
            };

            return encode(&res);
        },
    };

    let result = elementary::eval_expr(&req.expr, &req.vars);

    let ffi_res = match result {
        | Ok(v) => {
            FfiResult {
                ok: Some(v),
                err: None,
            }
        },
        | Err(e) => {
            FfiResult {
                ok: None,
                err: Some(e),
            }
        },
    };

    encode(&ffi_res)
}