rssn 0.2.9

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

use std::collections::HashMap;
use std::ffi::CStr;
use std::ffi::CString;
use std::os::raw::c_char;

use serde::Deserialize;

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>,
}

/// Evaluates an expression from a JSON string.
///
/// Input JSON format: `{"expr": <Expr>, "vars": {"x": 1.0, "y": 2.0}}`
///
/// # 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.
///
/// # Panics
///
/// This function may panic if the FFI input is malformed, null where not expected,
/// or if internal state synchronization fails (e.g., poisoned locks).
#[unsafe(no_mangle)]
pub unsafe extern "C" fn rssn_num_eval_json(json_ptr: *const c_char) -> *mut c_char {
    if json_ptr.is_null() {
        return std::ptr::null_mut();
    }

    let json_str = match unsafe { CStr::from_ptr(json_ptr).to_str() } {
        | Ok(s) => s,
        | Err(_) => {
            return std::ptr::null_mut();
        },
    };

    let req: EvalRequest = match serde_json::from_str(json_str) {
        | Ok(r) => r,
        | Err(e) => {
            let res: FfiResult<f64, String> = FfiResult {
                ok: None,
                err: Some(e.to_string()),
            };

            return CString::new(serde_json::to_string(&res).unwrap())
                .unwrap()
                .into_raw();
        },
    };

    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),
            }
        },
    };

    CString::new(serde_json::to_string(&ffi_res).unwrap())
        .unwrap()
        .into_raw()
}