rssn 0.2.9

A comprehensive scientific computing library for Rust, aiming for feature parity with NumPy and SymPy.
Documentation 
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//! JSON-based FFI API for physics sim Navier-Stokes functions.

use std::os::raw::c_char;

use ndarray::Array2;
use serde::Serialize;

use crate::ffi_apis::common::from_json_string;
use crate::ffi_apis::common::to_c_string;
use crate::ffi_apis::ffi_api::FfiResult;
use crate::physics::physics_sim::navier_stokes_fluid::NavierStokesParameters;
use crate::physics::physics_sim::navier_stokes_fluid::{
    self,
};

#[derive(Serialize)]
struct NavierStokesOutputData {
    pub u: Array2<f64>,
    pub v: Array2<f64>,
    pub p: Array2<f64>,
}

/// Solves the incompressible Navier-Stokes equations for fluid flow in a lid-driven cavity via JSON serialization.
///
/// The Navier-Stokes equations ∂u/∂t + (u·∇)u = -∇p/ρ + ν∇²u with incompressibility
/// constraint ∇·u = 0 govern viscous fluid dynamics. This solver uses a projection method
/// to enforce divergence-free velocity fields.
///
/// # Arguments
///
/// * `input` - A JSON string pointer containing:
///   - `nx`, `ny`: Grid dimensions
///   - `re`: Reynolds number Re = UL/ν (ratio of inertial to viscous forces)
///   - `dt`: Time step size
///   - `n_iter`: Number of time iterations
///   - `lid_velocity`: Velocity of the moving lid boundary
///
/// # Returns
///
/// A C string pointer containing JSON-encoded `FfiResult<NavierStokesOutputData, String>` with:
/// - `u`: Horizontal velocity field u(x,y)
/// - `v`: Vertical velocity field v(x,y)
/// - `p`: Pressure field p(x,y)
///
/// # Safety
///
/// This function is unsafe because it dereferences a raw C string pointer.
///
/// # 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_physics_sim_navier_stokes_run_json(
    input: *const c_char
) -> *mut c_char {
    let params: NavierStokesParameters = match from_json_string(input) {
        | Some(p) => p,
        | None => {
            return to_c_string(
                serde_json::to_string(&FfiResult::<NavierStokesOutputData, String>::err(
                    "Invalid JSON".to_string(),
                ))
                .unwrap(),
            );
        },
    };

    match navier_stokes_fluid::run_lid_driven_cavity(&params) {
        | Ok((u, v, p)) => {
            let out = NavierStokesOutputData { u, v, p };

            to_c_string(
                serde_json::to_string(&FfiResult::<NavierStokesOutputData, String>::ok(out))
                    .unwrap(),
            )
        },
        | Err(e) => {
            to_c_string(
                serde_json::to_string(&FfiResult::<NavierStokesOutputData, String>::err(e))
                    .unwrap(),
            )
        },
    }
}