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 FDTD electrodynamics functions.

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

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::fdtd_electrodynamics::FdtdParameters;
use crate::physics::physics_sim::fdtd_electrodynamics::{
    self,
};

/// Runs a Finite-Difference Time-Domain (FDTD) electromagnetic simulation via JSON serialization.
///
/// FDTD solves Maxwell's equations ∇×E = -∂B/∂t and ∇×H = ∂D/∂t + J using a staggered
/// Yee lattice grid, advancing the electric field Ez and magnetic field components in time.
///
/// # Arguments
///
/// * `input` - A JSON string pointer containing:
///   - `width`, `height`: Grid dimensions
///   - `dx`, `dy`: Spatial discretization steps
///   - `dt`: Time step size (must satisfy Courant-Friedrichs-Lewy stability condition)
///   - `steps`: Number of time steps to simulate
///   - `source_x`, `source_y`: Position of electromagnetic source
///   - `source_frequency`: Angular frequency ω of the source
///
/// # Returns
///
/// A C string pointer containing JSON-encoded `FfiResult<Vec<Vec<f64>>, String>` with
/// the final Ez field as a 2D vector array.
///
/// # 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_fdtd_run_json(input: *const c_char) -> *mut c_char {
    let params: FdtdParameters = match from_json_string(input) {
        | Some(p) => p,
        | None => {
            return to_c_string(
                serde_json::to_string(&FfiResult::<Vec<Vec<f64>>, String>::err(
                    "Invalid JSON".to_string(),
                ))
                .unwrap(),
            );
        },
    };

    let snapshots = fdtd_electrodynamics::run_fdtd_simulation(&params);

    // Return only the last Ez field as Vec<Vec<f64>> for simplicity in JSON
    if let Some(final_ez) = snapshots.last() {
        let mut out = Vec::with_capacity(params.width);

        for row in final_ez.axis_iter(ndarray::Axis(0)) {
            out.push(row.to_vec());
        }

        to_c_string(serde_json::to_string(&FfiResult::<Vec<Vec<f64>>, String>::ok(out)).unwrap())
    } else {
        to_c_string(
            serde_json::to_string(&FfiResult::<Vec<Vec<f64>>, String>::err(
                "No snapshots".to_string(),
            ))
            .unwrap(),
        )
    }
}