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 MTM functions.

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

use serde::Deserialize;

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_mtm;

#[derive(Deserialize)]
struct Multigrid1DInput {
    n_interior: usize,
    f: Vec<f64>,
    num_cycles: usize,
}

#[derive(Deserialize)]
struct Multigrid2DInput {
    n: usize,
    f: Vec<f64>,
    num_cycles: usize,
}

/// Solves the 1D Poisson equation using Multigrid Method via JSON serialization.
///
/// The Poisson equation -d²u/dx² = f is solved using the multigrid method, which achieves
/// optimal O(N) complexity through hierarchical coarse-grid correction.
///
/// # Arguments
///
/// * `input` - A JSON string pointer containing:
///   - `n_interior`: Number of interior grid points
///   - `f`: Right-hand side source term
///   - `num_cycles`: Number of V-cycles or W-cycles to perform
///
/// # Returns
///
/// A C string pointer containing JSON-encoded `FfiResult<Vec<f64>, String>` with
/// the solution vector u.
///
/// # Safety
///
/// This function is unsafe because it receives a raw C string pointer that must be
/// valid, null-terminated UTF-8. The caller must free the returned 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_mtm_solve_poisson_1d_json(
    input: *const c_char
) -> *mut c_char {
    let input: Multigrid1DInput = match from_json_string(input) {
        | Some(i) => i,
        | None => {
            return to_c_string(
                serde_json::to_string(&FfiResult::<Vec<f64>, String>::err(
                    "Invalid JSON".to_string(),
                ))
                .unwrap(),
            );
        },
    };

    match physics_mtm::solve_poisson_1d_multigrid(input.n_interior, &input.f, input.num_cycles) {
        | Ok(res) => {
            to_c_string(serde_json::to_string(&FfiResult::<Vec<f64>, String>::ok(res)).unwrap())
        },
        | Err(e) => {
            to_c_string(serde_json::to_string(&FfiResult::<Vec<f64>, String>::err(e)).unwrap())
        },
    }
}

/// Solves the 2D Poisson equation using Multigrid Method via JSON serialization.
///
/// The Poisson equation ∇²u = f is solved using the multigrid method, which achieves
/// optimal O(N) complexity through hierarchical coarse-grid correction.
///
/// # Arguments
///
/// * `input` - A JSON string pointer containing:
///   - `n`: Grid size (n×n interior points)
///   - `f`: Right-hand side source term (flattened 2D array)
///   - `num_cycles`: Number of V-cycles or W-cycles to perform
///
/// # Returns
///
/// A C string pointer containing JSON-encoded `FfiResult<Vec<f64>, String>` with
/// the solution vector u (flattened 2D array).
///
/// # Safety
///
/// This function is unsafe because it receives a raw C string pointer that must be
/// valid, null-terminated UTF-8. The caller must free the returned 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_mtm_solve_poisson_2d_json(
    input: *const c_char
) -> *mut c_char {
    let input: Multigrid2DInput = match from_json_string(input) {
        | Some(i) => i,
        | None => {
            return to_c_string(
                serde_json::to_string(&FfiResult::<Vec<f64>, String>::err(
                    "Invalid JSON".to_string(),
                ))
                .unwrap(),
            );
        },
    };

    match physics_mtm::solve_poisson_2d_multigrid(input.n, &input.f, input.num_cycles) {
        | Ok(res) => {
            to_c_string(serde_json::to_string(&FfiResult::<Vec<f64>, String>::ok(res)).unwrap())
        },
        | Err(e) => {
            to_c_string(serde_json::to_string(&FfiResult::<Vec<f64>, String>::err(e)).unwrap())
        },
    }
}