rssn 0.2.9

//! JSON-based FFI API for numerical sparse matrix operations.

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::sparse::SparseMatrixData;
use crate::numerical::sparse::{
    self,
};

#[derive(Deserialize)]
struct SpMvRequest {
    matrix: SparseMatrixData,
    vector: Vec<f64>,
}

/// Sparse matrix-vector multiplication from JSON.
///
/// # 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_sparse_spmv_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: SpMvRequest = match serde_json::from_str(json_str) {
        | Ok(r) => r,
        | Err(e) => {
            let res: FfiResult<Vec<f64>, String> = FfiResult {
                ok: None,
                err: Some(e.to_string()),
            };

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

    let mat = req.matrix.to_csmat();

    match sparse::sp_mat_vec_mul(&mat, &req.vector) {
        | Ok(res) => {
            let ffi_res: FfiResult<Vec<f64>, String> = FfiResult {
                ok: Some(res),
                err: None,
            };

            CString::new(serde_json::to_string(&ffi_res).unwrap())
                .unwrap()
                .into_raw()
        },
        | Err(e) => {
            let ffi_res: FfiResult<Vec<f64>, String> = FfiResult {
                ok: None,
                err: Some(e),
            };

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

/// Solves Ax=b using Conjugate Gradient from JSON.
#[derive(Deserialize)]
struct CgRequest {
    a: SparseMatrixData,
    b: Vec<f64>,
    x0: Option<Vec<f64>>,
    max_iter: usize,
    tolerance: f64,
}

/// Solves the linear system Ax = b using the Conjugate Gradient iterative method via JSON.
///
/// The Conjugate Gradient method is efficient for large sparse symmetric positive-definite matrices,
/// converging in at most N iterations (typically much fewer).
///
/// # Arguments
///
/// * `json_ptr` - A JSON string pointer containing:
///   - `a`: Sparse matrix A in CSR/COO format
///   - `b`: Right-hand side vector b
///   - `x0`: Optional initial guess for solution vector
///   - `max_iter`: Maximum number of iterations
///   - `tolerance`: Convergence tolerance for residual norm
///
/// # Returns
///
/// A C string pointer containing JSON-encoded `FfiResult<Vec<f64>, String>` with
/// the solution vector x.
///
/// # 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_num_sparse_solve_cg_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: CgRequest = match serde_json::from_str(json_str) {
        | Ok(r) => r,
        | Err(e) => {
            let res: FfiResult<Vec<f64>, String> = FfiResult {
                ok: None,
                err: Some(e.to_string()),
            };

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

    let a = req.a.to_csmat();

    let b = ndarray::Array1::from_vec(req.b);

    let x0 = req.x0.map(ndarray::Array1::from_vec);

    match sparse::solve_conjugate_gradient(&a, &b, x0.as_ref(), req.max_iter, req.tolerance) {
        | Ok(res) => {
            let ffi_res: FfiResult<Vec<f64>, String> = FfiResult {
                ok: Some(res.to_vec()),
                err: None,
            };

            CString::new(serde_json::to_string(&ffi_res).unwrap())
                .unwrap()
                .into_raw()
        },
        | Err(e) => {
            let ffi_res: FfiResult<Vec<f64>, String> = FfiResult {
                ok: None,
                err: Some(e),
            };

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