rssn 0.2.9

//! Handle-based FFI API for numerical calculus operations.

use std::ffi::CStr;
use std::os::raw::c_char;
use std::ptr;

use crate::ffi_apis::ffi_api::update_last_error;
use crate::numerical::calculus;
use crate::numerical::matrix::Matrix;
use crate::symbolic::core::Expr;

/// Computes the numerical partial derivative of a function with respect to a variable at a point.
///
/// # 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.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn rssn_num_calculus_partial_derivative(
    f: *const Expr,
    var: *const c_char,
    x: f64,
    result: *mut f64,
) -> i32 {
    unsafe {
        if f.is_null() || var.is_null() || result.is_null() {
            return -1;
        }

        let f_expr = &*f;

        let var_str = match CStr::from_ptr(var).to_str() {
            | Ok(s) => s,
            | Err(_) => {
                update_last_error(
                    "Invalid UTF-8 \
                     string for \
                     variable name"
                        .to_string(),
                );

                return -1;
            },
        };

        match calculus::partial_derivative(f_expr, var_str, x) {
            | Ok(val) => {
                *result = val;

                0
            },
            | Err(e) => {
                update_last_error(e);

                -1
            },
        }
    }
}

/// Computes the numerical gradient of a function at a point.
/// Returns a pointer to a `Vec<f64>` containing the gradient.
///
/// # 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.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn rssn_num_calculus_gradient(
    f: *const Expr,
    vars: *const *const c_char,
    point: *const f64,
    n_vars: usize,
) -> *mut Vec<f64> {
    unsafe {
        if f.is_null() || vars.is_null() || point.is_null() {
            return ptr::null_mut();
        }

        let f_expr = &*f;

        let mut vars_list = Vec::with_capacity(n_vars);

        for i in 0..n_vars {
            let v_ptr = *vars.add(i);

            if v_ptr.is_null() {
                update_last_error(format!(
                    "Variable at \
                         index {i} is \
                         null"
                ));

                return ptr::null_mut();
            }

            match CStr::from_ptr(v_ptr).to_str() {
                | Ok(s) => {
                    vars_list.push(s);
                },
                | Err(_) => {
                    update_last_error(format!("Invalid UTF-8 for variable at index {i}"));

                    return ptr::null_mut();
                },
            }
        }

        let point_slice = std::slice::from_raw_parts(point, n_vars);

        match calculus::gradient(f_expr, &vars_list, point_slice) {
            | Ok(grad) => Box::into_raw(Box::new(grad)),
            | Err(e) => {
                update_last_error(e);

                ptr::null_mut()
            },
        }
    }
}

/// Computes the numerical Jacobian matrix of a vector-valued function at a point.
/// Returns a pointer to a `Matrix<f64>`.
///
/// # 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.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn rssn_num_calculus_jacobian(
    funcs: *const *const Expr,
    n_funcs: usize,
    vars: *const *const c_char,
    point: *const f64,
    n_vars: usize,
) -> *mut Matrix<f64> {
    unsafe {
        if funcs.is_null() || vars.is_null() || point.is_null() {
            return ptr::null_mut();
        }

        let mut funcs_list = Vec::with_capacity(n_funcs);

        for i in 0..n_funcs {
            funcs_list.push((*(*funcs.add(i))).clone());
        }

        let mut vars_list = Vec::with_capacity(n_vars);

        for i in 0..n_vars {
            let v_ptr = *vars.add(i);

            match CStr::from_ptr(v_ptr).to_str() {
                | Ok(s) => {
                    vars_list.push(s);
                },
                | Err(_) => {
                    update_last_error(format!("Invalid UTF-8 for variable at index {i}"));

                    return ptr::null_mut();
                },
            }
        }

        let point_slice = std::slice::from_raw_parts(point, n_vars);

        match calculus::jacobian(&funcs_list, &vars_list, point_slice) {
            | Ok(jac_vecs) => {
                let rows = jac_vecs.len();

                let cols = if rows > 0 {
                    jac_vecs[0].len()
                } else {
                    0
                };

                let mut flattened = Vec::with_capacity(rows * cols);

                for row in jac_vecs {
                    flattened.extend(row);
                }

                Box::into_raw(Box::new(Matrix::new(rows, cols, flattened)))
            },
            | Err(e) => {
                update_last_error(e);

                ptr::null_mut()
            },
        }
    }
}

/// Computes the numerical Hessian matrix of a scalar function at a point.
/// Returns a pointer to a `Matrix<f64>`.
///
/// # 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.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn rssn_num_calculus_hessian(
    f: *const Expr,
    vars: *const *const c_char,
    point: *const f64,
    n_vars: usize,
) -> *mut Matrix<f64> {
    unsafe {
        if f.is_null() || vars.is_null() || point.is_null() {
            return ptr::null_mut();
        }

        let f_expr = &*f;

        let mut vars_list = Vec::with_capacity(n_vars);

        for i in 0..n_vars {
            let v_ptr = *vars.add(i);

            match CStr::from_ptr(v_ptr).to_str() {
                | Ok(s) => {
                    vars_list.push(s);
                },
                | Err(_) => {
                    update_last_error(format!("Invalid UTF-8 for variable at index {i}"));

                    return ptr::null_mut();
                },
            }
        }

        let point_slice = std::slice::from_raw_parts(point, n_vars);

        match calculus::hessian(f_expr, &vars_list, point_slice) {
            | Ok(hess_vecs) => {
                let rows = hess_vecs.len();

                let cols = if rows > 0 {
                    hess_vecs[0].len()
                } else {
                    0
                };

                let mut flattened = Vec::with_capacity(rows * cols);

                for row in hess_vecs {
                    flattened.extend(row);
                }

                Box::into_raw(Box::new(Matrix::new(rows, cols, flattened)))
            },
            | Err(e) => {
                update_last_error(e);

                ptr::null_mut()
            },
        }
    }
}