rssn 0.2.9

//! Handle-based FFI API for numerical series 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::series;
use crate::symbolic::core::Expr;

/// Computes the numerical Taylor series coefficients.
/// Returns a pointer to a `Vec<f64>` containing the coefficients.
///
/// # 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_numerical_taylor_coefficients(
    f: *const Expr,
    var: *const c_char,
    at_point: f64,
    order: usize,
) -> *mut Vec<f64> {
    unsafe {
        if f.is_null() || var.is_null() {
            return ptr::null_mut();
        }

        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 ptr::null_mut();
            },
        };

        match series::taylor_coefficients(f_expr, var_str, at_point, order) {
            | Ok(coeffs) => Box::into_raw(Box::new(coeffs)),
            | Err(e) => {
                update_last_error(e);

                ptr::null_mut()
            },
        }
    }
}

/// Evaluates a power series 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_numerical_evaluate_power_series(
    coeffs: *const Vec<f64>,
    at_point: f64,
    x: f64,
) -> f64 {
    unsafe {
        if coeffs.is_null() {
            return 0.0;
        }

        series::evaluate_power_series(&*coeffs, at_point, x)
    }
}

/// Computes the sum of a series.
///
/// # 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_numerical_sum_series(
    f: *const Expr,
    var: *const c_char,
    start: i64,
    end: i64,
    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 series::sum_series(f_expr, var_str, start, end) {
            | Ok(val) => {
                *result = val;

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

                -1
            },
        }
    }
}