rssn 0.2.9

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

use crate::symbolic::core::Expr;
use crate::symbolic::functional_analysis::BanachSpace;
use crate::symbolic::functional_analysis::HilbertSpace;
use crate::symbolic::functional_analysis::LinearOperator;
use crate::symbolic::functional_analysis::are_orthogonal;
use crate::symbolic::functional_analysis::banach_norm;
use crate::symbolic::functional_analysis::gram_schmidt;
use crate::symbolic::functional_analysis::inner_product;
use crate::symbolic::functional_analysis::norm;
use crate::symbolic::functional_analysis::project;

// --- HilbertSpace ---

/// Creates a new Hilbert space over a specified interval.
///
/// # Arguments
/// * `var` - The name of the independent variable defining the space.
/// * `lower_bound` - Symbolic expression for the lower bound of the interval.
/// * `upper_bound` - Symbolic expression for the upper bound of the interval.
///
/// # Returns
/// A raw pointer to the newly created `HilbertSpace`.
///
/// # 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_hilbert_space_create(
    var: *const c_char,
    lower_bound: *const Expr,
    upper_bound: *const Expr,
) -> *mut HilbertSpace {
    unsafe {
        let var_str = CStr::from_ptr(var).to_str().unwrap();

        let space = HilbertSpace::new(var_str, (*lower_bound).clone(), (*upper_bound).clone());

        Box::into_raw(Box::new(space))
    }
}

/// Frees a Hilbert space handle.
///
/// # Arguments
/// * `ptr` - Pointer to the `HilbertSpace` to free.
///
/// # 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_hilbert_space_free(ptr: *mut HilbertSpace) {
    unsafe {
        if !ptr.is_null() {
            let _ = Box::from_raw(ptr);
        }
    }
}

// --- BanachSpace ---

/// Creates a new Banach space $L^p$ over a specified interval.
///
/// # Arguments
/// * `var` - The name of the independent variable.
/// * `lower_bound` - Symbolic expression for the lower bound.
/// * `upper_bound` - Symbolic expression for the upper bound.
/// * `p` - Symbolic expression representing the $p$ parameter of the $L^p$ norm.
///
/// # Returns
/// A raw pointer to the newly created `BanachSpace`.
///
/// # 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_banach_space_create(
    var: *const c_char,
    lower_bound: *const Expr,
    upper_bound: *const Expr,
    p: *const Expr,
) -> *mut BanachSpace {
    unsafe {
        let var_str = CStr::from_ptr(var).to_str().unwrap();

        let space = BanachSpace::new(
            var_str,
            (*lower_bound).clone(),
            (*upper_bound).clone(),
            (*p).clone(),
        );

        Box::into_raw(Box::new(space))
    }
}

/// Frees a Banach space handle.
///
/// # Arguments
/// * `ptr` - Pointer to the `BanachSpace` to free.
///
/// # 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_banach_space_free(ptr: *mut BanachSpace) {
    unsafe {
        if !ptr.is_null() {
            let _ = Box::from_raw(ptr);
        }
    }
}

// --- LinearOperator ---

/// Creates a linear derivative operator handle.
///
/// # Arguments
/// * `var` - The name of the variable with respect to which differentiation is performed.
///
/// # Returns
/// A raw pointer to the `LinearOperator`.
///
/// # 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_linear_operator_derivative_create(
    var: *const c_char
) -> *mut LinearOperator {
    unsafe {
        let var_str = CStr::from_ptr(var).to_str().unwrap();

        let op = LinearOperator::Derivative(var_str.to_string());

        Box::into_raw(Box::new(op))
    }
}

/// Creates a linear integral operator handle.
///
/// # Arguments
/// * `lower_bound` - Symbolic expression for the lower integration limit.
/// * `var` - The integration variable.
///
/// # Returns
/// A raw pointer to the `LinearOperator`.
///
/// # 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_linear_operator_integral_create(
    lower_bound: *const Expr,
    var: *const c_char,
) -> *mut LinearOperator {
    unsafe {
        let var_str = CStr::from_ptr(var).to_str().unwrap();

        let op = LinearOperator::Integral((*lower_bound).clone(), var_str.to_string());

        Box::into_raw(Box::new(op))
    }
}

/// Applies a linear operator to a symbolic expression.
///
/// # Arguments
/// * `op` - Handle to the linear operator.
/// * `expr` - Handle to the expression to operate on.
///
/// # Returns
/// A raw pointer to the resulting symbolic expression.
///
/// # 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_linear_operator_apply(
    op: *const LinearOperator,
    expr: *const Expr,
) -> *mut Expr {
    unsafe {
        let result = (*op).apply(&*expr);

        Box::into_raw(Box::new(result))
    }
}

/// Frees a linear operator handle.
///
/// # Arguments
/// * `ptr` - Pointer to the `LinearOperator` to free.
///
/// # 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_linear_operator_free(ptr: *mut LinearOperator) {
    unsafe {
        if !ptr.is_null() {
            let _ = Box::from_raw(ptr);
        }
    }
}

// --- Functions ---

/// Computes the inner product of two functions in a Hilbert space.
///
/// # Arguments
/// * `space` - Handle to the Hilbert space.
/// * `f` - Handle to the first expression.
/// * `g` - Handle to the second expression.
///
/// # Returns
/// A raw pointer to the symbolic expression representing the inner product.
///
/// # 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_inner_product(
    space: *const HilbertSpace,
    f: *const Expr,
    g: *const Expr,
) -> *mut Expr {
    unsafe {
        let result = inner_product(&*space, &*f, &*g);

        Box::into_raw(Box::new(result))
    }
}

/// Computes the $L^2$ norm of a function in a Hilbert space.
///
/// # Arguments
/// * `space` - Handle to the Hilbert space.
/// * `f` - Handle to the expression.
///
/// # Returns
/// A raw pointer to the symbolic expression representing the norm.
///
/// # 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_norm(
    space: *const HilbertSpace,
    f: *const Expr,
) -> *mut Expr {
    unsafe {
        let result = norm(&*space, &*f);

        Box::into_raw(Box::new(result))
    }
}

/// Computes the $L^p$ norm of a function in a Banach space.
///
/// # Arguments
/// * `space` - Handle to the Banach space.
/// * `f` - Handle to the expression.
///
/// # Returns
/// A raw pointer to the symbolic expression representing the norm.
///
/// # 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_banach_norm(
    space: *const BanachSpace,
    f: *const Expr,
) -> *mut Expr {
    unsafe {
        let result = banach_norm(&*space, &*f);

        Box::into_raw(Box::new(result))
    }
}

/// Checks if two functions are orthogonal in a Hilbert space.
///
/// # Arguments
/// * `space` - Handle to the Hilbert space.
/// * `f` - Handle to the first expression.
/// * `g` - Handle to the second expression.
///
/// # Returns
/// `true` if orthogonal, `false` otherwise.
///
/// # 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_are_orthogonal(
    space: *const HilbertSpace,
    f: *const Expr,
    g: *const Expr,
) -> bool {
    unsafe { are_orthogonal(&*space, &*f, &*g) }
}

/// Projects one function onto another within a Hilbert space.
///
/// # Arguments
/// * `space` - Handle to the Hilbert space.
/// * `f` - Handle to the function to project.
/// * `g` - Handle to the function onto which $f$ is projected.
///
/// # Returns
/// A raw pointer to the resulting projection expression.
///
/// # 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_project(
    space: *const HilbertSpace,
    f: *const Expr,
    g: *const Expr,
) -> *mut Expr {
    unsafe {
        let result = project(&*space, &*f, &*g);

        Box::into_raw(Box::new(result))
    }
}

/// Performs the Gram-Schmidt process to produce an orthogonal basis.
///
/// # Arguments
/// * `space` - Handle to the Hilbert space.
/// * `basis_ptr` - Array of handles to the input basis expressions.
/// * `basis_len` - Number of input expressions.
/// * `out_len` - Pointer to store the number of orthogonal expressions produced.
///
/// # Returns
/// A raw pointer to an array of handles to the orthogonalized basis expressions.
///
/// # 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_gram_schmidt(
    space: *const HilbertSpace,
    basis_ptr: *const *const Expr,
    basis_len: usize,
    out_len: *mut usize,
) -> *mut *mut Expr {
    unsafe {
        let basis_slice = std::slice::from_raw_parts(basis_ptr, basis_len);

        let basis: Vec<Expr> = basis_slice.iter().map(|&p| (*p).clone()).collect();

        let orthogonal_basis = gram_schmidt(&*space, &basis);

        *out_len = orthogonal_basis.len();

        let mut out_ptrs = Vec::with_capacity(orthogonal_basis.len());

        for expr in orthogonal_basis {
            out_ptrs.push(Box::into_raw(Box::new(expr)));
        }

        let ptr = out_ptrs.as_mut_ptr();

        std::mem::forget(out_ptrs);

        ptr
    }
}