// -------------------------------------------------------------------------------------------------
//  Copyright (C) 2015-2026 Nautech Systems Pty Ltd. All rights reserved.
//  https://nautechsystems.io
//
//  Licensed under the GNU Lesser General Public License Version 3.0 (the "License");
//  You may not use this file except in compliance with the License.
//  You may obtain a copy of the License at https://www.gnu.org/licenses/lgpl-3.0.en.html
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.
// -------------------------------------------------------------------------------------------------

//! Utilities for safely moving UTF-8 strings across the FFI boundary.
//!
//! Interoperability between Rust and C/C++/Python often requires raw pointers to *null terminated*
//! strings.  This module provides convenience helpers that:
//!
//! * Convert raw `*const c_char` pointers to Rust [`String`], [`&str`], byte slices, or
//!   `ustr::Ustr` values.
//! * Perform the inverse conversion when Rust needs to hand ownership of a string to foreign
//!   code.
//!
//! The majority of these functions are marked `unsafe` because they accept raw pointers and rely
//! on the caller to uphold basic invariants (pointer validity, lifetime, UTF-8 correctness).  Each
//! function documents the specific safety requirements.

use std::{
    ffi::{CStr, CString, c_char},
    str,
};

#[cfg(feature = "python")]
use pyo3::{Bound, Python, ffi};
use ustr::Ustr;

use crate::ffi::abort_on_panic;

#[cfg(feature = "python")]
/// Returns an owned string from a valid Python object pointer.
///
/// # Safety
///
/// Assumes `ptr` is borrowed from a valid Python UTF-8 `str`.
///
/// # Panics
///
/// Panics if `ptr` is null.
#[must_use]
pub unsafe fn pystr_to_string(ptr: *mut ffi::PyObject) -> String {
    assert!(!ptr.is_null(), "`ptr` was NULL");
    // SAFETY: Caller guarantees ptr is borrowed from a valid Python UTF-8 str
    Python::attach(|py| unsafe { Bound::from_borrowed_ptr(py, ptr).to_string() })
}

/// Convert a C string pointer into an owned `String`.
///
/// # Safety
///
/// Assumes `ptr` is a valid C string pointer.
///
/// # Panics
///
/// Panics if `ptr` is null.
#[must_use]
pub unsafe fn cstr_to_ustr(ptr: *const c_char) -> Ustr {
    assert!(!ptr.is_null(), "`ptr` was NULL");
    // SAFETY: Caller guarantees ptr is valid per function contract
    let cstr = unsafe { CStr::from_ptr(ptr) };
    Ustr::from(cstr.to_str().expect("CStr::from_ptr failed"))
}

/// Convert a C string pointer into a borrowed byte slice.
///
/// # Safety
///
/// - Assumes `ptr` is a valid, null-terminated UTF-8 C string pointer.
/// - The returned slice borrows the underlying allocation; callers must ensure the
///   C buffer outlives every use of the slice.
///
/// # Panics
///
/// Panics if `ptr` is null.
#[must_use]
pub unsafe fn cstr_to_bytes<'a>(ptr: *const c_char) -> &'a [u8] {
    assert!(!ptr.is_null(), "`ptr` was NULL");
    // SAFETY: Caller guarantees ptr is valid per function contract
    let cstr = unsafe { CStr::from_ptr(ptr) };
    cstr.to_bytes()
}

/// Convert a C string pointer into an owned `Option<Ustr>`.
///
/// # Safety
///
/// Assumes `ptr` is a valid C string pointer or NULL.
///
/// # Panics
///
/// Panics if `ptr` is not null but not a valid UTF-8 C string.
#[must_use]
pub unsafe fn optional_cstr_to_ustr(ptr: *const c_char) -> Option<Ustr> {
    if ptr.is_null() {
        None
    } else {
        // SAFETY: Caller guarantees ptr is valid per function contract
        Some(unsafe { cstr_to_ustr(ptr) })
    }
}

/// Convert a C string pointer into a borrowed string slice.
///
/// # Safety
///
/// - Assumes `ptr` is a valid, null-terminated UTF-8 C string pointer.
/// - The returned `&str` borrows the underlying allocation; callers must ensure the
///   C buffer outlives every use of the string slice.
///
/// # Panics
///
/// Panics if `ptr` is null or contains invalid UTF-8.
#[must_use]
pub unsafe fn cstr_as_str<'a>(ptr: *const c_char) -> &'a str {
    assert!(!ptr.is_null(), "`ptr` was NULL");
    // SAFETY: Caller guarantees ptr is valid per function contract
    let cstr = unsafe { CStr::from_ptr(ptr) };
    cstr.to_str().expect("C string contains invalid UTF-8")
}

/// Convert an optional C string pointer into `Option<&str>`.
///
/// # Safety
///
/// - Assumes `ptr` is a valid, null-terminated UTF-8 C string pointer or NULL.
/// - Any borrowed string must not outlive the underlying allocation.
///
/// # Panics
///
/// Panics if `ptr` is not null but contains invalid UTF-8.
#[must_use]
pub unsafe fn optional_cstr_to_str<'a>(ptr: *const c_char) -> Option<&'a str> {
    if ptr.is_null() {
        None
    } else {
        // SAFETY: Caller guarantees ptr is valid per function contract
        Some(unsafe { cstr_as_str(ptr) })
    }
}

/// Create a C string pointer to newly allocated memory from a [`&str`].
///
/// # Panics
///
/// Panics if the input string contains interior null bytes.
#[must_use]
pub fn str_to_cstr(s: &str) -> *const c_char {
    CString::new(s).expect("CString::new failed").into_raw()
}

/// Drops the C string memory at the pointer.
///
/// # Safety
///
/// Assumes `ptr` is a valid C string pointer.
///
/// # Panics
///
/// Panics if `ptr` is null.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn cstr_drop(ptr: *const c_char) {
    abort_on_panic(|| {
        assert!(!ptr.is_null(), "`ptr` was NULL");
        // SAFETY: Caller guarantees ptr was allocated by str_to_cstr
        let cstring = unsafe { CString::from_raw(ptr.cast_mut()) };
        drop(cstring);
    });
}

#[cfg(test)]
mod tests {
    #[cfg(feature = "python")]
    use pyo3::types::PyString;
    use rstest::*;

    use super::*;

    #[cfg(feature = "python")]
    #[cfg_attr(miri, ignore)]
    #[rstest]
    fn test_pystr_to_string() {
        Python::initialize();
        // Create a valid Python object pointer
        let ptr = Python::attach(|py| PyString::new(py, "test string1").as_ptr());
        let result = unsafe { pystr_to_string(ptr) };
        assert_eq!(result, "test string1");
    }

    #[cfg(feature = "python")]
    #[rstest]
    #[should_panic(expected = "`ptr` was NULL")]
    fn test_pystr_to_string_with_null_ptr() {
        // Create a null Python object pointer
        let ptr: *mut ffi::PyObject = std::ptr::null_mut();
        unsafe {
            let _ = pystr_to_string(ptr);
        };
    }

    #[rstest]
    fn test_cstr_as_str() {
        // Create a valid C string pointer
        let c_string = CString::new("test string2").expect("CString::new failed");
        let ptr = c_string.as_ptr();
        let result = unsafe { cstr_as_str(ptr) };
        assert_eq!(result, "test string2");
    }

    #[rstest]
    fn test_cstr_to_bytes() {
        // Create a valid C string
        let sample_c_string = CString::new("Hello, world!").expect("CString::new failed");
        let cstr_ptr = sample_c_string.as_ptr();
        let result = unsafe { cstr_to_bytes(cstr_ptr) };
        assert_eq!(result, b"Hello, world!");
        assert_eq!(result.len(), 13);
    }

    #[rstest]
    #[should_panic(expected = "`ptr` was NULL")]
    fn test_cstr_to_bytes_with_null_ptr() {
        // Create a null C string pointer
        let ptr: *const c_char = std::ptr::null();
        unsafe {
            let _ = cstr_to_bytes(ptr);
        };
    }

    #[rstest]
    fn test_optional_cstr_to_str_with_null_ptr() {
        // Call optional_cstr_to_str with null pointer
        let ptr = std::ptr::null();
        let result = unsafe { optional_cstr_to_str(ptr) };
        assert!(result.is_none());
    }

    #[rstest]
    fn test_optional_cstr_to_str_with_valid_ptr() {
        // Create a valid C string
        let input_str = "hello world";
        let c_str = CString::new(input_str).expect("CString::new failed");
        let result = unsafe { optional_cstr_to_str(c_str.as_ptr()) };
        assert!(result.is_some());
        assert_eq!(result.unwrap(), input_str);
    }

    #[rstest]
    fn test_string_to_cstr() {
        let s = "test string";
        let c_str_ptr = str_to_cstr(s);
        let c_str = unsafe { CStr::from_ptr(c_str_ptr) };
        let result = c_str.to_str().expect("CStr::from_ptr failed");
        assert_eq!(result, s);
    }

    #[rstest]
    fn test_cstr_drop() {
        let c_string = CString::new("test string3").expect("CString::new failed");
        let ptr = c_string.into_raw(); // <-- pointer _must_ be obtained this way
        unsafe { cstr_drop(ptr) };
    }
}
