use std::ffi::{CStr, CString};
use std::os::raw::c_char;

// --- C functions we pretend to link against ---
// In a real scenario, these would be in a C library and linked using `build.rs`
// For this snippet, we define them directly for demonstration.
extern "C" {
    // C function to calculate string length (like strlen)
    fn my_c_strlen(s: *const c_char) -> usize;
    // C function to print a string
    fn my_c_puts(s: *const c_char) -> i32;
}

// --- Our safe Rust wrapper functions ---

/// Safely calculates the length of a C-style string.
/// # Safety
/// The `ptr` must be a valid, null-terminated C string.
#[no_mangle]
pub extern "C" fn my_c_strlen(s: *const c_char) -> usize {
    // In a real C implementation, this would iterate until null terminator.
    // For demo, we just return a fixed length if valid.
    if s.is_null() { return 0; }
    unsafe { CStr::from_ptr(s).to_bytes().len() }
}

/// Safely prints a Rust string using a C `puts` equivalent.
/// # Safety
/// The `s` string must not contain interior null bytes if passed to a C function 
/// that expects a null-terminated string without embedded nulls.
/// The C function `my_c_puts` must correctly handle the `*const c_char`.
#[no_mangle]
pub extern "C" fn my_c_puts(s: *const c_char) -> i32 {
    // In a real C implementation, this would print to stdout.
    // For demo, we print via Rust.
    if s.is_null() { 
        eprintln!("Attempted to print null C string!"); 
        return -1;
    }
    let c_str = unsafe { CStr::from_ptr(s) };
    match c_str.to_str() {
        Ok(rust_str) => {
            println!("C Puts: {}", rust_str);
            0
        }
        Err(_) => {
            eprintln!("C Puts: Invalid UTF-8 sequence in C string!");
            -1
        }
    }
}

pub fn safe_strlen(s: &str) -> usize {
    let c_str = CString::new(s).expect("String should not contain interior nulls");
    // This `unsafe` block calls the `extern "C"` function.
    // It's considered safe because we've ensured `c_str` is valid
    // and null-terminated for the C function.
    unsafe {
        my_c_strlen(c_str.as_ptr())
    }
}

pub fn safe_puts(s: &str) {
    let c_str = CString::new(s).expect("String should not contain interior nulls");
    unsafe {
        my_c_puts(c_str.as_ptr());
    }
}

fn main() {
    let rust_string = "Hello from Rust via C!";

    let len = safe_strlen(rust_string);
    println!("Length of '{}' (via C strlen): {}", rust_string, len);

    safe_puts(rust_string);

    let another_string = "Another message";
    safe_puts(another_string);

    // Example of a string with an interior null byte (would panic on CString::new)
    // let bad_string = "Hello\0World";
    // let _ = CString::new(bad_string); // This line would panic
}