use core::marker::{PhantomData, PhantomPinned};
use std::ffi::{c_char, c_int, CStr, CString};

#[repr(C)]
pub struct PAMHandle {
    _data: [u8; 0],
    _marker: PhantomData<(*mut u8, PhantomPinned)>,
}

pub const SUCCESS: c_int = 0;
pub const SESSION_ERR: c_int = 14;

extern "C" {
    fn pam_get_user(
        pamh: *const PAMHandle,
        user: &*const c_char,
        prompt: *const c_char,
    ) -> c_int;
}

impl PAMHandle {
    pub fn get_user<S: AsRef<CStr> + ?Sized>(
        &self,
        prompt: Option<&S>,
    ) -> Result<CString, c_int> {
        let ptr: *const c_char = std::ptr::null_mut();
        let prompt = match prompt {
            Some(prompt) => prompt.as_ref().as_ptr(),
            None => core::ptr::null(),
        };
        match unsafe { pam_get_user(self, &ptr, prompt) } {
            SUCCESS if !ptr.is_null() => {
                let cstr = unsafe { CStr::from_ptr(ptr) };
                Ok(CString::from(cstr))
            }
            e => Err(e),
        }
    }
}