use crate::error::ErrorStack;
use foreign_types::{ForeignType, ForeignTypeRef};
use libc::{c_char, c_int, c_void};
use std::any::Any;
use std::panic::{self, AssertUnwindSafe};
use std::slice;

/// Wraps a user-supplied callback and a slot for panics thrown inside the callback (while FFI
/// frames are on the stack).
///
/// When dropped, checks if the callback has panicked, and resumes unwinding if so.
pub struct CallbackState<F> {
    /// The user callback. Taken out of the `Option` when called.
    cb: Option<F>,
    /// If the callback panics, we place the panic object here, to be re-thrown once OpenSSL
    /// returns.
    panic: Option<Box<dyn Any + Send + 'static>>,
}

impl<F> CallbackState<F> {
    pub fn new(callback: F) -> Self {
        CallbackState {
            cb: Some(callback),
            panic: None,
        }
    }
}

impl<F> Drop for CallbackState<F> {
    fn drop(&mut self) {
        if let Some(panic) = self.panic.take() {
            panic::resume_unwind(panic);
        }
    }
}

/// Password callback function, passed to private key loading functions.
///
/// `cb_state` is expected to be a pointer to a `CallbackState`.
pub unsafe extern "C" fn invoke_passwd_cb<F>(
    buf: *mut c_char,
    size: c_int,
    _rwflag: c_int,
    cb_state: *mut c_void,
) -> c_int
where
    F: FnOnce(&mut [u8]) -> Result<usize, ErrorStack>,
{
    let callback = &mut *(cb_state as *mut CallbackState<F>);

    let result = panic::catch_unwind(AssertUnwindSafe(|| {
        let pass_slice = slice::from_raw_parts_mut(buf as *mut u8, size as usize);
        callback.cb.take().unwrap()(pass_slice)
    }));

    match result {
        Ok(Ok(len)) => len as c_int,
        Ok(Err(_)) => {
            // FIXME restore error stack
            0
        }
        Err(err) => {
            callback.panic = Some(err);
            0
        }
    }
}

#[allow(dead_code)]
pub trait ForeignTypeExt: ForeignType {
    unsafe fn from_ptr_opt(ptr: *mut Self::CType) -> Option<Self> {
        if ptr.is_null() {
            None
        } else {
            Some(Self::from_ptr(ptr))
        }
    }
}
impl<FT: ForeignType> ForeignTypeExt for FT {}

pub trait ForeignTypeRefExt: ForeignTypeRef {
    unsafe fn from_const_ptr<'a>(ptr: *const Self::CType) -> &'a Self {
        Self::from_ptr(ptr as *mut Self::CType)
    }

    unsafe fn from_const_ptr_opt<'a>(ptr: *const Self::CType) -> Option<&'a Self> {
        if ptr.is_null() {
            None
        } else {
            Some(Self::from_const_ptr(ptr as *mut Self::CType))
        }
    }
}
impl<FT: ForeignTypeRef> ForeignTypeRefExt for FT {}
