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/*
	https://github.com/tgstation/rust-g/tree/2e9b7724ba81894863d77fd1d27a2e24b79d67bf

	MIT License

	Copyright (c) 2018 Bjorn Neergaard, /tg/station contributors

	Permission is hereby granted, free of charge, to any person obtaining a copy
	of this software and associated documentation files (the "Software"), to deal
	in the Software without restriction, including without limitation the rights
	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	copies of the Software, and to permit persons to whom the Software is
	furnished to do so, subject to the following conditions:

	The above copyright notice and this permission notice shall be included in all
	copies or substantial portions of the Software.

	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	SOFTWARE.
*/

use std::{
	borrow::Cow,
	cell::RefCell,
	ffi::{CStr, CString},
	os::raw::{c_char, c_int},
	slice,
};

static EMPTY_STRING: c_char = 0;
thread_local! {
	static RETURN_STRING: RefCell<CString> = RefCell::new(CString::default());
}

pub unsafe fn parse_args<'a>(argc: c_int, argv: *const *const c_char) -> Vec<Cow<'a, str>> {
	slice::from_raw_parts(argv, argc as usize)
		.iter()
		.map(|ptr| CStr::from_ptr(*ptr))
		.map(|cstr| cstr.to_string_lossy())
		.collect()
}

pub fn byond_return(value: Option<Vec<u8>>) -> *const c_char {
	match value {
		None => &EMPTY_STRING,
		Some(vec) if vec.is_empty() => &EMPTY_STRING,
		Some(vec) => RETURN_STRING.with(|cell| {
			// Panicking over an FFI boundary is bad form, so if a NUL ends up
			// in the result, just truncate.
			let cstring = match CString::new(vec) {
				Ok(s) => s,
				Err(e) => {
					let (pos, mut vec) = (e.nul_position(), e.into_vec());
					vec.truncate(pos);
					CString::new(vec).unwrap_or_default()
				}
			};
			cell.replace(cstring);
			cell.borrow().as_ptr()
		}),
	}
}

/// Creates a normal byond ffi function that can be called in DM with [call](http://www.byond.com/docs/ref/#/proc/call).
///
/// You should favour [hooks](attr.hook.html) over these when working with auxtools.
///
/// # Examples
/// ```ignore
/// // byond_ffi_fn! { my_proc(_input) {
/// //     Some("Hello, BYOND!".to_owned())
/// // }
/// ```
#[macro_export]
macro_rules! byond_ffi_fn {
    ($name:ident() $body:block) => {
        #[no_mangle]
        #[allow(clippy::missing_safety_doc)]
        extern "C" fn $name(
            _argc: ::std::os::raw::c_int, _argv: *const *const ::std::os::raw::c_char
        ) -> *const ::std::os::raw::c_char {
            let closure = || ($body);
            $crate::byond_ffi::byond_return(closure().map(From::from))
        }
    };

    ($name:ident($($arg:ident),* $(, ...$rest:ident)?) $body:block) => {
        #[no_mangle]
        #[allow(clippy::missing_safety_doc)]
        extern "C" fn $name(
            _argc: ::std::os::raw::c_int, _argv: *const *const ::std::os::raw::c_char
        ) -> *const ::std::os::raw::c_char {
            let __args;
            unsafe {
                __args = $crate::byond_ffi::parse_args(_argc, _argv);
            }

            let mut __argn = 0;
            $(
                let $arg: &str = __args.get(__argn).map_or("", |cow| &*cow);
                __argn += 1;
            )*
            $(
                let $rest = __args.get(__argn..).unwrap_or(&[]);
            )?

            let closure = || ($body);
            $crate::byond_ffi::byond_return(closure().map(From::from))
        }
    };
}