use std::ffi::CString;
use std::mem::MaybeUninit;
use std::os::raw::c_char;

/// This must have the same size as the repr() of RocCallResult!
pub const ROC_CALL_RESULT_DISCRIMINANT_SIZE: usize = std::mem::size_of::<u64>();

#[repr(C)]
pub struct RocCallResult<T> {
    tag: u64,
    error_msg: *mut c_char,
    value: MaybeUninit<T>,
}

impl<T: Sized> From<RocCallResult<T>> for Result<T, String> {
    fn from(call_result: RocCallResult<T>) -> Self {
        match call_result.tag {
            0 => Ok(unsafe { call_result.value.assume_init() }),
            _ => Err({
                let raw = unsafe { CString::from_raw(call_result.error_msg) };

                let result = format!("{:?}", raw);

                // make sure rust does not try to free the Roc string
                std::mem::forget(raw);

                result
            }),
        }
    }
}

#[macro_export]
macro_rules! run_jit_function {
    ($lib: expr, $main_fn_name: expr, $ty:ty, $transform:expr) => {{
        let v: String = String::new();
        run_jit_function!($lib, $main_fn_name, $ty, $transform, v)
    }};

    ($lib: expr, $main_fn_name: expr, $ty:ty, $transform:expr, $errors:expr) => {{
        run_jit_function!($lib, $main_fn_name, $ty, $transform, $errors, &[])
    }};
    ($lib: expr, $main_fn_name: expr, $ty:ty, $transform:expr, $errors:expr, $expect_failures:expr) => {{
        use inkwell::context::Context;
        use roc_builtins::bitcode;
        use roc_gen_llvm::run_roc::RocCallResult;
        use std::mem::MaybeUninit;

        #[derive(Debug, Copy, Clone)]
        #[repr(C)]
        struct Failure {
            start_line: u32,
            end_line: u32,
            start_col: u16,
            end_col: u16,
        }

        unsafe {
            let main: libloading::Symbol<unsafe extern "C" fn(*mut RocCallResult<$ty>) -> ()> =
                $lib.get($main_fn_name.as_bytes())
                    .ok()
                    .ok_or(format!("Unable to JIT compile `{}`", $main_fn_name))
                    .expect("errored");

            #[repr(C)]
            struct Failures {
                failures: *const Failure,
                count: usize,
            }

            impl Drop for Failures {
                fn drop(&mut self) {
                    use std::alloc::{dealloc, Layout};
                    use std::mem;

                    unsafe {
                        let layout = Layout::from_size_align_unchecked(
                            mem::size_of::<Failure>(),
                            mem::align_of::<Failure>(),
                        );

                        dealloc(self.failures as *mut u8, layout);
                    }
                }
            }

            let get_expect_failures: libloading::Symbol<unsafe extern "C" fn() -> Failures> = $lib
                .get(bitcode::UTILS_GET_EXPECT_FAILURES.as_bytes())
                .ok()
                .ok_or(format!(
                    "Unable to JIT compile `{}`",
                    bitcode::UTILS_GET_EXPECT_FAILURES
                ))
                .expect("errored");
            let mut main_result = MaybeUninit::uninit();

            main(main_result.as_mut_ptr());
            let failures = get_expect_failures();

            if failures.count > 0 {
                // TODO tell the user about the failures!
                let failures =
                    unsafe { core::slice::from_raw_parts(failures.failures, failures.count) };

                panic!("Failed with {} failures. Failures: ", failures.len());
            }

            match main_result.assume_init().into() {
                Ok(success) => {
                    // only if there are no exceptions thrown, check for errors
                    assert!($errors.is_empty(), "Encountered errors:\n{}", $errors);

                    $transform(success)
                }
                Err(error_msg) => panic!("Roc failed with message: {}", error_msg),
            }
        }
    }};
}

/// In the repl, we don't know the type that is returned; it it's large enough to not fit in 2
/// registers (i.e. size bigger than 16 bytes on 64-bit systems), then we use this macro.
/// It explicitly allocates a buffer that the roc main function can write its result into.
#[macro_export]
macro_rules! run_jit_function_dynamic_type {
    ($lib: expr, $main_fn_name: expr, $bytes:expr, $transform:expr) => {{
        let v: String = String::new();
        run_jit_function_dynamic_type!($lib, $main_fn_name, $bytes, $transform, v)
    }};

    ($lib: expr, $main_fn_name: expr, $bytes:expr, $transform:expr, $errors:expr) => {{
        use inkwell::context::Context;
        use roc_gen_llvm::run_roc::RocCallResult;

        unsafe {
            let main: libloading::Symbol<unsafe extern "C" fn(*const u8)> = $lib
                .get($main_fn_name.as_bytes())
                .ok()
                .ok_or(format!("Unable to JIT compile `{}`", $main_fn_name))
                .expect("errored");

            let size = std::mem::size_of::<RocCallResult<()>>() + $bytes;
            let layout = std::alloc::Layout::array::<u8>(size).unwrap();
            let result = std::alloc::alloc(layout);
            main(result);

            let flag = *result;

            if flag == 0 {
                $transform(result.add(std::mem::size_of::<RocCallResult<()>>()) as usize)
            } else {
                use std::ffi::CString;
                use std::os::raw::c_char;

                // first field is a char pointer (to the error message)
                // read value, and transmute to a pointer
                let ptr_as_int = *(result as *const u64).offset(1);
                let ptr = std::mem::transmute::<u64, *mut c_char>(ptr_as_int);

                // make CString (null-terminated)
                let raw = CString::from_raw(ptr);

                let result = format!("{:?}", raw);

                // make sure rust doesn't try to free the Roc constant string
                std::mem::forget(raw);

                eprintln!("{}", result);
                panic!("Roc hit an error");
            }
        }
    }};
}