use crate::{account::KeyedAccount, instruction::InstructionError, pubkey::Pubkey};
use num_traits::{FromPrimitive, ToPrimitive};

// All native programs export a symbol named process()
pub const ENTRYPOINT: &str = "process";

// Native program ENTRYPOINT prototype
pub type Entrypoint = unsafe extern "C" fn(
    program_id: &Pubkey,
    keyed_accounts: &mut [KeyedAccount],
    data: &[u8],
) -> Result<(), InstructionError>;

// Convenience macro to define the native program entrypoint.  Supply a fn to this macro that
// conforms to the `Entrypoint` type signature.
#[macro_export]
macro_rules! solana_entrypoint(
    ($entrypoint:ident) => (
        #[no_mangle]
        pub extern "C" fn process(
            program_id: &$crate::pubkey::Pubkey,
            keyed_accounts: &mut [$crate::account::KeyedAccount],
            data: &[u8],
        ) -> Result<(), $crate::instruction::InstructionError> {
            $entrypoint(program_id, keyed_accounts, data)
        }
    )
);

impl<T> From<T> for InstructionError
where
    T: ToPrimitive,
{
    fn from(error: T) -> Self {
        InstructionError::CustomError(error.to_u32().unwrap_or(0xbad_c0de))
    }
}

/// Return the next KeyedAccount or a NotEnoughAccountKeys instruction error
pub fn next_keyed_account<I: Iterator>(iter: &mut I) -> Result<I::Item, InstructionError> {
    iter.next().ok_or(InstructionError::NotEnoughAccountKeys)
}

pub trait DecodeError<E> {
    fn decode_custom_error_to_enum(custom: u32) -> Option<E>
    where
        E: FromPrimitive,
    {
        E::from_u32(custom)
    }
    fn type_of() -> &'static str;
}

#[cfg(test)]
mod tests {
    use super::*;
    use num_derive::FromPrimitive;

    #[test]
    fn test_decode_custom_error_to_enum() {
        #[derive(Debug, FromPrimitive, PartialEq)]
        enum TestEnum {
            A,
            B,
            C,
        }
        impl<T> DecodeError<T> for TestEnum {
            fn type_of() -> &'static str {
                "TestEnum"
            }
        }
        assert_eq!(TestEnum::decode_custom_error_to_enum(0), Some(TestEnum::A));
        assert_eq!(TestEnum::decode_custom_error_to_enum(1), Some(TestEnum::B));
        assert_eq!(TestEnum::decode_custom_error_to_enum(2), Some(TestEnum::C));
        let option: Option<TestEnum> = TestEnum::decode_custom_error_to_enum(3);
        assert_eq!(option, None);
    }
}