//! # Mock Message Queue for XCM Simulator tests

#![cfg_attr(not(feature = "std"), no_std)]

use cumulus_primitives_core::{ParaId, XcmpMessageFormat, XcmpMessageHandler};
use frame_support::pallet_prelude::*;
use parity_scale_codec::{Decode, Encode};
use polkadot_parachain_primitives::primitives::DmpMessageHandler;
use sp_std::prelude::*;
use xcm::{
	v4::{prelude::*, Weight},
	VersionedXcm,
};

pub use module::*;

#[frame_support::pallet]
pub mod module {
	use super::*;

	type RelayBlockNumber = u32;

	#[pallet::config]
	pub trait Config: frame_system::Config {
		type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;
		type XcmExecutor: ExecuteXcm<Self::RuntimeCall>;
	}

	#[pallet::call]
	impl<T: Config> Pallet<T> {}

	#[pallet::pallet]
	#[pallet::without_storage_info]
	pub struct Pallet<T>(_);

	#[pallet::storage]
	#[pallet::getter(fn parachain_id)]
	pub(super) type ParachainId<T: Config> = StorageValue<_, ParaId, ValueQuery>;

	#[pallet::storage]
	#[pallet::getter(fn received_dmp)]
	/// A queue of received DMP messages
	pub(super) type ReceivedDmp<T: Config> = StorageValue<_, Vec<Xcm<T::RuntimeCall>>, ValueQuery>;

	impl<T: Config> Get<ParaId> for Pallet<T> {
		fn get() -> ParaId {
			Self::parachain_id()
		}
	}

	pub type MessageId = [u8; 32];

	#[pallet::event]
	#[pallet::generate_deposit(pub(super) fn deposit_event)]
	pub enum Event<T: Config> {
		// XCMP
		/// Some XCM was executed OK.
		Success(Option<T::Hash>),
		/// Some XCM failed.
		Fail(Option<T::Hash>, XcmError),
		/// Bad XCM version used.
		BadVersion(Option<T::Hash>),
		/// Bad XCM format used.
		BadFormat(Option<T::Hash>),

		// DMP
		/// Downward message is invalid XCM.
		InvalidFormat(MessageId),
		/// Downward message is unsupported version of XCM.
		UnsupportedVersion(MessageId),
		/// Downward message executed with the given outcome.
		ExecutedDownward(MessageId, Outcome),
	}

	impl<T: Config> Pallet<T> {
		pub fn set_para_id(para_id: ParaId) {
			ParachainId::<T>::put(para_id);
		}

		fn handle_xcmp_message(
			sender: ParaId,
			_sent_at: RelayBlockNumber,
			xcm: VersionedXcm<T::RuntimeCall>,
			max_weight: Weight,
		) -> Result<Weight, XcmError> {
			use sp_runtime::traits::Hash;
			let hash = Encode::using_encoded(&xcm, T::Hashing::hash);
			let mut message_hash = Encode::using_encoded(&xcm, sp_io::hashing::blake2_256);
			let (result, event) = match Xcm::<T::RuntimeCall>::try_from(xcm) {
				Ok(xcm) => {
					let location = (Parent, Parachain(sender.into()));
					match T::XcmExecutor::prepare_and_execute(
						location,
						xcm,
						&mut message_hash,
						max_weight,
						Weight::zero(),
					) {
						Outcome::Error { error } => (Err(error), Event::Fail(Some(hash), error)),
						Outcome::Complete { used } => (Ok(used), Event::Success(Some(hash))),
						// As far as the caller is concerned, this was dispatched without error, so
						// we just report the weight used.
						Outcome::Incomplete { used, error } => (Ok(used), Event::Fail(Some(hash), error)),
					}
				}
				Err(()) => (Err(XcmError::UnhandledXcmVersion), Event::BadVersion(Some(hash))),
			};
			Self::deposit_event(event);
			result
		}
	}

	impl<T: Config> XcmpMessageHandler for Pallet<T> {
		fn handle_xcmp_messages<'a, I: Iterator<Item = (ParaId, RelayBlockNumber, &'a [u8])>>(
			iter: I,
			max_weight: Weight,
		) -> Weight {
			for (sender, sent_at, data) in iter {
				let mut data_ref = data;
				let _ =
					XcmpMessageFormat::decode(&mut data_ref).expect("Simulator encodes with versioned xcm format; qed");

				let mut remaining_fragments = data_ref;
				while !remaining_fragments.is_empty() {
					if let Ok(xcm) = VersionedXcm::<T::RuntimeCall>::decode(&mut remaining_fragments) {
						let _ = Self::handle_xcmp_message(sender, sent_at, xcm, max_weight);
					} else {
						debug_assert!(false, "Invalid incoming XCMP message data");
					}
				}
			}
			max_weight
		}
	}

	impl<T: Config> DmpMessageHandler for Pallet<T> {
		fn handle_dmp_messages(iter: impl Iterator<Item = (RelayBlockNumber, Vec<u8>)>, limit: Weight) -> Weight {
			for (_sent_at, data) in iter {
				let mut id = sp_io::hashing::blake2_256(&data[..]);
				let maybe_versioned = VersionedXcm::<T::RuntimeCall>::decode(&mut &data[..]);
				match maybe_versioned {
					Err(_) => {
						Self::deposit_event(Event::InvalidFormat(id));
					}
					Ok(versioned) => match Xcm::try_from(versioned) {
						Err(()) => Self::deposit_event(Event::UnsupportedVersion(id)),
						Ok(x) => {
							let outcome =
								T::XcmExecutor::prepare_and_execute(Parent, x.clone(), &mut id, limit, Weight::zero());
							<ReceivedDmp<T>>::append(x);
							Self::deposit_event(Event::ExecutedDownward(id, outcome));
						}
					},
				}
			}
			limit
		}
	}
}