sea-orm-ffi 0.1.3

use crate::{
	FfiTransaction,
	backend::FfiBackend,
	db_err::FfiDbErr,
	exec_result::FfiExecResult,
	proxy_row::{FfiOptionalProxyRow, FfiProxyRow},
	result::FfiResult,
	statement::FfiStatement,
	string::StringPtr,
	vec::VecPtr
};
use async_compat::Compat;
use async_ffi::{BorrowingFfiFuture, FutureExt as _};
use async_trait::async_trait;
use futures_util::future::{BoxFuture, FutureExt as _};
use sea_orm::{
	ConnectionTrait, DatabaseBackend, DatabaseTransaction, DbErr, ExecResult,
	QueryResult, Statement, TransactionTrait
};
use std::{ffi::c_void, future::Future};

/// Common safety documentation for [`ConnectionPtr`] functions.
macro_rules! doc_safety {
	() => {
		concat!(
			"\n",
			"# Safety\n",
			"\n",
			"This function is only safe to be called on the same side of the FFI ",
			"boundary that was used to construct the connection pointer using the ",
			"[`new`](ConnectionPtr::new) function, or any binary that was compiled ",
			"using the exact same dependencies and the exact same compiler and linker."
		)
	};
}

/// Unfortunately, [`TransactionTrait`] is not `dyn`-compatible. Therefore, we extract
/// the `begin()` function and add it to this trait explicitly.
pub trait SeaOrmConnection: ConnectionTrait + Send + Sync {
	fn begin(&self) -> BoxFuture<'_, Result<DatabaseTransaction, DbErr>>;
}

impl<T> SeaOrmConnection for T
where
	T: ConnectionTrait + TransactionTrait + Send + Sync
{
	fn begin(&self) -> BoxFuture<'_, Result<DatabaseTransaction, DbErr>> {
		TransactionTrait::begin(self)
	}
}

/// Boxed [`SeaOrmConnection`].
///
/// We cannot directly move a `*mut dyn SeaOrmConnection` over an FFI boundary as this
/// type is not FFI safe. It a so called _fat pointer_, which means that it doesn't
/// have a guaranteed memory layout, even if we ignore the `SeaOrmConnection` part of
/// the pointer.
///
/// Therefore, we pass pointers to this struct instead. While this is technically a
/// pointer to a pointer, the devil is, as always, in the detail: A pointer to this
/// struct is a _thin pointer_, so we get a _thin pointer_ to a _fat pointer_. And a
/// _thin pointer_ can be casted to and from a `*mut c_void`, and that is an FFI-safe
/// pointer. Dereferencing that pointer is of course only safe if the memory layout
/// is equivalent, so the part of the FFI boundary that did not create the pointer
/// must treat it is opaque.
struct BoxedConnection(Box<dyn SeaOrmConnection + Send + Sync>);

/// A pointer to `dyn SeaOrmConnection`.
///
/// This pointer must be treated as opaque on the side of the FFI boundary that did not
/// create the pointer.
#[repr(transparent)]
struct ConnectionPtr(*mut c_void);

impl ConnectionPtr {
	fn new(inner: Box<dyn SeaOrmConnection + Send + Sync>) -> Self {
		Self(Box::into_raw(Box::new(BoxedConnection(inner))) as _)
	}

	/// Access the data stored in this pointer
	#[doc = doc_safety!()]
	unsafe fn get(&self) -> &(dyn SeaOrmConnection + Send + Sync) {
		let ptr: *mut BoxedConnection = self.0.cast();
		&*(&*ptr).0
	}

	/// Return the inner type this pointer points to.
	#[doc = doc_safety!()]
	#[allow(clippy::wrong_self_convention)] // well, `Drop` only gives `&mut Self`
	unsafe fn into_inner(&mut self) -> Box<dyn SeaOrmConnection + Send + Sync> {
		let ptr: *mut BoxedConnection = self.0.cast();
		(*Box::from_raw(ptr)).0
	}
}

/// The FFI callback type that is called when an [`FfiConnection`] is [drop]ped.
type DropConnection = extern "C" fn(&mut ConnectionPtr);

/// Drop the connection that this pointer points to.
#[doc = doc_safety!()]
extern "C" fn drop_connection(ptr: &mut ConnectionPtr) {
	drop(unsafe { ptr.into_inner() });
}

/// The FFI callback type that is called when
/// [`begin()`](FfiConnection::begin)
/// is called on [`FfiConnection`].
type BeginTransaction =
	extern "C" fn(
		&ConnectionPtr
	) -> BorrowingFfiFuture<'_, FfiResult<FfiTransaction, FfiDbErr>>;

/// FFI callback for [`begin()`](FfiConnection::begin).
#[doc = doc_safety!()]
extern "C" fn begin_transaction(
	ptr: &ConnectionPtr
) -> BorrowingFfiFuture<'_, FfiResult<FfiTransaction, FfiDbErr>> {
	let conn = unsafe { ptr.get() };
	Compat::new(async move {
		conn.begin()
			.await
			.map(FfiTransaction::new)
			.map_err(Into::into)
			.into()
	})
	.into_ffi()
}

/// The FFI callback type that is called when
/// [`get_database_backend()`](ConnectionTrait::get_database_backend)
/// is called on [`FfiConnection`].
type GetDatabaseBackend<Ptr> = extern "C" fn(&Ptr) -> FfiBackend;

/// FFI callback for [`get_database_backend()`](ConnectionTrait::get_database_backend).
#[doc = doc_safety!()]
extern "C" fn get_database_backend(ptr: &ConnectionPtr) -> FfiBackend {
	unsafe { ptr.get() }.get_database_backend().into()
}

/// The FFI callback type that is called when
/// [`execute()`](ConnectionTrait::execute)
/// is called on [`FfiConnection`].
type Execute<Ptr> =
	extern "C" fn(
		&Ptr,
		FfiStatement
	) -> BorrowingFfiFuture<'_, FfiResult<FfiExecResult, FfiDbErr>>;

/// FFI callback implementation for [`query_one()`](ConnectionTrait::query_one).
pub(crate) fn execute_impl<C>(
	conn: &C,
	stmt: FfiStatement
) -> BorrowingFfiFuture<'_, FfiResult<FfiExecResult, FfiDbErr>>
where
	C: ConnectionTrait + Send + Sync + ?Sized
{
	Compat::new(async move {
		conn.execute(stmt.into())
			.await
			.map(|exec_result| {
				FfiExecResult::new(conn.get_database_backend(), exec_result)
			})
			.map_err(Into::into)
			.into()
	})
	.into_ffi()
}

/// FFI callback for [`execute()`](ConnectionTrait::execute).
#[doc = doc_safety!()]
extern "C" fn execute(
	ptr: &ConnectionPtr,
	stmt: FfiStatement
) -> BorrowingFfiFuture<'_, FfiResult<FfiExecResult, FfiDbErr>> {
	execute_impl(unsafe { ptr.get() }, stmt)
}

/// The FFI callback type that is called when
/// [`execute()`](ConnectionTrait::execute)
/// is called on [`FfiConnection`].
type ExecuteUnprepared<Ptr> =
	extern "C" fn(
		&Ptr,
		StringPtr
	) -> BorrowingFfiFuture<'_, FfiResult<FfiExecResult, FfiDbErr>>;

/// FFI callback implementation for [`execute_unprepared()`](ConnectionTrait::execute_unprepared).
pub(crate) fn execute_unprepared_impl<C>(
	conn: &C,
	sql: StringPtr
) -> BorrowingFfiFuture<'_, FfiResult<FfiExecResult, FfiDbErr>>
where
	C: ConnectionTrait + Send + Sync + ?Sized
{
	Compat::new(async move {
		conn.execute_unprepared(sql.as_str())
			.await
			.map(|exec_result| {
				FfiExecResult::new(conn.get_database_backend(), exec_result)
			})
			.map_err(Into::into)
			.into()
	})
	.into_ffi()
}

/// FFI callback for [`execute_unprepared()`](ConnectionTrait::execute_unprepared).
#[doc = doc_safety!()]
extern "C" fn execute_unprepared(
	ptr: &ConnectionPtr,
	sql: StringPtr
) -> BorrowingFfiFuture<'_, FfiResult<FfiExecResult, FfiDbErr>> {
	execute_unprepared_impl(unsafe { ptr.get() }, sql)
}

/// The FFI callback type that is called when
/// [`query_one()`](ConnectionTrait::query_one)
/// is called on [`FfiConnection`].
type QueryOne<Ptr> =
	extern "C" fn(
		&Ptr,
		FfiStatement
	) -> BorrowingFfiFuture<'_, FfiResult<FfiOptionalProxyRow, FfiDbErr>>;

/// FFI callback implementation for [`query_one()`](ConnectionTrait::query_one).
pub(crate) fn query_one_impl<C>(
	conn: &C,
	stmt: FfiStatement
) -> BorrowingFfiFuture<'_, FfiResult<FfiOptionalProxyRow, FfiDbErr>>
where
	C: ConnectionTrait + Send + Sync + ?Sized
{
	Compat::new(async move {
		conn.query_one(stmt.into())
			.await
			.map(Into::into)
			.map_err(Into::into)
			.into()
	})
	.into_ffi()
}

/// FFI callback for [`query_one()`](ConnectionTrait::query_one).
#[doc = doc_safety!()]
extern "C" fn query_one(
	ptr: &ConnectionPtr,
	stmt: FfiStatement
) -> BorrowingFfiFuture<'_, FfiResult<FfiOptionalProxyRow, FfiDbErr>> {
	query_one_impl(unsafe { ptr.get() }, stmt)
}

/// The FFI callback type that is called when
/// [`query_all()`](ConnectionTrait::query_all)
/// is called on [`FfiConnection`].
type QueryAll<Ptr> =
	extern "C" fn(
		&Ptr,
		FfiStatement
	) -> BorrowingFfiFuture<'_, FfiResult<VecPtr<FfiProxyRow>, FfiDbErr>>;

/// FFI callback implementation for [`query_all()`](ConnectionTrait::query_all).
pub(crate) fn query_all_impl<C>(
	conn: &C,
	stmt: FfiStatement
) -> BorrowingFfiFuture<'_, FfiResult<VecPtr<FfiProxyRow>, FfiDbErr>>
where
	C: ConnectionTrait + Send + Sync + ?Sized
{
	Compat::new(async move {
		conn.query_all(stmt.into())
			.await
			.map(|rows| {
				rows.into_iter()
					.map(Into::into)
					.collect::<Vec<FfiProxyRow>>()
					.into()
			})
			.map_err(Into::into)
			.into()
	})
	.into_ffi()
}

/// FFI callback for [`query_all()`](ConnectionTrait::query_all).
#[doc = doc_safety!()]
extern "C" fn query_all(
	ptr: &ConnectionPtr,
	stmt: FfiStatement
) -> BorrowingFfiFuture<'_, FfiResult<VecPtr<FfiProxyRow>, FfiDbErr>> {
	query_all_impl(unsafe { ptr.get() }, stmt)
}

/// The FFI callback type that is called when
/// [`is_mock_connection()`](ConnectionTrait::is_mock_connection)
/// is called on [`FfiConnection`].
type IsMockConnection<Ptr> = extern "C" fn(&Ptr) -> bool;

/// FFI callback for [`is_mock_connection()`](ConnectionTrait::is_mock_connection).
#[doc = doc_safety!()]
extern "C" fn is_mock_connection(ptr: &ConnectionPtr) -> bool {
	unsafe { ptr.get() }.is_mock_connection()
}

#[repr(C)]
pub(crate) struct ConnectionVTable<Ptr> {
	pub(crate) backend: GetDatabaseBackend<Ptr>,
	pub(crate) execute: Execute<Ptr>,
	pub(crate) execute_unprepared: ExecuteUnprepared<Ptr>,
	pub(crate) query_one: QueryOne<Ptr>,
	pub(crate) query_all: QueryAll<Ptr>,
	pub(crate) is_mock_connection: IsMockConnection<Ptr>
}

/// An FFI-safe implementation of [`sea-orm`'s](sea_orm) [`ConnectionTrait`].
///
/// See the [crate level documentation](crate) for more details.
#[repr(C)]
pub struct FfiConnection {
	ptr: ConnectionPtr,
	drop: DropConnection,
	begin: BeginTransaction,
	vtable: ConnectionVTable<ConnectionPtr>
}

impl FfiConnection {
	pub fn new(inner: Box<dyn SeaOrmConnection + Send + Sync>) -> Self {
		Self {
			ptr: ConnectionPtr::new(inner),
			drop: drop_connection,
			begin: begin_transaction,
			vtable: ConnectionVTable {
				backend: get_database_backend,
				execute,
				execute_unprepared,
				query_one,
				query_all,
				is_mock_connection
			}
		}
	}

	pub fn begin(
		&self
	) -> impl Future<Output = Result<FfiTransaction, DbErr>> + Send + '_ {
		(self.begin)(&self.ptr).map(|res| res.into_result().map_err(Into::into))
	}
}

impl Drop for FfiConnection {
	fn drop(&mut self) {
		(self.drop)(&mut self.ptr)
	}
}

// Safety: The Box'ed `dyn Connection` has `+ Send` and `+ Sync` bounds,
// and the other types are just extern "C" fn pointers.
unsafe impl Send for ConnectionPtr {}
unsafe impl Sync for ConnectionPtr {}
unsafe impl<Ptr> Send for ConnectionVTable<Ptr> {}
unsafe impl<Ptr> Sync for ConnectionVTable<Ptr> {}
unsafe impl Send for FfiConnection {}
unsafe impl Sync for FfiConnection {}

impl<Ptr> ConnectionVTable<Ptr> {
	pub(crate) fn get_database_backend(&self, ptr: &Ptr) -> DatabaseBackend {
		(self.backend)(ptr).into()
	}

	pub(crate) async fn execute(
		&self,
		ptr: &Ptr,
		stmt: Statement
	) -> Result<ExecResult, DbErr> {
		(self.execute)(ptr, stmt.into())
			.await
			.map(Into::into)
			.map_err(Into::into)
			.into()
	}

	pub(crate) async fn execute_unprepared(
		&self,
		ptr: &Ptr,
		sql: &str
	) -> Result<ExecResult, DbErr> {
		// TODO we could introduce a StrPtr and not allocate here
		//      but I assume the number of calls to unprepared statements is quite low
		let sql: String = sql.into();

		(self.execute_unprepared)(ptr, sql.into())
			.await
			.map(Into::into)
			.map_err(Into::into)
			.into()
	}

	pub(crate) async fn query_one(
		&self,
		ptr: &Ptr,
		stmt: Statement
	) -> Result<Option<QueryResult>, DbErr> {
		(self.query_one)(ptr, stmt.into())
			.await
			.map(Into::into)
			.map_err(Into::into)
			.into()
	}

	pub(crate) async fn query_all(
		&self,
		ptr: &Ptr,
		stmt: Statement
	) -> Result<Vec<QueryResult>, DbErr> {
		(self.query_all)(ptr, stmt.into())
			.await
			.map(|rows| rows.into_vec().into_iter().map(Into::into).collect())
			.map_err(Into::into)
			.into()
	}

	pub(crate) fn is_mock_connection(&self, ptr: &Ptr) -> bool {
		(self.is_mock_connection)(ptr)
	}
}

#[async_trait]
impl ConnectionTrait for FfiConnection {
	fn get_database_backend(&self) -> DatabaseBackend {
		self.vtable.get_database_backend(&self.ptr)
	}

	async fn execute(&self, stmt: Statement) -> Result<ExecResult, DbErr> {
		self.vtable.execute(&self.ptr, stmt).await
	}

	async fn execute_unprepared(&self, sql: &str) -> Result<ExecResult, DbErr> {
		self.vtable.execute_unprepared(&self.ptr, sql).await
	}

	async fn query_one(&self, stmt: Statement) -> Result<Option<QueryResult>, DbErr> {
		self.vtable.query_one(&self.ptr, stmt).await
	}

	async fn query_all(&self, stmt: Statement) -> Result<Vec<QueryResult>, DbErr> {
		self.vtable.query_all(&self.ptr, stmt).await
	}

	fn is_mock_connection(&self) -> bool {
		self.vtable.is_mock_connection(&self.ptr)
	}
}