crossflow 0.0.6

/*
 * Copyright (C) 2024 Open Source Robotics Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
*/

use bevy_ecs::{
    prelude::{Entity, In},
    query::QueryEntityError,
};

use smallvec::SmallVec;
use thiserror::Error;

use crate::{BufferAccessMut, BufferKey};

#[derive(Debug, Error)]
pub enum BufferAccessError {
    #[error("The query does not match the entity {0}")]
    QueryDoesNotMatch(Entity),
    #[error("The entity {0} does not exist")]
    EntityDoesNotExist(Entity),
    #[error("The entity {0} was requested mutably more than once")]
    AliasedMutability(Entity),
}

pub(super) fn consume_buffer<const N: usize, T>(
    In(key): In<BufferKey<T>>,
    mut access: BufferAccessMut<T>,
) -> SmallVec<[T; N]>
where
    T: 'static + Send + Sync,
{
    let Ok(mut buffer) = access.get_mut(&key) else {
        return SmallVec::new();
    };

    buffer.drain(..).collect()
}

pub fn push_into_buffer<T: 'static + Send + Sync>(
    In((input, key)): In<(T, BufferKey<T>)>,
    mut access: BufferAccessMut<T>,
) -> Result<(), BufferAccessError> {
    access
        .get_mut(&key)
        .map_err(|err| match err {
            QueryEntityError::QueryDoesNotMatch(e, _) => BufferAccessError::QueryDoesNotMatch(e),
            QueryEntityError::EntityDoesNotExist(e) => {
                BufferAccessError::EntityDoesNotExist(e.entity)
            }
            QueryEntityError::AliasedMutability(e) => BufferAccessError::AliasedMutability(e),
        })?
        .push(input);
    Ok(())
}