mapf 0.3.0

Base traits and utilities for multi-agent planning
Documentation 
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/*
 * Copyright (C) 2023 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 super::*;
use crate::error::NoError;

/// Create actions that connect a state to a target. May produce multiple
/// actions, each of which represents a valid connection. If no actions are
/// produced, then a connection was not possible.
///
/// See also: [`Extrapolator`]
pub trait Connectable<State, Action, Target> {
    /// What kind of error can happen during connection
    type ConnectionError;

    type Connections<'a>: IntoIterator<Item = Result<(Action, State), Self::ConnectionError>> + 'a
    where
        Self: 'a,
        Self::ConnectionError: 'a,
        State: 'a,
        Action: 'a,
        Target: 'a;

    fn connect<'a>(&'a self, from_state: State, to_target: &'a Target) -> Self::Connections<'a>
    where
        Self: 'a,
        Self::ConnectionError: 'a,
        State: 'a,
        Action: 'a,
        Target: 'a;
}

// Allow an empty tuple to implement the Connectable trait by never attempting
// any connection.
impl<State, Action, Target> Connectable<State, Action, Target> for () {
    type ConnectionError = NoError;
    type Connections<'a>
        = [Result<(Action, State), NoError>; 0]
    where
        Action: 'a,
        State: 'a,
        Target: 'a;

    fn connect<'a>(&'a self, _: State, _: &'a Target) -> Self::Connections<'a>
    where
        Self: 'a,
        Self::ConnectionError: 'a,
        State: 'a,
        Action: 'a,
        Target: 'a,
    {
        []
    }
}

impl<Base, Prop, State, Action, Target> Connectable<State, Action, Target> for Chained<Base, Prop>
where
    Base: Connectable<State, Action, Target>,
    Base::ConnectionError: Into<Prop::ConnectionError>,
    Prop: Connectable<State, Action, Target>,
    State: Clone,
{
    type ConnectionError = Prop::ConnectionError;
    type Connections<'a>
        = ChainedConnections<'a, Base, Prop, State, Action, Target>
    where
        Self: 'a,
        Self::ConnectionError: 'a,
        State: 'a,
        Action: 'a,
        Target: 'a;

    fn connect<'a>(&'a self, from_state: State, to_target: &'a Target) -> Self::Connections<'a>
    where
        Self: 'a,
        Self::ConnectionError: 'a,
        State: 'a,
        Action: 'a,
        Target: 'a,
    {
        ChainedConnections::<Base, Prop, State, Action, Target> {
            base_connections: self.base.connect(from_state.clone(), to_target).into_iter(),
            prop_connections: self.prop.connect(from_state, to_target).into_iter(),
        }
    }
}

pub struct ChainedConnections<'a, Base, Prop, State, Action, Target>
where
    Base: Connectable<State, Action, Target> + 'a,
    Prop: Connectable<State, Action, Target> + 'a,
    Base::ConnectionError: 'a,
    State: 'a,
    Action: 'a,
    Target: 'a,
{
    base_connections: <Base::Connections<'a> as IntoIterator>::IntoIter,
    prop_connections: <Prop::Connections<'a> as IntoIterator>::IntoIter,
}

impl<'a, Base, Prop, State, Action, Target> Iterator
    for ChainedConnections<'a, Base, Prop, State, Action, Target>
where
    Base: Connectable<State, Action, Target> + 'a,
    Prop: Connectable<State, Action, Target> + 'a,
    Base::ConnectionError: 'a + Into<Prop::ConnectionError>,
    State: 'a,
    Action: 'a,
    Target: 'a,
{
    type Item = Result<(Action, State), Prop::ConnectionError>;
    fn next(&mut self) -> Option<Self::Item> {
        if let Some(next) = self.base_connections.next() {
            let next = next.map_err(Into::into);
            return Some(next);
        }

        self.prop_connections.next()
    }
}