maven-core/src/main/java/org/apache/maven/session/scope/internal/SessionScope.java

package org.apache.maven.session.scope.internal;

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;

import com.google.inject.Key;
import com.google.inject.OutOfScopeException;
import com.google.inject.Provider;
import com.google.inject.Scope;
import com.google.inject.util.Providers;

/**
 * SessionScope
 */
public class SessionScope
    implements Scope
{
    /**
     * @since 3.3.0
     */
    public static class Memento
    {
        final Map<Key<?>, Provider<?>> seeded;

        Memento( final Map<Key<?>, Provider<?>> seeded )
        {
            this.seeded = Collections.unmodifiableMap( new HashMap<>( seeded ) );
        }
    }

    private static final Provider<Object> SEEDED_KEY_PROVIDER = () ->
    {
        throw new IllegalStateException();
    };

    /**
     * ScopeState
     */
    private static final class ScopeState
    {
        private final Map<Key<?>, Provider<?>> seeded = new HashMap<>();

        private final Map<Key<?>, Object> provided = new HashMap<>();
    }

    private final ThreadLocal<LinkedList<ScopeState>> values = new ThreadLocal<>();

    public void enter()
    {
        LinkedList<ScopeState> stack = values.get();
        if ( stack == null )
        {
            stack = new LinkedList<>();
            values.set( stack );
        }
        stack.addFirst( new ScopeState() );
    }

    /**
     * @since 3.3.0
     */
    public void enter( Memento memento )
    {
        enter();
        getScopeState().seeded.putAll( memento.seeded );
    }

    private ScopeState getScopeState()
    {
        LinkedList<ScopeState> stack = values.get();
        if ( stack == null || stack.isEmpty() )
        {
            throw new IllegalStateException();
        }
        return stack.getFirst();
    }

    public void exit()
    {
        final LinkedList<ScopeState> stack = values.get();
        if ( stack == null || stack.isEmpty() )
        {
            throw new IllegalStateException();
        }
        stack.removeFirst();
        if ( stack.isEmpty() )
        {
            values.remove();
        }
    }

    /**
     * @since 3.3.0
     */
    public Memento memento()
    {
        LinkedList<ScopeState> stack = values.get();
        return new Memento( stack != null ? stack.getFirst().seeded : Collections.emptyMap() );
    }

    public <T> void seed( Class<T> clazz, Provider<T> value )
    {
        getScopeState().seeded.put( Key.get( clazz ), value );
    }

    public <T> void seed( Class<T> clazz, final T value )
    {
        getScopeState().seeded.put( Key.get( clazz ), Providers.of( value ) );
    }

    public <T> Provider<T> scope( final Key<T> key, final Provider<T> unscoped )
    {
        return () ->
        {
            LinkedList<ScopeState> stack = values.get();
            if ( stack == null || stack.isEmpty() )
            {
                throw new OutOfScopeException( "Cannot access " + key + " outside of a scoping block" );
            }

            ScopeState state = stack.getFirst();

            Provider<?> seeded = state.seeded.get( key );

            if ( seeded != null )
            {
                return (T) seeded.get();
            }

            T provided = (T) state.provided.get( key );
            if ( provided == null && unscoped != null )
            {
                provided = unscoped.get();
                state.provided.put( key, provided );
            }

            return provided;
        };
    }

    @SuppressWarnings( { "unchecked" } )
    public static <T> Provider<T> seededKeyProvider()
    {
        return (Provider<T>) SEEDED_KEY_PROVIDER;
    }
}