UIScopeProvider.java

/*
 *
 *  * Copyright (c) 2016. David Sowerby
 *  *
 *  * 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.
 *
 */
package uk.q3c.krail.core.guice.uiscope;

import com.google.inject.Key;
import com.google.inject.Provider;
import com.vaadin.ui.UI;
import com.vaadin.util.CurrentInstance;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import org.slf4j.Logger;
import uk.q3c.krail.core.ui.ScopedUI;

import java.util.Map;

import static org.slf4j.LoggerFactory.getLogger;

/**
 * @param <T>
 *
 * @author David Sowerby
 */
@SuppressFBWarnings({"CD_CIRCULAR_DEPENDENCY"})
class UIScopeProvider<T> implements Provider<T> {
    private static Logger log = getLogger(UIScopeProvider.class);
    private final UIScope uiScope;
    private final Key<T> key;
    private final Provider<T> unscoped;

    UIScopeProvider(UIScope uiScope, Key<T> key, Provider<T> unscoped) {
        this.uiScope = uiScope;
        this.key = key;
        this.unscoped = unscoped;
    }

    @Override
    public T get() {
        // get the scope cache for the current UI
        log.debug("looking for a UIScoped instance of {}", key.getClass()
                                                              .getName());

        // get the current UIKey. It should always be there, as it is created before the UI
        UIKey uiKey = CurrentInstance.get(UIKey.class);
        // this may be null if we are in the process of constructing the UI
        ScopedUI currentUI = (ScopedUI) UI.getCurrent();
        final String msg = "This can happen if you include UIScoped components in your ScopedUIProvider, " +
                "or you are testing and have not set up the test fixture correctly.  For the latter, use TestUIScopeModule, or " +
                "try sub-classing UITestBase and calling createTestUI() or createBasicUI() to prepare the UIScope " +
                "correctly.  If you are not testing please report a bug";
        if (uiKey == null) {
            if (currentUI == null) {
                throw new UIScopeException("UI and uiKey are null. " + msg);
            } else {
                // this can happen when the framework switches UIs
                uiKey = currentUI.getInstanceKey();
                if (uiKey == null) {
                    throw new UIScopeException("uiKey is null and cannot be obtained from the UI. " + msg);
                }
            }
        }

        // currentUI may be null if we are in the process of constructing the UI
        // if not null just check that it hasn't got out of sync with its uikey
        if (currentUI != null) {
            if (!uiKey.equals(currentUI.getInstanceKey())) {
                throw new UIScopeException("The UI and its UIKey have got out of sync.  Results are unpredictable. "
                        + msg);
            }
        }

        log.debug("looking for cache for key: {}", uiKey);
        Map<Key<?>, Object> scopedObjects = this.uiScope.getScopedObjectMap(uiKey);

        // retrieve an existing instance if possible

        @SuppressWarnings("unchecked") T current = (T) scopedObjects.get(key);

        if (current != null) {
            log.debug("returning existing instance of {}", current.getClass()
                                                                  .getSimpleName());
            return current;
        }

        // or create the first instance and cache it
        current = unscoped.get();
        scopedObjects.put(key, current);
        log.debug("new instance of {} created, as none in cache", current.getClass()
                                                                         .getSimpleName());
        return current;
    }
}