plugins/org.eclipse.sirius.services.graphql.workspace/src/org/eclipse/sirius/services/graphql/workspace/internal/schema/ContainerResourcesField.java

/*******************************************************************************
 * Copyright (c) 2019 Obeo.
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *    Obeo - initial API and implementation
 *******************************************************************************/
package org.eclipse.sirius.services.graphql.workspace.internal.schema;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Base64;
import java.util.List;
import java.util.Optional;

import org.eclipse.core.resources.IContainer;
import org.eclipse.core.resources.IResource;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Status;
import org.eclipse.sirius.services.graphql.common.api.directives.SiriusGraphQLCostDirective;
import org.eclipse.sirius.services.graphql.common.api.pagination.SiriusGraphQLConnection;
import org.eclipse.sirius.services.graphql.common.api.pagination.SiriusGraphQLPaginationArguments;
import org.eclipse.sirius.services.graphql.common.api.pagination.SiriusGraphQLPaginationDataFetcher;
import org.eclipse.sirius.services.graphql.workspace.internal.SiriusGraphQLWorkspacePlugin;

import graphql.schema.DataFetcher;
import graphql.schema.GraphQLFieldDefinition;
import graphql.schema.GraphQLTypeReference;

/**
 * Used to create the resources field of the container.
 *
 * @author sbegaudeau
 */
public final class ContainerResourcesField {

    /**
     * The name of the resources field.
     */
    private static final String RESOURCES_FIELD = "resources"; //$NON-NLS-1$

    /**
     * The complexity of the retrieval of a resource.
     */
    private static final int COMPLEXITY = 1;

    /**
     * The constructor.
     */
    private ContainerResourcesField() {
        // Prevent instantiation
    }

    /**
     * Returns the resources field.
     *
     * @return The resources field
     */
    public static GraphQLFieldDefinition build() {
        List<String> multipliers = new ArrayList<>();
        multipliers.add(SiriusGraphQLPaginationArguments.FIRST_ARG);
        multipliers.add(SiriusGraphQLPaginationArguments.LAST_ARG);

        // @formatter:off
        return GraphQLFieldDefinition.newFieldDefinition()
                .name(RESOURCES_FIELD)
                .type(new GraphQLTypeReference(ContainerTypesProvider.CONTAINER_RESOURCE_CONNECTION_TYPE))
                .argument(SiriusGraphQLPaginationArguments.build())
                .withDirective(new SiriusGraphQLCostDirective(COMPLEXITY, multipliers).build())
                .dataFetcher(ContainerResourcesField.getResourcesDataFetcher())
                .build();
        // @formatter:on
    }

    /**
     * Returns the resources data fetcher.
     *
     * @return The resources data fetcher
     */
    private static DataFetcher<SiriusGraphQLConnection> getResourcesDataFetcher() {
        // @formatter:off
        return SiriusGraphQLPaginationDataFetcher.build(environment -> {
            return Optional.of(environment.getSource())
                    .filter(IContainer.class::isInstance)
                    .map(IContainer.class::cast)
                    .map(ContainerResourcesField::getResources)
                    .map(Arrays::asList)
                    .orElseGet(ArrayList::new);
        }, ContainerResourcesField::computeCursor);
        // @formatter:on
    }

    /**
     * Computes the cursor of the given resource.
     * 
     * @param resource
     *            The resource
     * @return The cursor of the resource
     */
    private static String computeCursor(IResource resource) {
        String unEncodedCursor = resource.getName();
        return Base64.getEncoder().encodeToString(unEncodedCursor.getBytes());
    }

    /**
     * Returns the resources of the given container.
     *
     * @param iContainer
     *            The container
     * @return The resources of the given container
     */
    private static IResource[] getResources(IContainer iContainer) {
        try {
            return iContainer.members();
        } catch (CoreException exception) {
            IStatus status = new Status(IStatus.ERROR, SiriusGraphQLWorkspacePlugin.PLUGIN_ID, exception.getMessage(), exception);
            SiriusGraphQLWorkspacePlugin.getPlugin().log(status);
        }
        return new IResource[0];
    }
}