MongoInputStream.java

package org.emfjson.mongo.streams;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mongodb.client.MongoCollection;
import org.bson.Document;
import org.bson.codecs.DocumentCodec;
import org.bson.codecs.EncoderContext;
import org.eclipse.emf.common.util.URI;
import org.eclipse.emf.ecore.resource.Resource;
import org.eclipse.emf.ecore.resource.URIConverter.Loadable;
import org.emfjson.jackson.JacksonOptions;
import org.emfjson.jackson.module.EMFModule;
import org.emfjson.mongo.MongoHandler;
import org.emfjson.mongo.bson.codecs.JsonWriter;

import java.io.IOException;
import java.io.InputStream;
import java.io.StringWriter;
import java.util.Map;

public class MongoInputStream extends InputStream implements Loadable {

	private final Map<?, ?> options;
	private final URI uri;
	private MongoHandler handler;

	public MongoInputStream(MongoHandler handler, URI uri, Map<?, ?> options) {
		this.uri = uri;
		this.options = options;
		this.handler = handler;
	}

	@Override
	public void loadResource(Resource resource) throws IOException {
		final MongoCollection<Document> collection = handler.getCollection(uri);

		if (!resource.getContents().isEmpty()) {
			resource.getContents().clear();
		}

		final String id = uri.segment(2);
		final Document filter = new Document(MongoHandler.ID_FIELD, id);
		final Document document = collection
				.find(filter)
				.limit(1)
				.first();

		if (document == null) {
			throw new IOException("Cannot find document with " + MongoHandler.ID_FIELD + " " + id);
		}

		JsonWriter writer = new JsonWriter(new StringWriter());
		new DocumentCodec().encode(writer,
				document,
				EncoderContext
						.builder()
						.isEncodingCollectibleDocument(true)
						.build());
		readJson(resource, writer.getWriter().toString());
	}

	private void readJson(Resource resource, String data) throws IOException {
		final ObjectMapper mapper = new ObjectMapper();

		final JacksonOptions jacksonOptions = JacksonOptions.from(options);
		final EMFModule module = new EMFModule(resource.getResourceSet(), jacksonOptions);
		mapper.registerModule(module);

		final JsonNode rootNode = mapper.readTree(data);
		final JsonNode contents = rootNode.has(MongoHandler.CONTENTS_FIELD) ?
				rootNode.get(MongoHandler.CONTENTS_FIELD):
				null;

		if (contents != null) {
			mapper.reader()
					.withAttribute("resource", resource)
					.treeToValue(contents, Resource.class);
		}
	}

	@Override
	public int read() throws IOException {
		return 0;
	}

}