Reworked the client/spec/config/builder on how features are implemented and called.

connect/src/main/java/org/transdroid/connect/Configuration.java

@@ -4,22 +4,66 @@ import com.burgstaller.okhttp.digest.Credentials;
 
 import org.transdroid.connect.clients.Client;
 import org.transdroid.connect.clients.ClientSpec;
-import org.transdroid.connect.util.StringUtil;
 
+/**
+ * Configuration settings to connect to a torrent client.
+ */
 public final class Configuration {
 
 	private final Client client;
 	private final String baseUrl;
-	private final String endpoint;
-	private final Credentials credentials;
-	private final boolean loggingEnabled;
+	private String endpoint;
+	private Credentials credentials;
+	private boolean loggingEnabled;
 
-	public Configuration(Client client, String baseUrl, String endpoint, String user, String password, boolean loggingEnabled) {
+	public static class Builder {
+
+		private final Client client;
+		private String baseUrl;
+		private String endpoint;
+		private Credentials credentials;
+		private boolean loggingEnabled;
+
+		public Builder(Client client) {
+			this.client = client;
+		}
+
+		public Builder baseUrl(String baseUrl) {
+			this.baseUrl = baseUrl;
+			return this;
+		}
+
+		public Builder endpoint(String endpoint) {
+			this.endpoint = endpoint;
+			return this;
+		}
+
+		public Builder credentials(String user, String password) {
+			this.credentials = new Credentials(user, password);
+			return this;
+		}
+
+		public Builder loggingEnabled(boolean loggingEnabled) {
+			this.loggingEnabled = loggingEnabled;
+			return this;
+		}
+
+		public Configuration build() {
+			Configuration configuration = new Configuration(client, baseUrl);
+			configuration.endpoint = this.endpoint;
+			configuration.credentials = this.credentials;
+			return configuration;
+		}
+
+	}
+
+	private Configuration(Client client, String baseUrl) {
 		this.client = client;
 		this.baseUrl = baseUrl;
-		this.endpoint = endpoint;
-		this.credentials = (!StringUtil.isEmpty(user) && password != null) ? new Credentials(user, password) : null;
-		this.loggingEnabled = loggingEnabled;
+	}
+
+	public Client client() {
+		return client;
 	}
 
 	public String baseUrl() {
@@ -38,8 +82,8 @@ public final class Configuration {
 		return credentials;
 	}
 
-	public ClientSpec create() {
-		return client.create(this);
+	public ClientSpec createClient() {
+		return client.createClient(this);
 	}
 
 }

connect/src/main/java/org/transdroid/connect/clients/Client.java

@@ -2,29 +2,45 @@ package org.transdroid.connect.clients;
 
 import org.transdroid.connect.Configuration;
 import org.transdroid.connect.clients.rtorrent.Rtorrent;
+import org.transdroid.connect.clients.transmission.Transmission;
 
-import java.util.Set;
-
+/**
+ * Support clients enum, allowing you to create instances (given a configuration) and query for feature support.
+ */
+@SuppressWarnings("unchecked")
 public enum Client {
 
-	RTORRENT {
+	RTORRENT(Rtorrent.class) {
 		@Override
-		public ClientSpec create(Configuration configuration) {
+		public Rtorrent create(Configuration configuration) {
 			return new Rtorrent(configuration);
 		}
-
+	},
+	TRANSMISSION(Transmission.class) {
 		@Override
-		Set<Feature> features() {
-			return Rtorrent.FEATURES;
+		public Transmission create(Configuration configuration) {
+			return new Transmission();
 		}
 	};
 
-	public abstract ClientSpec create(Configuration configuration);
+	final Class<?> type;
+
+	Client(Class<?> type) {
+		this.type = type;
+	}
+
+	public final Class<?> type() {
+		return type;
+	}
+
+	abstract Object create(Configuration configuration);
 
-	abstract Set<Feature> features();
+	public final ClientSpec createClient(Configuration configuration) {
+		return new ClientDelegate(configuration.client(), create(configuration));
+	}
 
-	public boolean supports(Feature feature) {
-		return features().contains(feature);
+	public final boolean supports(Feature feature) {
+		return feature.type().isAssignableFrom(type);
 	}
 
 }

connect/src/main/java/org/transdroid/connect/clients/ClientDelegate.java

@@ -0,0 +1,42 @@
+package org.transdroid.connect.clients;
+
+import org.transdroid.connect.model.Torrent;
+
+import io.reactivex.Flowable;
+
+/**
+ * Wraps an actual client implementation by calling through the appropriate method only if it is supported. This allows the final
+ * {@link ClientSpec} API to expose all methods without forcing the individual implementations to implement unsupported featured with a no-op.
+ */
+final class ClientDelegate implements ClientSpec {
+
+	private final Client client;
+	private final Object actual;
+
+	ClientDelegate(Client client, Object actual) {
+		this.client = client;
+		this.actual = actual;
+	}
+
+	@Override
+	public Flowable<Torrent> torrents() {
+		if (client.supports(Feature.LISTING))
+			return ((Feature.Listing) actual).torrents();
+		throw new UnsupportedFeatureException(client, Feature.LISTING);
+	}
+
+	@Override
+	public Flowable<String> clientVersion() {
+		if (client.supports(Feature.VERSION))
+			return ((Feature.Version) actual).clientVersion();
+		throw new UnsupportedFeatureException(client, Feature.VERSION);
+	}
+
+	@Override
+	public Flowable<Torrent> forceStartTorrent() {
+		if (client.supports(Feature.FORCE_STARTING))
+			return ((Feature.ForceStarting) actual).forceStartTorrent();
+		throw new UnsupportedFeatureException(client, Feature.FORCE_STARTING);
+	}
+
+}

connect/src/main/java/org/transdroid/connect/clients/ClientSpec.java

@@ -1,13 +1,10 @@
 package org.transdroid.connect.clients;
 
-import org.transdroid.connect.model.Torrent;
-
-import io.reactivex.Flowable;
-
-public interface ClientSpec {
-
-	Flowable<String> clientVersion();
-
-	Flowable<Torrent> torrents();
+public interface ClientSpec extends
+		Feature.Version,
+		Feature.Listing,
+		Feature.StartingStopping,
+		Feature.ResumingPausing,
+		Feature.ForceStarting {
 
 }

connect/src/main/java/org/transdroid/connect/clients/Feature.java

@@ -1,11 +1,55 @@
 package org.transdroid.connect.clients;
 
+import org.transdroid.connect.model.Torrent;
+
+import io.reactivex.Flowable;
+
+/**
+ * Available feature enum which can be implemented by clients. Use {@link Client#supports(Feature)} to see if a certain {@link Client} support a
+ * {@link Feature}.
+ */
 public enum Feature {
 
-	VERSION,
-	STARTING,
-	STOPPING,
-	RESUMING,
-	PAUSING
+	VERSION(Version.class),
+	LISTING(Listing.class),
+	STARTING_STOPPING(StartingStopping.class),
+	RESUMING_PAUSING(ResumingPausing.class),
+	FORCE_STARTING(ForceStarting.class);
+
+	private final Class<?> type;
+
+	Feature(Class<?> type) {
+		this.type = type;
+	}
+
+	public Class<?> type() {
+		return type;
+	}
+
+	public interface Version {
+
+		Flowable<String> clientVersion();
+
+	}
+
+	public interface Listing {
+
+		Flowable<Torrent> torrents();
+
+	}
+
+	public interface StartingStopping {
+
+	}
+
+	public interface ResumingPausing {
+
+	}
+
+	public interface ForceStarting {
+
+		Flowable<Torrent> forceStartTorrent();
+
+	}
 
 }

connect/src/main/java/org/transdroid/connect/clients/UnsupportedFeatureException.java

@@ -0,0 +1,22 @@
+package org.transdroid.connect.clients;
+
+import sun.reflect.generics.reflectiveObjects.NotImplementedException;
+
+/**
+ * Thrown when trying to call into a client method for a feature which the client does not support.
+ */
+public class UnsupportedFeatureException extends NotImplementedException {
+
+	private final Client client;
+	private final Feature feature;
+
+	UnsupportedFeatureException(Client client, Feature feature) {
+		this.client = client;
+		this.feature = feature;
+	}
+
+	public String getMessage() {
+		return client.name() + " does not support " + feature.name();
+	}
+
+}

connect/src/main/java/org/transdroid/connect/clients/rtorrent/Rtorrent.java

@@ -3,7 +3,6 @@ package org.transdroid.connect.clients.rtorrent;
 import com.jakewharton.retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory;
 
 import org.transdroid.connect.Configuration;
-import org.transdroid.connect.clients.ClientSpec;
 import org.transdroid.connect.clients.Feature;
 import org.transdroid.connect.model.Torrent;
 import org.transdroid.connect.model.TorrentStatus;
@@ -11,8 +10,6 @@ import org.transdroid.connect.util.OkHttpBuilder;
 import org.transdroid.connect.util.RxUtil;
 
 import java.util.Date;
-import java.util.HashSet;
-import java.util.Set;
 
 import io.reactivex.Flowable;
 import io.reactivex.functions.Function;
@@ -20,17 +17,11 @@ import nl.nl2312.xmlrpc.Nothing;
 import nl.nl2312.xmlrpc.XmlRpcConverterFactory;
 import retrofit2.Retrofit;
 
-public final class Rtorrent implements ClientSpec {
-
-	public static final Set<Feature> FEATURES = new HashSet<>();
-
-	{
-		FEATURES.add(Feature.VERSION);
-		FEATURES.add(Feature.STARTING);
-		FEATURES.add(Feature.STOPPING);
-		FEATURES.add(Feature.RESUMING);
-		FEATURES.add(Feature.PAUSING);
-	}
+public final class Rtorrent implements
+		Feature.Version,
+		Feature.Listing,
+		Feature.StartingStopping,
+		Feature.ResumingPausing {
 
 	private final Configuration configuration;
 	private final Service service;

connect/src/main/java/org/transdroid/connect/clients/transmission/Transmission.java

@@ -0,0 +1,5 @@
+package org.transdroid.connect.clients.transmission;
+
+public final class Transmission {
+
+}

connect/src/test/java/org/transdroid/connect/clients/rtorrent/RtorrentTest.java

@@ -6,6 +6,7 @@ import org.transdroid.connect.Configuration;
 import org.transdroid.connect.clients.Client;
 import org.transdroid.connect.clients.ClientSpec;
 import org.transdroid.connect.clients.Feature;
+import org.transdroid.connect.clients.UnsupportedFeatureException;
 import org.transdroid.connect.model.Torrent;
 
 import java.io.IOException;
@@ -21,17 +22,19 @@ public final class RtorrentTest {
 
 	@Before
 	public void setUp() {
-		Configuration configuration = new Configuration(Client.RTORRENT, "http://localhost:8008/", "RPC2", null, null, true);
-		rtorrent = configuration.create();
+		rtorrent = new Configuration.Builder(Client.RTORRENT)
+				.baseUrl("http://localhost:8008/")
+				.endpoint("/RPC2")
+				.build()
+				.createClient();
 	}
 
 	@Test
 	public void features() {
 		assertThat(Client.RTORRENT.supports(Feature.VERSION)).isTrue();
-		assertThat(Client.RTORRENT.supports(Feature.STARTING)).isTrue();
-		assertThat(Client.RTORRENT.supports(Feature.STOPPING)).isTrue();
-		assertThat(Client.RTORRENT.supports(Feature.RESUMING)).isTrue();
-		assertThat(Client.RTORRENT.supports(Feature.PAUSING)).isTrue();
+		assertThat(Client.RTORRENT.supports(Feature.STARTING_STOPPING)).isTrue();
+		assertThat(Client.RTORRENT.supports(Feature.RESUMING_PAUSING)).isTrue();
+		assertThat(Client.RTORRENT.supports(Feature.FORCE_STARTING)).isFalse();
 	}
 
 	@Test
@@ -54,4 +57,10 @@ public final class RtorrentTest {
 				});
 	}
 
+	@Test(expected = UnsupportedFeatureException.class)
+	public void forceStart() throws IOException {
+		rtorrent.forceStartTorrent()
+				.test();
+	}
+
 }