--- /dev/null
+/*******************************************************************************
+ * Copyright (c) 2013, 2014 Sonatype, Inc.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ * Sonatype, Inc. - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.aether.collection;
+
+import java.util.Iterator;
+import java.util.List;
+
+import org.eclipse.aether.RepositoryException;
+import org.eclipse.aether.RepositorySystemSession;
+import org.eclipse.aether.graph.Dependency;
+import org.eclipse.aether.repository.ArtifactRepository;
+import org.eclipse.aether.repository.RemoteRepository;
+import org.eclipse.aether.version.Version;
+import org.eclipse.aether.version.VersionConstraint;
+
+/**
+ * Decides which versions matching a version range should actually be considered for the dependency graph. The version
+ * filter is not invoked for dependencies that do not declare a version range but a single version.
+ * <p>
+ * <strong>Note:</strong> Implementations must be stateless.
+ * <p>
+ * <em>Warning:</em> This hook is called from a hot spot and therefore implementations should pay attention to
+ * performance. Among others, implementations should provide a semantic {@link Object#equals(Object) equals()} method.
+ *
+ * @see org.eclipse.aether.RepositorySystemSession#getVersionFilter()
+ * @see org.eclipse.aether.RepositorySystem#collectDependencies(org.eclipse.aether.RepositorySystemSession,
+ * CollectRequest)
+ */
+public interface VersionFilter
+{
+
+ /**
+ * A context used during version filtering to hold relevant data.
+ *
+ * @noimplement This interface is not intended to be implemented by clients.
+ * @noextend This interface is not intended to be extended by clients.
+ */
+ interface VersionFilterContext
+ extends Iterable<Version>
+ {
+
+ /**
+ * Gets the repository system session during which the version filtering happens.
+ *
+ * @return The repository system session, never {@code null}.
+ */
+ RepositorySystemSession getSession();
+
+ /**
+ * Gets the dependency whose version range is being filtered.
+ *
+ * @return The dependency, never {@code null}.
+ */
+ Dependency getDependency();
+
+ /**
+ * Gets the total number of available versions. This count reflects any removals made during version filtering.
+ *
+ * @return The total number of available versions.
+ */
+ int getCount();
+
+ /**
+ * Gets an iterator over the available versions of the dependency. The iterator returns versions in ascending
+ * order. Use {@link Iterator#remove()} to exclude a version from further consideration in the dependency graph.
+ *
+ * @return The iterator of available versions, never {@code null}.
+ */
+ Iterator<Version> iterator();
+
+ /**
+ * Gets the version constraint that was parsed from the dependency's version string.
+ *
+ * @return The parsed version constraint, never {@code null}.
+ */
+ VersionConstraint getVersionConstraint();
+
+ /**
+ * Gets the repository from which the specified version was resolved.
+ *
+ * @param version The version whose source repository should be retrieved, must not be {@code null}.
+ * @return The repository from which the version was resolved or {@code null} if unknown.
+ */
+ ArtifactRepository getRepository( Version version );
+
+ /**
+ * Gets the remote repositories from which the versions were resolved.
+ *
+ * @return The (read-only) list of repositories, never {@code null}.
+ */
+ List<RemoteRepository> getRepositories();
+
+ }
+
+ /**
+ * Filters the available versions for a given dependency. Implementations will usually call
+ * {@link VersionFilterContext#iterator() context.iterator()} to inspect the available versions and use
+ * {@link java.util.Iterator#remove()} to delete unacceptable versions. If no versions remain after all filtering
+ * has been performed, the dependency collection process will automatically fail, i.e. implementations need not
+ * handle this situation on their own.
+ *
+ * @param context The version filter context, must not be {@code null}.
+ * @throws RepositoryException If the filtering could not be performed.
+ */
+ void filterVersions( VersionFilterContext context )
+ throws RepositoryException;
+
+ /**
+ * Derives a version filter for the specified collection context. The derived filter will be used to handle version
+ * ranges encountered in child dependencies of the current node. When calculating the child filter, implementors are
+ * strongly advised to simply return the current instance if nothing changed to help save memory.
+ *
+ * @param context The dependency collection context, must not be {@code null}.
+ * @return The version filter for the target node or {@code null} if versions should not be filtered any more.
+ */
+ VersionFilter deriveChildFilter( DependencyCollectionContext context );
+
+}