Adding Intent Impl and shell command to install simple intent
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/AbstractBlockAllocatorBasedIdGenerator.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/AbstractBlockAllocatorBasedIdGenerator.java
new file mode 100644
index 0000000..00b64da
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/AbstractBlockAllocatorBasedIdGenerator.java
@@ -0,0 +1,42 @@
+package org.onlab.onos.net.intent.impl;
+
+import org.onlab.onos.net.intent.IdGenerator;
+
+/**
+ * Base class of {@link IdGenerator} implementations which use {@link IdBlockAllocator} as
+ * backend.
+ *
+ * @param <T> the type of ID
+ */
+public abstract class AbstractBlockAllocatorBasedIdGenerator<T> implements IdGenerator<T> {
+    protected final IdBlockAllocator allocator;
+    protected IdBlock idBlock;
+
+    /**
+     * Constructs an ID generator which use {@link IdBlockAllocator} as backend.
+     *
+     * @param allocator
+     */
+    protected AbstractBlockAllocatorBasedIdGenerator(IdBlockAllocator allocator) {
+        this.allocator = allocator;
+        this.idBlock = allocator.allocateUniqueIdBlock();
+    }
+
+    @Override
+    public synchronized T getNewId() {
+        try {
+            return convertFrom(idBlock.getNextId());
+        } catch (UnavailableIdException e) {
+            idBlock = allocator.allocateUniqueIdBlock();
+            return convertFrom(idBlock.getNextId());
+        }
+    }
+
+    /**
+     * Returns an ID instance of {@code T} type from the long value.
+     *
+     * @param value original long value
+     * @return ID instance
+     */
+    protected abstract T convertFrom(long value);
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/DummyIdBlockAllocator.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/DummyIdBlockAllocator.java
new file mode 100644
index 0000000..f331aa2
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/DummyIdBlockAllocator.java
@@ -0,0 +1,31 @@
+package org.onlab.onos.net.intent.impl;
+
+public class DummyIdBlockAllocator implements IdBlockAllocator {
+    private long blockTop;
+    private static final long BLOCK_SIZE = 0x1000000L;
+
+    /**
+     * Returns a block of IDs which are unique and unused.
+     * Range of IDs is fixed size and is assigned incrementally as this method
+     * called.
+     *
+     * @return an IdBlock containing a set of unique IDs
+     */
+    @Override
+    public IdBlock allocateUniqueIdBlock() {
+        synchronized (this)  {
+            long blockHead = blockTop;
+            long blockTail = blockTop + BLOCK_SIZE;
+
+            IdBlock block = new IdBlock(blockHead, BLOCK_SIZE);
+            blockTop = blockTail;
+
+            return block;
+        }
+    }
+
+    @Override
+    public IdBlock allocateUniqueIdBlock(long range) {
+        throw new UnsupportedOperationException("Not supported yet");
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/HostToHostIntentCompiler.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/HostToHostIntentCompiler.java
new file mode 100644
index 0000000..a8bea2e
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/HostToHostIntentCompiler.java
@@ -0,0 +1,67 @@
+package org.onlab.onos.net.intent.impl;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Set;
+
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Reference;
+import org.apache.felix.scr.annotations.ReferenceCardinality;
+import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.Path;
+import org.onlab.onos.net.PortNumber;
+import org.onlab.onos.net.intent.HostToHostIntent;
+import org.onlab.onos.net.intent.IdGenerator;
+import org.onlab.onos.net.intent.Intent;
+import org.onlab.onos.net.intent.IntentCompiler;
+import org.onlab.onos.net.intent.IntentExtensionService;
+import org.onlab.onos.net.intent.IntentId;
+import org.onlab.onos.net.intent.PathIntent;
+import org.onlab.onos.net.topology.PathService;
+
+/**
+ * A intent compiler for {@link HostToHostIntent}.
+ */
+@Component(immediate = true)
+public class HostToHostIntentCompiler
+        implements IntentCompiler<HostToHostIntent> {
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected IntentExtensionService intentManager;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected PathService pathService;
+
+    private IdGenerator<IntentId> intentIdGenerator;
+
+    @Activate
+    public void activate() {
+        IdBlockAllocator idBlockAllocator = new DummyIdBlockAllocator();
+        intentIdGenerator = new IdBlockAllocatorBasedIntentIdGenerator(idBlockAllocator);
+        intentManager.registerCompiler(HostToHostIntent.class, this);
+    }
+
+    @Deactivate
+    public void deactivate() {
+        intentManager.unregisterCompiler(HostToHostIntent.class);
+    }
+
+    @Override
+    public List<Intent> compile(HostToHostIntent intent) {
+        Set<Path> paths = pathService.getPaths(intent.getSrc(), intent.getDst());
+        if (paths.isEmpty()) {
+            throw new PathNotFoundException();
+        }
+        Path path = paths.iterator().next();
+
+        return Arrays.asList((Intent) new PathIntent(
+                intentIdGenerator.getNewId(),
+                intent.getTrafficSelector(),
+                intent.getTrafficTreatment(),
+                new ConnectPoint(intent.getSrc(), PortNumber.ALL),
+                new ConnectPoint(intent.getDst(), PortNumber.ALL),
+                path));
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/IdBlock.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IdBlock.java
new file mode 100644
index 0000000..ce418ea
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IdBlock.java
@@ -0,0 +1,111 @@
+package org.onlab.onos.net.intent.impl;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import java.util.Objects;
+import java.util.concurrent.atomic.AtomicLong;
+
+import com.google.common.base.MoreObjects;
+
+/**
+ * A class representing an ID space.
+ */
+public final class IdBlock {
+    private final long start;
+    private final long size;
+
+    private final AtomicLong currentId;
+
+    /**
+     * Constructs a new ID block with the specified size and initial value.
+     *
+     * @param start initial value of the block
+     * @param size size of the block
+     * @throws IllegalArgumentException if the size is less than or equal to 0
+     */
+    public IdBlock(long start, long size) {
+        checkArgument(size > 0, "size should be more than 0, but %s", size);
+
+        this.start = start;
+        this.size = size;
+
+        this.currentId = new AtomicLong(start);
+    }
+
+    // TODO: consider if this method is needed or not
+    /**
+     * Returns the initial value.
+     *
+     * @return initial value
+     */
+    public long getStart() {
+        return start;
+    }
+
+    // TODO: consider if this method is needed or not
+    /**
+     * Returns the last value.
+     *
+     * @return last value
+     */
+    public long getEnd() {
+        return start + size - 1;
+    }
+
+    /**
+     * Returns the block size.
+     *
+     * @return block size
+     */
+    public long getSize() {
+        return size;
+    }
+
+    /**
+     * Returns the next ID in the block.
+     *
+     * @return next ID
+     * @throws UnavailableIdException if there is no available ID in the block.
+     */
+    public long getNextId() {
+        final long id = currentId.getAndIncrement();
+        if (id > getEnd()) {
+            throw new UnavailableIdException(String.format(
+                    "used all IDs in allocated space (size: %d, end: %d, current: %d)",
+                    size, getEnd(), id
+            ));
+        }
+
+        return id;
+    }
+
+    // TODO: Do we really need equals and hashCode? Should it contain currentId?
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        IdBlock that = (IdBlock) o;
+        return Objects.equals(this.start, that.start)
+                && Objects.equals(this.size, that.size)
+                && Objects.equals(this.currentId.get(), that.currentId.get());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(start, size, currentId);
+    }
+
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(getClass())
+                .add("start", start)
+                .add("size", size)
+                .add("currentId", currentId)
+                .toString();
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/IdBlockAllocator.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IdBlockAllocator.java
new file mode 100644
index 0000000..1adac02
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IdBlockAllocator.java
@@ -0,0 +1,21 @@
+package org.onlab.onos.net.intent.impl;
+
+/**
+ * An interface that gives unique ID spaces.
+ */
+public interface IdBlockAllocator {
+    /**
+     * Allocates a unique Id Block.
+     *
+     * @return Id Block.
+     */
+    IdBlock allocateUniqueIdBlock();
+
+    /**
+     * Allocates next unique id and retrieve a new range of ids if needed.
+     *
+     * @param range range to use for the identifier
+     * @return Id Block.
+     */
+    IdBlock allocateUniqueIdBlock(long range);
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/IdBlockAllocatorBasedIntentIdGenerator.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IdBlockAllocatorBasedIntentIdGenerator.java
new file mode 100644
index 0000000..b8c5c9b
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IdBlockAllocatorBasedIntentIdGenerator.java
@@ -0,0 +1,25 @@
+package org.onlab.onos.net.intent.impl;
+
+import org.onlab.onos.net.intent.IntentId;
+
+/**
+ * An implementation of {@link net.onrc.onos.core.util.IdGenerator} of intent ID,
+ * which uses {@link IdBlockAllocator}.
+ */
+public class IdBlockAllocatorBasedIntentIdGenerator extends AbstractBlockAllocatorBasedIdGenerator<IntentId> {
+
+    /**
+     * Constructs an intent ID generator, which uses the specified ID block allocator
+     * to generate a global unique intent ID.
+     *
+     * @param allocator the ID block allocator to use for generating intent IDs
+     */
+    public IdBlockAllocatorBasedIntentIdGenerator(IdBlockAllocator allocator) {
+        super(allocator);
+    }
+
+    @Override
+    protected IntentId convertFrom(long value) {
+        return new IntentId(value);
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentCompilationException.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentCompilationException.java
new file mode 100644
index 0000000..bf739df
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentCompilationException.java
@@ -0,0 +1,22 @@
+package org.onlab.onos.net.intent.impl;
+
+import org.onlab.onos.net.intent.IntentException;
+
+/**
+ * An exception thrown when a intent compilation fails.
+ */
+public class IntentCompilationException extends IntentException {
+    private static final long serialVersionUID = 235237603018210810L;
+
+    public IntentCompilationException() {
+        super();
+    }
+
+    public IntentCompilationException(String message) {
+        super(message);
+    }
+
+    public IntentCompilationException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentInstallationException.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentInstallationException.java
new file mode 100644
index 0000000..3b17cf1
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentInstallationException.java
@@ -0,0 +1,22 @@
+package org.onlab.onos.net.intent.impl;
+
+import org.onlab.onos.net.intent.IntentException;
+
+/**
+ * An exception thrown when intent installation fails.
+ */
+public class IntentInstallationException extends IntentException {
+    private static final long serialVersionUID = 3720268258616014168L;
+
+    public IntentInstallationException() {
+        super();
+    }
+
+    public IntentInstallationException(String message) {
+        super(message);
+    }
+
+    public IntentInstallationException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentManager.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentManager.java
new file mode 100644
index 0000000..f1c9de3
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentManager.java
@@ -0,0 +1,363 @@
+package org.onlab.onos.net.intent.impl;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.onlab.onos.net.intent.IntentState.FAILED;
+import static org.onlab.onos.net.intent.IntentState.INSTALLED;
+import static org.onlab.onos.net.intent.IntentState.WITHDRAWING;
+import static org.onlab.onos.net.intent.IntentState.WITHDRAWN;
+import static org.slf4j.LoggerFactory.getLogger;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.CopyOnWriteArrayList;
+
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Reference;
+import org.apache.felix.scr.annotations.ReferenceCardinality;
+import org.apache.felix.scr.annotations.Service;
+import org.onlab.onos.event.AbstractListenerRegistry;
+import org.onlab.onos.event.EventDeliveryService;
+import org.onlab.onos.net.intent.InstallableIntent;
+import org.onlab.onos.net.intent.Intent;
+import org.onlab.onos.net.intent.IntentCompiler;
+import org.onlab.onos.net.intent.IntentEvent;
+import org.onlab.onos.net.intent.IntentException;
+import org.onlab.onos.net.intent.IntentExtensionService;
+import org.onlab.onos.net.intent.IntentId;
+import org.onlab.onos.net.intent.IntentInstaller;
+import org.onlab.onos.net.intent.IntentListener;
+import org.onlab.onos.net.intent.IntentOperations;
+import org.onlab.onos.net.intent.IntentService;
+import org.onlab.onos.net.intent.IntentState;
+import org.onlab.onos.net.intent.IntentStore;
+import org.onlab.onos.net.intent.IntentStoreDelegate;
+import org.slf4j.Logger;
+
+import com.google.common.collect.ImmutableMap;
+
+/**
+ * An implementation of Intent Manager.
+ */
+@Component(immediate = true)
+@Service
+public class IntentManager
+        implements IntentService, IntentExtensionService {
+    private final Logger log = getLogger(getClass());
+
+    public static final String INTENT_NULL = "Intent cannot be null";
+    public static final String INTENT_ID_NULL = "Intent ID cannot be null";
+
+    // Collections for compiler, installer, and listener are ONOS instance local
+    private final ConcurrentMap<Class<? extends Intent>,
+            IntentCompiler<? extends Intent>> compilers = new ConcurrentHashMap<>();
+    private final ConcurrentMap<Class<? extends InstallableIntent>,
+            IntentInstaller<? extends InstallableIntent>> installers = new ConcurrentHashMap<>();
+    private final CopyOnWriteArrayList<IntentListener> listeners = new CopyOnWriteArrayList<>();
+
+    private final AbstractListenerRegistry<IntentEvent, IntentListener>
+        listenerRegistry = new AbstractListenerRegistry<>();
+
+    private final IntentStoreDelegate delegate = new InternalStoreDelegate();
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected IntentStore store;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected EventDeliveryService eventDispatcher;
+
+    @Activate
+    public void activate() {
+        store.setDelegate(delegate);
+        eventDispatcher.addSink(IntentEvent.class, listenerRegistry);
+
+//        this.intentEvents = new IntentMap<>("intentState", IntentEvent.class, collectionsService);
+//        this.installableIntents =
+//                new IntentMap<>("installableIntents", IntentCompilationResult.class, collectionsService);
+//
+//
+//        this.intentEvents.addListener(new InternalEntryListener(new InternalIntentEventListener()));
+
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        store.unsetDelegate(delegate);
+        eventDispatcher.removeSink(IntentEvent.class);
+        log.info("Stopped");
+    }
+
+    @Override
+    public void submit(Intent intent) {
+        checkNotNull(intent, INTENT_NULL);
+        registerSubclassCompilerIfNeeded(intent);
+        IntentEvent event = store.createIntent(intent);
+        eventDispatcher.post(event);
+        processStoreEvent(event);
+    }
+
+    @Override
+    public void withdraw(Intent intent) {
+        checkNotNull(intent, INTENT_NULL);
+        IntentEvent event = store.setState(intent, WITHDRAWING);
+        eventDispatcher.post(event);
+        processStoreEvent(event);
+    }
+
+    // FIXME: implement this method
+    @Override
+    public void execute(IntentOperations operations) {
+        throw new UnsupportedOperationException("execute() is not implemented yet");
+    }
+
+    @Override
+    public Iterable<Intent> getIntents() {
+        return store.getIntents();
+    }
+
+    @Override
+    public long getIntentCount() {
+        return store.getIntentCount();
+    }
+
+    @Override
+    public Intent getIntent(IntentId id) {
+        checkNotNull(id, INTENT_ID_NULL);
+        return store.getIntent(id);
+    }
+
+    @Override
+    public IntentState getIntentState(IntentId id) {
+        checkNotNull(id, INTENT_ID_NULL);
+        return store.getIntentState(id);
+    }
+
+    @Override
+    public void addListener(IntentListener listener) {
+        listenerRegistry.addListener(listener);
+    }
+
+    @Override
+    public void removeListener(IntentListener listener) {
+        listenerRegistry.removeListener(listener);
+    }
+
+    @Override
+    public <T extends Intent> void registerCompiler(Class<T> cls, IntentCompiler<T> compiler) {
+        compilers.put(cls, compiler);
+    }
+
+    @Override
+    public <T extends Intent> void unregisterCompiler(Class<T> cls) {
+        compilers.remove(cls);
+    }
+
+    @Override
+    public Map<Class<? extends Intent>, IntentCompiler<? extends Intent>> getCompilers() {
+        return ImmutableMap.copyOf(compilers);
+    }
+
+    @Override
+    public <T extends InstallableIntent> void registerInstaller(Class<T> cls, IntentInstaller<T> installer) {
+        installers.put(cls, installer);
+    }
+
+    @Override
+    public <T extends InstallableIntent> void unregisterInstaller(Class<T> cls) {
+        installers.remove(cls);
+    }
+
+    @Override
+    public Map<Class<? extends InstallableIntent>, IntentInstaller<? extends InstallableIntent>> getInstallers() {
+        return ImmutableMap.copyOf(installers);
+    }
+
+    /**
+     * Invokes all of registered intent event listener.
+     *
+     * @param event event supplied to a listener as an argument
+     */
+    private void invokeListeners(IntentEvent event) {
+        for (IntentListener listener : listeners) {
+            listener.event(event);
+        }
+    }
+
+    /**
+     * Returns the corresponding intent compiler to the specified intent.
+     *
+     * @param intent intent
+     * @param <T> the type of intent
+     * @return intent compiler corresponding to the specified intent
+     */
+    private <T extends Intent> IntentCompiler<T> getCompiler(T intent) {
+        @SuppressWarnings("unchecked")
+        IntentCompiler<T> compiler = (IntentCompiler<T>) compilers.get(intent.getClass());
+        if (compiler == null) {
+            throw new IntentException("no compiler for class " + intent.getClass());
+        }
+        return compiler;
+    }
+
+    /**
+     * Returns the corresponding intent installer to the specified installable intent.
+     * @param intent intent
+     * @param <T> the type of installable intent
+     * @return intent installer corresponding to the specified installable intent
+     */
+    private <T extends InstallableIntent> IntentInstaller<T> getInstaller(T intent) {
+        @SuppressWarnings("unchecked")
+        IntentInstaller<T> installer = (IntentInstaller<T>) installers.get(intent.getClass());
+        if (installer == null) {
+            throw new IntentException("no installer for class " + intent.getClass());
+        }
+        return installer;
+    }
+
+    /**
+     * Compiles an intent.
+     *
+     * @param intent intent
+     */
+    private void compileIntent(Intent intent) {
+        // FIXME: To make SDN-IP workable ASAP, only single level compilation is implemented
+        // TODO: implement compilation traversing tree structure
+        List<InstallableIntent> installable = new ArrayList<>();
+        for (Intent compiled : getCompiler(intent).compile(intent)) {
+            installable.add((InstallableIntent) compiled);
+        }
+        IntentEvent event = store.addInstallableIntents(intent.getId(), installable);
+        eventDispatcher.post(event);
+        processStoreEvent(event);
+    }
+
+    /**
+     * Installs an intent.
+     *
+     * @param intent intent
+     */
+    private void installIntent(Intent intent) {
+        for (InstallableIntent installable : store.getInstallableIntents(intent.getId())) {
+            registerSubclassInstallerIfNeeded(installable);
+            getInstaller(installable).install(installable);
+        }
+
+        IntentEvent event = store.setState(intent, INSTALLED);
+        eventDispatcher.post(event);
+        processStoreEvent(event);
+
+    }
+
+    /**
+     * Uninstalls an intent.
+     *
+     * @param intent intent
+     */
+    private void uninstallIntent(Intent intent) {
+        for (InstallableIntent installable : store.getInstallableIntents(intent.getId())) {
+            getInstaller(installable).uninstall(installable);
+        }
+
+        store.removeInstalledIntents(intent.getId());
+        store.setState(intent, WITHDRAWN);
+    }
+
+    /**
+     * Registers an intent compiler of the specified intent if an intent compiler
+     * for the intent is not registered. This method traverses the class hierarchy of
+     * the intent. Once an intent compiler for a parent type is found, this method
+     * registers the found intent compiler.
+     *
+     * @param intent intent
+     */
+    private void registerSubclassCompilerIfNeeded(Intent intent) {
+        if (!compilers.containsKey(intent.getClass())) {
+            Class<?> cls = intent.getClass();
+            while (cls != Object.class) {
+                // As long as we're within the Intent class descendants
+                if (Intent.class.isAssignableFrom(cls)) {
+                    IntentCompiler<?> compiler = compilers.get(cls);
+                    if (compiler != null) {
+                        compilers.put(intent.getClass(), compiler);
+                        return;
+                    }
+                }
+                cls = cls.getSuperclass();
+            }
+        }
+    }
+
+    /**
+     * Registers an intent installer of the specified intent if an intent installer
+     * for the intent is not registered. This method traverses the class hierarchy of
+     * the intent. Once an intent installer for a parent type is found, this method
+     * registers the found intent installer.
+     *
+     * @param intent intent
+     */
+    private void registerSubclassInstallerIfNeeded(InstallableIntent intent) {
+        if (!installers.containsKey(intent.getClass())) {
+            Class<?> cls = intent.getClass();
+            while (cls != Object.class) {
+                // As long as we're within the InstallableIntent class descendants
+                if (InstallableIntent.class.isAssignableFrom(cls)) {
+                    IntentInstaller<?> installer = installers.get(cls);
+                    if (installer != null) {
+                        installers.put(intent.getClass(), installer);
+                        return;
+                    }
+                }
+                cls = cls.getSuperclass();
+            }
+        }
+    }
+
+    /**
+     * Handles state transition of submitted intents.
+     */
+    private void processStoreEvent(IntentEvent event) {
+            invokeListeners(event);
+            Intent intent = event.getIntent();
+
+            try {
+                switch (event.getState()) {
+                    case SUBMITTED:
+                        compileIntent(intent);
+                        break;
+                    case COMPILED:
+                        installIntent(intent);
+                        break;
+                    case INSTALLED:
+                        break;
+                    case WITHDRAWING:
+                        uninstallIntent(intent);
+                        break;
+                    case WITHDRAWN:
+                        break;
+                    case FAILED:
+                        break;
+                    default:
+                        throw new IllegalStateException(
+                                "the state of IntentEvent is illegal: " + event.getState());
+                }
+            } catch (IntentException e) {
+                store.setState(intent, FAILED);
+            }
+
+    }
+
+    // Store delegate to re-post events emitted from the store.
+    private class InternalStoreDelegate implements IntentStoreDelegate {
+        @Override
+        public void notify(IntentEvent event) {
+            processStoreEvent(event);
+            eventDispatcher.post(event);
+        }
+    }
+
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentRemovalException.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentRemovalException.java
new file mode 100644
index 0000000..5ee4ee4
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentRemovalException.java
@@ -0,0 +1,22 @@
+package org.onlab.onos.net.intent.impl;
+
+import org.onlab.onos.net.intent.IntentException;
+
+/**
+ * An exception thrown when intent removal failed.
+ */
+public class IntentRemovalException extends IntentException {
+    private static final long serialVersionUID = -5259226322037891951L;
+
+    public IntentRemovalException() {
+        super();
+    }
+
+    public IntentRemovalException(String message) {
+        super(message);
+    }
+
+    public IntentRemovalException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/PathIntentInstaller.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/PathIntentInstaller.java
new file mode 100644
index 0000000..9202684
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/PathIntentInstaller.java
@@ -0,0 +1,79 @@
+package org.onlab.onos.net.intent.impl;
+
+import java.util.Iterator;
+
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Reference;
+import org.apache.felix.scr.annotations.ReferenceCardinality;
+import org.onlab.onos.ApplicationId;
+import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.Link;
+import org.onlab.onos.net.flow.DefaultFlowRule;
+import org.onlab.onos.net.flow.DefaultTrafficSelector;
+import org.onlab.onos.net.flow.DefaultTrafficTreatment;
+import org.onlab.onos.net.flow.FlowRule;
+import org.onlab.onos.net.flow.FlowRuleService;
+import org.onlab.onos.net.flow.TrafficSelector;
+import org.onlab.onos.net.flow.TrafficTreatment;
+import org.onlab.onos.net.flow.criteria.Criterion;
+import org.onlab.onos.net.intent.IntentExtensionService;
+import org.onlab.onos.net.intent.IntentInstaller;
+import org.onlab.onos.net.intent.PathIntent;
+
+/**
+ * An intent installer for {@link PathIntent}.
+ */
+@Component(immediate = true)
+public class PathIntentInstaller
+        implements IntentInstaller<PathIntent> {
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected IntentExtensionService intentManager;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    private FlowRuleService flowRuleService;
+
+    private final ApplicationId appId = ApplicationId.valueOf(1);
+
+    @Activate
+    public void activate() {
+        intentManager.registerInstaller(PathIntent.class, this);
+    }
+
+    @Deactivate
+    public void deactivate() {
+        intentManager.unregisterInstaller(PathIntent.class);
+    }
+
+    @Override
+    public void install(PathIntent intent) {
+        TrafficSelector.Builder builder = new DefaultTrafficSelector.Builder();
+        TrafficSelector selector = intent.getTrafficSelector();
+        for (Criterion c : selector.criteria()) {
+            builder.add(c);
+        }
+
+        Iterator<Link> links = intent.getPath().links().iterator();
+        ConnectPoint prev = links.next().dst();
+        while (links.hasNext()) {
+            builder.matchInport(prev.port());
+            Link link = links.next();
+
+            TrafficTreatment.Builder treat = new DefaultTrafficTreatment.Builder();
+            treat.setOutput(link.src().port());
+
+            FlowRule f = new DefaultFlowRule(link.src().deviceId(),
+                    builder.build(), treat.build(), 0, appId);
+            flowRuleService.applyFlowRules(f);
+
+            prev = link.dst();
+        }
+
+    }
+
+    @Override
+    public void uninstall(PathIntent intent) {
+        //TODO
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/PathNotFoundException.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/PathNotFoundException.java
new file mode 100644
index 0000000..a1fd63a
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/PathNotFoundException.java
@@ -0,0 +1,22 @@
+package org.onlab.onos.net.intent.impl;
+
+import org.onlab.onos.net.intent.IntentException;
+
+/**
+ * An exception thrown when a path is not found.
+ */
+public class PathNotFoundException extends IntentException {
+    private static final long serialVersionUID = -2087045731049914733L;
+
+    public PathNotFoundException() {
+        super();
+    }
+
+    public PathNotFoundException(String message) {
+        super(message);
+    }
+
+    public PathNotFoundException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/UnavailableIdException.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/UnavailableIdException.java
new file mode 100644
index 0000000..fd4f122
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/UnavailableIdException.java
@@ -0,0 +1,34 @@
+package org.onlab.onos.net.intent.impl;
+
+/**
+ * Represents that there is no available IDs.
+ */
+public class UnavailableIdException extends RuntimeException {
+
+    private static final long serialVersionUID = -2287403908433720122L;
+
+    /**
+     * Constructs an exception with no message and no underlying cause.
+     */
+    public UnavailableIdException() {
+    }
+
+    /**
+     * Constructs an exception with the specified message.
+     *
+     * @param message the message describing the specific nature of the error
+     */
+    public UnavailableIdException(String message) {
+        super(message);
+    }
+
+    /**
+     * Constructs an exception with the specified message and the underlying cause.
+     *
+     * @param message the message describing the specific nature of the error
+     * @param cause the underlying cause of this error
+     */
+    public UnavailableIdException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/package-info.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/package-info.java
new file mode 100644
index 0000000..fa8248e
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/package-info.java
@@ -0,0 +1,4 @@
+/**
+ * Intent Service Implementation. TODO
+ */
+package org.onlab.onos.net.intent.impl;
\ No newline at end of file