Refactors McastHandler to optimize network failures

Changes:
- Introduces a paths store
- Optimizes SINKS_ADDED, SINKS_REMOVED
- Uses SINKS_REMOVED to handle egress failures
- Optimizes SOURCES_ADDED, SOURCES_REMOVED
- Leverages SOURCES_REMOVED to handle ingress failures
- Optimizes infra failures

Change-Id: I16d264f58d6fe11cfce4a546f7b4ab82a9fcc21b
diff --git a/app/src/main/java/org/onosproject/segmentrouting/mcast/McastPathStoreKey.java b/app/src/main/java/org/onosproject/segmentrouting/mcast/McastPathStoreKey.java
new file mode 100644
index 0000000..76f46fe
--- /dev/null
+++ b/app/src/main/java/org/onosproject/segmentrouting/mcast/McastPathStoreKey.java
@@ -0,0 +1,100 @@
+/*
+ * Copyright 2020-present Open Networking Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.segmentrouting.mcast;
+
+import org.onlab.packet.IpAddress;
+import org.onosproject.net.ConnectPoint;
+
+import java.util.Objects;
+
+import static com.google.common.base.MoreObjects.toStringHelper;
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Key of multicast path store.
+ */
+public class McastPathStoreKey {
+    // Identify path using group address and source
+    private final IpAddress mcastIp;
+    private final ConnectPoint source;
+
+    /**
+     * Constructs the key of multicast path store.
+     *
+     * @param mcastIp multicast group IP address
+     * @param source source connect point
+     */
+    public McastPathStoreKey(IpAddress mcastIp, ConnectPoint source) {
+        checkNotNull(mcastIp, "mcastIp cannot be null");
+        checkNotNull(source, "source cannot be null");
+        checkArgument(mcastIp.isMulticast(), "mcastIp must be a multicast address");
+        this.mcastIp = mcastIp;
+        this.source = source;
+    }
+
+    // Constructor for serialization
+    private McastPathStoreKey() {
+        this.mcastIp = null;
+        this.source = null;
+    }
+
+    /**
+     * Returns the multicast IP address of this key.
+     *
+     * @return multicast IP
+     */
+    public IpAddress mcastIp() {
+        return mcastIp;
+    }
+
+    /**
+     * Returns the device ID of this key.
+     *
+     * @return device ID
+     */
+    public ConnectPoint source() {
+        return source;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (!(o instanceof McastPathStoreKey)) {
+            return false;
+        }
+        McastPathStoreKey that =
+                (McastPathStoreKey) o;
+        return (Objects.equals(this.mcastIp, that.mcastIp) &&
+                Objects.equals(this.source, that.source));
+    }
+
+    @Override
+    public int hashCode() {
+         return Objects.hash(mcastIp, source);
+    }
+
+    @Override
+    public String toString() {
+        return toStringHelper(getClass())
+                .add("mcastIp", mcastIp)
+                .add("source", source)
+                .toString();
+    }
+}