Refactor UPF entities to have consistent naming and string representations

Also, add slice ID into applications and interfaces entities

Change-Id: I159bcf04af1504b4e5c7210aa1402218fae3eb8f
(cherry picked from commit de1f1f7806716ac6e368e55eaf0b887ab89530d4)
diff --git a/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfGtpTunnelPeer.java b/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfGtpTunnelPeer.java
new file mode 100644
index 0000000..04b216b
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfGtpTunnelPeer.java
@@ -0,0 +1,187 @@
+/*
+ * Copyright 2021-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.net.behaviour.upf;
+
+import com.google.common.annotations.Beta;
+import org.onlab.packet.Ip4Address;
+
+import java.util.Objects;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+/**
+ * A structure representing a UPF GTP tunnel peer.
+ * The GTP Tunnel Peer is used by UPF to identify a second end of a GTP tunnel.
+ * The source and destination tunnel IPv4 addresses, and source UDP port are set
+ * based on the information from this structure.
+ */
+@Beta
+public final class UpfGtpTunnelPeer implements UpfEntity {
+    // Match keys
+    private final byte tunPeerId;
+    // Action parameters
+    private final Ip4Address src;  // The source address of the unidirectional tunnel
+    private final Ip4Address dst;  // The destination address of the unidirectional tunnel
+    private final short srcPort;   // Tunnel source port, default 2152
+
+    private UpfGtpTunnelPeer(byte tunPeerId, Ip4Address src, Ip4Address dst, short srcPort) {
+        this.tunPeerId = tunPeerId;
+        this.src = src;
+        this.dst = dst;
+        this.srcPort = srcPort;
+    }
+
+    public static UpfGtpTunnelPeer.Builder builder() {
+        return new UpfGtpTunnelPeer.Builder();
+    }
+
+    @Override
+    public String toString() {
+        return String.format("UpfGtpTunnelPeer(tunn_peer_id=%s -> src=%s, dst=%s src_port=%s)",
+                             tunPeerId, src.toString(), dst.toString(), srcPort);
+    }
+
+    public boolean equals(Object object) {
+        if (this == object) {
+            return true;
+        }
+
+        if (object == null) {
+            return false;
+        }
+
+        if (getClass() != object.getClass()) {
+            return false;
+        }
+
+        UpfGtpTunnelPeer that = (UpfGtpTunnelPeer) object;
+        return this.tunPeerId == that.tunPeerId &&
+                this.src.equals(that.src) &&
+                this.dst.equals(that.dst) &&
+                this.srcPort == that.srcPort;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(tunPeerId, src, dst, srcPort);
+    }
+
+    /**
+     * Get the ID of the UPF GTP tunnel peer.
+     *
+     * @return GTP tunnel peer ID
+     */
+    public byte tunPeerId() {
+        return tunPeerId;
+    }
+
+    /**
+     * Get the source IP address of this unidirectional UPF GTP tunnel.
+     *
+     * @return tunnel source IP
+     */
+    public Ip4Address src() {
+        return this.src;
+    }
+
+    /**
+     * Get the destination address of this unidirectional UPF GTP tunnel.
+     *
+     * @return tunnel destination IP
+     */
+    public Ip4Address dst() {
+        return this.dst;
+    }
+
+    /**
+     * Get the source L4 port of this unidirectional UPF GTP tunnel.
+     *
+     * @return tunnel source port
+     */
+    public short srcPort() {
+        return this.srcPort;
+    }
+
+    @Override
+    public UpfEntityType type() {
+        return UpfEntityType.TUNNEL_PEER;
+    }
+
+    public static class Builder {
+        private Byte tunPeerId = null;
+        private Ip4Address src = null;
+        private Ip4Address dst = null;
+        private short srcPort = 2152;  // Default value is equal to GTP tunnel dst port
+
+        public Builder() {
+
+        }
+
+        /**
+         * Set the ID of the UPF GTP Tunnel peer.
+         *
+         * @param tunPeerId GTP tunnel peer ID
+         * @return This builder object
+         */
+        public UpfGtpTunnelPeer.Builder withTunnelPeerId(byte tunPeerId) {
+            this.tunPeerId = tunPeerId;
+            return this;
+        }
+
+        /**
+         * Set the source IP address of the unidirectional UPF GTP tunnel.
+         *
+         * @param src GTP tunnel source IP
+         * @return This builder object
+         */
+        public UpfGtpTunnelPeer.Builder withSrcAddr(Ip4Address src) {
+            this.src = src;
+            return this;
+        }
+
+        /**
+         * Set the destination IP address of the unidirectional UPF GTP tunnel.
+         *
+         * @param dst GTP tunnel destination IP
+         * @return This builder object
+         */
+        public UpfGtpTunnelPeer.Builder withDstAddr(Ip4Address dst) {
+            this.dst = dst;
+            return this;
+        }
+
+        /**
+         * Set the source port of this unidirectional UPF GTP tunnel.
+         *
+         * @param srcPort tunnel source port
+         * @return this builder object
+         */
+        public UpfGtpTunnelPeer.Builder withSrcPort(short srcPort) {
+            this.srcPort = srcPort;
+            return this;
+        }
+
+        public UpfGtpTunnelPeer build() {
+            checkArgument(tunPeerId != null, "Tunnel Peer ID must be provided");
+            checkArgument(src != null, "Tunnel source address cannot be null");
+            checkArgument(dst != null, "Tunnel destination address cannot be null");
+            return new UpfGtpTunnelPeer(this.tunPeerId, this.src, this.dst, srcPort);
+        }
+
+    }
+
+}