ENH: NAV-53 - Add direct walk type to the walk

- A walk from a location to a stop, the first leg of a connection.
- A walk from a stop to a location, the last leg of a connection.
- A walk between two locations, the only leg of a connection.

src/main/java/ch/naviqore/service/Transfer.java

@@ -2,6 +2,12 @@
 
 import java.time.LocalDateTime;
 
+/**
+ * A transfer is a walk between two stops.
+ * <p>
+ * Typically, a transfer occurs between two public transit legs within a connection. However, a connection might consist
+ * solely of a transfer if it directly links two stops via walking.
+ */
 public interface Transfer extends Leg {
 
     LocalDateTime getArrivalTime();

src/main/java/ch/naviqore/service/Walk.java

@@ -1,12 +1,10 @@
 package ch.naviqore.service;
 
 import java.time.LocalDateTime;
+import java.util.Optional;
 
 public interface Walk extends Leg {
 
-    /**
-     * Determines if this is first or a last mile walk.
-     */
     WalkType getWalkType();
 
     LocalDateTime getArrivalTime();
@@ -18,8 +16,8 @@ public interface Walk extends Leg {
     Location getTargetLocation();
 
     /**
-     * The source or target stop of this first or last mile walk.
+     * The source or target stop of a first or last mile walk or none if it is a direct walk.
      */
-    Stop getStop();
+    Optional<Stop> getStop();
 
 }

src/main/java/ch/naviqore/service/WalkType.java

@@ -1,6 +1,20 @@
 package ch.naviqore.service;
 
 public enum WalkType {
+
+    /**
+     * A walk from a location to a stop, the first leg of a connection.
+     */
     FIRST_MILE,
-    LAST_MILE
+
+    /**
+     * A walk from a stop to a location, the last leg of a connection.
+     */
+    LAST_MILE,
+
+    /**
+     * A walk between two locations, the only leg of a connection.
+     */
+    DIRECT
+
 }

src/main/java/ch/naviqore/service/impl/WalkImpl.java

@@ -1,10 +1,13 @@
 package ch.naviqore.service.impl;
 
 import ch.naviqore.service.*;
+import lombok.AccessLevel;
 import lombok.Getter;
 import lombok.ToString;
+import org.jetbrains.annotations.Nullable;
 
 import java.time.LocalDateTime;
+import java.util.Optional;
 
 @Getter
 @ToString(callSuper = true)
@@ -15,10 +18,15 @@ public class WalkImpl extends LegImpl implements Walk {
     private final LocalDateTime arrivalTime;
     private final Location sourceLocation;
     private final Location targetLocation;
+    @Getter(AccessLevel.NONE)
+    @Nullable
     private final Stop stop;
 
+    /**
+     * Create a first or last mile walk between a station and a location.
+     */
     WalkImpl(int distance, int duration, WalkType walkType, LocalDateTime departureTime, LocalDateTime arrivalTime,
-             Location sourceLocation, Location targetLocation, Stop stop) {
+             Location sourceLocation, Location targetLocation, @Nullable Stop stop) {
         super(LegType.WALK, distance, duration);
         this.walkType = walkType;
         this.departureTime = departureTime;
@@ -28,9 +36,22 @@ public class WalkImpl extends LegImpl implements Walk {
         this.stop = stop;
     }
 
+    /**
+     * Create a direct walk between two locations.
+     */
+    WalkImpl(int distance, int duration, LocalDateTime departureTime, LocalDateTime arrivalTime,
+             Location sourceLocation, Location targetLocation) {
+        this(distance, duration, WalkType.DIRECT, departureTime, arrivalTime, sourceLocation, targetLocation, null);
+    }
+
     @Override
     public <T> T accept(LegVisitor<T> visitor) {
         return visitor.visit(this);
     }
 
+    @Override
+    public Optional<Stop> getStop() {
+        return Optional.ofNullable(stop);
+    }
+
 }