Report overlapping arena regions on load.

This commit introduces an `intersects()` method on ArenaRegion that
allows us to check whether two regions intersect.

The new method is employed in ArenaMasterImpl during arena load. If an
arena's region intersects with any other arena's region (in the same
world), we print a warning to the server log.

Fixes #367

src/main/java/com/garbagemule/MobArena/ArenaMasterImpl.java

@@ -532,6 +532,8 @@ public class ArenaMasterImpl implements ArenaMaster
         if (arenaNames == null || arenaNames.isEmpty()) {
             return;
         }
+
+        List<Arena> arenas = new ArrayList<>();
         for (String arenaName : arenaNames) {
             Arena arena = getArenaWithName(arenaName);
             if (arena != null) continue;
@@ -539,7 +541,31 @@ public class ArenaMasterImpl implements ArenaMaster
             String arenaWorld = config.getString("arenas." + arenaName + ".settings.world", "");
             if (!arenaWorld.equals(worldName)) continue;
 
-            loadArena(arenaName);
+            Arena loaded = loadArena(arenaName);
+            if (loaded != null) {
+                arenas.add(loaded);
+            }
+        }
+
+        reportOverlappingRegions(arenas);
+    }
+
+    private void reportOverlappingRegions(List<Arena> arenas) {
+        // If we iterate the upper/lower triangular matrix of the cartesian
+        // product of the arena list, we avoid not only duplicate reports like
+        // "a vs. b and b vs. a", but also "self comparisons" (j = i + 1).
+        for (int i = 0; i < arenas.size(); i++) {
+            Arena a = arenas.get(i);
+            for (int j = i + 1; j < arenas.size(); j++) {
+                Arena b = arenas.get(j);
+                if (a.getRegion().intersects(b.getRegion())) {
+                    plugin.getLogger().warning(String.format(
+                        "Regions of arenas '%s' and '%s' overlap!",
+                        a.configName(),
+                        b.configName()
+                    ));
+                }
+            }
         }
     }
 

src/main/java/com/garbagemule/MobArena/region/ArenaRegion.java

@@ -242,6 +242,23 @@ public class ArenaRegion
                 (y + radius >= p1.getBlockY() && y - radius <= p2.getBlockY()));
     }
 
+    public boolean intersects(ArenaRegion other) {
+        if (lobbySetup && other.lobbySetup) {
+            if (intersects(l1, l2, other.l1, other.l2)) {
+                return true;
+            }
+        }
+        return intersects(p1, p2, other.p1, other.p2);
+    }
+
+    private boolean intersects(Location a1, Location a2, Location b1, Location b2) {
+        return (
+            b1.getBlockX() <= a2.getBlockX() && a1.getBlockX() <= b2.getBlockX() &&
+            b1.getBlockZ() <= a2.getBlockZ() && a1.getBlockZ() <= b2.getBlockZ() &&
+            b1.getBlockY() <= a2.getBlockY() && a1.getBlockY() <= b2.getBlockY()
+        );
+    }
+
     // Region expand
     public void expandUp(int amount) {
         int x = p2.getBlockX();