Call player spectator target events and improve implementation

Use a proper teleport for teleporting to entities in different
worlds.

Implementation improvements authored by Spottedleaf <Spottedleaf@users.noreply.github.com>
Validate that the target entity is valid and deny spectate
requests from frozen players.

Also, make sure the entity is spawned to the client before
sending the camera packet. If the entity isn't spawned clientside
when it receives the camera packet, then the client will not
spectate the target entity.

Co-authored-by: Spottedleaf <Spottedleaf@users.noreply.github.com>

paper-server/patches/sources/net/minecraft/server/level/ServerPlayer.java.patch

@@ -114,7 +114,7 @@
      @Nullable
      private Vec3 startingToFallPosition;
      @Nullable
-@@ -258,7 +293,31 @@
+@@ -258,6 +293,30 @@
      private final CommandSource commandSource;
      private int containerCounter;
      public boolean wonGame;
@@ -123,7 +123,7 @@
 +    public boolean queueHealthUpdatePacket;
 +    public net.minecraft.network.protocol.game.ClientboundSetHealthPacket queuedHealthUpdatePacket;
 +    // Paper end - cancellable death event
- 
++
 +    // CraftBukkit start
 +    public CraftPlayer.TransferCookieConnection transferCookieConnection;
 +    public String displayName;
@@ -142,10 +142,9 @@
 +    // CraftBukkit end
 +    public boolean isRealPlayer; // Paper
 +    public com.destroystokyo.paper.event.entity.PlayerNaturallySpawnCreaturesEvent playerNaturallySpawnedEvent; // Paper - PlayerNaturallySpawnCreaturesEvent
-+
+ 
      public ServerPlayer(MinecraftServer server, ServerLevel world, GameProfile profile, ClientInformation clientOptions) {
          super(world, world.getSharedSpawnPos(), world.getSharedSpawnAngle(), profile);
-         this.chatVisibility = ChatVisiblity.FULL;
 @@ -266,7 +325,7 @@
          this.canChatColor = true;
          this.lastActionTime = Util.getMillis();
@@ -380,12 +379,10 @@
                              Logger logger = ServerPlayer.LOGGER;
  
                              Objects.requireNonNull(logger);
-@@ -684,7 +833,30 @@
-             }
-         }
+@@ -686,6 +835,29 @@
+ 
+     }
  
-+    }
-+
 +    // CraftBukkit start - World fallback code, either respawn location or global spawn
 +    public void spawnIn(Level world) {
 +        this.setLevel(world);
@@ -406,11 +403,12 @@
 +            this.setPos(position);
 +        }
 +        this.gameMode.setLevel((ServerLevel) world);
-     }
++    }
 +    // CraftBukkit end
- 
++
      public void setExperiencePoints(int points) {
          float f = (float) this.getXpNeededForNextLevel();
+         float f1 = (f - 1.0F) / f;
 @@ -744,6 +916,11 @@
  
      @Override
@@ -448,19 +446,19 @@
                  this.lastSentHealth = this.getHealth();
                  this.lastSentFood = this.foodData.getFoodLevel();
                  this.lastFoodSaturationZero = this.foodData.getSaturationLevel() == 0.0F;
-@@ -851,6 +1032,12 @@
+@@ -850,6 +1031,12 @@
+                 this.lastRecordedExperience = this.totalExperience;
                  this.updateScoreForCriteria(ObjectiveCriteria.EXPERIENCE, Mth.ceil((float) this.lastRecordedExperience));
              }
- 
++
 +            // CraftBukkit start - Force max health updates
 +            if (this.maxHealthCache != this.getMaxHealth()) {
 +                this.getBukkitEntity().updateScaledHealth();
 +            }
 +            // CraftBukkit end
-+
+ 
              if (this.experienceLevel != this.lastRecordedLevel) {
                  this.lastRecordedLevel = this.experienceLevel;
-                 this.updateScoreForCriteria(ObjectiveCriteria.LEVEL, Mth.ceil((float) this.lastRecordedLevel));
 @@ -865,6 +1052,20 @@
                  CriteriaTriggers.LOCATION.trigger(this);
              }
@@ -545,12 +543,12 @@
 +        }
 +        this.gameEvent(GameEvent.ENTITY_DIE); // moved from the top of this method
 +        // Paper end
- 
++
 +        // SPIGOT-943 - only call if they have an inventory open
 +        if (this.containerMenu != this.inventoryMenu) {
 +            this.closeContainer(org.bukkit.event.inventory.InventoryCloseEvent.Reason.DEATH); // Paper - Inventory close reason
 +        }
-+
+ 
 +        net.kyori.adventure.text.Component deathMessage = event.deathMessage() != null ? event.deathMessage() : net.kyori.adventure.text.Component.empty(); // Paper - Adventure
 +
 +        if (deathMessage != null && deathMessage != net.kyori.adventure.text.Component.empty() && flag) { // Paper - Adventure // TODO: allow plugins to override?
@@ -1291,7 +1289,27 @@
          this.requestedViewDistance = clientOptions.viewDistance();
          this.chatVisibility = clientOptions.chatVisibility();
          this.canChatColor = clientOptions.chatColors();
-@@ -1962,7 +2426,7 @@
+@@ -1957,12 +2421,27 @@
+ 
+         this.camera = (Entity) (entity == null ? this : entity);
+         if (entity1 != this.camera) {
++            // Paper start - Add PlayerStartSpectatingEntityEvent and PlayerStopSpectatingEntity
++            if (this.camera == this) {
++                com.destroystokyo.paper.event.player.PlayerStopSpectatingEntityEvent playerStopSpectatingEntityEvent = new com.destroystokyo.paper.event.player.PlayerStopSpectatingEntityEvent(this.getBukkitEntity(), entity1.getBukkitEntity());
++                if (!playerStopSpectatingEntityEvent.callEvent()) {
++                    this.camera = entity1; // rollback camera entity again
++                    return;
++                }
++            } else {
++                com.destroystokyo.paper.event.player.PlayerStartSpectatingEntityEvent playerStartSpectatingEntityEvent = new com.destroystokyo.paper.event.player.PlayerStartSpectatingEntityEvent(this.getBukkitEntity(), entity1.getBukkitEntity(), entity.getBukkitEntity());
++                if (!playerStartSpectatingEntityEvent.callEvent()) {
++                    this.camera = entity1; // rollback camera entity again
++                    return;
++                }
++            }
++            // Paper end - Add PlayerStartSpectatingEntityEvent and PlayerStopSpectatingEntity
+             Level world = this.camera.level();
+ 
              if (world instanceof ServerLevel) {
                  ServerLevel worldserver = (ServerLevel) world;
  
@@ -1300,7 +1318,7 @@
              }
  
              if (entity != null) {
-@@ -1999,11 +2463,11 @@
+@@ -1999,11 +2478,11 @@
  
      @Nullable
      public Component getTabListDisplayName() {
@@ -1314,7 +1332,7 @@
      }
  
      @Override
-@@ -2046,17 +2510,43 @@
+@@ -2046,17 +2525,43 @@
      }
  
      public void setRespawnPosition(ResourceKey<Level> dimension, @Nullable BlockPos pos, float angle, boolean forced, boolean sendMessage) {
@@ -1365,7 +1383,7 @@
          } else {
              this.respawnPosition = null;
              this.respawnDimension = Level.OVERWORLD;
-@@ -2088,18 +2578,44 @@
+@@ -2088,18 +2593,44 @@
      }
  
      @Override
@@ -1414,7 +1432,7 @@
                  }
  
                  this.awardStat(Stats.DROP);
-@@ -2375,16 +2891,160 @@
+@@ -2375,16 +2906,160 @@
          return TicketType.ENDER_PEARL.timeout();
      }
  
@@ -1447,8 +1465,8 @@
 +        } else {
 +            // Adds timeOffset to the beginning of this day.
 +            return this.level().getDayTime() - (this.level().getDayTime() % 24000) + this.timeOffset;
-         }
-     }
++        }
++    }
 +
 +    public WeatherType weather = null;
 +
@@ -1469,8 +1487,8 @@
 +            this.connection.send(new ClientboundGameEventPacket(ClientboundGameEventPacket.STOP_RAINING, 0));
 +        } else {
 +            this.connection.send(new ClientboundGameEventPacket(ClientboundGameEventPacket.START_RAINING, 0));
-+        }
-+    }
+         }
+     }
 +
 +    private float pluginRainPosition;
 +    private float pluginRainPositionPrevious;