Add Player Chat Completion Suggestions (#6419)

* Add player chat completion suggestions

* Add method exists check

* Syntax adjustment and remove DataFlowIssue suppression

* Docs improvements

* Requested changes

* Update src/main/java/ch/njol/skript/expressions/ExprPlayerChatCompletions.java

Co-authored-by: sovdee <10354869+sovdeeth@users.noreply.github.com>

* Remove license header (#6684)

* Java 17 ready

---------

Co-authored-by: sovdee <10354869+sovdeeth@users.noreply.github.com>
Co-authored-by: Moderocky <admin@moderocky.com>

src/main/java/ch/njol/skript/expressions/ExprPlayerChatCompletions.java

@@ -0,0 +1,93 @@
+package ch.njol.skript.expressions;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.bukkit.entity.Player;
+import org.bukkit.event.Event;
+import org.jetbrains.annotations.Nullable;
+
+import ch.njol.skript.Skript;
+import ch.njol.skript.classes.Changer.ChangeMode;
+import ch.njol.skript.doc.Description;
+import ch.njol.skript.doc.Examples;
+import ch.njol.skript.doc.Name;
+import ch.njol.skript.doc.RequiredPlugins;
+import ch.njol.skript.doc.Since;
+import ch.njol.skript.expressions.base.SimplePropertyExpression;
+import ch.njol.util.coll.CollectionUtils;
+
+@Name("Player Chat Completions")
+@Description({
+	"The custom chat completion suggestions. You can add, set, remove, and clear them. Removing the names of online players with this expression is ineffective.",
+	"This expression will not return anything due to Bukkit limitations."
+})
+@Examples({
+	"add \"Skript\" and \"Njol\" to chat completions of all players",
+	"remove \"text\" from {_p}'s chat completions",
+	"clear player's chat completions"
+})
+@RequiredPlugins("Spigot 1.19+")
+@Since("INSERT VERSION")
+public class ExprPlayerChatCompletions extends SimplePropertyExpression<Player, String> {
+
+	static {
+		if (Skript.methodExists(Player.class, "addCustomChatCompletions", Collection.class))
+			register(ExprPlayerChatCompletions.class, String.class, "[custom] chat completion[s]", "players");
+	}
+
+	@Override
+	public @Nullable String convert(Player player) {
+		return null; // Due to Bukkit limitations
+	}
+
+	@Override
+	public @Nullable Class<?>[] acceptChange(ChangeMode mode) {
+        return switch (mode) {
+            case ADD, SET, REMOVE, DELETE, RESET -> CollectionUtils.array(String[].class);
+            default -> null;
+        };
+	}
+
+	@Override
+	public void change(Event event, Object @Nullable [] delta, ChangeMode mode) {
+		Player[] players = getExpr().getArray(event);
+		if (players.length == 0)
+			return;
+		List<String> completions = new ArrayList<>();
+		if (delta != null && (mode == ChangeMode.ADD || mode == ChangeMode.REMOVE || mode == ChangeMode.SET)) {
+			completions = Arrays.stream(delta)
+				.filter(String.class::isInstance)
+				.map(String.class::cast)
+				.collect(Collectors.toList());
+		}
+		switch (mode) {
+			case DELETE, RESET, SET -> {
+				for (Player player : players)
+					player.setCustomChatCompletions(completions);
+			}
+            case ADD -> {
+				for (Player player : players)
+					player.addCustomChatCompletions(completions);
+			}
+            case REMOVE -> {
+				for (Player player : players)
+					player.removeCustomChatCompletions(completions);
+			}
+        }
+	}
+
+	@Override
+	public Class<? extends String> getReturnType() {
+		return String.class;
+	}
+
+	@Override
+	protected String getPropertyName() {
+		return "custom chat completions";
+	}
+
+}