From ff504c21ef3f3f9147da1a0f8d14271058523129 Mon Sep 17 00:00:00 2001
From: Hugo Manrique <contact@hugmanrique.me>
Date: Sat, 5 Jun 2021 18:31:00 +0200
Subject: [PATCH] Suggestions provider

---
 .../proxy/command/SuggestionsProvider.java    | 120 ++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 proxy/src/main/java/com/velocitypowered/proxy/command/SuggestionsProvider.java

diff --git a/proxy/src/main/java/com/velocitypowered/proxy/command/SuggestionsProvider.java b/proxy/src/main/java/com/velocitypowered/proxy/command/SuggestionsProvider.java
new file mode 100644
index 000000000..7a1ea903b
--- /dev/null
+++ b/proxy/src/main/java/com/velocitypowered/proxy/command/SuggestionsProvider.java
@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2018 Velocity Contributors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package com.velocitypowered.proxy.command;
+
+import com.google.common.base.Preconditions;
+import com.mojang.brigadier.CommandDispatcher;
+import com.mojang.brigadier.ParseResults;
+import com.mojang.brigadier.StringReader;
+import com.mojang.brigadier.context.CommandContextBuilder;
+import com.mojang.brigadier.context.StringRange;
+import com.mojang.brigadier.suggestion.Suggestions;
+import com.mojang.brigadier.tree.CommandNode;
+import com.mojang.brigadier.tree.LiteralCommandNode;
+import com.mojang.brigadier.tree.RootCommandNode;
+import java.util.Collection;
+import java.util.concurrent.CompletableFuture;
+
+/**
+ * Provides suggestions for a given command input.
+ *
+ * <p>Similar to {@link CommandDispatcher#getCompletionSuggestions(ParseResults)}, except it
+ * avoids fully parsing the given input and performs exactly one requirement predicate check
+ * per considered node.
+ *
+ * @param <S> the type of the command source
+ */
+final class SuggestionsProvider<S> {
+
+  private final CommandDispatcher<S> dispatcher;
+
+  SuggestionsProvider(final CommandDispatcher<S> dispatcher) {
+    this.dispatcher = Preconditions.checkNotNull(dispatcher, "dispatcher");
+  }
+
+  /**
+   * Provides suggestions for the given input and source.
+   *
+   * @param input the partial input
+   * @param source the command source invoking the command
+   * @return a future that completes with the suggestions
+   */
+  public CompletableFuture<Suggestions> provideSuggestions(final String input, final S source) {
+    final CommandContextBuilder<S> context = new CommandContextBuilder<>(
+            this.dispatcher, source, this.dispatcher.getRoot(), 0);
+    return this.provideSuggestions(new StringReader(input), context);
+  }
+
+  /**
+   * Provides suggestions for the given input and context.
+   *
+   * @param reader the input reader
+   * @param context an empty context
+   * @return a future that completes with the suggestions
+   */
+  private CompletableFuture<Suggestions> provideSuggestions(
+          final StringReader reader, final CommandContextBuilder<S> context) {
+    final StringRange aliasRange = this.consumeAlias(reader);
+    final String alias = aliasRange.get(reader); // TODO #toLowerCase and test
+    final LiteralCommandNode<S> literal =
+            (LiteralCommandNode<S>) context.getRootNode().getChild(alias);
+
+    final boolean hasArguments = reader.canRead();
+    if (hasArguments) {
+      if (literal == null) {
+        // Input has arguments for non-registered alias
+        return Suggestions.empty();
+      }
+      context.withNode(literal, aliasRange);
+      reader.skip(); // separator
+      // TODO Provide arguments suggestions
+    } else {
+      // TODO Provide alias suggestions
+    }
+  }
+
+  private StringRange consumeAlias(final StringReader reader) {
+    final int firstSep = reader.getString().indexOf(
+            CommandDispatcher.ARGUMENT_SEPARATOR_CHAR, reader.getCursor());
+    final StringRange range = StringRange.between(
+            reader.getCursor(), firstSep == -1 ? reader.getTotalLength() : firstSep);
+    reader.setCursor(range.getEnd());
+    return range;
+  }
+
+  /**
+   * Returns alias suggestions for the given input.
+   *
+   * @param reader the input reader
+   * @param contextSoFar an empty context
+   * @return a future that completes with the suggestions
+   */
+  private CompletableFuture<Suggestions> provideAliasSuggestions(
+          final StringReader reader, final CommandContextBuilder<S> contextSoFar) {
+    final S source = contextSoFar.getSource();
+    final String input = reader.getRead();
+
+    final Collection<CommandNode<S>> aliases = contextSoFar.getRootNode().getChildren();
+    final CompletableFuture<Suggestions>[] futures = new CompletableFuture[aliases.size()];
+
+  }
+
+  /*private RootCommandNode<S> getRoot() {
+    return this.dispatcher.getRoot();
+  }*/
+}