2 files changed, 142 insertions, 0 deletions
diff --git a/src/main/java/io/github/cottonmc/cotton/gui/widget/focus/FocusModel.java b/src/main/java/io/github/cottonmc/cotton/gui/widget/focus/FocusModel.java
index 615f686..c3a5204 100644
--- a/src/main/java/io/github/cottonmc/cotton/gui/widget/focus/FocusModel.java
+++ b/src/main/java/io/github/cottonmc/cotton/gui/widget/focus/FocusModel.java
@@ -11,6 +11,8 @@ import java.util.stream.Stream;
  *
  * @param <K> the focus key type
  * @since 7.0.0
+ * @see #simple(WWidget) FocusModel.simple()
+ * @see SimpleKeyedFocusModel
  */
 public interface FocusModel<K> {
 	/**
diff --git a/src/main/java/io/github/cottonmc/cotton/gui/widget/focus/SimpleKeyedFocusModel.java b/src/main/java/io/github/cottonmc/cotton/gui/widget/focus/SimpleKeyedFocusModel.java
new file mode 100644
index 0000000..491f4db
--- /dev/null
+++ b/src/main/java/io/github/cottonmc/cotton/gui/widget/focus/SimpleKeyedFocusModel.java
@@ -0,0 +1,140 @@
+package io.github.cottonmc.cotton.gui.widget.focus;
+
+import io.github.cottonmc.cotton.gui.widget.data.Rect2i;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+import java.util.stream.Stream;
+
+/**
+ * A {@link FocusModel} implementation that wraps a {@link List} of foci.
+ * New instances can be created with the constructor or the {@linkplain Builder builder}.
+ *
+ * @param <K> the focus key type
+ * @since 7.0.0
+ */
+public final class SimpleKeyedFocusModel<K> implements FocusModel<K> {
+	private final List<Focus<K>> foci;
+	private @Nullable K focused;
+
+	/**
+	 * Constructs a keyed focus model.
+	 *
+	 * @param foci the foci
+	 * @throws IllegalArgumentException if there are duplicate keys
+	 */
+	public SimpleKeyedFocusModel(List<Focus<K>> foci) {
+		this.foci = Objects.requireNonNull(foci, "foci");
+
+		Set<K> keys = new HashSet<>();
+		for (Focus<K> focus : foci) {
+			if (!keys.add(focus.key())) {
+				throw new IllegalArgumentException("Duplicate focus key: " + focus.key());
+			}
+		}
+	}
+
+	/**
+	 * {@return the focused key, or {@code null} if not available}
+	 */
+	public @Nullable K getFocusedKey() {
+		return focused;
+	}
+
+	@Override
+	public boolean isFocused(Focus<K> focus) {
+		return Objects.equals(focus.key(), focused);
+	}
+
+	@Override
+	public void setFocused(Focus<K> focus) {
+		focused = focus.key();
+	}
+
+	@Override
+	public Stream<Focus<K>> foci() {
+		return foci.stream();
+	}
+
+	/**
+	 * Creates a builder for {@code SimpleKeyedFocusModel}.
+	 *
+	 * @param <K> the focus key type
+	 * @return the builder
+	 */
+	@Contract("-> new")
+	public static <K> Builder<K> builder() {
+		return new Builder<>();
+	}
+
+	/**
+	 * A builder for {@code SimpleKeyedFocusModel}.
+	 * New instances can be obtained using {@link #builder()}.
+	 *
+	 * <p>This builder class is reusable &ndash; created instances are not
+	 * affected by data added to this builder afterwards.
+	 *
+	 * @param <K> the focus key type
+	 */
+	public static final class Builder<K> {
+		private final List<Focus<K>> foci = new ArrayList<>();
+
+		private Builder() {
+		}
+
+		/**
+		 * Adds a focus to this builder.
+		 *
+		 * @param focus the focus to add
+		 * @return this builder
+		 */
+		@Contract("null -> fail; _ -> this")
+		public Builder<K> add(Focus<K> focus) {
+			Objects.requireNonNull(focus, "Focus cannot be null");
+			foci.add(focus);
+			return this;
+		}
+
+		/**
+		 * Adds a focus to this builder.
+		 *
+		 * @param key  the focus key
+		 * @param area the focus area
+		 * @return this builder
+		 */
+		@Contract("_, null -> fail; _, _ -> this")
+		public Builder<K> add(K key, Rect2i area) {
+			Objects.requireNonNull(area, "Focus area cannot be null");
+			return add(new Focus<>(key, area));
+		}
+
+		/**
+		 * Adds foci from a collection to this builder.
+		 *
+		 * @param foci the foci to add
+		 * @return this builder
+		 */
+		@Contract("null -> fail; _ -> this")
+		public Builder<K> addAll(Collection<Focus<K>> foci) {
+			Objects.requireNonNull(foci, "Foci cannot be null");
+			this.foci.addAll(foci);
+			return this;
+		}
+
+		/**
+		 * Builds a new {@code SimpleKeyedFocusModel} from the data in this builder.
+		 *
+		 * @return the created model
+		 */
+		@Contract("-> new")
+		public SimpleKeyedFocusModel<K> build() {
+			return new SimpleKeyedFocusModel<>(List.copyOf(foci));
+		}
+	}
+}