G2-1609 Move reduce strategy to alexandria

ax-adt/src/main/java/com/g2forge/alexandria/adt/ReduceStrategy.java

@@ -0,0 +1,66 @@
+package com.g2forge.alexandria.adt;
+
+import java.util.Objects;
+
+import com.g2forge.alexandria.java.core.error.UnreachableCodeError;
+import com.g2forge.alexandria.java.function.IConsumer1;
+import com.g2forge.alexandria.java.function.IFunction1;
+import com.g2forge.alexandria.java.function.IFunction2;
+
+/**
+ * Strategies for reducing fields of POJOs.
+ */
+public enum ReduceStrategy {
+	NullIsNone {
+		@Override
+		public <T, V> void reduce(T t0, T t1, IFunction1<? super T, ? extends V> getter, IConsumer1<? super V> setter, IFunction2<? super V, ? super V, ? extends V> merge) {
+			final V v0 = getter.apply(t0);
+			final V v1 = getter.apply(t1);
+			switch (computeIndex(v0, v1)) {
+				case 0:
+					break;
+				case 1:
+					setter.accept(v0);
+					break;
+				case 2:
+					setter.accept(v1);
+					break;
+				case 3:
+					if (merge != null) {
+						final V merged = merge.apply(v0, v1);
+						setter.accept(merged);
+						break;
+					} else if (Objects.equals(v0, v1)) {
+						setter.accept(v0);
+						break;
+					} else throw new IllegalArgumentException(String.format("Cannot merge non-null values (%1$s and %2$s), as no merging function as supplied", v0, v1));
+				default:
+					throw new UnreachableCodeError();
+			}
+		}
+	},
+	NullIsNoneSkip0 {
+		@Override
+		public <T, V> void reduce(T t0, T t1, IFunction1<? super T, ? extends V> getter, IConsumer1<? super V> setter, IFunction2<? super V, ? super V, ? extends V> merge) {
+			final V v0 = getter.apply(t0);
+			final V v1 = getter.apply(t1);
+			switch (computeIndex(v0, v1)) {
+				case 0:
+				case 1:
+					break;
+				case 2:
+				case 3:
+					setter.accept(v1);
+					break;
+				default:
+					throw new UnreachableCodeError();
+			}
+		}
+	};
+
+	protected <V> int computeIndex(final V v0, final V v1) {
+		return ((v1 != null) ? 2 : 0) | ((v0 != null) ? 1 : 0);
+	}
+
+	public abstract <T, V> void reduce(T t0, T t1, IFunction1<? super T, ? extends V> getter, IConsumer1<? super V> setter, IFunction2<? super V, ? super V, ? extends V> merge);
+}

ax-adt/src/test/java/com/g2forge/alexandria/adt/TestReduceStrategy.java

@@ -0,0 +1,47 @@
+package com.g2forge.alexandria.adt;
+
+import org.junit.Test;
+
+import com.g2forge.alexandria.test.HAssert;
+
+import lombok.Builder;
+import lombok.Data;
+import lombok.RequiredArgsConstructor;
+
+public class TestReduceStrategy {
+	@Data
+	@Builder(toBuilder = true)
+	@RequiredArgsConstructor
+	public static class Record {
+		protected final String field;
+	}
+
+	@Test
+	public void none() {
+		final Record.RecordBuilder builder = Record.builder();
+		ReduceStrategy.NullIsNone.reduce(new Record(null), new Record(null), Record::getField, builder::field, null);
+		HAssert.assertNull(builder.build().getField());
+	}
+
+	@Test
+	public void a() {
+		final Record.RecordBuilder builder = Record.builder();
+		ReduceStrategy.NullIsNone.reduce(new Record("A"), new Record(null), Record::getField, builder::field, null);
+		HAssert.assertEquals("A", builder.build().getField());
+	}
+
+	@Test
+	public void b() {
+		final Record.RecordBuilder builder = Record.builder();
+		ReduceStrategy.NullIsNone.reduce(new Record(null), new Record("B"), Record::getField, builder::field, null);
+		HAssert.assertEquals("B", builder.build().getField());
+	}
+
+	@Test
+	public void merge() {
+		final Record.RecordBuilder builder = Record.builder();
+		final Record a = new Record("A");
+		final Record b = new Record("B");
+		HAssert.assertThrows(IllegalArgumentException.class, () -> ReduceStrategy.NullIsNone.reduce(a, b, Record::getField, builder::field, null));
+	}
+}