Add h3_cell_to_latlng

src/main/java/com/foursquare/presto/h3/CellToLatLngFunction.java

@@ -0,0 +1,37 @@
+package com.foursquare.presto.h3;
+
+import static com.facebook.presto.common.type.DoubleType.DOUBLE;
+
+import com.facebook.presto.common.block.Block;
+import com.facebook.presto.common.block.BlockBuilder;
+import com.facebook.presto.common.type.StandardTypes;
+import com.facebook.presto.spi.function.Description;
+import com.facebook.presto.spi.function.ScalarFunction;
+import com.facebook.presto.spi.function.SqlNullable;
+import com.facebook.presto.spi.function.SqlType;
+import com.uber.h3core.util.LatLng;
+
+/**
+ * Wraps {@link com.uber.h3core.H3Core#cellToLatLng(long)}. Produces a row of latitude, longitude
+ * degrees.
+ */
+public final class CellToLatLngFunction {
+  @ScalarFunction(value = "h3_cell_to_latlng")
+  @Description("Convert H3 index to degrees lat/lng")
+  @SqlNullable
+  @SqlType("ARRAY(DOUBLE)")
+  public static Block cellToLatLng(@SqlType(StandardTypes.BIGINT) long h3) {
+    try {
+      LatLng latLng = H3Plugin.h3.cellToLatLng(h3);
+      // TODO: It would be nice to return this as a ROW(lat DOUBLE, lng DOUBLE)
+      // but that is blocked on https://github.com/prestodb/presto/issues/18494
+      // (determining how to build the Block to return)
+      BlockBuilder blockBuilder = DOUBLE.createFixedSizeBlockBuilder(2);
+      DOUBLE.writeDouble(blockBuilder, latLng.lat);
+      DOUBLE.writeDouble(blockBuilder, latLng.lng);
+      return blockBuilder.build();
+    } catch (Exception e) {
+      return null;
+    }
+  }
+}

src/main/java/com/foursquare/presto/h3/H3Plugin.java

@@ -33,7 +33,7 @@ static int longToInt(long l) {
   @Override
   public Set<Class<?>> getFunctions() {
     return ImmutableSet.<Class<?>>builder()
-        .add(LatLngToCellFunction.class, CellToParentFunction.class)
+        .add(LatLngToCellFunction.class, CellToLatLngFunction.class, CellToParentFunction.class)
         .build();
   }
 }

src/test/java/com/foursquare/presto/h3/CellToLatLngFunctionTest.java

@@ -0,0 +1,34 @@
+package com.foursquare.presto.h3;
+
+import static com.foursquare.presto.h3.H3PluginTest.assertQueryResults;
+import static com.foursquare.presto.h3.H3PluginTest.createQueryRunner;
+
+import com.facebook.presto.testing.QueryRunner;
+import com.google.common.collect.ImmutableList;
+import java.util.Collections;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInstance;
+import org.junit.jupiter.api.TestInstance.Lifecycle;
+
+@TestInstance(Lifecycle.PER_CLASS)
+public class CellToLatLngFunctionTest {
+  @Test
+  public void testCellToLatLng() {
+    try (QueryRunner queryRunner = createQueryRunner()) {
+      assertQueryResults(
+          queryRunner,
+          "SELECT h3_cell_to_latlng(578536630256664575)",
+          ImmutableList.of(
+              ImmutableList.of(ImmutableList.of(2.300882111626747, -5.245390296777327))));
+
+      assertQueryResults(
+          queryRunner,
+          "SELECT h3_cell_to_latlng(null)",
+          ImmutableList.of(Collections.singletonList(null)));
+      assertQueryResults(
+          queryRunner,
+          "SELECT h3_cell_to_latlng(-1)",
+          ImmutableList.of(Collections.singletonList(null)));
+    }
+  }
+}