flink-table/flink-table-common/src/main/java/org/apache/flink/table/types/extraction/FunctionTemplate.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.table.types.extraction;

import org.apache.flink.annotation.Internal;
import org.apache.flink.table.annotation.DataTypeHint;
import org.apache.flink.table.annotation.FunctionHint;
import org.apache.flink.table.catalog.DataTypeFactory;

import javax.annotation.Nullable;

import java.util.Arrays;
import java.util.Objects;
import java.util.function.Function;
import java.util.stream.Collectors;

import static org.apache.flink.table.types.extraction.ExtractionUtils.extractionError;

/**
 * Internal representation of a {@link FunctionHint}.
 *
 * <p>All parameters of a template are optional. An empty annotation results in a template where all
 * members are {@code null}.
 */
@Internal
final class FunctionTemplate {

	private static final FunctionHint DEFAULT_ANNOTATION = getDefaultAnnotation();

	private final @Nullable FunctionSignatureTemplate signatureTemplate;

	private final @Nullable FunctionResultTemplate accumulatorTemplate;

	private final @Nullable FunctionResultTemplate outputTemplate;

	private FunctionTemplate(
			@Nullable FunctionSignatureTemplate signatureTemplate,
			@Nullable FunctionResultTemplate accumulatorTemplate,
			@Nullable FunctionResultTemplate outputTemplate) {
		this.signatureTemplate = signatureTemplate;
		this.accumulatorTemplate = accumulatorTemplate;
		this.outputTemplate = outputTemplate;
	}

	/**
	 * Creates an instance using the given {@link FunctionHint}. It resolves explicitly defined data
	 * types.
	 */
	static FunctionTemplate fromAnnotation(DataTypeFactory typeFactory, FunctionHint hint) {
		return new FunctionTemplate(
			createSignatureTemplate(
				typeFactory,
				defaultAsNull(hint, FunctionHint::input),
				defaultAsNull(hint, FunctionHint::argumentNames),
				hint.isVarArgs()),
			createResultTemplate(typeFactory, defaultAsNull(hint, FunctionHint::accumulator)),
			createResultTemplate(typeFactory, defaultAsNull(hint, FunctionHint::output))
		);
	}

	/**
	 * Creates an instance of {@link FunctionResultTemplate} from a {@link DataTypeHint}.
	 */
	static @Nullable FunctionResultTemplate createResultTemplate(
			DataTypeFactory typeFactory,
			@Nullable DataTypeHint hint) {
		if (hint == null) {
			return null;
		}
		final DataTypeTemplate template;
		try {
			template = DataTypeTemplate.fromAnnotation(typeFactory, hint);
		} catch (Throwable t) {
			throw extractionError(t, "Error in data type hint annotation.");
		}
		if (template.dataType != null) {
			return FunctionResultTemplate.of(template.dataType);
		}
		throw extractionError(
			"Data type hint does not specify a data type for use as function result.");
	}

	@Nullable FunctionSignatureTemplate getSignatureTemplate() {
		return signatureTemplate;
	}

	@Nullable FunctionResultTemplate getAccumulatorTemplate() {
		return accumulatorTemplate;
	}

	@Nullable FunctionResultTemplate getOutputTemplate() {
		return outputTemplate;
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		FunctionTemplate template = (FunctionTemplate) o;
		return Objects.equals(signatureTemplate, template.signatureTemplate) &&
			Objects.equals(accumulatorTemplate, template.accumulatorTemplate) &&
			Objects.equals(outputTemplate, template.outputTemplate);
	}

	@Override
	public int hashCode() {
		return Objects.hash(signatureTemplate, accumulatorTemplate, outputTemplate);
	}

	// --------------------------------------------------------------------------------------------

	@FunctionHint
	private static class DefaultAnnotationHelper {
		// no implementation
	}

	private static FunctionHint getDefaultAnnotation() {
		return DefaultAnnotationHelper.class.getAnnotation(FunctionHint.class);
	}

	private static <T> T defaultAsNull(FunctionHint hint, Function<FunctionHint, T> accessor) {
		final T defaultValue = accessor.apply(DEFAULT_ANNOTATION);
		final T actualValue = accessor.apply(hint);
		if (Objects.deepEquals(defaultValue, actualValue)) {
			return null;
		}
		return actualValue;
	}

	private static @Nullable FunctionSignatureTemplate createSignatureTemplate(
			DataTypeFactory typeFactory,
			@Nullable DataTypeHint[] input,
			@Nullable String[] argumentNames,
			boolean isVarArg) {
		if (input == null) {
			return null;
		}
		return FunctionSignatureTemplate.of(
			Arrays.stream(input)
				.map(dataTypeHint -> createArgumentTemplate(typeFactory, dataTypeHint))
				.collect(Collectors.toList()),
			isVarArg,
			argumentNames);
	}

	private static FunctionArgumentTemplate createArgumentTemplate(
			DataTypeFactory typeFactory,
			DataTypeHint hint) {
		final DataTypeTemplate template = DataTypeTemplate.fromAnnotation(typeFactory, hint);
		if (template.dataType != null) {
			return FunctionArgumentTemplate.of(template.dataType);
		} else if (template.inputGroup != null) {
			return FunctionArgumentTemplate.of(template.inputGroup);
		}
		throw extractionError(
			"Data type hint does neither specify a data type nor input group for use as function argument.");
	}
}