/*
 * Licensed 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 com.facebook.presto.operator.scalar;

import com.facebook.presto.common.function.OperatorType;
import com.facebook.presto.common.type.Type;
import com.facebook.presto.metadata.BoundVariables;
import com.facebook.presto.metadata.FunctionAndTypeManager;
import com.facebook.presto.metadata.SqlOperator;
import com.google.common.collect.ImmutableList;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;

import static com.facebook.presto.common.type.TypeSignature.parseTypeSignature;
import static com.facebook.presto.operator.scalar.ScalarFunctionImplementationChoice.ArgumentProperty.valueTypeArgumentProperty;
import static com.facebook.presto.operator.scalar.ScalarFunctionImplementationChoice.NullConvention.RETURN_NULL_ON_NULL;
import static com.facebook.presto.spi.function.Signature.typeVariable;
import static com.google.common.base.Preconditions.checkArgument;

public class IdentityCast
        extends SqlOperator
{
    public static final IdentityCast IDENTITY_CAST = new IdentityCast();

    protected IdentityCast()
    {
        super(OperatorType.CAST,
                ImmutableList.of(typeVariable("T")),
                ImmutableList.of(),
                parseTypeSignature("T"),
                ImmutableList.of(parseTypeSignature("T")));
    }

    @Override
    public BuiltInScalarFunctionImplementation specialize(BoundVariables boundVariables, int arity, FunctionAndTypeManager functionAndTypeManager)
    {
        checkArgument(boundVariables.getTypeVariables().size() == 1, "Expected only one type");
        Type type = boundVariables.getTypeVariable("T");
        MethodHandle identity = MethodHandles.identity(type.getJavaType());
        return new BuiltInScalarFunctionImplementation(
                false,
                ImmutableList.of(valueTypeArgumentProperty(RETURN_NULL_ON_NULL)),
                identity);
    }
}
