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// Copyright 2023 Google LLC
//
// 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
//
//      https://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 dev.cel.common.values;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.errorprone.annotations.Immutable;
import java.util.Map;
import java.util.Optional;

/** CelValueProvider is an interface for constructing new struct values. */
@Immutable
public interface CelValueProvider {

  /**
   * Constructs a new struct value.
   *
   * Note that the return type is defined as CelValue rather than StructValue to account for
   * special cases such as wrappers where its primitive is returned.
   */
  Optional newValue(String structType, Map fields);

  /**
   * The {@link CombinedCelValueProvider} takes one or more {@link CelValueProvider} instances and
   * attempts to create a {@link CelValue} instance for a given struct type name by calling each
   * value provider in the order that they are provided to the constructor.
   */
  @Immutable
  final class CombinedCelValueProvider implements CelValueProvider {
    private final ImmutableList celValueProviders;

    public CombinedCelValueProvider(CelValueProvider first, CelValueProvider second) {
      Preconditions.checkNotNull(first);
      Preconditions.checkNotNull(second);
      celValueProviders = ImmutableList.of(first, second);
    }

    @Override
    public Optional newValue(String structType, Map fields) {
      for (CelValueProvider provider : celValueProviders) {
        Optional newValue = provider.newValue(structType, fields);
        if (newValue.isPresent()) {
          return newValue;
        }
      }

      return Optional.empty();
    }
  }
}