// Copyright 2014 The Bazel Authors. All rights reserved.
//
// 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.google.devtools.build.lib.analysis;

import com.google.devtools.build.lib.packages.ClassObjectConstructor;
import com.google.devtools.build.lib.packages.SkylarkClassObject;
import com.google.devtools.build.lib.packages.SkylarkProviderIdentifier;
import javax.annotation.Nullable;
import javax.annotation.concurrent.Immutable;

/**
 * Provides a mapping between an identifier for transitive information and its instance.
 * (between provider identifier and provider instance)
 *
 * We have three kinds of provider identifiers:
 * <ul>
 *   <li>Declared providers. They are exposed to Skylark and identified by
 *   {@link ClassObjectConstructor.Key}. Provider instances are {@link SkylarkClassObject}s.</li>
 *   <li>Native providers. They are identified by their {@link Class} and their instances
 *   are instances of that class. They should implement {@link TransitiveInfoProvider} marker
 *   interface.
 *   </li>
 *   <li>Legacy Skylark providers (deprecated). They are identified by simple strings,
 *   and their instances are more-less random objects.</li>
 * </ul>
 */
@Immutable
public interface TransitiveInfoProviderMap {
  /** Returns the instance for the provided providerClass, or {@code null}  if not present. */
  @Nullable
  <P extends TransitiveInfoProvider> P getProvider(Class<P> providerClass);

  /**
   * Returns the instance of declared provider with the given {@code key},
   * or {@code null} if not present.
   */
  @Nullable
  SkylarkClassObject getProvider(ClassObjectConstructor.Key key);

  /**
   * Returns the instance of a legacy Skylark  with the given name, or {@code null} if not present.
   *
   * todo(dslomov,skylark): remove this as part of legacy provider removal.
   */
  @Nullable
  Object getProvider(String legacyKey);

  /**
   * Helper method to access SKylark provider with a give {@code id} and validate its type.
   */
  @Nullable
  default <T> T getProvider(
      SkylarkProviderIdentifier id, Class<T> result) {
    return result.cast(
        id.isLegacy() ? this.getProvider(id.getLegacyId()) : this.getProvider(id.getKey())
    );
  }

  /**
   * Returns a count of providers.
   *
   * Upper bound for {@code index} in {@link #getProviderKeyAt(int index)}
   * and {@link #getProviderInstanceAt(int index)} }.
   *
   * Low-level method, use with care.
   */
  int getProviderCount();

  /**
   * Return value is one of:
   * <ul>
   *   <li>{@code Class<? extends TransitiveInfoProvider>}</li>
   *   <li>String</li>
   *   <li>{@link ClassObjectConstructor.Key}</li>
   * </ul>
   *
   * Low-level method, use with care.
   */
  Object getProviderKeyAt(int index);

  Object getProviderInstanceAt(int index);
}