/*
 * Copyright (c) 2015 Spotify AB
 *
 * 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.spotify.dns;

import static com.google.common.base.Throwables.throwIfUnchecked;
import static java.util.Objects.requireNonNull;

import com.spotify.dns.statistics.DnsReporter;
import com.spotify.dns.statistics.DnsTimingContext;

import java.util.List;
import java.util.concurrent.CompletionStage;

/**
 * Tracks metrics for DnsSrvResolver calls.
 */
class MeteredDnsSrvResolver implements DnsSrvResolver {
  private final DnsSrvResolver delegate;
  private final DnsReporter reporter;

  MeteredDnsSrvResolver(DnsSrvResolver delegate, DnsReporter reporter) {
    this.delegate = requireNonNull(delegate, "delegate");
    this.reporter = requireNonNull(reporter, "reporter");
  }

    @Override
    public List<LookupResult> resolve(String fqdn) {
        // Only catch and report RuntimeException to avoid Error's since that would
        // most likely only aggravate any condition that causes them to be thrown.

        final DnsTimingContext resolveTimer = reporter.resolveTimer();

        final List<LookupResult> result;

        try {
            result = delegate.resolve(fqdn);
        } catch (RuntimeException error) {
            reporter.reportFailure(error);
            throw error;
        } finally {
            resolveTimer.stop();
        }

        if (result.isEmpty()) {
            reporter.reportEmpty();
        }

        return result;
    }

  @Override
  public CompletionStage<List<LookupResult>> resolveAsync(String fqdn) {
    // Only catch and report RuntimeException to avoid Error's since that would
    // most likely only aggravate any condition that causes them to be thrown.

    final DnsTimingContext resolveTimer = reporter.resolveTimer();

    return delegate
        .resolveAsync(fqdn)
        .handle(
            (result, error) -> {
              resolveTimer.stop();
              if (error == null) {
                if (result.isEmpty()) {
                  reporter.reportEmpty();
                }

                return result;
              } else {
                reporter.reportFailure(error);
                throwIfUnchecked(error);
                throw new RuntimeException(error);
              }
            });
  }
}