// Copyright 2016 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.bazel.repository.downloader;

import com.google.common.base.Splitter;
import com.google.common.base.Strings;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.hash.HashCode;
import com.google.common.hash.Hashing;
import com.google.common.io.ByteStreams;
import com.google.devtools.build.lib.bazel.repository.downloader.RetryingInputStream.Reconnector;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadCompatible;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import java.io.ByteArrayInputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.SequenceInputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.zip.GZIPInputStream;
import javax.annotation.WillCloseWhenClosed;

/**
 * Input stream that validates checksum resumes downloads on error.
 *
 * <p>This class is not thread safe, but it is safe to message pass its objects between threads.
 */
@ThreadCompatible
final class HttpStream extends FilterInputStream {

  static final int PRECHECK_BYTES = 32 * 1024;
  private static final int GZIP_BUFFER_BYTES = 8192;  // same as ByteStreams#copy
  private static final ImmutableSet<String> GZIPPED_EXTENSIONS = ImmutableSet.of("gz", "tgz");
  private static final ImmutableSet<String> GZIP_CONTENT_ENCODING =
      ImmutableSet.of("gzip", "x-gzip");

  /** Factory for {@link HttpStream}. */
  @ThreadSafe
  static class Factory {

    private final ProgressInputStream.Factory progressInputStreamFactory;

    Factory(ProgressInputStream.Factory progressInputStreamFactory) {
      this.progressInputStreamFactory = progressInputStreamFactory;
    }

    @SuppressWarnings("resource")
    HttpStream create(
        @WillCloseWhenClosed URLConnection connection,
        URL originalUrl,
        String sha256,
        Reconnector reconnector)
            throws IOException {
      InputStream stream = new InterruptibleInputStream(connection.getInputStream());
      try {
        // If server supports range requests, we can retry on read errors. See RFC7233 § 2.3.
        RetryingInputStream retrier = null;
        if (Iterables.contains(
                Splitter.on(',')
                    .trimResults()
                    .split(Strings.nullToEmpty(connection.getHeaderField("Accept-Ranges"))),
                "bytes")) {
          retrier = new RetryingInputStream(stream, reconnector);
          stream = retrier;
        }

        stream = progressInputStreamFactory.create(stream, connection.getURL(), originalUrl);

        // Determine if we need to transparently gunzip. See RFC2616 § 3.5 and § 14.11. Please note
        // that some web servers will send Content-Encoding: gzip even when we didn't request it if
        // the file is a .gz file.
        if (GZIP_CONTENT_ENCODING.contains(Strings.nullToEmpty(connection.getContentEncoding()))
            && !GZIPPED_EXTENSIONS.contains(HttpUtils.getExtension(connection.getURL().getPath()))
            && !GZIPPED_EXTENSIONS.contains(HttpUtils.getExtension(originalUrl.getPath()))) {
          stream = new GZIPInputStream(stream, GZIP_BUFFER_BYTES);
        }

        if (!sha256.isEmpty()) {
          stream = new HashInputStream(stream, Hashing.sha256(), HashCode.fromString(sha256));
          if (retrier != null) {
            retrier.disabled = true;
          }
          byte[] buffer = new byte[PRECHECK_BYTES];
          int read = 0;
          while (read < PRECHECK_BYTES) {
            int amount;
            amount = stream.read(buffer, read, PRECHECK_BYTES - read);
            if (amount == -1) {
              break;
            }
            read += amount;
          }
          if (read < PRECHECK_BYTES) {
            stream.close();
            stream = ByteStreams.limit(new ByteArrayInputStream(buffer), read);
          } else {
            stream = new SequenceInputStream(new ByteArrayInputStream(buffer), stream);
            if (retrier != null) {
              retrier.disabled = false;
            }
          }
        }
      } catch (Exception e) {
        try {
          stream.close();
        } catch (IOException e2) {
          e.addSuppressed(e2);
        }
        throw e;
      }
      return new HttpStream(stream, connection.getURL());
    }
  }

  private final URL url;

  HttpStream(@WillCloseWhenClosed InputStream delegate, URL url) {
    super(delegate);
    this.url = url;
  }

  /** Returns final redirected URL. */
  URL getUrl() {
    return url;
  }
}