// Copyright 2021 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.remote.zstd;

import static java.lang.Math.max;

import com.github.luben.zstd.ZstdOutputStream;
import com.google.common.base.Preconditions;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;

/** A {@link FilterInputStream} that use zstd to compress the content. */
public class ZstdCompressingInputStream extends FilterInputStream {
  // We want the buffer to be able to contain at least:
  //   - Magic number: 4 bytes
  //   - FrameHeader 14 bytes
  //   - Block Header: 3 bytes
  //   - First block byte
  // This guarantees that we can always compress at least
  // 1 byte and write it to the pipe without blocking.
  public static final int MIN_BUFFER_SIZE = 4 + 14 + 3 + 1;

  private final PipedInputStream pis;
  private ZstdOutputStream zos;
  private final int size;

  public ZstdCompressingInputStream(InputStream in) throws IOException {
    this(in, 512);
  }

  ZstdCompressingInputStream(InputStream in, int size) throws IOException {
    super(in);
    Preconditions.checkArgument(
        size >= MIN_BUFFER_SIZE,
        String.format("The buffer size must be at least %d bytes", MIN_BUFFER_SIZE));
    this.size = size;
    this.pis = new PipedInputStream(size);
    this.zos = new ZstdOutputStream(new PipedOutputStream(pis));
  }

  private void reFill() throws IOException {
    byte[] buf = new byte[size];
    int len = super.read(buf, 0, max(0, size - pis.available() - MIN_BUFFER_SIZE + 1));
    if (len == -1) {
      zos.close();
      zos = null;
    } else {
      zos.write(buf, 0, len);
      zos.flush();
    }
  }

  @Override
  public int read() throws IOException {
    if (pis.available() == 0) {
      if (zos == null) {
        return -1;
      }
      reFill();
    }
    return pis.read();
  }

  @Override
  public int read(byte[] b) throws IOException {
    return read(b, 0, b.length);
  }

  @Override
  public int read(byte[] b, int off, int len) throws IOException {
    int count = 0;
    int n = len > 0 ? -1 : 0;
    while (count < len && (pis.available() > 0 || zos != null)) {
      if (pis.available() == 0) {
        reFill();
      }
      n = pis.read(b, count + off, len - count);
      count += max(0, n);
    }
    return count > 0 ? count : n;
  }

  @Override
  public void close() throws IOException {
    if (zos != null) {
      zos.close();
    }
    in.close();
  }
}