// Copyright (c) 2011 The LevelDB Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file. See the AUTHORS file for names of contributors.

#include "table/format.h"

#include "leveldb/env.h"

#include "leveldb/options.h"

#include "port/port.h"

#include "table/block.h"

#include "util/coding.h"

#include "util/crc32c.h"

namespace leveldb {

void BlockHandle::EncodeTo(std::string* dst) const {

  // Sanity check that all fields have been set

  assert(offset_ != ~static_cast<uint64_t>(0));

  assert(size_ != ~static_cast<uint64_t>(0));

  PutVarint64(dst, offset_);

  PutVarint64(dst, size_);

}

Status BlockHandle::DecodeFrom(Slice* input) {

  if (GetVarint64(input, &offset_) && GetVarint64(input, &size_)) {

    return Status::OK();

  } else {

    return Status::Corruption("bad block handle");

  }

}

void Footer::EncodeTo(std::string* dst) const {

  const size_t original_size = dst->size();

  metaindex_handle_.EncodeTo(dst);

  index_handle_.EncodeTo(dst);

  dst->resize(2 * BlockHandle::kMaxEncodedLength);  // Padding

  PutFixed32(dst, static_cast<uint32_t>(kTableMagicNumber & 0xffffffffu));

  PutFixed32(dst, static_cast<uint32_t>(kTableMagicNumber >> 32));

  assert(dst->size() == original_size + kEncodedLength);

  (void)original_size;  // Disable unused variable warning.

}

Status Footer::DecodeFrom(Slice* input) {

  if (input->size() < kEncodedLength) {

    return Status::Corruption("not an sstable (footer too short)");

  }

  const char* magic_ptr = input->data() + kEncodedLength - 8;

  const uint32_t magic_lo = DecodeFixed32(magic_ptr);

  const uint32_t magic_hi = DecodeFixed32(magic_ptr + 4);

  const uint64_t magic = ((static_cast<uint64_t>(magic_hi) << 32) |

                          (static_cast<uint64_t>(magic_lo)));

  if (magic != kTableMagicNumber) {

    return Status::Corruption("not an sstable (bad magic number)");

  }

  Status result = metaindex_handle_.DecodeFrom(input);

  if (result.ok()) {

    result = index_handle_.DecodeFrom(input);

  }

  if (result.ok()) {

    // We skip over any leftover data (just padding for now) in "input"

    const char* end = magic_ptr + 8;

    *input = Slice(end, input->data() + input->size() - end);

  }

  return result;

}

Status ReadBlock(RandomAccessFile* file, const ReadOptions& options,

                 const BlockHandle& handle, BlockContents* result) {

  result->data = Slice();

  result->cachable = false;

  result->heap_allocated = false;

  // Read the block contents as well as the type/crc footer.

  // See table_builder.cc for the code that built this structure.

  size_t n = static_cast<size_t>(handle.size());

  char* buf = new char[n + kBlockTrailerSize];

  Slice contents;

  Status s = file->Read(handle.offset(), n + kBlockTrailerSize, &contents, buf);

  if (!s.ok()) {

    delete[] buf;

    return s;

  }

  if (contents.size() != n + kBlockTrailerSize) {

    delete[] buf;

    return Status::Corruption("truncated block read");

  }

  // Check the crc of the type and the block contents

  const char* data = contents.data();  // Pointer to where Read put the data

  if (options.verify_checksums) {

    const uint32_t crc = crc32c::Unmask(DecodeFixed32(data + n + 1));

    const uint32_t actual = crc32c::Value(data, n + 1);

    if (actual != crc) {

      delete[] buf;

      s = Status::Corruption("block checksum mismatch");

      return s;

    }

  }

  switch (data[n]) {

    case kNoCompression:

      if (data != buf) {

        // File implementation gave us pointer to some other data.

        // Use it directly under the assumption that it will be live

        // while the file is open.

        delete[] buf;

        result->data = Slice(data, n);

        result->heap_allocated = false;

        result->cachable = false;  // Do not double-cache

      } else {

        result->data = Slice(buf, n);

        result->heap_allocated = true;

        result->cachable = true;

      }

      // Ok

      break;

    case kSnappyCompression: {

      size_t ulength = 0;

      if (!port::Snappy_GetUncompressedLength(data, n, &ulength)) {

        delete[] buf;

        return Status::Corruption("corrupted snappy compressed block length");

      }

      char* ubuf = new char[ulength];

      if (!port::Snappy_Uncompress(data, n, ubuf)) {

        delete[] buf;

        delete[] ubuf;

        return Status::Corruption("corrupted snappy compressed block contents");

      }

      delete[] buf;

      result->data = Slice(ubuf, ulength);

      result->heap_allocated = true;

      result->cachable = true;

      break;

    }

    case kZstdCompression: {

      size_t ulength = 0;

      if (!port::Zstd_GetUncompressedLength(data, n, &ulength)) {

        delete[] buf;

        return Status::Corruption("corrupted zstd compressed block length");

      }

      char* ubuf = new char[ulength];

      if (!port::Zstd_Uncompress(data, n, ubuf)) {

        delete[] buf;

        delete[] ubuf;

        return Status::Corruption("corrupted zstd compressed block contents");

      }

      delete[] buf;

      result->data = Slice(ubuf, ulength);

      result->heap_allocated = true;

      result->cachable = true;

      break;

    }

    default:

      delete[] buf;

      return Status::Corruption("bad block type");

  }

  return Status::OK();

}

}  // namespace leveldb