// Copyright 2021 The Pigweed Authors

//

// 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

//

//     https://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.

#include "pw_varint/stream.h"

#include <cstddef>

#include <cstdint>

#include "pw_span/span.h"

#include "pw_status/status_with_size.h"

#include "pw_stream/stream.h"

#include "pw_varint/varint.h"

namespace pw {

namespace varint {

StatusWithSize Read(stream::Reader& reader, int64_t* output, size_t max_size) {

  uint64_t value = 0;

  StatusWithSize count = Read(reader, &value, max_size);

  if (!count.ok()) {

    return count;

  }

  *output = ZigZagDecode(value);

  return count;

}

StatusWithSize Read(stream::Reader& reader, uint64_t* output, size_t max_size) {

  uint64_t value = 0;

  size_t count = 0;

  while (true) {

    if (count >= varint::kMaxVarint64SizeBytes) {

      // Varint can't fit a uint64_t, this likely means we're reading binary

      // data that is not actually a varint.

      return StatusWithSize::DataLoss(count);

    }

    if (count >= max_size) {

      // Varint didn't fit within the range given; return OutOfRange() if

      // max_size was 0, but DataLoss if we were reading something we thought

      // was going to be a varint.

      return count > 0 ? StatusWithSize::DataLoss(count)

                       : StatusWithSize::OutOfRange();

    }

    std::byte b;

    if (auto result = reader.Read(span(&b, 1)); !result.ok()) {

      if (count > 0 && result.status().IsOutOfRange()) {

        // Status::OutOfRange on the first byte means we tried to read a varint

        // when we reached the end of file. But after the first byte it means we

        // failed to decode a varint we were in the middle of, and that's not

        // a normal error condition.

        return StatusWithSize::DataLoss(count);

      }

      return StatusWithSize(result.status(), count);

    }

    value |= static_cast<uint64_t>(b & std::byte(0b01111111)) << (7 * count);

    ++count;

    // MSB == 0 indicates last byte of the varint.

    if ((b & std::byte(0b10000000)) == std::byte(0)) {

      break;

    }

  }

  *output = value;

  return StatusWithSize(count);

}

}  // namespace varint

}  // namespace pw