// Copyright 2020 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_tokenizer/detokenize.h"

#include <algorithm>

#include <cstring>

#include "pw_bytes/bit.h"

#include "pw_bytes/endian.h"

#include "pw_tokenizer/base64.h"

#include "pw_tokenizer/internal/decode.h"

#include "pw_tokenizer/nested_tokenization.h"

namespace pw::tokenizer {

namespace {

class NestedMessageDetokenizer {

 public:

  NestedMessageDetokenizer(const Detokenizer& detokenizer)

      : detokenizer_(detokenizer) {}

  void Detokenize(std::string_view chunk) {

    for (char next_char : chunk) {

      Detokenize(next_char);

    }

  }

  void Detokenize(char next_char) {

    switch (state_) {

      case kNonMessage:

        if (next_char == PW_TOKENIZER_NESTED_PREFIX) {

          message_buffer_.push_back(next_char);

          state_ = kMessage;

        } else {

          output_.push_back(next_char);

        }

        break;

      case kMessage:

        if (base64::IsValidChar(next_char)) {

          message_buffer_.push_back(next_char);

        } else {

          HandleEndOfMessage();

          if (next_char == PW_TOKENIZER_NESTED_PREFIX) {

            message_buffer_.push_back(next_char);

          } else {

            output_.push_back(next_char);

            state_ = kNonMessage;

          }

        }

        break;

    }

  }

  std::string Flush() {

    if (state_ == kMessage) {

      HandleEndOfMessage();

      state_ = kNonMessage;

    }

    return std::move(output_);

  }

 private:

  void HandleEndOfMessage() {

    if (auto result = detokenizer_.DetokenizeBase64Message(message_buffer_);

        result.ok()) {

      output_ += result.BestString();

    } else {

      output_ += message_buffer_;  // Keep the original if it doesn't decode.

    }

    message_buffer_.clear();

  }

  const Detokenizer& detokenizer_;

  std::string output_;

  std::string message_buffer_;

  enum { kNonMessage, kMessage } state_ = kNonMessage;

};

std::string UnknownTokenMessage(uint32_t value) {

  std::string output(PW_TOKENIZER_ARG_DECODING_ERROR_PREFIX "unknown token ");

  // Output a hexadecimal version of the token.

  for (int shift = 28; shift >= 0; shift -= 4) {

    output.push_back("0123456789abcdef"[(value >> shift) & 0xF]);

  }

  output.append(PW_TOKENIZER_ARG_DECODING_ERROR_SUFFIX);

  return output;

}

// Decoding result with the date removed, for sorting.

using DecodingResult = std::pair<DecodedFormatString, uint32_t>;

// Determines if one result is better than the other if collisions occurred.

// Returns true if lhs is preferred over rhs. This logic should match the

// collision resolution logic in detokenize.py.

bool IsBetterResult(const DecodingResult& lhs, const DecodingResult& rhs) {

  // Favor the result for which decoding succeeded.

  if (lhs.first.ok() != rhs.first.ok()) {

    return lhs.first.ok();

  }

  // Favor the result for which all bytes were decoded.

  if ((lhs.first.remaining_bytes() == 0u) !=

      (rhs.first.remaining_bytes() == 0u)) {

    return lhs.first.remaining_bytes() == 0u;

  }

  // Favor the result with fewer decoding errors.

  if (lhs.first.decoding_errors() != rhs.first.decoding_errors()) {

    return lhs.first.decoding_errors() < rhs.first.decoding_errors();

  }

  // Favor the result that successfully decoded the most arguments.

  if (lhs.first.argument_count() != rhs.first.argument_count()) {

    return lhs.first.argument_count() > rhs.first.argument_count();

  }

  // Favor the result that was removed from the database most recently.

  return lhs.second > rhs.second;

}

}  // namespace

DetokenizedString::DetokenizedString(

    uint32_t token,

    const span<const TokenizedStringEntry>& entries,

    const span<const uint8_t>& arguments)

    : token_(token), has_token_(true) {

  std::vector<DecodingResult> results;

  for (const auto& [format, date_removed] : entries) {

    results.push_back(DecodingResult{format.Format(arguments), date_removed});

  }

  std::sort(results.begin(), results.end(), IsBetterResult);

  for (auto& result : results) {

    matches_.push_back(std::move(result.first));

  }

}

std::string DetokenizedString::BestString() const {

  return matches_.empty() ? std::string() : matches_[0].value();

}

std::string DetokenizedString::BestStringWithErrors() const {

  if (matches_.empty()) {

    return has_token_ ? UnknownTokenMessage(token_)

                      : PW_TOKENIZER_ARG_DECODING_ERROR("missing token");

  }

  return matches_[0].value_with_errors();

}

Detokenizer::Detokenizer(const TokenDatabase& database) {

  for (const auto& entry : database) {

    database_[entry.token].emplace_back(entry.string, entry.date_removed);

  }

}

DetokenizedString Detokenizer::Detokenize(

    const span<const uint8_t>& encoded) const {

  // The token is missing from the encoded data; there is nothing to do.

  if (encoded.empty()) {

    return DetokenizedString();

  }

  uint32_t token = bytes::ReadInOrder<uint32_t>(

      endian::little, encoded.data(), encoded.size());

  const auto result = database_.find(token);

  return DetokenizedString(

      token,

      result == database_.end() ? span<TokenizedStringEntry>()

                                : span(result->second),

      encoded.size() < sizeof(token) ? span<const uint8_t>()

                                     : encoded.subspan(sizeof(token)));

}

DetokenizedString Detokenizer::DetokenizeBase64Message(

    std::string_view text) const {

  std::string buffer(text);

  buffer.resize(PrefixedBase64DecodeInPlace(buffer));

  return Detokenize(buffer);

}

std::string Detokenizer::DetokenizeBase64(std::string_view text) const {

  NestedMessageDetokenizer nested_detokenizer(*this);

  nested_detokenizer.Detokenize(text);

  return nested_detokenizer.Flush();

}

}  // namespace pw::tokenizer