// Copyright (c) Google LLC 2019

//

// Use of this source code is governed by an MIT-style

// license that can be found in the LICENSE file or at

// https://opensource.org/licenses/MIT.

#include "./lehmer_code.h"

#include <utility>

#include <vector>

namespace brunsli {

void ComputeLehmerCode(const uint32_t* sigma, const size_t len,

                       uint32_t* code) {

  std::vector<uint32_t> items(len);

  for (size_t i = 0; i < len; ++i) items[i] = static_cast<uint32_t>(i);

  for (size_t i = 0; i < len; ++i) {

    std::vector<uint32_t>::iterator it =

        std::find(items.begin(), items.end(), sigma[i]);

    BRUNSLI_DCHECK(it != items.end());

    code[i] = static_cast<uint32_t>(it - items.begin());

    items.erase(it);

  }

}

bool DecodeLehmerCode(const uint32_t* code, size_t len, uint32_t* sigma) {

  std::vector<uint32_t> items(len);

  for (size_t i = 0; i < len; ++i) items[i] = static_cast<uint32_t>(i);

  for (size_t i = 0; i < len; ++i) {

    uint32_t index = code[i];

    if (index >= items.size()) return false;

    const uint32_t value = items[index];

    items.erase(items.begin() + index);

    sigma[i] = value;

  }

  return true;

}

}  // namespace brunsli