PMTiles/cpp/pmtiles.hpp

#ifndef PMTILES_HPP
#define PMTILES_HPP

#include <string>
#include <sstream>
#include <vector>

namespace pmtiles {

struct headerv3 {
  uint64_t root_dir_offset;
  uint64_t root_dir_bytes;
  uint64_t json_metadata_offset;
  uint64_t json_metadata_bytes;
  uint64_t leaf_dirs_offset;
  uint64_t leaf_dirs_bytes;
  uint64_t tile_data_offset;
  uint64_t tile_data_bytes;
  uint64_t addressed_tiles_count;
  uint64_t tile_entries_count;
  uint64_t tile_contents_count;
  bool clustered;
  uint8_t internal_compression;
  uint8_t tile_compression;
  uint8_t tile_type;
  uint8_t min_zoom;
  uint8_t max_zoom;
  int32_t min_lon_e7;
  int32_t min_lat_e7;
  int32_t max_lon_e7;
  int32_t max_lat_e7;
  uint8_t center_zoom;
  int32_t center_lon_e7;
  int32_t center_lat_e7;

  // WARNING: this is limited to little-endian
  std::string serialize() {
    std::stringstream ss;
    ss << "PMTiles";
    uint8_t version = 3;
    ss.write((char *)&version,1);
    ss.write((char *)&root_dir_offset,8);
    ss.write((char *)&root_dir_bytes,8);
    ss.write((char *)&json_metadata_offset,8);
    ss.write((char *)&json_metadata_bytes,8);
    ss.write((char *)&leaf_dirs_offset,8);
    ss.write((char *)&leaf_dirs_bytes,8);
    ss.write((char *)&tile_data_offset,8);
    ss.write((char *)&tile_data_bytes,8);
    ss.write((char *)&addressed_tiles_count,8);
    ss.write((char *)&tile_entries_count,8);
    ss.write((char *)&tile_contents_count,8);

    uint8_t clustered_val = 0x0;
    if (clustered) {
      clustered_val = 0x1;
    }

    ss.write((char *)&clustered_val,1);
    ss.write((char *)&internal_compression,1);
    ss.write((char *)&tile_compression,1);
    ss.write((char *)&tile_type,1);
    ss.write((char *)&min_zoom,1);
    ss.write((char *)&max_zoom,1);
    ss.write((char *)&min_lon_e7,4);
    ss.write((char *)&min_lat_e7,4);
    ss.write((char *)&max_lon_e7,4);
    ss.write((char *)&max_lat_e7,4);
    ss.write((char *)&center_zoom,1);
    ss.write((char *)&center_lon_e7,4);
    ss.write((char *)&center_lat_e7,4);

    return ss.str();
  }
};

struct zxy {
  uint8_t z;
  uint32_t x;
  uint32_t y;

  zxy(int _z, int _x, int _y) : z(_z), x(_x), y(_y) {
  }
};

struct entryv3 {
  uint64_t tile_id;
  uint64_t offset;
  uint32_t length;
  uint32_t run_length;

  entryv3() : tile_id(0), offset(0), length(0), run_length(0) {
  }

  entryv3(uint64_t _tile_id, uint64_t _offset, uint32_t _length, uint32_t _run_length)
    : tile_id(_tile_id), offset(_offset), length(_length), run_length(_run_length) {
  }
};

struct varint_too_long_exception : std::exception {
  const char* what() const noexcept override {
    return "varint too long exception";
  }
};

struct end_of_buffer_exception : std::exception {
  const char* what() const noexcept override {
      return "end of buffer exception";
  }
};

namespace detail {
  constexpr const int8_t max_varint_length = sizeof(uint64_t) * 8 / 7 + 1;

  // from https://github.com/mapbox/protozero/blob/master/include/protozero/varint.hpp
  inline uint64_t decode_varint_impl(const char** data, const char* end) {
    const auto* begin = reinterpret_cast<const int8_t*>(*data);
    const auto* iend = reinterpret_cast<const int8_t*>(end);
    const int8_t* p = begin;
    uint64_t val = 0;

    if (iend - begin >= max_varint_length) {  // fast path
      do {
        int64_t b = *p++;
                  val  = ((uint64_t(b) & 0x7fU)       ); if (b >= 0) { break; }
        b = *p++; val |= ((uint64_t(b) & 0x7fU) <<  7U); if (b >= 0) { break; }
        b = *p++; val |= ((uint64_t(b) & 0x7fU) << 14U); if (b >= 0) { break; }
        b = *p++; val |= ((uint64_t(b) & 0x7fU) << 21U); if (b >= 0) { break; }
        b = *p++; val |= ((uint64_t(b) & 0x7fU) << 28U); if (b >= 0) { break; }
        b = *p++; val |= ((uint64_t(b) & 0x7fU) << 35U); if (b >= 0) { break; }
        b = *p++; val |= ((uint64_t(b) & 0x7fU) << 42U); if (b >= 0) { break; }
        b = *p++; val |= ((uint64_t(b) & 0x7fU) << 49U); if (b >= 0) { break; }
        b = *p++; val |= ((uint64_t(b) & 0x7fU) << 56U); if (b >= 0) { break; }
        b = *p++; val |= ((uint64_t(b) & 0x01U) << 63U); if (b >= 0) { break; }
        throw varint_too_long_exception{};
      } while (false);
    } else {
      unsigned int shift = 0;
      while (p != iend && *p < 0) {
        val |= (uint64_t(*p++) & 0x7fU) << shift;
        shift += 7;
      }
      if (p == iend) {
        throw end_of_buffer_exception{};
      }
      val |= uint64_t(*p++) << shift;
    }

    *data = reinterpret_cast<const char*>(p);
    return val;
  }

  inline uint64_t decode_varint(const char** data, const char* end) {
    // If this is a one-byte varint, decode it here.
    if (end != *data && ((static_cast<uint64_t>(**data) & 0x80U) == 0)) {
      const auto val = static_cast<uint64_t>(**data);
      ++(*data);
      return val;
    }
    // If this varint is more than one byte, defer to complete implementation.
    return detail::decode_varint_impl(data, end);
  }

  inline void rotate(int64_t n, int64_t &x, int64_t &y, int64_t rx, int64_t ry) {
    if (ry == 0) {
      if (rx == 1) {
          x = n-1 - x;
          y = n-1 - y;
      }
      int64_t t = x;
      x = y;
      y = t;
    }
  }

  zxy t_on_level(uint8_t z, uint64_t pos) {
    int64_t n = 1 << z;
    int64_t rx, ry, s, t = pos;
    int64_t tx = 0;
    int64_t ty = 0;

    for (s=1; s<n; s*=2) {
      rx = 1 & (t/2);
      ry = 1 & (t ^ rx);
      rotate(s, tx, ty, rx, ry);
      tx += s * rx;
      ty += s * ry;
      t /= 4;
    }
    return zxy(z,tx,ty);
  }
} // end namespace detail

inline int write_varint(std::back_insert_iterator<std::string> data, uint64_t value) {
  int n = 1;

  while (value >= 0x80U) {
    *data++ = char((value & 0x7fU) | 0x80U);
    value >>= 7U;
    ++n;
  }
  *data = char(value);

  return n;
}

zxy tileid_to_zxy(uint64_t tileid) {
  uint64_t acc = 0;
  uint8_t t_z = 0;
  while(true) {
    uint64_t num_tiles = (1 << t_z) * (1 << t_z);
    if (acc + num_tiles > tileid) {
        return detail::t_on_level(t_z, tileid - acc);
    }
    acc += num_tiles;
    t_z++;
  }
}

uint64_t zxy_to_tileid(uint8_t z, uint32_t x, uint32_t y) {
  uint64_t acc = 0;
  for (uint8_t t_z = 0; t_z < z; t_z++) acc += (0x1 << t_z) * (0x1 << t_z);
  int64_t n = 1 << z;
  int64_t rx, ry, s, d=0;
  int64_t tx = x;
  int64_t ty = y;
  for (s=n/2; s>0; s/=2) {
    rx = (tx & s) > 0;
    ry = (ty & s) > 0;
    d += s * s * ((3 * rx) ^ ry);
    detail::rotate(s, tx, ty, rx, ry);
  }
  return acc + d;
}

// returns an uncompressed byte buffer
std::string serialize_directory(const std::vector<entryv3>& entries) {
  std::string data;

  write_varint(std::back_inserter(data), entries.size());

  uint64_t last_id = 0;
  for (auto const &entry : entries) {
    write_varint(std::back_inserter(data), entry.tile_id - last_id);
    last_id = entry.tile_id;
  }

  for (auto const &entry : entries) {
    write_varint(std::back_inserter(data), entry.run_length);
  }

  for (auto const &entry : entries) {
    write_varint(std::back_inserter(data), entry.length);
  }

  for (size_t i = 0; i < entries.size(); i++) {
    if (i > 0 && entries[i].offset == entries[i-1].offset + entries[i-1].length) {
      write_varint(std::back_inserter(data), 0);
    } else {
      write_varint(std::back_inserter(data), entries[i].offset+1);
    }
  }

  return data;
}

// takes an uncompressed byte buffer
std::vector<entryv3> deserialize_directory(const std::string &decompressed) {
  const char *t = decompressed.data();
  const char *end = t + decompressed.size();

  uint64_t num_entries = detail::decode_varint(&t,end);

  std::vector<entryv3> result;
  result.resize(num_entries);

  uint64_t last_id = 0;
  for (size_t i = 0; i < num_entries; i++) {
    uint64_t tile_id = last_id + detail::decode_varint(&t,end);
    result[i].tile_id = tile_id;
    last_id = tile_id;
  }

  for (size_t i = 0; i < num_entries; i++) {
    result[i].run_length = detail::decode_varint(&t,end);
  }

  for (size_t i = 0; i < num_entries; i++) {
    result[i].length = detail::decode_varint(&t,end);
  }

  for (size_t i = 0; i < num_entries; i++) {
    uint64_t tmp = detail::decode_varint(&t,end);

    if (i > 0 && tmp == 0) {
      result[i].offset = result[i-1].offset + result[i-1].length;
    } else {
      result[i].offset = tmp - 1;
    }
  }

  // assert the directory has been fully consumed
  if (t != end) {
    fprintf(stderr, "Error: malformed pmtiles directory\n");
    exit(EXIT_FAILURE);
  }

  return result;
}

}
#endif