bindings/merkle.h

// Copyright 2026 Google LLC
//
// 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.
//

#ifndef THIRD_PARTY_CREDENTIO_BINDINGS_MERKLE_H_
#define THIRD_PARTY_CREDENTIO_BINDINGS_MERKLE_H_

#include <cstdint>
#include <optional>
#include <string>
#include <vector>

#include "absl/status/statusor.h"
#include "crypto/hash.h"
#include "proto/bmff_based_hash_assertion.pb.h"
#include "riegeli/bytes/reader.h"

namespace credentio {

struct DerivedTreeData {
  int64_t full_leaf_count;
  int64_t full_hashes_count;
  int64_t delta_rows;

  bool operator==(const DerivedTreeData& other) const {
    return full_leaf_count == other.full_leaf_count &&
           full_hashes_count == other.full_hashes_count &&
           delta_rows == other.delta_rows;
  }
};

// Derives the data needed to validate a Merkle Tree from the leaf count, hashes
// count, and auxiliary data count.
absl::StatusOr<DerivedTreeData> DeriveMerkleTreeData(int64_t leaf_count,
                                                     int64_t hashes_count,
                                                     int64_t auxiliary_count);

// Derives the block sizes for a given Merkle map and total leaf data size.
absl::StatusOr<std::vector<int64_t>> DeriveMerkleBlockSizes(
    const BmffMerkle& merkle, uint64_t mdat_box_size);

using MerkleTree = std::vector<std::vector<std::string>>;

// Options for creating a Merkle Tree.
// - `fixed_block_size`: blocks of equal sizes
// - `variable_block_sizes`: blocks of the specified sizes
// - neither: the entire input string will treated as a single block
// - both: then an error will be returned
struct CreateMerkleTreeOptions {
  std::optional<int64_t> fixed_block_size = std::nullopt;
  std::vector<int64_t> variable_block_sizes = {};
};

// Creates a Merkle Tree from a riegeli::Reader with the options indicating
// how the input should be broken into blocks.
absl::StatusOr<MerkleTree> CreateMerkleTree(
    HasherFactory* factory, riegeli::Reader& input, int64_t starting_offset,
    int64_t length, CreateMerkleTreeOptions options = {});

// Creates a Merkle Tree from a vector of strings, each which represent a single
// leaf node.
absl::StatusOr<MerkleTree> CreateMerkleTree(HasherFactory* factory,
                                            riegeli::Reader& input,
                                            int64_t starting_offset,
                                            int64_t length,
                                            std::vector<int64_t> block_sizes);

}  // namespace credentio

#endif  // THIRD_PARTY_CREDENTIO_BINDINGS_MERKLE_H_