chunks.h

// Copyright 2025 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.
#pragma once
 
#include <type_traits>
 
#include "pw_multibuf/internal/chunk_iterator.h"
 
namespace pw::multibuf {
 
// Forward declaration for friending.
namespace test {
class IteratorTest;
}  // namespace test
 
namespace internal {
 
template <typename Deque,
          ChunkContiguity kContiguity,
          ChunkMutability kMutability>
class ChunksImpl {
 public:
  using size_type = typename Deque::size_type;
  using value_type = typename Deque::value_type;
  using difference_type = typename Deque::difference_type;
  using iterator = ChunkIterator<size_type, kContiguity, kMutability>;
  using const_iterator =
      ChunkIterator<size_type, kContiguity, ChunkMutability::kConst>;
 
  constexpr ChunksImpl() = default;
 
  constexpr size_type size() const {
    if constexpr (kContiguity == ChunkContiguity::kKeepAll) {
      return deque().size() / begin_.entries_per_chunk_;
    }
    return static_cast<size_type>(std::distance(begin_, end_));
  }
 
  constexpr iterator begin() const { return begin_; }
  constexpr iterator end() const { return end_; }
 
  constexpr const_iterator cbegin() const { return begin_; }
  constexpr const_iterator cend() const { return end_; }
 
 private:
  friend class GenericMultiBuf;
 
  // For unit testing.
  friend class ::pw::multibuf::test::IteratorTest;
 
  using DequeRefType =
      std::conditional_t<kMutability == ChunkMutability::kConst,
                         const Deque&,
                         Deque&>;
 
  constexpr ChunksImpl(DequeRefType& deque, size_type entries_per_chunk) {
    begin_.deque_ = &deque;
    begin_.entries_per_chunk_ = entries_per_chunk;
    end_.deque_ = &deque;
    end_.entries_per_chunk_ = entries_per_chunk;
    end_.chunk_ = deque.size() / entries_per_chunk;
  }
 
  constexpr const Deque& deque() const { return *(begin_.deque_); }
 
  iterator begin_;
  iterator end_;
};
 
template <typename Deque>
using Chunks =
    ChunksImpl<Deque, ChunkContiguity::kCoalesce, ChunkMutability::kMutable>;
 
template <typename Deque>
using ConstChunks =
    ChunksImpl<Deque, ChunkContiguity::kCoalesce, ChunkMutability::kConst>;
 
template <typename Deque>
using RawChunks =
    ChunksImpl<Deque, ChunkContiguity::kKeepAll, ChunkMutability::kMutable>;
 
template <typename Deque>
using RawConstChunks =
    ChunksImpl<Deque, ChunkContiguity::kKeepAll, ChunkMutability::kConst>;
 
}  // namespace internal
}  // namespace pw::multibuf