src/iceberg/file_reader.h

/*
 * Licensed to the Apache Software Foundation (ASF) under one
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 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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
 *
 *   http://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
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#pragma once

/// \file iceberg/file_reader.h
/// Reader interface for file formats like Parquet, Avro and ORC.

#include <functional>
#include <memory>
#include <optional>

#include "iceberg/arrow_c_data.h"
#include "iceberg/file_format.h"
#include "iceberg/result.h"
#include "iceberg/type_fwd.h"
#include "iceberg/util/config.h"

namespace iceberg {

/// \brief Base reader class to read data from different file formats.
class ICEBERG_EXPORT Reader {
 public:
  virtual ~Reader() = default;
  Reader() = default;
  Reader(const Reader&) = delete;
  Reader& operator=(const Reader&) = delete;

  /// \brief Open the reader.
  virtual Status Open(const ReaderOptions& options) = 0;

  /// \brief Close the reader.
  virtual Status Close() = 0;

  /// \brief Read next data from file.
  ///
  /// \return std::nullopt if the reader has no more data, otherwise `ArrowArray`.
  virtual Result<std::optional<ArrowArray>> Next() = 0;

  /// \brief Get the schema of the data.
  virtual Result<ArrowSchema> Schema() = 0;

  /// \brief Get the metadata of the file.
  virtual Result<std::unordered_map<std::string, std::string>> Metadata() = 0;
};

/// \brief A split of the file to read.
struct ICEBERG_EXPORT Split {
  /// \brief The offset of the split.
  size_t offset;
  /// \brief The length of the split.
  size_t length;
};

class ReaderProperties : public ConfigBase<ReaderProperties> {
 public:
  template <typename T>
  using Entry = const ConfigBase<ReaderProperties>::Entry<T>;

  /// \brief The batch size to read.
  inline static Entry<int64_t> kBatchSize{"read.batch-size", 4096};
  /// \brief Skip GenericDatum in Avro reader for better performance.
  /// When true, decode directly from Avro to Arrow without GenericDatum intermediate.
  /// Default: true (skip GenericDatum for better performance).
  inline static Entry<bool> kAvroSkipDatum{"read.avro.skip-datum", true};
  /// \brief The buffer size used by Avro input stream.
  inline static Entry<int64_t> kAvroBufferSize{"read.avro.buffer-size", 1024 * 1024};

  /// \brief Create a ReaderProperties instance from a map of key-value pairs.
  static ReaderProperties FromMap(
      const std::unordered_map<std::string, std::string>& properties);
};

/// \brief Options for creating a reader.
struct ICEBERG_EXPORT ReaderOptions {
  /// \brief The path to the file to read.
  std::string path;
  /// \brief The total length of the file.
  std::optional<size_t> length;
  /// \brief The split to read.
  std::optional<Split> split;
  /// \brief FileIO instance to open the file. Reader implementations should down cast it
  /// to the specific FileIO implementation. By default, the `iceberg-bundle` library uses
  /// `ArrowFileSystemFileIO` as the default implementation.
  std::shared_ptr<class FileIO> io;
  /// \brief The projection schema to read from the file. This field is required.
  std::shared_ptr<class Schema> projection;
  /// \brief The filter to apply to the data. Reader implementations may ignore this if
  /// the file format does not support filtering.
  std::shared_ptr<class Expression> filter;
  /// \brief Name mapping for schema evolution compatibility. Used when reading files
  /// that may have different field names than the current schema.
  std::shared_ptr<class NameMapping> name_mapping;
  /// \brief Format-specific or implementation-specific properties.
  ReaderProperties properties;
};

/// \brief Factory function to create a reader of a specific file format.
using ReaderFactory = std::function<Result<std::unique_ptr<Reader>>()>;

/// \brief Registry of reader factories for different file formats.
struct ICEBERG_EXPORT ReaderFactoryRegistry {
  /// \brief Register a factory function for a specific file format.
  ReaderFactoryRegistry(FileFormatType format_type, ReaderFactory factory);

  /// \brief Get the factory function for a specific file format.
  static ReaderFactory& GetFactory(FileFormatType format_type);

  /// \brief Open a reader for a specific file format.
  static Result<std::unique_ptr<Reader>> Open(FileFormatType format_type,
                                              const ReaderOptions& options);
};

}  // namespace iceberg