// Licensed to the Apache Software Foundation (ASF) under one

// or more contributor license agreements.  See the NOTICE file

// 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

// under the License.

#pragma once

#include <gen_cpp/data.pb.h>

#include <memory>

#include <string>

#include <vector>

#include "common/status.h"

#include "core/pod_array.h"

#include "core/pod_array_fwd.h"

#include "io/fs/file_reader_writer_fwd.h"

#include "runtime/runtime_profile.h"

#include "runtime/workload_management/resource_context.h"

#include "util/slice.h"

namespace doris {

class RuntimeState;

class Block;

class SpillDataDir;

/// SpillFileReader reads blocks sequentially across all parts of a SpillFile.

///

/// Usage:

///   auto reader = spill_file->create_reader(state, profile);

///   RETURN_IF_ERROR(reader->open());

///   bool eos = false;

///   while (!eos) { RETURN_IF_ERROR(reader->read(&block, &eos)); }

///

/// Part boundaries are transparent to the caller. When the current part is

/// exhausted, the reader automatically opens the next part.

///

/// Parts are opened on the SpillDataDir's file system (local disk or object storage).

/// Part sizes are known from the writer, so no size lookup is needed on open.

///

/// On object storage every read is a GET, so the reader keeps the request count low:

/// the part footer is fetched with one tail read of at most `_coalesce_bytes` (plus one more

/// read for the rest of a block offset array that does not fit), adjacent blocks are coalesced

/// into one read of at most `_coalesce_bytes`, and a part no larger than that is fetched whole.

/// A single block, or the rest of the offset array, larger than `_coalesce_bytes` is read whole.

class SpillFileReader {

public:

    SpillFileReader(RuntimeState* state, RuntimeProfile* profile, SpillDataDir* data_dir,

                    std::string spill_dir, std::vector<int64_t> part_sizes);

    ~SpillFileReader() { (void)close(); }

    /// Open the first part and read its footer metadata.

    Status open();

    /// Read the next block. Automatically advances across part boundaries.

    /// Sets *eos = true when all parts are exhausted.

    Status read(Block* block, bool* eos);

    /// Seek to a global block index within the whole spill file.

    /// block_index is 0-based across all parts.

    /// If block_index is out of range, the reader is positioned at EOS.

    Status seek(size_t block_index);

    Status close();

private:

    /// Open a specific part file and read its footer. With `fetch_small_part`, a part that

    /// fits in one coalesced read is fetched whole, so its blocks need no further reads.

    Status _open_part(size_t part_index, bool fetch_small_part);

    /// Read the footer (block offsets, max sub block size, block count) of the current part.

    Status _read_footer(size_t file_size, bool fetch_small_part);

    /// Point `out` at the serialized bytes of block `index` of the current part, reading

    /// them (and the following blocks that fit in the coalesce window) if not buffered.

    Status _block_slice(size_t index, Slice* out);

    /// Read exactly `len` bytes at `offset` of the current part into `data`.

    Status _read_exact(size_t offset, char* data, size_t len);

    /// Seek implementation with status propagation.

    Status _seek_to_block(size_t block_index);

    /// Close the current part's file reader.

    void _close_current_part();

    /// Make the read buffer hold at least `size` bytes.

    void _ensure_read_buff(size_t size);

    /// Account bytes read from the store (local or remote) as one request.

    void _record_read(size_t bytes_read);

    // ── Configuration ──

    SpillDataDir* _data_dir = nullptr;

    std::string _spill_dir;

    std::vector<int64_t> _part_sizes;

    size_t _part_count;

    bool _is_remote = false;

    // Upper bound of one coalesced read; 0 reads block by block (local disk).

    size_t _coalesce_bytes = 0;

    // ── Current part state ──

    size_t _current_part_index = 0;

    bool _is_open = false;

    bool _part_opened = false;

    io::FileReaderSPtr _file_reader;

    size_t _part_block_count = 0;

    size_t _part_read_block_index = 0;

    size_t _part_max_sub_block_size = 0;

    // Holds the bytes of [_window_begin, _window_end) of the current part.

    PaddedPODArray<char> _read_buff;

    size_t _window_begin = 0;

    size_t _window_end = 0;

    std::vector<size_t> _block_start_offsets;

    PBlock _pb_block;

    // ── Counters ──

    RuntimeProfile::Counter* _read_file_timer = nullptr;

    RuntimeProfile::Counter* _deserialize_timer = nullptr;

    RuntimeProfile::Counter* _read_block_count = nullptr;

    RuntimeProfile::Counter* _read_block_data_size = nullptr;

    RuntimeProfile::Counter* _read_file_size = nullptr;

    RuntimeProfile::Counter* _read_rows_count = nullptr;

    RuntimeProfile::Counter* _read_file_count = nullptr;

    // Remote only, may be null when the profile does not register it.

    RuntimeProfile::Counter* _remote_read_requests = nullptr;

    std::shared_ptr<ResourceContext> _resource_ctx = nullptr;

};

using SpillFileReaderSPtr = std::shared_ptr<SpillFileReader>;

} // namespace doris