// Copyright (C) 2019-2020 Zilliz. All rights reserved.
//
// 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
//
// 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 <atomic>
#include <memory>
#include <mutex>
#include <string>

#include "WalDefinations.h"
#include "WalFileHandler.h"
#include "WalMetaHandler.h"
#include "utils/Error.h"

namespace milvus {
namespace engine {
namespace wal {

#pragma pack(push)
#pragma pack(1)

struct MXLogRecordHeader {
    uint64_t mxl_lsn;  // log sequence number (high 32 bits: file No. inc by 1, low 32 bits: offset in file, max 4GB)
    uint8_t mxl_type;  // record type, insert/delete/update/flush...
    uint16_t table_id_size;
    uint16_t partition_tag_size;
    uint32_t vector_num;
    uint32_t data_size;
};

const uint32_t SizeOfMXLogRecordHeader = sizeof(MXLogRecordHeader);

#pragma pack(pop)

struct MXLogBufferHandler {
    uint32_t max_offset;
    uint32_t file_no;
    uint32_t buf_offset;
    uint8_t buf_idx;
};

using BufferPtr = std::shared_ptr<char[]>;

class MXLogBuffer {
 public:
    MXLogBuffer(const std::string& mxlog_path, const uint32_t buffer_size);
    ~MXLogBuffer();

    bool
    Init(uint64_t read_lsn, uint64_t write_lsn);

    // ignore all old wal file
    void
    Reset(uint64_t lsn);

    // Note: record.lsn will be set inner
    ErrorCode
    Append(MXLogRecord& record);

    ErrorCode
    Next(const uint64_t last_applied_lsn, MXLogRecord& record);

    uint64_t
    GetReadLsn();

    bool
    ResetWriteLsn(uint64_t lsn);

    void
    SetFileNoFrom(uint32_t file_no);

    void
    RemoveOldFiles(uint64_t flushed_lsn);

    uint32_t
    GetBufferSize();

    uint32_t
    SurplusSpace();

 private:
    uint32_t
    RecordSize(const MXLogRecord& record);

 private:
    uint32_t mxlog_buffer_size_;  // from config
    BufferPtr buf_[2];
    std::mutex mutex_;
    uint32_t file_no_from_;
    MXLogBufferHandler mxlog_buffer_reader_;
    MXLogBufferHandler mxlog_buffer_writer_;
    MXLogFileHandler mxlog_writer_;
};

using MXLogBufferPtr = std::shared_ptr<MXLogBuffer>;

}  // namespace wal
}  // namespace engine
}  // namespace milvus
