// Copyright 2023 PingCAP, Inc.
//
// 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 <boost/noncopyable.hpp>
#include <memory>
#include <mutex>
#include <unordered_map>

#include "DateLUTImpl.h"
#include "defines.h"


/// This class provides lazy initialization and lookup of singleton DateLUTImpl objects for a given timezone.
class DateLUT : private boost::noncopyable
{
public:
    /// Return singleton DateLUTImpl instance for the default time zone.
    static ALWAYS_INLINE const DateLUTImpl & instance()
    {
        const auto & date_lut = getInstance();
        return *date_lut.default_impl.load(std::memory_order_acquire);
    }

    /// Return singleton DateLUTImpl instance for a given time zone.
    static ALWAYS_INLINE const DateLUTImpl & instance(const std::string & time_zone)
    {
        const auto & date_lut = getInstance();
        if (time_zone.empty())
            return *date_lut.default_impl.load(std::memory_order_acquire);

        return date_lut.getImplementation(time_zone);
    }
    static void setDefaultTimezone(const std::string & time_zone)
    {
        auto & date_lut = getInstance();
        const auto & impl = date_lut.getImplementation(time_zone);
        date_lut.default_impl.store(&impl, std::memory_order_release);
    }

protected:
    DateLUT();

private:
    static DateLUT & getInstance();

    const DateLUTImpl & getImplementation(const std::string & time_zone) const;

    using DateLUTImplPtr = std::unique_ptr<DateLUTImpl>;

    /// Time zone name -> implementation.
    mutable std::unordered_map<std::string, DateLUTImplPtr> impls;
    mutable std::mutex mutex;

    std::atomic<const DateLUTImpl *> default_impl;
};