function_timer.hpp

// Copyright Take Vos 2022.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "required.hpp"
#include "chrono.hpp"
#include <vector>
#include <algorithm>
#include <chrono>
#include <functional>
 
namespace hi::inline v1 {
 
template<typename Proto = void()>
class function_timer {
public:
    using function_type = std::function<Proto>;
    using token_type = std::shared_ptr<function_type>;
    using weak_token_type = std::weak_ptr<function_type>;
    
    using result_type = function_type::result_type;
 
    constexpr function_timer() noexcept = default;
 
    [[nodiscard]] constexpr bool empty() const noexcept
    {
        return _functions.empty();
    }
 
    std::pair<token_type, bool> delay_function(utc_nanoseconds time_point, auto&& func) noexcept
    {
        hilet it = std::lower_bound(_functions.begin(), _functions.end(), time_point, [](hilet& x, hilet& time_point) {
            return x.time_point > time_point;
        });
 
        hilet next_to_call = it == _functions.end();
 
        auto token = std::make_shared<function_type>(hi_forward(func));
        _functions.emplace(it, time_point, std::chrono::nanoseconds::max(), token);
        return {std::move(token), next_to_call};
    }
 
    std::pair<token_type, bool> repeat_function(std::chrono::nanoseconds period, utc_nanoseconds time_point, auto&& func) noexcept
    {
        auto it = std::lower_bound(_functions.begin(), _functions.end(), time_point, [](hilet& x, hilet& time_point) {
            return x.time_point > time_point;
        });
 
        auto token = std::make_shared<function_type>(hi_forward(func));
        it = _functions.emplace(it, time_point, period, token);
        return {std::move(token), it + 1 == _functions.end()};
    }
 
    std::pair<token_type, bool> repeat_function(std::chrono::nanoseconds period, auto&& func) noexcept
    {
        return repeat_function(period, std::chrono::utc_clock::now(), hi_forward(func));
    }
 
    utc_nanoseconds current_deadline() const noexcept
    {
        if (_functions.empty()) {
            return utc_nanoseconds::max();
        } else {
            return _functions.back().time_point;
        }
    }
 
    void run_all(utc_nanoseconds current_time, auto&&...args) noexcept
    {
        while (current_deadline() <= current_time) {
            run_one(current_time, args...);
        }
    }
 
private:
    struct timer_type {
        utc_nanoseconds time_point;
        std::chrono::nanoseconds period;
        weak_token_type token;
 
        timer_type() noexcept = default;
        timer_type(timer_type const&) noexcept = default;
        timer_type(timer_type&&) noexcept = default;
        timer_type& operator=(timer_type const&) noexcept = default;
        timer_type& operator=(timer_type&&) noexcept = default;
 
        timer_type(utc_nanoseconds time_point, std::chrono::nanoseconds period, weak_token_type token) noexcept :
            time_point(time_point), period(period), token(std::move(token))
        {
        }
 
        timer_type(utc_nanoseconds time_point, weak_token_type token) noexcept :
            timer_type(time_point, std::chrono::nanoseconds::max(), std::move(token))
        {
        }
 
        timer_type(std::chrono::nanoseconds period, weak_token_type token) noexcept :
            timer_type(std::chrono::utc_clock::now(), period, std::move(token))
        {
        }
 
        [[nodiscard]] constexpr bool repeats() const noexcept
        {
            return period != std::chrono::nanoseconds::max();
        }
    };
 
    void remove_or_reinsert(utc_nanoseconds current_time) noexcept
    {
        hi_axiom(not _functions.empty());
 
        if (_functions.back().repeats() and not _functions.back().token.expired()) {
            // When the function is repeating, calculate the new.
            auto item = std::move(_functions.back());
            _functions.pop_back();
 
            // Delay the function to be called on the next period.
            // However if the current_time already is passed the deadline, delay it even further.
            item.time_point += item.period;
            if (item.time_point > current_time) {
                item.time_point = current_time + item.period;
            }
 
            // Reinsert the function in the sorted list of functions.
            hilet it = std::lower_bound(_functions.begin(), _functions.end(), item.time_point, [](hilet& x, hilet& time_point) {
                return x.time_point > time_point;
            });
 
            _functions.insert(it, std::move(item));
 
        } else {
            _functions.pop_back();
        }
    }
 
    result_type run_one(utc_nanoseconds current_time, auto&&...args)
    {
        hi_axiom(not _functions.empty());
 
        if constexpr (std::is_same_v<result_type, void>) {
            if (auto token = _functions.back().token.lock()) {
                (*token)(hi_forward(args)...);
            }
            remove_or_reinsert(current_time);
            return;
        } else {
            if (auto token = _functions.back().token.lock()) {
                auto result = (*token)(hi_forward(args)...);
                remove_or_reinsert(current_time);
                return result;
            } else {
                return {};
            }
        }
    }
 
    std::vector<timer_type> _functions;
};
 
} // namespace hi::inline v1