scheduler.hpp

#ifndef ENTT_PROCESS_SCHEDULER_HPP
#define ENTT_PROCESS_SCHEDULER_HPP
 
#include <cstddef>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
#include "../config/config.h"
#include "../core/compressed_pair.hpp"
#include "fwd.hpp"
#include "process.hpp"
 
namespace entt {

namespace internal {
 
template<typename Delta>
struct basic_process_handler {
    virtual ~basic_process_handler() = default;
 
    virtual bool update(Delta, void *) = 0;
    virtual void abort(bool) = 0;
 
    // std::shared_ptr because of its type erased allocator which is useful here
    std::shared_ptr<basic_process_handler> next;
};
 
template<typename Delta, typename Type>
struct process_handler final: basic_process_handler<Delta> {
    template<typename... Args>
    process_handler(Args &&...args)
        : process{std::forward<Args>(args)...} {}
 
    bool update(const Delta delta, void *data) override {
        if(process.tick(delta, data); process.rejected()) {
            this->next.reset();
        }
 
        return (process.rejected() || process.finished());
    }
 
    void abort(const bool immediate) override {
        process.abort(immediate);
    }
 
    Type process;
};
 
} // namespace internal

template<typename Delta, typename Allocator>
class basic_scheduler {
    template<typename Type>
    using handler_type = internal::process_handler<Delta, Type>;
 
    // std::shared_ptr because of its type erased allocator which is useful here
    using process_type = std::shared_ptr<internal::basic_process_handler<Delta>>;
 
    using alloc_traits = std::allocator_traits<Allocator>;
    using container_allocator = typename alloc_traits::template rebind_alloc<process_type>;
    using container_type = std::vector<process_type, container_allocator>;
 
public:
    using allocator_type = Allocator;
    using size_type = std::size_t;
    using delta_type = Delta;

    basic_scheduler()
        : basic_scheduler{allocator_type{}} {}

    explicit basic_scheduler(const allocator_type &allocator)
        : handlers{allocator, allocator} {}

    basic_scheduler(const basic_scheduler &) = delete;

    basic_scheduler(basic_scheduler &&other) noexcept
        : handlers{std::move(other.handlers)} {}

    basic_scheduler(basic_scheduler &&other, const allocator_type &allocator)
        : handlers{container_type{std::move(other.handlers.first()), allocator}, allocator} {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || get_allocator() == other.get_allocator(), "Copying a scheduler is not allowed");
    }

    ~basic_scheduler() = default;

    basic_scheduler &operator=(const basic_scheduler &) = delete;

    basic_scheduler &operator=(basic_scheduler &&other) noexcept {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || get_allocator() == other.get_allocator(), "Copying a scheduler is not allowed");
        swap(other);
        return *this;
    }

    void swap(basic_scheduler &other) noexcept {
        using std::swap;
        swap(handlers, other.handlers);
    }

    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return handlers.second();
    }

    [[nodiscard]] size_type size() const noexcept {
        return handlers.first().size();
    }

    [[nodiscard]] bool empty() const noexcept {
        return handlers.first().empty();
    }

    void clear() {
        handlers.first().clear();
    }

    template<typename Proc, typename... Args>
    basic_scheduler &attach(Args &&...args) {
        static_assert(std::is_base_of_v<process<Proc, Delta>, Proc>, "Invalid process type");
        auto &ref = handlers.first().emplace_back(std::allocate_shared<handler_type<Proc>>(handlers.second(), std::forward<Args>(args)...));
        // forces the process to exit the uninitialized state
        ref->update({}, nullptr);
        return *this;
    }

    template<typename Func>
    basic_scheduler &attach(Func &&func) {
        using Proc = process_adaptor<std::decay_t<Func>, Delta>;
        return attach<Proc>(std::forward<Func>(func));
    }

    template<typename Proc, typename... Args>
    basic_scheduler &then(Args &&...args) {
        static_assert(std::is_base_of_v<process<Proc, Delta>, Proc>, "Invalid process type");
        ENTT_ASSERT(!handlers.first().empty(), "Process not available");
        auto *curr = handlers.first().back().get();
        for(; curr->next; curr = curr->next.get()) {}
        curr->next = std::allocate_shared<handler_type<Proc>>(handlers.second(), std::forward<Args>(args)...);
        return *this;
    }

    template<typename Func>
    basic_scheduler &then(Func &&func) {
        using Proc = process_adaptor<std::decay_t<Func>, Delta>;
        return then<Proc>(std::forward<Func>(func));
    }

    void update(const delta_type delta, void *data = nullptr) {
        for(auto next = handlers.first().size(); next; --next) {
            if(const auto pos = next - 1u; handlers.first()[pos]->update(delta, data)) {
                // updating might spawn/reallocate, cannot hold refs until here
                if(auto &curr = handlers.first()[pos]; curr->next) {
                    curr = std::move(curr->next);
                    // forces the process to exit the uninitialized state
                    curr->update({}, nullptr);
                } else {
                    curr = std::move(handlers.first().back());
                    handlers.first().pop_back();
                }
            }
        }
    }

    void abort(const bool immediate = false) {
        for(auto &&curr: handlers.first()) {
            curr->abort(immediate);
        }
    }
 
private:
    compressed_pair<container_type, allocator_type> handlers;
};
 
} // namespace entt
 
#endif