InputRingBuffer.hpp

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#pragma once
 
#include "ecs/components/InputSnapshot.hpp"
 
#include <array>
#include <cstddef>
#include <cstdint>
 
class InputRingBuffer
{
public:
    static constexpr size_t k_capacity = 256;
 
    struct Entry
    {
        uint32_t tick = 0;     
        InputSnapshot input{}; 
        bool valid = false;    
    };

    void push(uint32_t tick, const InputSnapshot& input)
    {
        entries_[head_] = Entry{.tick = tick, .input = input, .valid = true};
        head_ = (head_ + 1) % k_capacity;
        if (count_ < k_capacity)
            ++count_;
    }

    [[nodiscard]] const InputSnapshot* find(uint32_t tick) const
    {
        // Walk newest-to-oldest. Most replays start near the head so this
        // is typically a 1-2 step search; worst case k_capacity steps.
        for (size_t i = 0; i < count_; ++i) {
            const size_t idx = (head_ + k_capacity - 1 - i) % k_capacity;
            const Entry& e = entries_[idx];
            if (!e.valid)
                continue;
            if (e.tick == tick)
                return &e.input;
            if (e.tick < tick)
                break; // ring is monotonically increasing — no point searching further
        }
        return nullptr;
    }

    [[nodiscard]] size_t size() const noexcept { return count_; }

    void clear() noexcept
    {
        head_ = 0;
        count_ = 0;
        for (auto& e : entries_)
            e.valid = false;
    }
 
private:
    std::array<Entry, k_capacity> entries_{};
    size_t head_ = 0;  
    size_t count_ = 0; 
};