#pragma once
#include <array>
#include <cstdint>
#include <span>

template <uint16_t N>
struct ring_buffer {
    std::array<uint8_t, N> data = {};
    uint16_t head = 0;
    uint16_t tail = 0;

    uint16_t used() const { return tail - head; }
    uint16_t free() const { return N - used(); }
    bool empty() const { return head == tail; }

    void push(std::span<const uint8_t> src) {
        if (src.size() > free()) return;
        for (auto b : src)
            data[(tail++) % N] = b;
    }

    uint16_t peek(std::span<uint8_t> dst) const {
        uint16_t len = dst.size() < used() ? dst.size() : used();
        for (uint16_t i = 0; i < len; i++)
            dst[i] = data[(head + i) % N];
        return len;
    }

    void consume(uint16_t len) {
        head += len;
        if (head >= N) {
            head -= N;
            tail -= N;
        }
    }

    std::span<const uint8_t> read_contiguous() const {
        uint16_t offset = head % N;
        uint16_t contig = N - offset;
        uint16_t pending = used();
        uint16_t len = pending < contig ? pending : contig;
        return {data.data() + offset, len};
    }
};