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

// Fixed-capacity FIFO with wrap-around. push_overwrite drops the oldest entry
// when full -- used by the debug log so dlog never blocks or fails. Iteration
// walks logical positions head..tail, hiding the modular indexing.
template <typename T, uint16_t N>
struct ring_buffer {
    std::array<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; }

    bool push(std::span<const T> src) {
        if (src.size() > free()) return false;
        for (auto& v : src)
            data[(tail++) % N] = v;
        return true;
    }

    bool push(const T& v) {
        if (free() == 0) return false;
        data[(tail++) % N] = v;
        return true;
    }

    void push_overwrite(const T& v) {
        if (free() == 0) head++;
        data[(tail++) % N] = v;
    }

    uint16_t peek(std::span<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 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};
    }

    struct iterator {
        const ring_buffer* rb;
        uint16_t index;
        const T& operator*() const { return rb->data[(rb->head + index) % N]; }
        iterator& operator++() { index++; return *this; }
        bool operator!=(const iterator& o) const { return index != o.index; }
    };

    iterator begin() const { return {this, 0}; }
    iterator end() const { return {this, used()}; }
};