using System;

// A fixed-size ring buffer that overwrites the oldest entries when full.
public class CircularBuffer<T> {
    readonly T[] buffer;
    int head, tail;
    public int Count { get; private set; }
    public int Capacity => buffer.Length;

    public CircularBuffer(int size) {
        if (size <= 0) throw new ArgumentOutOfRangeException(nameof(size));
        buffer = new T[size];
    }

    public void Enqueue(T item) {
        buffer[head] = item;
        head = (head + 1) % Capacity;
        if (Count == Capacity) tail = (tail + 1) % Capacity;
        else Count++;
    }

    public T Dequeue() {
        if (Count == 0) throw new InvalidOperationException("Buffer is empty");
        var item = buffer[tail];
        tail = (tail + 1) % Capacity;
        Count--;
        return item;
    }
    
    // Access elements by logical index (0 = oldest, Count-1 = newest)
    public T this[int index] {
        get {
            if ((uint)index >= (uint)Count) throw new ArgumentOutOfRangeException(nameof(index));
            if (Capacity == 0 || buffer == null) throw new InvalidOperationException();
            return buffer[(tail + index) % Capacity];
        }
    }
}