import '../proto/messages.pb.dart';

/// Fixed-capacity ring buffer of log entries. Same semantics as PacketBuffer
/// but tuned for log throughput (much lower than data).
class LogBuffer {
  LogBuffer({required this.capacity}) : _storage = List.filled(capacity, null);

  int capacity;
  List<LogPacket?> _storage;
  int _head = 0;
  int _length = 0;

  int get length => _length;
  bool get isEmpty => _length == 0;

  void add(LogPacket entry) {
    _storage[_head] = entry;
    _head = (_head + 1) % capacity;
    if (_length < capacity) _length++;
  }

  void clear() {
    _head = 0;
    _length = 0;
    for (var i = 0; i < _storage.length; i++) {
      _storage[i] = null;
    }
  }

  void resize(int newCapacity) {
    if (newCapacity == capacity) return;
    final preserve = newCapacity < _length ? newCapacity : _length;
    final newStorage = List<LogPacket?>.filled(newCapacity, null);
    final start = (_head - preserve + capacity) % capacity;
    for (var i = 0; i < preserve; i++) {
      newStorage[i] = _storage[(start + i) % capacity];
    }
    _storage = newStorage;
    capacity = newCapacity;
    _head = preserve % newCapacity;
    _length = preserve;
  }

  /// Iterate from oldest to newest.
  Iterable<LogPacket> iterate() sync* {
    if (_length == 0) return;
    final start = (_head - _length + capacity) % capacity;
    for (var i = 0; i < _length; i++) {
      yield _storage[(start + i) % capacity]!;
    }
  }
}