// Copyright (C) 2022 WYATT GROUP
// Please see the AUTHORS file for details.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

import 'dart:core';
import 'dart:math';

/// Defines some delay functions.
abstract class Delay {
  /// Returns a delay based on the [attempt].
  static Duration getRetryDelay(int attempt) {
    assert(attempt >= 0, 'attempt cannot be negative');
    if (attempt <= 0) {
      return Duration.zero;
    }
    final rand = Random();
    const Duration delayFactor = Duration(milliseconds: 200);
    const double randomizationFactor = 0.25;
    const Duration maxDelay = Duration(seconds: 30);

    final rf = randomizationFactor * (rand.nextDouble() * 2 - 1) + 1;
    final exp = min(attempt, 31); // prevent overflows.
    final delay = delayFactor * pow(2.0, exp) * rf;
    return delay < maxDelay ? delay : maxDelay;
  }
}