#pragma once

#include <cstdint>

#include <memory>

#include "envoy/common/pure.h"

#include "envoy/common/time.h"

namespace Envoy {

/**

 * This class defines an interface for the token bucket algorithm.

 *

 * https://en.wikipedia.org/wiki/Token_bucket

 */

class TokenBucket {

public:

  /**

   * @param tokens supplies the number of tokens to be consumed.

   * @param allow_partial supplies whether the token bucket will allow consumption of less tokens

   *                      than asked for. If allow_partial is true, the bucket contains 3 tokens,

   *                      and the caller asks for 5, the bucket will return 3 tokens and now be

   *                      empty.

   * @return the number of tokens actually consumed.

   */

  virtual uint64_t consume(uint64_t tokens, bool allow_partial) PURE;

  /**

   * @param tokens supplies the number of tokens to be consumed.

   * @param allow_partial supplies whether the token bucket will allow consumption of less tokens

   *                      than asked for. If allow_partial is true, the bucket contains 3 tokens,

   *                      and the caller asks for 5, the bucket will return 3 tokens and now be

   *                      empty.

   * @param time_to_next_token out param indicating the approx time until next token is available.

   * @return the number of tokens actually consumed.

   */

  virtual uint64_t consume(uint64_t tokens, bool allow_partial,

                           std::chrono::milliseconds& time_to_next_token) PURE;

  /**

   * @return returns the approximate time until a next token is available. Currently it

   * returns the upper bound on the amount of time until a next token is available.

   */

  virtual std::chrono::milliseconds nextTokenAvailable() PURE;

  /**

   * Reset the bucket with a specific number of tokens. Refill will begin again from the time that

   * this routine is called.

   * Note: The reset call might be honored only the first time this method is called. Check the

   * concrete implementation to confirm.

   */

  virtual void maybeReset(uint64_t num_tokens) PURE;

};

using TokenBucketPtr = std::unique_ptr<TokenBucket>;

}; // namespace Envoy