text: // Copyright (c) 2018-2020, The Monero Project
  // 
  // All rights reserved.
  // 
  // Redistribution and use in source and binary forms, with or without modification, are
  // permitted provided that the following conditions are met:
  // 
  // 1. Redistributions of source code must retain the above copyright notice, this list of
  //    conditions and the following disclaimer.
  // 
  // 2. Redistributions in binary form must reproduce the above copyright notice, this list
  //    of conditions and the following disclaimer in the documentation and/or other
  //    materials provided with the distribution.
  // 
  // 3. Neither the name of the copyright holder nor the names of its contributors may be
  //    used to endorse or promote products derived from this software without specific
  //    prior written permission.
  // 
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
  // EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  // MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
  // THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  // PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  // STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
  // THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #pragma once
  
  #include <type_traits>
  
  namespace
  {
    // credits to yrp (https://stackoverflow.com/questions/87372/check-if-a-class-has-a-member-function-of-a-given-signature
    template <typename T>
    struct HasCredits
    {
      template<typename U, uint64_t (U::*)> struct SFINAE {};
      template<typename U> static char Test(SFINAE<U, &U::credits>*);
      template<typename U> static int Test(...);
      static const bool Has = sizeof(Test<T>(0)) == sizeof(char);
    };
  }
  
  namespace tools
  {
    struct rpc_payment_state_t
    {
      uint64_t credits;
      uint64_t expected_spent;
      uint64_t discrepancy;
      std::string top_hash;
      bool stale;
  
      rpc_payment_state_t(): credits(0), expected_spent(0), discrepancy(0), stale(true) {}
    };
  
    static inline void check_rpc_cost(rpc_payment_state_t &rpc_payment_state, const char *call, uint64_t post_call_credits, uint64_t pre_call_credits, double expected_cost)
    {
      uint64_t expected_credits = (uint64_t)expected_cost;
      if (expected_credits == 0)
        expected_credits = 1;
  
      rpc_payment_state.credits = post_call_credits;
      rpc_payment_state.expected_spent += expected_credits;
  
      if (pre_call_credits <= post_call_credits)
        return;
  
      uint64_t cost = pre_call_credits - post_call_credits;
  
      if (cost == expected_credits)
      {
        MDEBUG("Call " << call << " cost " << cost << " credits");
        return;
      }
      MWARNING("Call " << call << " cost " << cost << " credits, expected " << expected_credits);
  
      if (cost > expected_credits)
      {
        uint64_t d = cost - expected_credits;
        if (rpc_payment_state.discrepancy > std::numeric_limits<uint64_t>::max() - d)
        {
          MERROR("Integer overflow in credit discrepancy calculation, setting to max");
          rpc_payment_state.discrepancy = std::numeric_limits<uint64_t>::max();
        }
        else
        {
          rpc_payment_state.discrepancy += d;
        }
      }
    }
  }
  