text: //------------------------------------------------------------------------------
  /*
      This file is part of rippled: https://github.com/ripple/rippled
      Copyright (c) 2012, 2013 Ripple Labs Inc.
  
      Permission to use, copy, modify, and/or distribute this software for any
      purpose  with  or without fee is hereby granted, provided that the above
      copyright notice and this permission notice appear in all copies.
  
      THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
      WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
      MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
      ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
      WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
      ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
      OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
  //==============================================================================
  
  #include <ripple/app/paths/Credit.h>
  #include <ripple/app/paths/Flow.h>
  #include <ripple/app/paths/impl/AmountSpec.h>
  #include <ripple/app/paths/impl/StrandFlow.h>
  #include <ripple/app/paths/impl/Steps.h>
  #include <ripple/basics/Log.h>
  #include <ripple/protocol/IOUAmount.h>
  #include <ripple/protocol/XRPAmount.h>
  
  #include <boost/container/flat_set.hpp>
  
  #include <numeric>
  #include <sstream>
  
  namespace ripple {
  
  template<class FlowResult>
  static
  auto finishFlow (PaymentSandbox& sb,
      Issue const& srcIssue, Issue const& dstIssue,
      FlowResult&& f)
  {
      path::RippleCalc::Output result;
      if (f.ter == tesSUCCESS)
          f.sandbox->apply (sb);
      else
          result.removableOffers = std::move (f.removableOffers);
  
      result.setResult (f.ter);
      result.actualAmountIn = toSTAmount (f.in, srcIssue);
      result.actualAmountOut = toSTAmount (f.out, dstIssue);
  
      return result;
  };
  
  path::RippleCalc::Output
  flow (
      PaymentSandbox& sb,
      STAmount const& deliver,
      AccountID const& src,
      AccountID const& dst,
      STPathSet const& paths,
      bool defaultPaths,
      bool partialPayment,
      bool ownerPaysTransferFee,
      bool offerCrossing,
      boost::optional<Quality> const& limitQuality,
      boost::optional<STAmount> const& sendMax,
      beast::Journal j,
      path::detail::FlowDebugInfo* flowDebugInfo)
  {
      Issue const srcIssue = [&] {
          if (sendMax)
              return sendMax->issue ();
          if (!isXRP (deliver.issue ().currency))
              return Issue (deliver.issue ().currency, src);
          return xrpIssue ();
      }();
  
      Issue const dstIssue = deliver.issue ();
  
      boost::optional<Issue> sendMaxIssue;
      if (sendMax)
          sendMaxIssue = sendMax->issue ();
  
      // convert the paths to a collection of strands. Each strand is the collection
      // of account->account steps and book steps that may be used in this payment.
      auto sr = toStrands (sb, src, dst, dstIssue, limitQuality, sendMaxIssue,
          paths, defaultPaths, ownerPaysTransferFee, offerCrossing, j);
  
      if (sr.first != tesSUCCESS)
      {
          path::RippleCalc::Output result;
          result.setResult (sr.first);
          return result;
      }
  
      auto& strands = sr.second;
  
      if (j.trace())
      {
          j.trace() << "\nsrc: " << src << "\ndst: " << dst
              << "\nsrcIssue: " << srcIssue << "\ndstIssue: " << dstIssue;
          j.trace() << "\nNumStrands: " << strands.size ();
          for (auto const& curStrand : strands)
          {
              j.trace() << "NumSteps: " << curStrand.size ();
              for (auto const& step : curStrand)
              {
                  j.trace() << '\n' << *step << '\n';
              }
          }
      }
  
      const bool srcIsXRP = isXRP (srcIssue.currency);
      const bool dstIsXRP = isXRP (dstIssue.currency);
  
      auto const asDeliver = toAmountSpec (deliver);
  
      // The src account may send either xrp or iou. The dst account may receive
      // either xrp or iou. Since XRP and IOU amounts are represented by different
      // types, use templates to tell `flow` about the amount types.
      if (srcIsXRP && dstIsXRP)
      {
          return finishFlow (sb, srcIssue, dstIssue,
              flow<XRPAmount, XRPAmount> (
                  sb, strands, asDeliver.xrp, partialPayment, offerCrossing,
                  limitQuality, sendMax, j, flowDebugInfo));
      }
  
      if (srcIsXRP && !dstIsXRP)
      {
          return finishFlow (sb, srcIssue, dstIssue,
              flow<XRPAmount, IOUAmount> (
                  sb, strands, asDeliver.iou, partialPayment, offerCrossing,
                  limitQuality, sendMax, j, flowDebugInfo));
      }
  
      if (!srcIsXRP && dstIsXRP)
      {
          return finishFlow (sb, srcIssue, dstIssue,
              flow<IOUAmount, XRPAmount> (
                  sb, strands, asDeliver.xrp, partialPayment, offerCrossing,
                  limitQuality, sendMax, j, flowDebugInfo));
      }
  
      assert (!srcIsXRP && !dstIsXRP);
      return finishFlow (sb, srcIssue, dstIssue,
          flow<IOUAmount, IOUAmount> (
              sb, strands, asDeliver.iou, partialPayment, offerCrossing,
              limitQuality, sendMax, j, flowDebugInfo));
  
  }
  
  } // ripple
  