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 // This file is part of the Acts project.
 //
 // Copyright (C) 2017 CERN for the benefit of the Acts project
 //
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 #pragma once
 
 #include <cmath>
 #include <exception>
 #include <functional>
 #include <sstream>
 #include <vector>
 
 #include "TDictionary.h"
 #include "TTreeReaderValue.h"
 
 // Pairs of elements of the same type
 template <typename T>
 using HomogeneousPair = std::pair<T, T>;
 
 // === TYPE ERASURE FOR CONCRETE DATA ===
 
 // Minimal type-erasure wrapper for std::vector<T>. This will be used as a
 // workaround to compensate for the absence of C++17's std::any in Cling.
 class AnyVector {
  public:
   // Create a type-erased vector<T>, using proposed constructor arguments.
   // Returns a pair containing the type-erased vector and a pointer to the
   // underlying concrete vector.
   template <typename T, typename... Args>
   static std::pair<AnyVector, std::vector<T>*> create(Args&&... args) {
     std::vector<T>* vector = new std::vector<T>(std::forward<Args>(args)...);
     std::function<void()> deleter = [vector] { delete vector; };
     return std::make_pair(
         AnyVector{static_cast<void*>(vector), std::move(deleter)}, vector);
   }
 
   // Default-construct a null type-erased vector
   AnyVector() = default;
 
   // Move-construct a type-erased vector
   AnyVector(AnyVector&& other)
       : m_vector{other.m_vector}, m_deleter{std::move(other.m_deleter)} {
     other.m_vector = nullptr;
   }
 
   // Move-assign a type-erased vector
   AnyVector& operator=(AnyVector&& other) {
     if (&other != this) {
       m_vector = other.m_vector;
       m_deleter = std::move(other.m_deleter);
       other.m_vector = nullptr;
     }
     return *this;
   }
 
   // Forbid copies of type-erased vectors
   AnyVector(const AnyVector&) = delete;
   AnyVector& operator=(const AnyVector&) = delete;
 
   // Delete a type-erased vector
   ~AnyVector() {
     if (m_vector != nullptr) {
       m_deleter();
     }
   }
 
  private:
   // Construct a type-erased vector from a concrete vector
   AnyVector(void* vector, std::function<void()>&& deleter)
       : m_vector{vector}, m_deleter{std::move(deleter)} {}
 
   void* m_vector{nullptr};          // Casted std::vector<T>*
   std::function<void()> m_deleter;  // Deletes the underlying vector
 };
 
 // === GENERIC DATA ORDERING ===
 
 // We want to check, in a single operation, how two pieces of data are ordered
 enum class Ordering { SMALLER, EQUAL, GREATER };
 
 // In general, any type which implements comparison operators that behave as a
 // mathematical total order can use this comparison function...
 template <typename T>
 Ordering compare(const T& x, const T& y) {
   if (x < y) {
     return Ordering::SMALLER;
   } else if (x == y) {
     return Ordering::EQUAL;
   } else {
     return Ordering::GREATER;
   }
 }
 
 // ...but we'll want to tweak that a little for floats, to handle NaNs better...
 template <typename T>
 Ordering compareFloat(const T& x, const T& y) {
   if (std::isless(x, y)) {
     return Ordering::SMALLER;
   } else if (std::isgreater(x, y)) {
     return Ordering::GREATER;
   } else {
     return Ordering::EQUAL;
   }
 }
 
 template <>
 Ordering compare(const float& x, const float& y) {
   return compareFloat(x, y);
 }
 
 template <>
 Ordering compare(const double& x, const double& y) {
   return compareFloat(x, y);
 }
 
 // ...and for vectors, where the default lexicographic comparison cannot
 // efficiently tell all of what we want in a single vector iteration pass.
 template <typename U>
 Ordering compare(const std::vector<U>& v1, const std::vector<U>& v2) {
   // First try to order by size...
   if (v1.size() < v2.size()) {
     return Ordering::SMALLER;
   } else if (v1.size() > v2.size()) {
     return Ordering::GREATER;
   }
   // ...if the size is identical...
   else {
     // ...then try to order by contents of increasing index...
     for (std::size_t i = 0; i < v1.size(); ++i) {
       if (v1[i] < v2[i]) {
         return Ordering::SMALLER;
       } else if (v1[i] > v2[i]) {
         return Ordering::GREATER;
       }
     }
 
     // ...and declare the vectors equal if the contents are equal
     return Ordering::EQUAL;
   }
 }
 
 // === GENERIC SORTING MECHANISM ===
 
 // The following functions are generic implementations of sorting algorithms,
 // which require only a comparison operator, a swapping operator, and an
 // inclusive range of indices to be sorted in order to operate
 using IndexComparator = std::function<Ordering(std::size_t, std::size_t)>;
 using IndexSwapper = std::function<void(std::size_t, std::size_t)>;
 
 // Selection sort has pertty bad asymptotic scaling, but it is non-recursive
 // and in-place, which makes it a good choice for smaller inputs
 void selectionSort(const std::size_t firstIndex, const std::size_t lastIndex,
                    const IndexComparator& compare, const IndexSwapper& swap) {
   for (std::size_t targetIndex = firstIndex; targetIndex < lastIndex;
        ++targetIndex) {
     std::size_t minIndex = targetIndex;
     for (std::size_t readIndex = targetIndex + 1; readIndex <= lastIndex;
          ++readIndex) {
       if (compare(readIndex, minIndex) == Ordering::SMALLER) {
         minIndex = readIndex;
       }
     }
     if (minIndex != targetIndex) {
       swap(minIndex, targetIndex);
     }
   }
 }
 
 // Quick sort is used as the top-level sorting algorithm for our datasets
 void quickSort(const std::size_t firstIndex, const std::size_t lastIndex,
                const IndexComparator& compare, const IndexSwapper& swap) {
   // We switch to non-recursive selection sort when the range becomes too small.
   // This optimization voids the need for detection of 0- and 1-element input.
   static const std::size_t NON_RECURSIVE_THRESHOLD = 25;
   if (lastIndex - firstIndex < NON_RECURSIVE_THRESHOLD) {
     selectionSort(firstIndex, lastIndex, compare, swap);
     return;
   }
 
   // We'll use the midpoint as a pivot. Later on, we can switch to more
   // elaborate pivot selection schemes if their usefulness for our use case
   // (pseudorandom events with thread-originated reordering) is demonstrated.
   std::size_t pivotIndex = firstIndex + (lastIndex - firstIndex) / 2;
 
   // Partition the data around the pivot using Hoare's scheme
   std::size_t splitIndex = 0;
   {
     // Start with two indices one step beyond each side of the array
     std::size_t i = firstIndex - 1;
     std::size_t j = lastIndex + 1;
     while (true) {
       // Move left index forward at least once, and until an element which is
       // greater than or equal to the pivot is detected.
       do {
         i = i + 1;
       } while (compare(i, pivotIndex) == Ordering::SMALLER);
 
       // Move right index backward at least once, and until an element which is
       // smaller than or equal to the pivot is detected
       do {
         j = j - 1;
       } while (compare(j, pivotIndex) == Ordering::GREATER);
 
       // By transitivity of inequality, the element at location i is greater
       // than or equal to the one at location j, and a swap could be required
       if (i < j) {
         // These elements are in the wrong order, swap them
         swap(i, j);
 
         // Don't forget to keep track the pivot's index along the way, as this
         // is currently the only way by which we can refer to the pivot element.
         if (i == pivotIndex) {
           pivotIndex = j;
         } else if (j == pivotIndex) {
           pivotIndex = i;
         }
       } else {
         // If i and j went past each other, our partitioning is done
         splitIndex = j;
         break;
       }
     }
   }
 
   // Now, we'll recursively sort both partitions using quicksort. We should
   // recurse in the smaller range first, so as to leverage compiler tail call
   // optimization if available.
   if (splitIndex - firstIndex <= lastIndex - splitIndex - 1) {
     quickSort(firstIndex, splitIndex, compare, swap);
     quickSort(splitIndex + 1, lastIndex, compare, swap);
   } else {
     quickSort(splitIndex + 1, lastIndex, compare, swap);
     quickSort(firstIndex, splitIndex, compare, swap);
   }
 }
 
 // === GENERIC TTREE BRANCH MANIPULATION MECHANISM ===
 
 // When comparing a pair of TTrees, we'll need to set up quite a few facilities
 // for each branch. Since this setup is dependent on the branch data type, which
 // is only known at runtime, it is quite involved, which is why we extracted it
 // to a separate struct and its constructor.
 struct BranchComparisonHarness {
   // We'll keep track of the branch name for debugging purposes
   std::string branchName;
 
   // Type-erased event data for the current branch, in both trees being compared
   HomogeneousPair<AnyVector> eventData;
 
   // Function which loads the active event data for the current branch. This is
   // to be performed for each branch and combined with TTreeReader-based event
   // iteration on both trees.
   void loadCurrentEvent() { (*m_eventLoaderPtr)(); }
 
   // Functors which compare two events within a given tree and order them
   // with respect to one another, and which swap two events. By combining such
   // functionality for each branch, a global tree order can be produced.
   HomogeneousPair<std::pair<IndexComparator, IndexSwapper>> sortHarness;
 
   // Functor which compares the current event data in *both* trees and tells
   // whether it is identical. The comparison is order-sensitive, so events
   // should previously have been sorted in a canonical order in both trees.
   // By combining the results for each branch, global tree equality is defined.
   using TreeComparator = std::function<bool()>;
   TreeComparator eventDataEqual;
 
   // Functor which dumps the event data for the active event side by side, in
   // two columns. This enables manual comparison during debugging.
   std::function<void()> dumpEventData;
 
   // General metadata about the tree which is identical for every branch
   struct TreeMetadata {
     TTreeReader& tree1Reader;
     TTreeReader& tree2Reader;
     const std::size_t entryCount;
   };
 
   // This exception will be thrown if an unsupported branch type is encountered
   class UnsupportedBranchType : public std::exception {};
 
   // Type-erased factory of branch comparison harnesses, taking ROOT run-time
   // type information as input in order to select an appropriate C++ constructor
   static BranchComparisonHarness create(TreeMetadata& treeMetadata,
                                         const std::string& branchName,
                                         const EDataType dataType,
                                         const std::string& className) {
     switch (dataType) {
       case kChar_t:
         return BranchComparisonHarness::create<char>(treeMetadata, branchName);
       case kUChar_t:
         return BranchComparisonHarness::create<unsigned char>(treeMetadata,
                                                               branchName);
       case kShort_t:
         return BranchComparisonHarness::create<short>(treeMetadata, branchName);
       case kUShort_t:
         return BranchComparisonHarness::create<unsigned short>(treeMetadata,
                                                                branchName);
       case kInt_t:
         return BranchComparisonHarness::create<int>(treeMetadata, branchName);
       case kUInt_t:
         return BranchComparisonHarness::create<unsigned int>(treeMetadata,
                                                              branchName);
       case kLong_t:
         return BranchComparisonHarness::create<long>(treeMetadata, branchName);
       case kULong_t:
         return BranchComparisonHarness::create<unsigned long>(treeMetadata,
                                                               branchName);
       case kULong64_t:
         return BranchComparisonHarness::create<unsigned long long>(treeMetadata,
                                                                    branchName);
 
       case kFloat_t:
         return BranchComparisonHarness::create<float>(treeMetadata, branchName);
       case kDouble_t:
         return BranchComparisonHarness::create<double>(treeMetadata,
                                                        branchName);
       case kBool_t:
         return BranchComparisonHarness::create<bool>(treeMetadata, branchName);
       case kOther_t:
         if (className.substr(0, 6) == "vector") {
           std::string elementType = className.substr(7, className.size() - 8);
           return BranchComparisonHarness::createVector(treeMetadata, branchName,
                                                        std::move(elementType));
         } else {
           throw UnsupportedBranchType();
         }
       default:
         throw UnsupportedBranchType();
     }
   }
 
  private:
   // Under the hood, the top-level factory calls the following function
   // template, parametrized with the proper C++ data type
   template <typename T>
   static BranchComparisonHarness create(TreeMetadata& treeMetadata,
                                         const std::string& branchName) {
     // Our result will eventually go there
     BranchComparisonHarness result;
 
     // Save the branch name for debugging purposes
     result.branchName = branchName;
 
     // Setup type-erased event data storage
     auto tree1DataStorage = AnyVector::create<T>();
     auto tree2DataStorage = AnyVector::create<T>();
     result.eventData = std::make_pair(std::move(tree1DataStorage.first),
                                       std::move(tree2DataStorage.first));
     std::vector<T>& tree1Data = *tree1DataStorage.second;
     std::vector<T>& tree2Data = *tree2DataStorage.second;
 
     // Use our advance knowledge of the event count to preallocate storage
     tree1Data.reserve(treeMetadata.entryCount);
     tree2Data.reserve(treeMetadata.entryCount);
 
     // Setup event data readout
     result.m_eventLoaderPtr.reset(
         new EventLoaderT<T>{treeMetadata.tree1Reader, treeMetadata.tree2Reader,
                             branchName, tree1Data, tree2Data});
 
     // Setup event comparison and swapping for each tree
     result.sortHarness = std::make_pair(
         std::make_pair(
             [&tree1Data](std::size_t i, std::size_t j) -> Ordering {
               return compare(tree1Data[i], tree1Data[j]);
             },
             [&tree1Data](std::size_t i, std::size_t j) {
               std::swap(tree1Data[i], tree1Data[j]);
             }),
         std::make_pair(
             [&tree2Data](std::size_t i, std::size_t j) -> Ordering {
               return compare(tree2Data[i], tree2Data[j]);
             },
             [&tree2Data](std::size_t i, std::size_t j) {
               std::swap(tree2Data[i], tree2Data[j]);
             }));
 
     // Setup order-sensitive tree comparison
     result.eventDataEqual = [&tree1Data, &tree2Data]() -> bool {
       for (std::size_t i = 0; i < tree1Data.size(); ++i) {
         if (compare(tree1Data[i], tree2Data[i]) != Ordering::EQUAL) {
           return false;
         }
       }
       return true;
     };
 
     // Add a debugging method to dump event data
     result.dumpEventData = [&tree1Data, &tree2Data] {
       std::cout << "File 1                \tFile 2" << std::endl;
       for (std::size_t i = 0; i < tree1Data.size(); ++i) {
         std::cout << toString(tree1Data[i]) << "      \t"
                   << toString(tree2Data[i]) << std::endl;
       }
     };
 
     // ...and we're good to go!
     return std::move(result);
   }
 
   // Because the people who created TTreeReaderValue could not bother to make it
   // movable (for moving it into a lambda), or even just virtually destructible
   // (for moving a unique_ptr into the lambda), loadEventData can only be
   // implemented through lots of unpleasant C++98-ish boilerplate.
   class IEventLoader {
    public:
     virtual ~IEventLoader() = default;
     virtual void operator()() = 0;
   };
 
   template <typename T>
   class EventLoaderT : public IEventLoader {
    public:
     EventLoaderT(TTreeReader& tree1Reader, TTreeReader& tree2Reader,
                  const std::string& branchName, std::vector<T>& tree1Data,
                  std::vector<T>& tree2Data)
         : branch1Reader{tree1Reader, branchName.c_str()},
           branch2Reader{tree2Reader, branchName.c_str()},
           branch1Data(tree1Data),
           branch2Data(tree2Data) {}
 
     void operator()() override {
       branch1Data.push_back(*branch1Reader);
       branch2Data.push_back(*branch2Reader);
     }
 
    private:
     TTreeReaderValue<T> branch1Reader, branch2Reader;
     std::vector<T>& branch1Data;
     std::vector<T>& branch2Data;
   };
 
   std::unique_ptr<IEventLoader> m_eventLoaderPtr;
 
   // This helper factory helps building branches associated with std::vectors
   // of data, which are the only STL collection that we support at the moment.
   static BranchComparisonHarness createVector(TreeMetadata& treeMetadata,
                                               const std::string& branchName,
                                               const std::string elemType) {
 // We support vectors of different types by switching across type (strings)
 #define CREATE_VECTOR__HANDLE_TYPE(type_name)                       \
   if (elemType == #type_name) {                                     \
     return BranchComparisonHarness::create<std::vector<type_name>>( \
         treeMetadata, branchName);                                  \
   }
 
     // Handle vectors of booleans
     CREATE_VECTOR__HANDLE_TYPE(bool)
 
     // Handle vectors of all standard floating-point types
     else CREATE_VECTOR__HANDLE_TYPE(float) else CREATE_VECTOR__HANDLE_TYPE(
         double)
 
 // For integer types, we'll want to handle both signed and unsigned versions
 #define CREATE_VECTOR__HANDLE_INTEGER_TYPE(integer_type_name) \
   CREATE_VECTOR__HANDLE_TYPE(integer_type_name)               \
   else CREATE_VECTOR__HANDLE_TYPE(unsigned integer_type_name)
 
         // Handle vectors of all standard integer types
         else CREATE_VECTOR__HANDLE_INTEGER_TYPE(char) else CREATE_VECTOR__HANDLE_INTEGER_TYPE(short) else CREATE_VECTOR__HANDLE_INTEGER_TYPE(
             int) else CREATE_VECTOR__HANDLE_INTEGER_TYPE(long) else CREATE_VECTOR__HANDLE_INTEGER_TYPE(long long)
 
         // Throw an exception if the vector element type is not recognized
         else throw UnsupportedBranchType();
   }
 
   // This helper method provides general string conversion for all supported
   // branch event data types.
   template <typename T>
   static std::string toString(const T& data) {
     std::ostringstream oss;
     oss << data;
     return oss.str();
   }
 
   template <typename U>
   static std::string toString(const std::vector<U>& vector) {
     std::ostringstream oss{"{ "};
     for (const auto& data : vector) {
       oss << data << "  \t";
     }
     oss << " }";
     return oss.str();
   }
 };

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