fix(Core/Battlegrounds) Rewrite RandomBG and enabling bg/arenas weights (#2516)

src/common/Containers.h

@@ -13,9 +13,11 @@
 #include <iterator>
 #include <utility>
 #include <list>
+#include <vector>
 
 //! Because circular includes are bad
 extern uint32 urand(uint32 min, uint32 max);
+extern uint32 urandweighted(size_t count, double const* chances);
 
 namespace acore
 {
@@ -97,6 +99,14 @@ namespace acore
             std::advance(it, urand(0, container.size() - 1));
             return *it;
         }
+
+        /*  Select a random element from a container where each element has a different chance to be selected. */
+        template <class C> typename C::value_type const& SelectRandomWeightedContainerElement(C const& container, std::vector<double> const& weights)
+        {
+            typename C::const_iterator it = container.begin();
+            std::advance(it, urandweighted(weights.size(), weights.data()));
+            return *it;
+        }
     }
     //! namespace Containers
 }

src/common/Utilities/Util.cpp

@@ -18,9 +18,11 @@
 #include <array>
 #include <cwchar>
 #include <string>
+#include <random>
 
 typedef ACE_TSS<SFMTRand> SFMTRandTSS;
 static SFMTRandTSS sfmtRand;
+static SFMTEngine engine;
 
 int32 irand(int32 min, int32 max)
 {
@@ -55,6 +57,17 @@ double rand_chance()
     return sfmtRand->Random() * 100.0;
 }
 
+uint32 urandweighted(size_t count, double const* chances)
+{
+    std::discrete_distribution<uint32> dd(chances, chances + count);
+    return dd(SFMTEngine::Instance());
+}
+
+SFMTEngine& SFMTEngine::Instance()
+{
+    return engine;
+}
+
 Tokenizer::Tokenizer(const std::string &src, const char sep, uint32 vectorReserve)
 {
     m_str = new char[src.length() + 1];

src/common/Utilities/Util.h

@@ -82,6 +82,8 @@ double rand_norm();
 /* Return a random double from 0.0 to 100.0 (exclusive). */
 double rand_chance();
 
+uint32 urandweighted(size_t count, double const* chances);
+
 /* Return true if a random roll fits in the specified chance (range 0-100). */
 inline bool roll_chance_f(float chance)
 {
@@ -555,6 +557,21 @@ bool CompareValues(ComparisionType type, T val1, T val2)
     }
 }
 
+/*
+* SFMT wrapper satisfying UniformRandomNumberGenerator concept for use in <random> algorithms
+*/
+class SFMTEngine
+{
+public:
+    typedef uint32 result_type;
+
+    static constexpr result_type min() { return std::numeric_limits<result_type>::min(); }
+    static constexpr result_type max() { return std::numeric_limits<result_type>::max(); }
+    result_type operator()() const { return rand32(); }
+
+    static SFMTEngine& Instance();
+};
+
 class EventMap
 {
     typedef std::multimap<uint32, uint32> EventStore;