Add representation of an opening book.

src/learn/opening_book.cpp

@@ -0,0 +1,43 @@
+#include "opening_book.h"
+
+#include <fstream>
+
+namespace Learner {
+
+    EpdOpeningBook::EpdOpeningBook(const std::string& file, PRNG& prng) :
+        OpeningBook(file)
+    {
+        std::ifstream in(file);
+        if (!in)
+        {
+            return;
+        }
+
+        std::string line;
+        while (std::getline(in, line))
+        {
+            if (line.empty())
+                continue;
+
+            fens.emplace_back(line);
+        }
+
+        Algo::shuffle(fens, prng);
+    }
+
+    static bool ends_with(const std::string& lhs, const std::string& end)
+    {
+        if (end.size() > lhs.size()) return false;
+
+        return std::equal(end.rbegin(), end.rend(), lhs.rbegin());
+    }
+
+    std::unique_ptr<OpeningBook> open_opening_book(const std::string& filename, PRNG& prng)
+    {
+        if (ends_with(filename, ".epd"))
+            return std::make_unique<EpdOpeningBook>(filename, prng);
+
+        return nullptr;
+    }
+
+}