Add representation of an opening book.

src/Makefile

@@ -63,6 +63,7 @@ SRCS = benchmark.cpp bitbase.cpp bitboard.cpp endgame.cpp evaluate.cpp main.cpp
 	learn/sfen_packer.cpp \
 	learn/learn.cpp \
 	learn/gensfen.cpp \
+	learn/opening_book.cpp \
 	learn/convert.cpp
 
 OBJS = $(notdir $(SRCS:.cpp=.o))

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;
+    }
+
+}

src/learn/opening_book.h

@@ -0,0 +1,56 @@
+#ifndef LEARN_OPENING_BOOK_H
+#define LEARN_OPENING_BOOK_H
+
+#include "misc.h"
+#include "position.h"
+#include "thread.h"
+
+#include <vector>
+#include <random>
+#include <optional>
+#include <string>
+#include <cstdint>
+#include <memory>
+
+namespace Learner {
+
+    struct OpeningBook {
+
+        const std::string& next_fen()
+        {
+            assert(fens.size() > 0);
+
+            auto& fen = fens[current_index++];
+            if (current_index >= fens.size())
+                current_index = 0;
+
+            return fen;
+        }
+
+        std::size_t size() const { return fens.size(); }
+
+        const std::string& get_filename() const { return filename; }
+
+    protected:
+        OpeningBook(const std::string& file) :
+            filename(file),
+            current_index(0)
+        {
+        }
+
+
+        std::string filename;
+        std::vector<std::string> fens;
+        std::size_t current_index;
+    };
+
+    struct EpdOpeningBook : OpeningBook {
+
+        EpdOpeningBook(const std::string& file, PRNG& prng);
+    };
+
+    std::unique_ptr<OpeningBook> open_opening_book(const std::string& filename, PRNG& prng);
+
+}
+
+#endif