From 0c73ac5fea0e1e14a890fec4e3826120a88b2b00 Mon Sep 17 00:00:00 2001
From: Arsentiy Milchakov <milcars@mapswithme.com>
Date: Wed, 27 May 2020 12:00:53 +0300
Subject: [PATCH] [base] id generator is added

---
 base/CMakeLists.txt                    |  1 +
 base/base_tests/CMakeLists.txt         |  1 +
 base/base_tests/id_generator_tests.cpp | 33 ++++++++++++
 base/id_generator.hpp                  | 69 ++++++++++++++++++++++++++
 4 files changed, 104 insertions(+)
 create mode 100644 base/base_tests/id_generator_tests.cpp
 create mode 100644 base/id_generator.hpp

diff --git a/base/CMakeLists.txt b/base/CMakeLists.txt
index 53856cdc92..bfbacb116e 100644
--- a/base/CMakeLists.txt
+++ b/base/CMakeLists.txt
@@ -33,6 +33,7 @@ set(
   get_time.hpp
   gmtime.cpp
   gmtime.hpp
+  id_generator.hpp
   internal/message.cpp
   internal/message.hpp
   levenshtein_dfa.cpp
diff --git a/base/base_tests/CMakeLists.txt b/base/base_tests/CMakeLists.txt
index f3d7bdd061..072d3f7849 100644
--- a/base/base_tests/CMakeLists.txt
+++ b/base/base_tests/CMakeLists.txt
@@ -17,6 +17,7 @@ set(
   condition_test.cpp
   containers_test.cpp
   control_flow_tests.cpp
+  id_generator_tests.cpp
   fifo_cache_test.cpp
   file_name_utils_tests.cpp
   geo_object_id_tests.cpp
diff --git a/base/base_tests/id_generator_tests.cpp b/base/base_tests/id_generator_tests.cpp
new file mode 100644
index 0000000000..e557dcc84e
--- /dev/null
+++ b/base/base_tests/id_generator_tests.cpp
@@ -0,0 +1,33 @@
+#include "testing/testing.hpp"
+
+#include "base/id_generator.hpp"
+
+#include <limits>
+#include <string>
+#include <vector>
+
+UNIT_TEST(IdGenerator_Smoke)
+{
+  auto const initial = base::IdGenerator<uint8_t>::GetInitialId();
+  TEST_EQUAL(initial, "1", ());
+
+  auto constexpr kOverflowCount = 5;
+  auto constexpr kItemsCount = std::numeric_limits<uint8_t>::max();
+
+  auto id = initial;
+  auto i = 2;
+  for (auto k = 0; k < kOverflowCount; ++k)
+  {
+    for (; i <= kItemsCount; ++i)
+    {
+      std::string target;
+      for (auto j = 0; j < k; ++j)
+        target += std::to_string(kItemsCount);
+
+      target += std::to_string(i);
+      id = base::IdGenerator<uint8_t>::GetNextId(id);
+      TEST_EQUAL(target, id, ());
+    }
+    i = 1;
+  }
+}
diff --git a/base/id_generator.hpp b/base/id_generator.hpp
new file mode 100644
index 0000000000..7043868198
--- /dev/null
+++ b/base/id_generator.hpp
@@ -0,0 +1,69 @@
+#pragma once
+
+#include "base/string_utils.hpp"
+
+#include <string>
+#include <type_traits>
+#include <vector>
+
+namespace base
+{
+// Simple id generator which increments received value and concatenates when
+// BaseIntegralUnsigned max value is reached.
+template <typename BaseIntegralUnsigned = uint64_t>
+class IdGenerator
+{
+public:
+  static_assert(std::is_integral<BaseIntegralUnsigned>::value, "Integral types is supported only");
+  static_assert(std::is_unsigned<BaseIntegralUnsigned>::value, "Unsigned types is supported only");
+
+  using Id = std::string;
+
+  static Id GetInitialId()
+  {
+    return std::to_string(kMinIdInternal);
+  }
+
+  static Id GetNextId(Id const & id)
+  {
+    std::vector<Id> idParts;
+    auto first = id.begin();
+    auto last = id.end();
+    while (last - first > kMaxSymbolsIdInternal)
+    {
+      idParts.emplace_back(first, first + kMaxSymbolsIdInternal);
+      first += kMaxSymbolsIdInternal;
+    }
+    idParts.emplace_back(first, last);
+
+    IdInternal internalId;
+    if (!strings::to_any(idParts.back(), internalId))
+      return {};
+
+    auto const newId = MakeNextInternalId(internalId);
+
+    if (newId < internalId)
+      idParts.emplace_back(std::to_string(newId));
+    else
+      idParts.back() = std::to_string(newId);
+
+    return strings::JoinAny(idParts, "");
+  }
+
+private:
+  using IdInternal = BaseIntegralUnsigned;
+
+  static IdInternal constexpr kIncorrectId = 0;
+  static IdInternal constexpr kMinIdInternal = 1;
+  static IdInternal constexpr kMaxIdInternal = std::numeric_limits<IdInternal>::max();
+  static auto constexpr kMaxSymbolsIdInternal = std::numeric_limits<IdInternal>::digits10 + 1;
+
+  static constexpr IdInternal MakeNextInternalId(IdInternal id)
+  {
+    if (id == kMaxIdInternal)
+      return kMinIdInternal;
+
+    return ++id;
+  }
+};
+}  // namespace base