added timezone support

CMakeLists.txt

@@ -1,6 +1,14 @@
 cmake_minimum_required(VERSION 3.6)
 
 project(top)
+
+option(LIBCRON_BUILD_TZ_CLOCK "Build timezone clock" OFF)
+
+if(LIBCRON_BUILD_TZ_CLOCK)
+    set(BUILD_TZ_LIB ON CACHE BOOL "Build the tz library" FORCE)
+    add_subdirectory(libcron/externals/date)
+endif()
+
 add_subdirectory(libcron)
 add_subdirectory(test)
 
@@ -9,4 +17,3 @@ add_dependencies(cron_test libcron)
 install(TARGETS libcron DESTINATION lib)
 install(DIRECTORY libcron/include/libcron DESTINATION include)
 install(DIRECTORY libcron/externals/date/include/date DESTINATION include)
-

README.md

@@ -131,6 +131,34 @@ This library uses `std::chrono::system_clock::timepoint` as its time unit. While
 uses a `LocalClock` by default which offsets `system_clock::now()` by the current UTC-offset. If you wish to work in
 UTC, then construct the Cron instance, passing it a `libcron::UTCClock`.  
 
+## TzClock
+
+This library also offers a `libcron::TzClock` as its time unit. Which makes use of the timezone support of date's library.
+With `libcron::TzClock` you can set one of available regions from the iana Timezone database: 
+
+```
+Cron<TzClock> cron;
+if(cron.get_clock().set_time_zone("Africa/Maputo"))
+  std::cout << "Successfully set timezone to: Africa/Maputo \n";
+else
+  std::cout << "Failed to set timezone to:  Africa/Maputo \n";
+```
+
+`libcron::TzClock` behaves like `libcron::UTCClock` if no timezone is set.
+
+If you want to use TzClock you have to set -DLIBCRON_BUILD_TZ_CLOCK=ON when building libcron. TzClock is a fully optional feature
+if you don't enable it, it won't be build at all.
+
+Using TzClock has the following side effects:
+  1. Date requires linkage to `libcurl`
+  2. First time TzClocks timezone lookup will occur it will download the most up to date timezone: "~/Downloads/tzdata" ("%homedrive%\%homepath%\downloads\tzdata" on Windows).
+  3. TzClock uses a `std::mutex` to protect the time zone in multithreaded envoirements.
+  4. This implementation might decrease performance a lot based on point 2 and 3.
+
+[More Info about date-tz](https://howardhinnant.github.io/date/tz.html)
+
+[Available Regions](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones)
+
 # Supported formatting
 
 This implementation supports cron format, as specified below.  

libcron/CMakeLists.txt

@@ -35,6 +35,13 @@ target_include_directories(${PROJECT_NAME}
 		PRIVATE ${CMAKE_CURRENT_LIST_DIR}/externals/date/include
 		PUBLIC include)
 
+if(LIBCRON_BUILD_TZ_CLOCK)
+	target_link_libraries(${PROJECT_NAME} PUBLIC
+		date-tz
+	)
+	target_compile_definitions(${PROJECT_NAME} PUBLIC -DBUILD_TZ_CLOCK)
+endif()
+
 if(NOT MSVC)
 	# Assume a modern compiler (gcc 9.3)
 	target_compile_definitions (${PROJECT_NAME} PRIVATE -DHAS_UNCAUGHT_EXCEPTIONS)

libcron/include/libcron/CronClock.h

@@ -1,6 +1,10 @@
 #pragma once
 
 #include <chrono>
+#ifdef BUILD_TZ_CLOCK
+#include <date/tz.h>
+#include <mutex>
+#endif
 
 namespace libcron
 {
@@ -39,4 +43,22 @@ namespace libcron
 
 			std::chrono::seconds utc_offset(std::chrono::system_clock::time_point now) const override;
     };
+
+#ifdef BUILD_TZ_CLOCK
+    class TzClock : public ICronClock
+    {
+        public:
+            std::chrono::system_clock::time_point now() const override
+            {
+                auto now = std::chrono::system_clock::now();
+                return now + utc_offset(now);
+            }
+
+            bool set_time_zone(std::string_view tz_name);
+            std::chrono::seconds utc_offset(std::chrono::system_clock::time_point now) const override;
+        private:
+            mutable std::mutex time_zone_mtx{};
+            const date::time_zone* time_zone{nullptr};
+    };
+#endif
 }

libcron/src/CronClock.cpp

@@ -36,4 +36,35 @@ namespace libcron
 #endif
 		return offset;
 	}
+
+#ifdef BUILD_TZ_CLOCK
+	bool TzClock::set_time_zone(std::string_view tz_name)
+	{
+		const date::time_zone *new_zone{nullptr};
+
+		try
+		{
+			new_zone = date::locate_zone(tz_name);
+		}
+		catch (std::runtime_error &err)
+		{
+			return false;
+		}
+
+		std::lock_guard<std::mutex> lock(time_zone_mtx);
+		time_zone = new_zone;
+		return true;
+	}
+
+	std::chrono::seconds TzClock::utc_offset(std::chrono::system_clock::time_point now) const
+	{
+		using namespace std::chrono;
+		// If we don't have a timezone we use utc
+		std::lock_guard<std::mutex> lock(time_zone_mtx);
+		if (time_zone)
+			return time_zone->get_info(now).offset;
+		else
+			return 0s;
+	}
+#endif
 }

test/CMakeLists.txt

@@ -38,6 +38,13 @@ else()
 	target_link_libraries(${PROJECT_NAME} libcron)
 endif()
 
+if(LIBCRON_BUILD_TZ_CLOCK)
+	target_link_libraries(${PROJECT_NAME}
+		date-tz
+	)
+	target_compile_definitions(${PROJECT_NAME} PUBLIC -DBUILD_TZ_CLOCK)
+endif()
+
 set_target_properties(${PROJECT_NAME} PROPERTIES
         ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_CURRENT_LIST_DIR}/out"
         LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_LIST_DIR}/out"

test/CronTest.cpp

@@ -448,3 +448,36 @@ SCENARIO("Tasks can be added and removed from the scheduler")
         }
     }
 }
+
+#ifdef BUILD_TZ_CLOCK
+
+SCENARIO("TzClock: Timezone is not set fallback to utc")
+{
+    GIVEN("No timezone")
+    {
+        TzClock tz_clock{};
+        auto now = std::chrono::system_clock::now();
+        REQUIRE(tz_clock.utc_offset(now) == 0s);
+    }
+    GIVEN("A wrong timezone")
+    {
+        TzClock tz_clock{};
+        auto now = std::chrono::system_clock::now();
+        tz_clock.set_time_zone("404Not/Found");
+        REQUIRE(tz_clock.utc_offset(now) == 0s);
+    }
+}
+
+SCENARIO("TzClock: Setting time zone")
+{
+    TzClock tz_clock;
+    GIVEN("Valid time zone")
+    {
+        REQUIRE(tz_clock.set_time_zone("Europe/Berlin"));
+    }
+    GIVEN("Invalid time zone")
+    {
+        REQUIRE_FALSE(tz_clock.set_time_zone("404Not/Found"));
+    }
+}
+#endif