Feature/add executed on time check (#7)

* Initial commit on executed on time feature. A task was executed on time if the function call happened within one second since it expired.

* Adding tests, fixing some errors.

* Using recursirve mutex to allowing to call safely call was_executed_on_time in an Mt-environment

* Changing from boolean expression to get_delay, being even more flexibel

* Cleanup

* Adding dedicated TaskContext

* Changing to Interface-Class Approach

* Renaming to TaskInformation, making it pure virtual

* Removing unnecessary Proxy-Class

* Cleaning up

* Passing a const reference instead of a pointer to avoid nullptr checks in the callback

* Cleaning up add_schedule.

* Adding TaskInformation API to readme.

Co-authored-by: Heinz-Peter Liechtenecker <h.liechtenecker@fh-kaernten.at>

CMakeLists.txt

@@ -1,5 +1,6 @@
 cmake_minimum_required(VERSION 3.6)
 
+project(top)
 add_subdirectory(libcron)
 add_subdirectory(test)
 

README.md

@@ -1,7 +1,89 @@
 # libcron
 A C++ scheduling library using cron formatting.
 
-# Local time vs UTC
+# Using the Scheduler
+
+Libcron offers an easy to use API to add callbacks with corresponding cron-formatted strings:
+
+```
+libcron::Cron cron;
+
+cron.add_schedule("Hello from Cron", "* * * * * ?", [=](auto&) {
+	std::cout << "Hello from libcron!" std::endl;
+});
+```
+
+To trigger the execution of callbacks, one must call `libcron::Cron::tick` at least once a second to prevent missing schedules:
+
+```
+while(true)
+{
+	cron.tick();
+	std::this_thread::sleep_for(500mS);
+}
+```
+
+The callback must have the following signature:
+
+```
+std::function<void(const libcron::TaskInformation&)>
+```
+
+`libcron::Taskinformation` offers a convenient API to retrieve further information:
+
+- `libcron::TaskInformation::get_delay` informs about the delay between planned and actual execution of the callback. Hence, it is possible to ensure that a task was executed within a specific tolerance:
+
+```
+libcron::Cron cron;
+
+cron.add_schedule("Hello from Cron", "* * * * * ?", [=](auto& i) {
+	using namespace std::chrono_literals;
+	if (i.get_delay() >= 1s)
+	{
+		std::cout << "The Task was executed too late..." << std::endl;
+	}
+});
+```
+
+
+
+## Removing schedules from `libcron::Cron`
+
+libcron::Cron offers two convenient functions to remove schedules:
+
+- `clear_schedules()` will remove all schedules
+- `remove_schedule(std::string)` will remove a specific schedule
+
+For example, `cron.remove_schedule("Hello from Cron")` will remove the previously added task.
+
+
+
+## Removing/Adding tasks at runtime in a multithreaded environment
+
+When Calling `libcron::Cron::tick` from another thread than `add_schedule`, `clear_schedule` and `remove_schedule`, one must take care to protect the internal resources of `libcron::Cron` so that tasks are not removed or added while `libcron::Cron` is iterating over the schedules. `libcron::Cron` can take care of that, you simply have to define your own aliases:
+
+```
+/* The default class uses NullLock, which does not lock the resources at runtime */
+template<typename ClockType = libcron::LocalClock, typename LockType = libcron::NullLock>
+class Cron
+{
+	...
+}
+
+/* Define an alias for a thread-safe Cron scheduler which automatically locks ressources when needed */ 
+using CronMt = libcron::Cron<libcron::LocalClock, libcron::Locker>
+
+CronMt cron;
+cron.add_schedule("Hello from Cron", "* * * * * ?", [=]() {
+	std::cout << "Hello from CronMt!" std::endl;
+});
+
+....
+```
+
+However, this comes with costs: Whenever you call `tick`, a `std::mutex` will be locked and unlocked.  So only use the `libcron::Locker` to protect resources when you really need too.
+
+## Local time vs UTC
 
 This library uses `std::chrono::system_clock::timepoint` as its time unit. While that is UTC by default, the Cron-class
 uses a `LocalClock` by default which offsets `system_clock::now()` by the current UTC-offset. If you wish to work in
@@ -55,6 +137,7 @@ Each part is separated by one or more whitespaces. It is thus important to keep
 * Invalid:
   * 0, 3, 40-50 * * * * ?
   
+
 `Day of month` and `day of week` are mutually exclusive so one of them must at always be ignored using
 the '?'-character to ensure that it is not possible to specify a statement which results in an impossible mix of these fields. 
 
@@ -71,8 +154,8 @@ the '?'-character to ensure that it is not possible to specify a statement which
 
 The standard cron format does not allow for randomization, but with the use of `CronRandomization` you can generate random
 schedules using the following format: `R(range_start-range_end)`, where `range_start` and `range_end` follow the same rules
-as for a regular cron range with the addition that only numbers are allowed. All the rules for a regular cron expression 
+as for a regular cron range (step-syntax is not supported). All the rules for a regular cron expression still applies
-still applies when using randomization, i.e. mutual exclusiveness and not extra spaces.
+when using randomization, i.e. mutual exclusiveness and no extra spaces.
 
 ## Examples
 |Expression | Meaning
@@ -80,9 +163,9 @@ still applies when using randomization, i.e. mutual exclusiveness and not extra
 | 0 0 R(13-20) * * ? | On the hour, on a random hour 13-20, inclusive.
 | 0 0 0 ? * R(0-6) | A random weekday, every week, at midnight.
 | 0 R(45-15) */12 ? * * | A random minute between 45-15, inclusive, every 12 hours.
+|0 0 0 ? R(DEC-MAR) R(SAT-SUN)| On the hour, on a random month december to march, on a random weekday saturday to sunday. 
 
 
 # Used Third party libraries
 
 Howard Hinnant's [date libraries](https://github.com/HowardHinnant/date/)
-

libcron/CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.6)
 project(libcron)
 
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 17)
 
 if( MSVC )
 	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4")

libcron/include/libcron/Cron.h

@@ -4,23 +4,41 @@
 #include <chrono>
 #include <queue>
 #include <memory>
+#include <mutex>
 #include "Task.h"
 #include "CronClock.h"
 
 namespace libcron
 {
-    template<typename ClockType>
+    class NullLock 
+    {
+        public:
+            void lock() {}
+            void unlock() {}
+    };
+
+    class Locker
+    {
+        public:
+            void lock() { m.lock(); }
+            void unlock() { m.unlock(); }
+        private:
+            std::recursive_mutex m{};
+    };
+
+    template<typename ClockType, typename LockType>
     class Cron;
 
-    template<typename ClockType>
+    template<typename ClockType, typename LockType>
-    std::ostream& operator<<(std::ostream& stream, const Cron<ClockType>& c);
+    std::ostream& operator<<(std::ostream& stream, const Cron<ClockType, LockType>& c);
 
-    template<typename ClockType = libcron::LocalClock>
+    template<typename ClockType = libcron::LocalClock, typename LockType = libcron::NullLock>
     class Cron
     {
         public:
-
+            bool add_schedule(std::string name, const std::string& schedule, Task::TaskFunction work);
-            bool add_schedule(std::string name, const std::string& schedule, std::function<void()> work);
+            void clear_schedules();
+            void remove_schedule(const std::string& name);
 
             size_t count() const
             {
@@ -48,7 +66,7 @@ namespace libcron
             void get_time_until_expiry_for_tasks(
                     std::vector<std::tuple<std::string, std::chrono::system_clock::duration>>& status) const;
 
-            friend std::ostream& operator<<<>(std::ostream& stream, const Cron<ClockType>& c);
+            friend std::ostream& operator<<<>(std::ostream& stream, const Cron<ClockType, LockType>& c);
 
         private:
             class Queue
@@ -66,6 +84,50 @@ namespace libcron
                     {
                         return c;
                     }
+
+                    void clear()
+                    {
+                        lock.lock();
+
+                        while (!empty())
+                            pop();
+
+                        lock.unlock();
+                    }
+
+                    template<typename T>
+                    void remove(T to_remove)
+                    {
+                        lock.lock();
+
+                        /* Copy current elements */
+                        std::vector<Task> temp{};
+                        std::swap(temp, c);
+
+                        /* Refill with elements ensuring correct order by calling push */
+                        for (const auto& task : temp)
+                        {
+                            if (task != to_remove)
+                                push(task);
+                        }
+
+                        lock.unlock();
+                    }
+
+                    void lock_queue()
+                    {
+                        /* Do not allow to manipulate the Queue */
+                        lock.lock();
+                    }
+
+                    void release_queue()
+                    {
+                        /* Allow Access to the Queue Manipulating-Functions */
+                        lock.unlock();
+                    }
+                    
+                private:
+                    LockType lock;
             };
 
 
@@ -75,25 +137,39 @@ namespace libcron
             std::chrono::system_clock::time_point last_tick{};
     };
     
-    template<typename ClockType>
+    template<typename ClockType, typename LockType>
-    bool Cron<ClockType>::add_schedule(std::string name, const std::string& schedule, std::function<void()> work)
+    bool Cron<ClockType, LockType>::add_schedule(std::string name, const std::string& schedule, Task::TaskFunction work)
     {
         auto cron = CronData::create(schedule);
         bool res = cron.is_valid();
         if (res)
         {
-            Task t{std::move(name), CronSchedule{cron}, std::move(work)};
+            tasks.lock_queue();
+            Task t{std::move(name), CronSchedule{cron}, work };
             if (t.calculate_next(clock.now()))
             {
                 tasks.push(t);
             }
+            tasks.release_queue();
         }
 
         return res;
     }
 
-    template<typename ClockType>
+    template<typename ClockType, typename LockType>
-    std::chrono::system_clock::duration Cron<ClockType>::time_until_next() const
+    void Cron<ClockType, LockType>::clear_schedules()
+    {
+        tasks.clear();
+    }
+    
+    template<typename ClockType, typename LockType>
+    void Cron<ClockType, LockType>::remove_schedule(const std::string& name)
+    {
+        tasks.remove(name);
+    }
+
+    template<typename ClockType, typename LockType>
+    std::chrono::system_clock::duration Cron<ClockType, LockType>::time_until_next() const
     {
         std::chrono::system_clock::duration d{};
         if (tasks.empty())
@@ -108,9 +184,10 @@ namespace libcron
         return d;
     }
 
-    template<typename ClockType>
+    template<typename ClockType, typename LockType>
-    size_t Cron<ClockType>::tick(std::chrono::system_clock::time_point now)
+    size_t Cron<ClockType, LockType>::tick(std::chrono::system_clock::time_point now)
     {
+        tasks.lock_queue();
         size_t res = 0;
 
         if(!first_tick)
@@ -189,11 +266,12 @@ namespace libcron
             }
         });
 
+        tasks.release_queue();
         return res;
     }
 
-    template<typename ClockType>
+    template<typename ClockType, typename LockType>
-    void Cron<ClockType>::get_time_until_expiry_for_tasks(std::vector<std::tuple<std::string,
+    void Cron<ClockType, LockType>::get_time_until_expiry_for_tasks(std::vector<std::tuple<std::string,
                                                           std::chrono::system_clock::duration>>& status) const
     {
         auto now = clock.now();
@@ -206,8 +284,8 @@ namespace libcron
                       });
     }
 
-    template<typename ClockType>
+    template<typename ClockType, typename LockType>
-    std::ostream& operator<<(std::ostream& stream, const Cron<ClockType>& c)
+    std::ostream& operator<<(std::ostream& stream, const Cron<ClockType, LockType>& c)
     {
         std::for_each(c.tasks.get_tasks().cbegin(), c.tasks.get_tasks().cend(),
                       [&stream, &c](const Task& t)

libcron/include/libcron/CronData.h

@@ -16,7 +16,7 @@ namespace libcron
 
             static CronData create(const std::string& cron_expression);
 
-            CronData();
+            CronData() = default;
 
             CronData(const CronData&) = default;
 
@@ -77,6 +77,9 @@ namespace libcron
             template<typename T>
             bool convert_from_string_range_to_number_range(const std::string& range, std::set<T>& numbers);
 
+            template<typename T>
+            static std::string& replace_string_name_with_numeric(std::string& s);
+
         private:
             void parse(const std::string& cron_expression);
 
@@ -121,8 +124,8 @@ namespace libcron
             std::set<DayOfWeek> day_of_week{};
             bool valid = false;
 
-            std::vector<std::string> month_names;
+            static const std::vector<std::string> month_names;
-            std::vector<std::string> day_names;
+            static const std::vector<std::string> day_names;
 
             template<typename T>
             void add_full_range(std::set<T>& set);
@@ -343,4 +346,40 @@ namespace libcron
 
         return res;
     }
+
+    template<typename T>
+    std::string & CronData::replace_string_name_with_numeric(std::string& s)
+    {
+        auto value = static_cast<int>(T::First);
+
+        const std::vector<std::string>* name_source{};
+
+        static_assert(std::is_same<T, libcron::Months>()
+                      || std::is_same<T, libcron::DayOfWeek>(),
+                        "T must be either Months or DayOfWeek");
+
+        if constexpr (std::is_same<T, libcron::Months>())
+        {
+            name_source = &month_names;
+        }
+        else
+        {
+            name_source = &day_names;
+        }
+
+        for (const auto& name : *name_source)
+        {
+            std::regex m(name, std::regex_constants::ECMAScript | std::regex_constants::icase);
+
+            std::string replaced;
+
+            std::regex_replace(std::back_inserter(replaced), s.begin(), s.end(), m, std::to_string(value));
+
+            s = replaced;
+
+            ++value;
+        }
+
+        return s;
+    }
 }

libcron/include/libcron/CronRandomization.h

@@ -44,7 +44,7 @@ namespace libcron
 
         std::smatch random_match;
 
-        if (std::regex_match(section.begin(), section.end(), random_match, rand_expression))
+        if (std::regex_match(section.cbegin(), section.cend(), random_match, rand_expression))
         {
             // Random range, get left and right numbers.
             auto left = std::stoi(random_match[1].str());

libcron/include/libcron/Task.h

@@ -1,26 +1,42 @@
 #pragma once
 
 #include <functional>
-#include "CronData.h"
-#include "CronSchedule.h"
 #include <chrono>
 #include <utility>
+#include "CronData.h"
+#include "CronSchedule.h"
 
 namespace libcron
 {
-    class Task
+    class TaskInformation
     {
         public:
+            virtual ~TaskInformation() = default;
+            virtual std::chrono::system_clock::duration get_delay() const = 0;
+    };
 
-            Task(std::string name, const CronSchedule schedule, std::function<void()> task)
+    class Task : public TaskInformation
+    {
+        public:
+            using TaskFunction = std::function<void(const TaskInformation&)>;
+
+            Task(std::string name, const CronSchedule schedule, TaskFunction task)
                     : name(std::move(name)), schedule(std::move(schedule)), task(std::move(task))
             {
             }
 
             void execute(std::chrono::system_clock::time_point now)
             {
+                // Next Schedule is still the current schedule, calculate delay (actual execution - planned execution)
+                delay = now - next_schedule;
+
                 last_run = now;
-                task();
+                task(*this);
+            }
+
+            std::chrono::system_clock::duration get_delay() const override
+            {
+                return delay;
             }
 
             Task(const Task& other) = default;
@@ -50,8 +66,29 @@ namespace libcron
             std::string name;
             CronSchedule schedule;
             std::chrono::system_clock::time_point next_schedule;
-            std::function<void()> task;
+            std::chrono::system_clock::duration delay = std::chrono::seconds(-1);
+            TaskFunction task;
             bool valid = false;
             std::chrono::system_clock::time_point last_run = std::numeric_limits<std::chrono::system_clock::time_point>::min();
     };
 }
+
+inline bool operator==(const std::string &lhs, const libcron::Task &rhs)
+{
+    return lhs == rhs.get_name();
+}
+
+inline bool operator==(const libcron::Task &lhs, const std::string &rhs)
+{
+    return lhs.get_name() == rhs;
+}
+
+inline bool operator!=(const std::string &lhs, const libcron::Task &rhs)
+{
+    return !(lhs == rhs);
+}
+
+inline bool operator!=(const libcron::Task &lhs, const std::string &rhs)
+{
+    return !(lhs == rhs);
+}

libcron/src/CronData.cpp

@@ -13,6 +13,9 @@ namespace libcron
                                                                                Months::October,
                                                                                Months::December };
 
+    const std::vector<std::string> CronData::month_names{ "JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC" };
+    const std::vector<std::string> CronData::day_names{ "SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT" };
+
     CronData CronData::create(const std::string& cron_expression)
     {
         CronData c;
@@ -21,12 +24,6 @@ namespace libcron
         return c;
     }
 
-    CronData::CronData()
-            : month_names({ "JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC" }),
-              day_names({ "SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT" })
-    {
-    }
-
     void CronData::parse(const std::string& cron_expression)
     {
         // First, split on white-space. We expect six parts.

libcron/src/CronRandomization.cpp

@@ -18,14 +18,46 @@ namespace libcron
     std::tuple<bool, std::string> CronRandomization::parse(const std::string& cron_schedule)
     {
         // Split on space to get each separate part, six parts expected
-        std::regex split{ R"#(^\s*(.*?)\s+(.*?)\s+(.*?)\s+(.*?)\s+(.*?)\s+(.*?)\s*$)#",
+        const std::regex split{ R"#(^\s*(.*?)\s+(.*?)\s+(.*?)\s+(.*?)\s+(.*?)\s+(.*?)\s*$)#",
                                 std::regex_constants::ECMAScript };
 
         std::smatch all_sections;
+        auto res = std::regex_match(cron_schedule.cbegin(), cron_schedule.cend(), all_sections, split);
 
-        std::string final_cron_schedule;
+        // Replace text with numbers
+        std::string working_copy{};
 
-        auto res = std::regex_match(cron_schedule.begin(), cron_schedule.end(), all_sections, split);
+        if (res)
+        {
+            // Merge seconds, minutes, hours and day of month back together
+            working_copy += all_sections[1].str();
+            working_copy += " ";
+            working_copy += all_sections[2].str();
+            working_copy += " ";
+            working_copy += all_sections[3].str();
+            working_copy += " ";
+            working_copy += all_sections[4].str();
+            working_copy += " ";
+
+            // Replace month names
+            auto month = all_sections[5].str();
+            CronData::replace_string_name_with_numeric<libcron::Months>(month);
+
+            working_copy += " ";
+            working_copy += month;
+
+            // Replace day names
+            auto dow = all_sections[6].str();
+            CronData::replace_string_name_with_numeric<libcron::DayOfWeek>(dow);
+
+            working_copy += " ";
+            working_copy += dow;
+        }
+
+        std::string final_cron_schedule{};
+
+        // Split again on space
+        res = res && std::regex_match(working_copy.cbegin(), working_copy.cend(), all_sections, split);
 
         if (res)
         {

libcron/src/CronSchedule.cpp

@@ -46,7 +46,7 @@ namespace libcron
                 //Add days until the current weekday is one of the allowed weekdays
                 year_month_weekday ymw = date::floor<days>(curr);
 
-                if (data.get_day_of_week().find(static_cast<DayOfWeek>(unsigned(ymw.weekday()))) ==
+                if (data.get_day_of_week().find(static_cast<DayOfWeek>(ymw.weekday().c_encoding())) ==
                     data.get_day_of_week().end())
                 {
                     sys_days s = ymd;

libcron/src/Task.cpp

@@ -1,4 +1,3 @@
-#include <iostream>
 #include "libcron/Task.h"
 
 using namespace std::chrono;

test/CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.6)
 project(cron_test)
 
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 17)
 
 if( MSVC )
 	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4")

test/CronDataTest.cpp

@@ -225,3 +225,16 @@ SCENARIO("Date that exist in one of the months")
 {
     REQUIRE(CronData::create("0 0 * 31 APR,MAY ?").is_valid());
 }
+
+SCENARIO("Replacing text with numbers")
+{
+    {
+        std::string s = "SUN-TUE";
+        REQUIRE(CronData::replace_string_name_with_numeric<libcron::DayOfWeek>(s) == "0-2");
+    }
+
+    {
+        std::string s = "JAN-DEC";
+        REQUIRE(CronData::replace_string_name_with_numeric<libcron::Months>(s) == "1-12");
+    }
+}

test/CronRandomizationTest.cpp

@@ -7,21 +7,31 @@
 #include <iostream>
 
 using namespace libcron;
+const auto EXPECT_FAILURE = true;
 
-void test(const char* const random_schedule)
+void test(const char* const random_schedule, bool expect_failure = false)
 {
     libcron::CronRandomization cr;
-    std::unordered_map<int, std::unordered_map<int, int>> results{};
 
     for (int i = 0; i < 5000; ++i)
     {
         auto res = cr.parse(random_schedule);
-        REQUIRE(std::get<0>(res));
         auto schedule = std::get<1>(res);
 
-        INFO("schedule:" << schedule);
         Cron<> cron;
-        REQUIRE(cron.add_schedule("validate schedule", schedule, []() {}));
+
+        if(expect_failure)
+        {
+            // Parsing of random might succeed, but it yields an invalid schedule.
+            auto r = std::get<0>(res) && cron.add_schedule("validate schedule", schedule, [](auto&) {});
+            REQUIRE_FALSE(r);
+        }
+        else
+        {
+            REQUIRE(std::get<0>(res));
+            REQUIRE(cron.add_schedule("validate schedule", schedule, [](auto&) {}));
+
+        }
     }
 }
 
@@ -103,3 +113,68 @@ SCENARIO("Test readme examples")
         }
     }
 }
+
+SCENARIO("Randomization using text versions of days and months")
+{
+    GIVEN("0 0 0 ? * R(TUE-FRI)")
+    {
+        THEN("Valid schedule generated")
+        {
+           test("0 0 0 ? * R(TUE-FRI)");
+        }
+    }
+
+    GIVEN("Valid schedule")
+    {
+        THEN("Valid schedule generated")
+        {
+            test("0 0 0 ? R(JAN-DEC) R(MON-FRI)");
+        }
+        AND_WHEN("Given 0 0 0 ? R(DEC-MAR) R(SAT-SUN)")
+        {
+            THEN("Valid schedule generated")
+            {
+                test("0 0 0 ? R(DEC-MAR) R(SAT-SUN)");
+            }
+        }
+        AND_THEN("Given 0 0 0 ? R(JAN-FEB) *")
+        {
+            THEN("Valid schedule generated")
+            {
+                test("0 0 0 ? R(JAN-FEB) *");
+            }
+        }
+        AND_THEN("Given 0 0 0 ? R(OCT-OCT) *")
+        {
+            THEN("Valid schedule generated")
+            {
+                test("0 0 0 ? R(OCT-OCT) *");
+            }
+        }
+    }
+
+    GIVEN("Invalid schedule")
+    {
+        THEN("No schedule generated")
+        {
+            // Day of month specified - not allowed with day of week
+            test("0 0 0 1 R(JAN-DEC) R(MON-SUN)", EXPECT_FAILURE);
+        }
+        AND_THEN("No schedule generated")
+        {
+            // Invalid range
+            test("0 0 0 ? R(JAN) *", EXPECT_FAILURE);
+        }
+        AND_THEN("No schedule generated")
+        {
+            // Days in month field
+            test("0 0 0 ? R(MON-TUE) *", EXPECT_FAILURE);
+        }
+        AND_THEN("No schedule generated")
+        {
+            // Month in day field
+            test("0 0 0 ? * R(JAN-JUN)", EXPECT_FAILURE);
+        }
+
+    }
+}

test/CronTest.cpp

@@ -35,7 +35,7 @@ SCENARIO("Adding a task")
         WHEN("Adding a task that runs every second")
         {
             REQUIRE(c.add_schedule("A task", "* * * * * ?",
-                                   [&expired]()
+                                   [&expired](auto&)
                                    {
                                        expired = true;
                                    })
@@ -68,7 +68,7 @@ SCENARIO("Adding a task that expires in the future")
         Cron<> c;
         REQUIRE(c.add_schedule("A task",
                                create_schedule_expiring_in(c.get_clock().now(), hours{0}, minutes{0}, seconds{3}),
-                               [&expired]()
+                               [&expired](auto&)
                                {
                                    expired = true;
                                })
@@ -99,6 +99,50 @@ SCENARIO("Adding a task that expires in the future")
     }
 }
 
+SCENARIO("Get delay using Task-Information")
+{
+    using namespace std::chrono_literals;
+
+    GIVEN("A Cron instance with one task expiring in  2 seconds, but taking 3 seconds to execute")
+    {
+        auto _2_second_expired = 0;
+        auto _delay = std::chrono::system_clock::duration(-1s);
+
+        Cron<> c;
+        REQUIRE(c.add_schedule("Two",
+                               "*/2 * * * * ?",
+                               [&_2_second_expired, &_delay](auto& i)
+                               {
+                                   _2_second_expired++;
+                                   _delay = i.get_delay();
+                                   std::this_thread::sleep_for(3s);
+                               })
+        );
+        THEN("Not yet expired")
+        {
+            REQUIRE_FALSE(_2_second_expired);
+            REQUIRE(_delay <= 0s);
+        }
+        WHEN("Exactly schedule task")
+        {
+            while (_2_second_expired == 0)
+                c.tick();
+
+            THEN("Task should have expired within a valid time")
+            {
+                REQUIRE(_2_second_expired == 1);
+                REQUIRE(_delay <= 1s);
+            }
+            AND_THEN("Executing another tick again, leading to execute task again immediatly, but not on time as execution has taken 3 seconds.")
+            {
+                c.tick();
+                REQUIRE(_2_second_expired == 2);
+                REQUIRE(_delay >= 1s);
+            }
+        }
+    }
+}
+
 SCENARIO("Task priority")
 {
     GIVEN("A Cron instance with two tasks expiring in 3 and 5 seconds, added in 'reverse' order")
@@ -110,7 +154,7 @@ SCENARIO("Task priority")
         Cron<> c;
         REQUIRE(c.add_schedule("Five",
                                create_schedule_expiring_in(c.get_clock().now(), hours{0}, minutes{0}, seconds{5}),
-                               [&_5_second_expired]()
+                               [&_5_second_expired](auto&)
                                {
                                    _5_second_expired++;
                                })
@@ -118,7 +162,7 @@ SCENARIO("Task priority")
 
         REQUIRE(c.add_schedule("Three",
                                create_schedule_expiring_in(c.get_clock().now(), hours{0}, minutes{0}, seconds{3}),
-                               [&_3_second_expired]()
+                               [&_3_second_expired](auto&)
                                {
                                    _3_second_expired++;
                                })
@@ -231,7 +275,7 @@ SCENARIO("Clock changes")
         clock.set(sys_days{2018_y / 05 / 05});
 
         // Every hour
-        REQUIRE(c.add_schedule("Clock change task", "0 0 * * * ?", []()
+        REQUIRE(c.add_schedule("Clock change task", "0 0 * * * ?", [](auto&)
         {
         })
         );
@@ -309,7 +353,7 @@ SCENARIO("Multiple ticks per second")
     int run_count = 0;
 
     // Every 10 seconds
-    REQUIRE(c.add_schedule("Clock change task", "*/10 0 * * * ?", [&run_count]()
+    REQUIRE(c.add_schedule("Clock change task", "*/10 0 * * * ?", [&run_count](auto&)
     {
         run_count++;
     })
@@ -335,3 +379,70 @@ SCENARIO("Multiple ticks per second")
     }
 
 }
+
+SCENARIO("Tasks can be added and removed from the scheduler")
+{
+    GIVEN("A Cron instance with no task")
+    {
+        Cron<> c;
+        auto expired = false;
+
+        WHEN("Adding 5 tasks that runs every second")
+        {
+            REQUIRE(c.add_schedule("Task-1", "* * * * * ?",
+                                   [&expired](auto&)
+                                   {
+                                       expired = true;
+                                   })
+            );
+
+            REQUIRE(c.add_schedule("Task-2", "* * * * * ?",
+                                   [&expired](auto&)
+                                   {
+                                       expired = true;
+                                   })
+            );
+
+            REQUIRE(c.add_schedule("Task-3", "* * * * * ?",
+                                   [&expired](auto&)
+                                   {
+                                       expired = true;
+                                   })
+            );
+
+            REQUIRE(c.add_schedule("Task-4", "* * * * * ?",
+                                   [&expired](auto&)
+                                   {
+                                       expired = true;
+                                   })
+            );
+
+            REQUIRE(c.add_schedule("Task-5", "* * * * * ?",
+                                   [&expired](auto&)
+                                   {
+                                       expired = true;
+                                   })
+            );
+
+            THEN("Count is 5")
+            {
+                REQUIRE(c.count() == 5);
+            }
+            AND_THEN("Removing all scheduled tasks")
+            {
+                c.clear_schedules();
+                REQUIRE(c.count() == 0);
+            }
+            AND_THEN("Removing a task that does not exist")
+            {
+                c.remove_schedule("Task-6");
+                REQUIRE(c.count() == 5);
+            }
+            AND_THEN("Removing a task that does exist")
+            {
+                c.remove_schedule("Task-5");
+                REQUIRE(c.count() == 4);
+            }
+        }
+    }
+}