// This program demonstrates how to set priority to a task.
//
// Currently, Taskflow supports only three priority levels:
// + tf::TaskPriority::HIGH (numerical value = 0)
// + tf::TaskPriority::NORMAL (numerical value = 1)
// + tf::TaskPriority::LOW (numerical value = 2)
// 
// Priority-based execution is non-preemptive. Once a task 
// has started to execute, it will execute to completion,
// even if a higher priority task has been spawned or enqueued. 

#include <taskflow/taskflow.hpp>

int main() {
 
 // create an executor of only one worker to enable 
 // deterministic behavior
 tf::Executor executor(1);

 tf::Taskflow taskflow;

 int counter {0};
 
 // Here we create five tasks and print thier execution
 // orders which should align with assigned priorities
 auto [A, B, C, D, E] = taskflow.emplace(
 [] () { },
 [&] () { 
 std::cout << "Task B: " << counter++ << '\n'; // 0
 },
 [&] () { 
 std::cout << "Task C: " << counter++ << '\n'; // 2
 },
 [&] () { 
 std::cout << "Task D: " << counter++ << '\n'; // 1
 },
 [] () { }
 );

 A.precede(B, C, D); 
 E.succeed(B, C, D);
 
 // By default, all tasks are of tf::TaskPriority::HIGH
 B.priority(tf::TaskPriority::HIGH);
 C.priority(tf::TaskPriority::LOW);
 D.priority(tf::TaskPriority::NORMAL);

 assert(B.priority() == tf::TaskPriority::HIGH);
 assert(C.priority() == tf::TaskPriority::LOW);
 assert(D.priority() == tf::TaskPriority::NORMAL);
 
 // we should see B, D, and C in their priority order
 executor.run(taskflow).wait();
}