// Demonstrates the use of observer to monitor worker activities.

#include <taskflow/taskflow.hpp>

struct MyObserver : public tf::ObserverInterface {

 MyObserver(const std::string& name) {
 std::cout << "constructing observer " << name << '\n';
 }

 // set_up is a constructor-like method that will be called exactly once
 // passing the number of workers
 void set_up(size_t num_workers) override final {
 std::cout << "setting up observer with " << num_workers << " workers\n";
 }

 // on_entry will be called before a worker runs a task
 void on_entry(tf::WorkerView wv, tf::TaskView tv) override final {
 std::ostringstream oss;
 oss << "worker " << wv.id() << " ready to run " << tv.name() << '\n';
 std::cout << oss.str();
 }

 // on_exit will be called after a worker completes a task
 void on_exit(tf::WorkerView wv, tf::TaskView tv) override final {
 std::ostringstream oss;
 oss << "worker " << wv.id() << " finished running " << tv.name() << '\n';
 std::cout << oss.str();
 }

};

int main(){

 tf::Executor executor;

 // Create a taskflow of eight tasks
 tf::Taskflow taskflow;

 taskflow.emplace([] () { std::cout << "1\n"; }).name("A");
 taskflow.emplace([] () { std::cout << "2\n"; }).name("B");
 taskflow.emplace([] () { std::cout << "3\n"; }).name("C");
 taskflow.emplace([] () { std::cout << "4\n"; }).name("D");
 taskflow.emplace([] () { std::cout << "5\n"; }).name("E");
 taskflow.emplace([] () { std::cout << "6\n"; }).name("F");
 taskflow.emplace([] () { std::cout << "7\n"; }).name("G");
 taskflow.emplace([] () { std::cout << "8\n"; }).name("H");

 // create a default observer
 std::shared_ptr<MyObserver> observer = executor.make_observer<MyObserver>("MyObserver");

 // run the taskflow
 executor.run(taskflow).get();

 // remove the observer (optional)
 executor.remove_observer(std::move(observer));

 return 0;
}