//Copyright (c) 2018 Emil Dotchevski
//Copyright (c) 2018 Second Spectrum, Inc.

//Distributed under the Boost Software License, Version 1.0. (See accompanying
//file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

//This is a simple program that demonstrates the use of LEAF to transport error info between threads,
//when using exception handling to report failures. See transport_ec.cpp for the variant that doesn't
//use exception handling.

#include <boost/leaf/capture_exception.hpp>
#include <vector>
#include <future>
#include <iterator>
#include <iostream>
#include <algorithm>

namespace leaf = boost::leaf;

//Define several error info types.
struct failed_thread_id { std::thread::id value; };
struct failure_info1 { std::string value; };
struct failure_info2 { int value; };
struct failure_info3 { long value; };
struct failure_info4 { float value; };

//A type that represents a successfully returned result from a task.
struct task_result { };

//An exception type thrown in case of task failure.
struct failure : virtual std::exception { };

//This is a test task which succeeds or fails depending on its argument. In case of success, it returns
//task_result, in case of error it throws failure.
task_result
task( bool succeed )
	{
	if( succeed )
		return task_result(); //Simulate successful result.
	else
		leaf::throw_exception( failure(),
			failed_thread_id{std::this_thread::get_id()},
			failure_info1{"info"},
			failure_info2{42},
			failure_info4{42} );
	}

//Launch the specified number of asynchronous tasks. In case an asynchronous task fails, its error info
//(of the type list used to instantiate leaf::capture) is captured in a leaf::captured_result<task_result>, which
//transports it to the main thread.
template <class... ErrorInfo>
std::vector<std::future<task_result>>
launch_async_tasks( int thread_count )
	{
	std::vector<std::future<task_result>> fut;
	std::generate_n( std::inserter(fut,fut.end()), thread_count, [ ]
		{
		return std::async( std::launch::async,
			leaf::capture_exception<ErrorInfo...>( [ ] //leaf::capture<T...> returns leaf::captured_result<T...>...
				{
				return task(rand()%4); //...from the T returned by the task.
				} ) );
		} );
	return fut;
	}

int
main()
	{
	//Launch tasks, transport the specified types of error info. For demonstration, note that the task provides
	//failure_info4 which we don't care about, and that we say we could use failure_info3, but which the
	//task doesn't provide. So, we'll only get failed_thread_id, failure_info1 and failure_info2.
	auto fut = launch_async_tasks<failed_thread_id, failure_info1, failure_info2, failure_info3>(42);

	//Collect results or deal with failures.
	for( auto & f : fut )
		{
		f.wait();

		//Storage for error info.
		leaf::expect<failed_thread_id, failure_info1, failure_info2, failure_info3> exp;

		try
			{
			//Instead of calling future::get we pass the future object to leaf::get. In case the future finished with an exception,
			//this will rethrow that exception, after setting its captured error info.
			task_result r = leaf::get(f);

			//Success!
			std::cout << "Success!" << std::endl;
			}
		catch(
		failure const & e )
			{
			//Failure! Handle error, print failure info.
			handle_error( exp, e,
				leaf::match<failure_info1, failure_info2, failed_thread_id>( [ ] ( std::string const & v1, int v2, std::thread::id tid )
					{
					std::cerr << "Error in thread " << tid << "! failure_info1: " << v1 << ", failure_info2: " << v2 << std::endl;
					} ) );
			}
		}
	}