gplib/include/gp/system/system.hpp

#pragma once

#include "gp/algorithms/foreach.hpp"
#include "gp/algorithms/reference.hpp"
#include "gp/utils/allocators/allocator.hpp"
#include "gp/containers/vector.hpp"
#include "gp/ipc/file_description.hpp"
#include "gp/ipc/filesystem.hpp"
#include "gp/system/task_queue.hpp"
#include "gp/system/scheduler.hpp"

// THIS FILE IS A MESS
// Reworking will be suffering

namespace gp{
// TODO: thread safety
	namespace system {
		class scheduling_scheme {
		public: 
			virtual task_queue::node_ptr one(size_t token) = 0;
			virtual task_queue::node_ptr next(size_t token, task_queue::node_ptr current) = 0;
			virtual void push(task_queue::node_ptr current) = 0;
			virtual void link(system&) = 0;
			virtual scheduler& current_scheduler() = 0;
		};

		class system {
			friend struct scheduler;
		public:
			gp::reference_wrapper<gp::allocator> system_allocator;
			gp::vector<gp::filesystem*> filesystems{system_allocator};
			gp::vector<gp::system::scheduler> process_managers;
			scheduling_scheme& scheme;
			task_queue::node main_context;

			system(allocator& v, scheduling_scheme& scheme_, gp::buffer<char> stack_estimate = gp::buffer<char>{nullptr, nullptr})
			: system_allocator{v}
			, process_managers{system_allocator}
			, scheme{scheme_}
			{
				[[maybe_unused]] volatile char a;
				if(stack_estimate.size() == 0) {
					auto seed = (char*)&a;
					auto jump = (uintptr_t)seed % gp_config::limits::process_stack;
					seed -= jump + (jump == 0)*gp_config::limits::process_stack;
					auto page_cnt = 1;
					if(jump == 0) page_cnt++;
					stack_estimate = gp::buffer<char>{seed, (size_t)(gp_config::limits::process_stack*page_cnt)};
				} 
				main_context.value = (process_data*)system_allocator.get().allocate(sizeof(process_data));
				new(main_context.value) process_data(gp::function<void()>([]() -> void{}, nullopt), stack_estimate.begin().data, stack_estimate.size(), gp::unique_ptr<base_process_info>::make(system_allocator));
				gp_config::assertion(main_context.value != nullptr, "failed to allocate return to main switch");
				scheme.link(*this);
			}

			size_t spawn(gp::function<void()> fn) {
				constexpr size_t stack_sz = gp_config::limits::process_stack;
				void* stack = system_allocator.get().allocate(stack_sz);
				gp_config::assertion(stack != nullptr, "failed to allocate a stack");
				process_data* created_process = (process_data*)system_allocator.get().allocate(sizeof(process_data));
				gp_config::assertion(stack != nullptr, "failed to allocate a process data");
				new(created_process) process_data(fn, stack, stack_sz, gp::unique_ptr<base_process_info>::make(system_allocator));

				task_queue::node_ptr pp = (task_queue::node_ptr)system_allocator.get().allocate(
					sizeof(task_queue::node)
				);
				new(pp) task_queue::node();
				pp->value = created_process;
				auto pid = pp->value->pid;
				scheme.push(pp);
				return pid;
			}

			template<typename threading_function>
			void run(threading_function thread_starter) {
				for(auto& i : process_managers) {
					gp::function<void(void)> runner{
						[&](){
							i.run();
						},
						system_allocator
					};
					thread_starter(
						runner
					);
				}
			}

			void yield() {
				scheme.current_scheduler().yield();
			}
		};

		scheduler::scheduler(class system& v, size_t token)
		: id(token)
		, sys(v)
		, main_context_data{gp::function<void()>{[](){}, v.system_allocator}, nullptr, size_t(0), gp::unique_ptr<base_process_info>::make(v.system_allocator)}
		, main_context()
		{
			main_context.value = &main_context_data;
			gp_config::assertion(!main_context.try_acquire(), "node should be not aquired on creation");
		}

		no_inline_decl(inline scheduler* spawner (scheduler* new_p)) {
			auto& proc = *new_p->current->value;
			if(proc.state == gp::system::process_status::inactive) {
				proc.state = gp::system::process_status::running;
				proc.fn();
				proc.state = gp::system::process_status::finished;
			}
			return new_p;
		}

		void scheduler::yield_to(task_queue::node_ptr target)
		{
			previous = current;
			current->value->specifics.pull();
			current = target;
			auto new_p = this;
			do{
				new_p = spawner(static_cast<scheduler*>(target->value->specifics.push(new_p)));
				target = new_p->sys.scheme.next(new_p->id, new_p->current);
				new_p->previous = new_p->current;
				new_p->current->value->specifics.pull();
				new_p->current = target;
			} while(true);
		}


		void scheduler::yield(){
			current = sys.scheme.next(id, current);
			yield_to(current);
		}


		void scheduler::run()
		{
			main_context_data.pid = 0;
			main_context_data.state = process_status::running;
			main_context_data.specifics.pull();
			current = &main_context;
			sys.scheme.push(&main_context);
			auto new_p = spawner(static_cast<scheduler*>(current->value->specifics.push(this)));
			new_p->yield_to(new_p->sys.scheme.next(new_p->id, new_p->current));
		}
	}
}