/*************************************************************************/
/*  step_2d_sw.cpp                                                       */
/*************************************************************************/
/*                         This file is part of:                         */
/*                          PANDEMONIUM ENGINE                           */
/*             https://github.com/Relintai/pandemonium_engine            */
/*************************************************************************/
/* Copyright (c) 2022-present Péter Magyar.                              */
/* Copyright (c) 2014-2022 Godot Engine contributors (cf. AUTHORS.md).   */
/* Copyright (c) 2007-2022 Juan Linietsky, Ariel Manzur.                 */
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/*************************************************************************/

#include "step_2d_sw.h"
#include "core/os/os.h"

void Step2DSW::_populate_island(Body2DSW *p_body, Body2DSW **p_island, Constraint2DSW **p_constraint_island) {
	p_body->set_island_step(_step);
	p_body->set_island_next(*p_island);
	*p_island = p_body;

	for (RBMap<Constraint2DSW *, int>::Element *E = p_body->get_constraint_map().front(); E; E = E->next()) {
		Constraint2DSW *c = (Constraint2DSW *)E->key();
		if (c->get_island_step() == _step) {
			continue; //already processed
		}
		c->set_island_step(_step);
		c->set_island_next(*p_constraint_island);
		*p_constraint_island = c;

		for (int i = 0; i < c->get_body_count(); i++) {
			if (i == E->get()) {
				continue;
			}
			Body2DSW *b = c->get_body_ptr()[i];
			if (b->get_island_step() == _step || b->get_mode() == Physics2DServer::BODY_MODE_STATIC || b->get_mode() == Physics2DServer::BODY_MODE_KINEMATIC) {
				continue; //no go
			}
			_populate_island(c->get_body_ptr()[i], p_island, p_constraint_island);
		}
	}
}

bool Step2DSW::_setup_island(Constraint2DSW *p_island, real_t p_delta) {
	Constraint2DSW *ci = p_island;
	Constraint2DSW *prev_ci = nullptr;
	bool removed_root = false;
	while (ci) {
		bool process = ci->setup(p_delta);

		if (!process) {
			//remove from island if process fails
			if (prev_ci) {
				prev_ci->set_island_next(ci->get_island_next());
			} else {
				removed_root = true;
				prev_ci = ci;
			}
		} else {
			prev_ci = ci;
		}
		ci = ci->get_island_next();
	}

	return removed_root;
}

void Step2DSW::_solve_island(Constraint2DSW *p_island, int p_iterations, real_t p_delta) {
	for (int i = 0; i < p_iterations; i++) {
		Constraint2DSW *ci = p_island;
		while (ci) {
			ci->solve(p_delta);
			ci = ci->get_island_next();
		}
	}
}

void Step2DSW::_check_suspend(Body2DSW *p_island, real_t p_delta) {
	bool can_sleep = true;

	Body2DSW *b = p_island;
	while (b) {
		if (b->get_mode() == Physics2DServer::BODY_MODE_STATIC || b->get_mode() == Physics2DServer::BODY_MODE_KINEMATIC) {
			b = b->get_island_next();
			continue; //ignore for static
		}

		if (!b->sleep_test(p_delta)) {
			can_sleep = false;
		}

		b = b->get_island_next();
	}

	//put all to sleep or wake up everyoen

	b = p_island;
	while (b) {
		if (b->get_mode() == Physics2DServer::BODY_MODE_STATIC || b->get_mode() == Physics2DServer::BODY_MODE_KINEMATIC) {
			b = b->get_island_next();
			continue; //ignore for static
		}

		bool active = b->is_active();

		if (active == can_sleep) {
			b->set_active(!can_sleep);
		}

		b = b->get_island_next();
	}
}

void Step2DSW::step(Space2DSW *p_space, real_t p_delta, int p_iterations) {
	p_space->lock(); // can't access space during this
	p_space->set_step(p_delta);
	p_space->setup(); //update inertias, etc

	const SelfList<Body2DSW>::List *body_list = &p_space->get_active_body_list();

	/* INTEGRATE FORCES */

	uint64_t profile_begtime = OS::get_singleton()->get_ticks_usec();
	uint64_t profile_endtime = 0;

	int active_count = 0;

	const SelfList<Body2DSW> *b = body_list->first();
	while (b) {
		b->self()->integrate_forces(p_delta);
		b = b->next();
		active_count++;
	}

	p_space->set_active_objects(active_count);

	// Update the broadphase to register collision pairs.
	p_space->update();

	{ //profile
		profile_endtime = OS::get_singleton()->get_ticks_usec();
		p_space->set_elapsed_time(Space2DSW::ELAPSED_TIME_INTEGRATE_FORCES, profile_endtime - profile_begtime);
		profile_begtime = profile_endtime;
	}

	/* GENERATE CONSTRAINT ISLANDS */

	Body2DSW *island_list = nullptr;
	Constraint2DSW *constraint_island_list = nullptr;
	b = body_list->first();

	int island_count = 0;

	while (b) {
		Body2DSW *body = b->self();

		if (body->get_island_step() != _step) {
			Body2DSW *island = nullptr;
			Constraint2DSW *constraint_island = nullptr;
			_populate_island(body, &island, &constraint_island);

			island->set_island_list_next(island_list);
			island_list = island;

			if (constraint_island) {
				constraint_island->set_island_list_next(constraint_island_list);
				constraint_island_list = constraint_island;
				island_count++;
			}
		}
		b = b->next();
	}

	p_space->set_island_count(island_count);

	const SelfList<Area2DSW>::List &aml = p_space->get_moved_area_list();

	while (aml.first()) {
		for (const RBSet<Constraint2DSW *>::Element *E = aml.first()->self()->get_constraints().front(); E; E = E->next()) {
			Constraint2DSW *c = E->get();
			if (c->get_island_step() == _step) {
				continue;
			}
			c->set_island_step(_step);
			c->set_island_next(nullptr);
			c->set_island_list_next(constraint_island_list);
			constraint_island_list = c;
		}
		p_space->area_remove_from_moved_list((SelfList<Area2DSW> *)aml.first()); //faster to remove here
	}

	{ //profile
		profile_endtime = OS::get_singleton()->get_ticks_usec();
		p_space->set_elapsed_time(Space2DSW::ELAPSED_TIME_GENERATE_ISLANDS, profile_endtime - profile_begtime);
		profile_begtime = profile_endtime;
	}

	/* SETUP CONSTRAINT ISLANDS */

	{
		Constraint2DSW *ci = constraint_island_list;
		Constraint2DSW *prev_ci = nullptr;
		while (ci) {
			if (_setup_island(ci, p_delta)) {
				//removed the root from the island graph because it is not to be processed

				Constraint2DSW *next = ci->get_island_next();

				if (next) {
					//root from list being deleted no longer exists, replace by next
					next->set_island_list_next(ci->get_island_list_next());
					if (prev_ci) {
						prev_ci->set_island_list_next(next);
					} else {
						constraint_island_list = next;
					}
					prev_ci = next;
				} else {
					//list is empty, just skip
					if (prev_ci) {
						prev_ci->set_island_list_next(ci->get_island_list_next());

					} else {
						constraint_island_list = ci->get_island_list_next();
					}
				}
			} else {
				prev_ci = ci;
			}

			ci = ci->get_island_list_next();
		}
	}

	{ //profile
		profile_endtime = OS::get_singleton()->get_ticks_usec();
		p_space->set_elapsed_time(Space2DSW::ELAPSED_TIME_SETUP_CONSTRAINTS, profile_endtime - profile_begtime);
		profile_begtime = profile_endtime;
	}

	/* SOLVE CONSTRAINT ISLANDS */

	{
		Constraint2DSW *ci = constraint_island_list;
		while (ci) {
			//iterating each island separatedly improves cache efficiency
			_solve_island(ci, p_iterations, p_delta);
			ci = ci->get_island_list_next();
		}
	}

	{ //profile
		profile_endtime = OS::get_singleton()->get_ticks_usec();
		p_space->set_elapsed_time(Space2DSW::ELAPSED_TIME_SOLVE_CONSTRAINTS, profile_endtime - profile_begtime);
		profile_begtime = profile_endtime;
	}

	/* INTEGRATE VELOCITIES */

	b = body_list->first();
	while (b) {
		const SelfList<Body2DSW> *n = b->next();
		b->self()->integrate_velocities(p_delta);
		b = n; // in case it shuts itself down
	}

	/* SLEEP / WAKE UP ISLANDS */

	{
		Body2DSW *bi = island_list;
		while (bi) {
			_check_suspend(bi, p_delta);
			bi = bi->get_island_list_next();
		}
	}

	{ //profile
		profile_endtime = OS::get_singleton()->get_ticks_usec();
		p_space->set_elapsed_time(Space2DSW::ELAPSED_TIME_INTEGRATE_VELOCITIES, profile_endtime - profile_begtime);
		//profile_begtime=profile_endtime;
	}

	p_space->unlock();
	_step++;
}

Step2DSW::Step2DSW() {
	_step = 1;
}