/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.

 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * $URL$
 * $Id$
 *
 */

#include "sci/engine/gc.h"

namespace Sci {

#define WORKLIST_CHUNK_SIZE 32

//#define DEBUG_GC
//#define DEBUG_GC_VERBOSE

struct worklist_t {
	int used;
	reg_t entries[WORKLIST_CHUNK_SIZE];
	worklist_t *next;
};

static worklist_t *fresh_worklist(worklist_t *old) {
	worklist_t *retval = (worklist_t*)sci_malloc(sizeof(worklist_t));
	retval->used = 0;
	retval->next = old;
	return retval;
}

static worklist_t *new_worklist() {
	return fresh_worklist(NULL);
}

static void worklist_push(worklist_t **wlp, reg_t_hash_map *hashmap, reg_t reg) {
	worklist_t *wl = *wlp;

	if (!reg.segment) // No numbers
		return;

#ifdef DEBUG_GC_VERBOSE
	sciprintf("[GC] Adding "PREG"\n", PRINT_REG(reg));
#endif

	if (hashmap->contains(reg))
		return; // already dealt with it

	hashmap->setVal(reg, true);

	if (!wl || wl->used == WORKLIST_CHUNK_SIZE)
		*wlp = wl = fresh_worklist(wl);

	wl->entries[wl->used++] = reg;
}

static int worklist_has_next(worklist_t *wl) {
	return (wl && wl->used);
}

static reg_t worklist_pop(worklist_t **wlp) {
	worklist_t *wl = *wlp;
	reg_t retval;

	if (!wl || !wl->used) {
		error("Attempt to pop from empty worklist");
	}

	retval = wl->entries[--wl->used];

	if (!wl->used) {
		*wlp = wl->next;
		free(wl);
	}

	return retval;
}

static void free_worklist(worklist_t *wl) {
	if (wl) {
		if (wl->next)
			free_worklist(wl->next);
		free(wl);
	}
}

static reg_t_hash_map * normalise_hashmap_ptrs(reg_t_hash_map *nonnormal_map, SegInterface **interfaces, int interfaces_nr) {
	reg_t_hash_map *normal_map = new reg_t_hash_map();

	for (reg_t_hash_map::iterator i = nonnormal_map->begin(); i != nonnormal_map->end(); ++i) {
		SegInterface *interfce;
		reg_t reg = i->_key;
		interfce = (reg.segment < interfaces_nr) ? interfaces[reg.segment] : NULL;

		if (interfce) {
			reg = interfce->find_canonic_address(interfce, reg);
			normal_map->setVal(reg, true);
		}
	}

	return normal_map;
}


struct worklist_manager_t {
	reg_t_hash_map *nonnormal_map;
	worklist_t **worklist_ref;
};

void add_outgoing_refs(void *pre_wm, reg_t addr) {
	worklist_manager_t *wm = (worklist_manager_t *) pre_wm;
	worklist_push(wm->worklist_ref, wm->nonnormal_map, addr);
}

reg_t_hash_map *find_all_used_references(EngineState *s) {
	SegManager *sm = s->seg_manager;
	SegInterface **interfaces = (SegInterface **)sci_calloc(sizeof(SegInterface *), sm->heap_size);
	reg_t_hash_map *nonnormal_map = new reg_t_hash_map();
	reg_t_hash_map *normal_map = NULL;
	worklist_t *worklist = new_worklist();
	worklist_manager_t worklist_manager;
	int i;

	worklist_manager.worklist_ref = &worklist;
	worklist_manager.nonnormal_map = nonnormal_map;

	for (i = 1; i < sm->heap_size; i++)
		if (sm->heap[i] == NULL)
			interfaces[i] = NULL;
		else
			interfaces[i] = sm->getSegInterface(i);

	// Initialise
	// Init: Registers
	worklist_push(&worklist, nonnormal_map, s->r_acc);
	worklist_push(&worklist, nonnormal_map, s->r_prev);
	// Init: Value Stack
	// We do this one by hand since the stack doesn't know the current execution stack
	{
		exec_stack_t *xs = s->execution_stack + s->execution_stack_pos;
		reg_t *pos;

		for (pos = s->stack_base; pos < xs->sp; pos++)
			worklist_push(&worklist, nonnormal_map, *pos);
	}
#ifdef DEBUG_GC_VERBOSE
	sciprintf("[GC] -- Finished adding value stack");
#endif

	// Init: Execution Stack
	for (i = 0; i <= s->execution_stack_pos; i++) {
		exec_stack_t *es = s->execution_stack + i;

		if (es->type != EXEC_STACK_TYPE_KERNEL) {
			worklist_push(&worklist, nonnormal_map, es->objp);
			worklist_push(&worklist, nonnormal_map, es->sendp);
			if (es->type == EXEC_STACK_TYPE_VARSELECTOR)
				worklist_push(&worklist, nonnormal_map, *(es->addr.varp));
		}
	}
#ifdef DEBUG_GC_VERBOSE
	sciprintf("[GC] -- Finished adding execution stack");
#endif

	// Init: Explicitly loaded scripts
	for (i = 1; i < sm->heap_size; i++)
		if (interfaces[i]
		        && interfaces[i]->type_id == MEM_OBJ_SCRIPT) {
			script_t *script = &(interfaces[i]->mobj->data.script);

			if (script->lockers) { // Explicitly loaded?
				int obj_nr;

				// Locals, if present
				worklist_push(&worklist, nonnormal_map, make_reg(script->locals_segment, 0));

				// All objects (may be classes, may be indirectly reachable)
				for (obj_nr = 0; obj_nr < script->objects_nr; obj_nr++) {
					object_t *obj = script->objects + obj_nr;
					worklist_push(&worklist, nonnormal_map, obj->pos);
				}
			}
		}
#ifdef DEBUG_GC_VERBOSE
	sciprintf("[GC] -- Finished explicitly loaded scripts, done with root set");
#endif

	// Run Worklist Algorithm
	while (worklist_has_next(worklist)) {
		reg_t reg = worklist_pop(&worklist);
		if (reg.segment != s->stack_segment) { // No need to repeat this one
#ifdef DEBUG_GC_VERBOSE
			sciprintf("[GC] Checking "PREG"\n", PRINT_REG(reg));
#endif
			if (reg.segment < sm->heap_size && interfaces[reg.segment])
				interfaces[reg.segment]->list_all_outgoing_references(interfaces[reg.segment], s, reg,
																		&worklist_manager, add_outgoing_refs);
		}
	}

	// Normalise
	normal_map = normalise_hashmap_ptrs(nonnormal_map, interfaces, sm->heap_size);

	// Cleanup
	for (i = 1; i < sm->heap_size; i++)
		if (interfaces[i])
			interfaces[i]->deallocate_self(interfaces[i]);

	free(interfaces);
	delete nonnormal_map;

	return normal_map;
}

struct deallocator_t {
	SegInterface *interfce;
#ifdef DEBUG_GC
	char *segnames[MEM_OBJ_MAX + 1];
	int segcount[MEM_OBJ_MAX + 1];
#endif
	reg_t_hash_map *use_map;
};

void free_unless_used(void *pre_use_map, reg_t addr) {
	deallocator_t *deallocator = (deallocator_t *)pre_use_map;
	reg_t_hash_map *use_map = deallocator->use_map;

	if (!use_map->contains(addr)) {
		// Not found -> we can free it
		deallocator->interfce->free_at_address(deallocator->interfce, addr);
#ifdef DEBUG_GC
		sciprintf("[GC] Deallocating "PREG"\n", PRINT_REG(addr));
		deallocator->segcount[deallocator->interfce->type_id]++;
#endif
	}

}

void run_gc(EngineState *s) {
	int seg_nr;
	deallocator_t deallocator;
	SegManager *sm = s->seg_manager;

#ifdef DEBUG_GC
	c_segtable(s);
	sciprintf("[GC] Running...\n");
	memset(&(deallocator.segcount), 0, sizeof(int) * (MEM_OBJ_MAX + 1));
#endif

	deallocator.use_map = find_all_used_references(s);

	for (seg_nr = 1; seg_nr < sm->heap_size; seg_nr++) {
		if (sm->heap[seg_nr] != NULL) {
			deallocator.interfce = sm->getSegInterface(seg_nr);
#ifdef DEBUG_GC
			deallocator.segnames[deallocator.interfce->type_id] = deallocator.interfce->type;
#endif
			deallocator.interfce->list_all_deallocatable(deallocator.interfce, &deallocator, free_unless_used);
			deallocator.interfce->deallocate_self(deallocator.interfce);
		}
	}

	delete deallocator.use_map;

#ifdef DEBUG_GC
	{
		int i;
		sciprintf("[GC] Summary:\n");
		for (i = 0; i <= MEM_OBJ_MAX; i++)
			if (deallocator.segcount[i])
				sciprintf("\t%d\t* %s\n", deallocator.segcount[i], deallocator.segnames[i]);
	}
#endif
}

} // End of namespace Sci