/* 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"
#include "common/array.h"

namespace Sci {

struct WorklistManager {
	Common::Array<reg_t> _worklist;
	reg_t_hash_map _map;

	void push(reg_t reg) {
		if (!reg.segment) // No numbers
			return;

		debugC(2, kDebugLevelGC, "[GC] Adding %04x:%04x", PRINT_REG(reg));

		if (_map.contains(reg))
			return; // already dealt with it

		_map.setVal(reg, true);
		_worklist.push_back(reg);
	}

	void push(const Common::Array<reg_t> &tmp) {
		for (Common::Array<reg_t>::const_iterator it = tmp.begin(); it != tmp.end(); ++it)
			push(*it);
	}
};

static reg_t_hash_map *normalise_hashmap_ptrs(SegManager *segMan, reg_t_hash_map &nonnormal_map) {
	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) {
		reg_t reg = i->_key;
		SegmentObj *mobj = (reg.segment < segMan->_heap.size()) ? segMan->_heap[reg.segment] : NULL;

		if (mobj) {
			reg = mobj->findCanonicAddress(segMan, reg);
			normal_map->setVal(reg, true);
		}
	}

	return normal_map;
}


reg_t_hash_map *find_all_used_references(EngineState *s) {
	SegManager *segMan = s->_segMan;
	reg_t_hash_map *normal_map = NULL;
	WorklistManager wm;
	uint i;

	assert(!s->_executionStack.empty());

	// Initialise
	// Init: Registers
	wm.push(s->r_acc);
	wm.push(s->r_prev);
	// Init: Value Stack
	// We do this one by hand since the stack doesn't know the current execution stack
	Common::List<ExecStack>::iterator iter;
	{
		iter = s->_executionStack.reverse_begin();

		// Skip fake kernel stack frame if it's on top
		if (((*iter).type == EXEC_STACK_TYPE_KERNEL))
			--iter;

		assert((iter != s->_executionStack.end()) && ((*iter).type != EXEC_STACK_TYPE_KERNEL));

		ExecStack &xs = *iter;
		reg_t *pos;

		for (pos = s->stack_base; pos < xs.sp; pos++)
			wm.push(*pos);
	}

	debugC(2, kDebugLevelGC, "[GC] -- Finished adding value stack");

	// Init: Execution Stack
	for (iter = s->_executionStack.begin();
	     iter != s->_executionStack.end(); ++iter) {
		ExecStack &es = *iter;

		if (es.type != EXEC_STACK_TYPE_KERNEL) {
			wm.push(es.objp);
			wm.push(es.sendp);
			if (es.type == EXEC_STACK_TYPE_VARSELECTOR)
				wm.push(*(es.getVarPointer(s->_segMan)));
		}
	}

	debugC(2, kDebugLevelGC, "[GC] -- Finished adding execution stack");

	// Init: Explicitly loaded scripts
	for (i = 1; i < segMan->_heap.size(); i++)
		if (segMan->_heap[i]
		        && segMan->_heap[i]->getType() == SEG_TYPE_SCRIPT) {
			Script *script = (Script *)segMan->_heap[i];

			if (script->getLockers()) { // Explicitly loaded?
				wm.push(script->listObjectReferences());
			}
		}

	debugC(2, kDebugLevelGC, "[GC] -- Finished explicitly loaded scripts, done with root set");

	// Run Worklist Algorithm
	SegmentId stack_seg = segMan->findSegmentByType(SEG_TYPE_STACK);
	while (!wm._worklist.empty()) {
		reg_t reg = wm._worklist.back();
		wm._worklist.pop_back();
		if (reg.segment != stack_seg) { // No need to repeat this one
			debugC(2, kDebugLevelGC, "[GC] Checking %04x:%04x", PRINT_REG(reg));
			if (reg.segment < segMan->_heap.size() && segMan->_heap[reg.segment]) {
				// Valid heap object? Find its outgoing references!
				wm.push(segMan->_heap[reg.segment]->listAllOutgoingReferences(reg));
			}
		}
	}

	// Normalise
	normal_map = normalise_hashmap_ptrs(segMan, wm._map);

	return normal_map;
}

void run_gc(EngineState *s) {
	SegManager *segMan = s->_segMan;

	// Some debug stuff
	debugC(2, kDebugLevelGC, "[GC] Running...");
	const char *segnames[SEG_TYPE_MAX + 1];
	int segcount[SEG_TYPE_MAX + 1];
	memset(segnames, 0, sizeof(segnames));
	memset(segcount, 0, sizeof(segcount));

	// Compute the set of all segments references currently in use.
	reg_t_hash_map *activeRefs = find_all_used_references(s);

	// Iterate over all segments, and check for each whether it
	// contains stuff that can be collected.
	for (uint seg = 1; seg < segMan->_heap.size(); seg++) {
		SegmentObj *mobj = segMan->_heap[seg];
		if (mobj != NULL) {
			const SegmentType type = mobj->getType();
			segnames[type] = SegmentObj::getSegmentTypeName(type);
			
			// Get a list of all deallocatable objects in this segment,
			// then free any which are not referenced from somewhere.
			const Common::Array<reg_t> tmp = mobj->listAllDeallocatable(seg);
			for (Common::Array<reg_t>::const_iterator it = tmp.begin(); it != tmp.end(); ++it) {
				const reg_t addr = *it;
				if (!activeRefs->contains(addr)) {
					// Not found -> we can free it
					mobj->freeAtAddress(segMan, addr);
					debugC(2, kDebugLevelGC, "[GC] Deallocating %04x:%04x", PRINT_REG(addr));
					segcount[type]++;
				}
			}

		}
	}

	delete activeRefs;

	// Output debug summary of garbage collection
	debugC(2, kDebugLevelGC, "[GC] Summary:");
	for (int i = 0; i <= SEG_TYPE_MAX; i++)
		if (segcount[i])
			debugC(2, kDebugLevelGC, "\t%d\t* %s", segcount[i], segnames[i]);
}

} // End of namespace Sci