/* 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 3 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, see <http://www.gnu.org/licenses/>.
 *
 */

//=============================================================================
//
// jump point search grid navigation with navpoint refinement
// (c) 2018 Martin Sedlak
//
//=============================================================================

#include "common/std/queue.h"
#include "common/std/vector.h"
#include "common/std/algorithm.h"
#include "common/std/functional.h"
#include "common/std/xutility.h"

#include "ags/lib/std.h"

namespace AGS3 {

// TODO: this could be cleaned up/simplified ...

// further optimizations possible:
//    - forward refinement should use binary search

class Navigation {
public:
	Navigation();

	void Resize(int width, int height);

	enum NavResult {
		// unreachable
		NAV_UNREACHABLE,
		// straight line exists
		NAV_STRAIGHT,
		// path used
		NAV_PATH
	};

	// ncpath = navpoint-compressed path
	// opath = path composed of individual grid elements
	NavResult NavigateRefined(int sx, int sy, int ex, int ey, std::vector<int> &opath,
	                          std::vector<int> &ncpath);

	NavResult Navigate(int sx, int sy, int ex, int ey, std::vector<int> &opath);

	bool TraceLine(int srcx, int srcy, int targx, int targy, int &lastValidX, int &lastValidY) const;
	bool TraceLine(int srcx, int srcy, int targx, int targy, std::vector<int> *rpath = nullptr) const;

	inline void SetMapRow(int y, const unsigned char *row) {
		map[y] = row;
	}

	inline static int PackSquare(int x, int y);
	inline static void UnpackSquare(int sq, int &x, int &y);

private:
	// priority queue entry
	struct Entry {
		float cost;
		int index;

		inline Entry() {}

		inline Entry(float ncost, int nindex)
			: cost(ncost)
			, index(nindex) {
		}

		inline bool operator <(const Entry &b) const {
			return cost < b.cost;
		}

		inline bool operator >(const Entry &b) const {
			return cost > b.cost;
		}
	};

	int mapWidth;
	int mapHeight;
	std::vector<const unsigned char *> map;

	typedef unsigned short tFrameId;
	typedef int tPrev;

	struct NodeInfo {
		// quantized min distance from origin
		unsigned short dist;
		// frame id (counter to detect new search)
		tFrameId frameId;
		// previous node index (packed, relative to current node)
		tPrev prev;

		inline NodeInfo()
			: dist(0)
			, frameId(0)
			, prev(-1) {
		}
	};

	static const float DIST_SCALE_PACK;
	static const float DIST_SCALE_UNPACK;

	std::vector<NodeInfo> mapNodes;
	tFrameId frameId;

	std::priority_queue<Entry, std::vector<Entry>, Common::Less<Entry> > pq;

	// temporary buffers:
	mutable std::vector<int> fpath;
	std::vector<int> ncpathIndex;
	std::vector<int> rayPath, orayPath;

	// temps for routing towards unreachable areas
	int cnode;
	int closest;

	// orthogonal only (this should correspond to what AGS is doing)
	bool nodiag;

	bool navLock;

	void IncFrameId();

	// outside map test
	inline bool Outside(int x, int y) const;
	// stronger inside test
	bool Passable(int x, int y) const;
	// plain access, unchecked
	inline bool Walkable(int x, int y) const;

	void AddPruned(int *buf, int &bcount, int x, int y) const;
	bool HasForcedNeighbor(int x, int y, int dx, int dy) const;
	int FindJump(int x, int y, int dx, int dy, int ex, int ey);
	int FindOrthoJump(int x, int y, int dx, int dy, int ex, int ey);

	// neighbor reachable (nodiag only)
	bool Reachable(int x0, int y0, int x1, int y1) const;

	static inline int sign(int n) {
		return n < 0 ? -1 : (n > 0 ? 1 : 0);
	}

	static inline int iabs(int n) {
		return n < 0 ? -n : n;
	}

	static inline int iclamp(int v, int min, int max) {
		return v < min ? min : (v > max ? max : v);
	}

	static inline int ClosestDist(int dx, int dy) {
		return dx * dx + dy * dy;
		// Manhattan?
		//return iabs(dx) + iabs(dy);
	}
};

// Navigation

// scale pack of 2 means we can route up to 32767 units (euclidean distance) from starting point
// this means that the maximum routing bitmap size we can handle is 23169x23169; should be more than enough!
const float Navigation::DIST_SCALE_PACK = 2.0f;
const float Navigation::DIST_SCALE_UNPACK = 1.0f / Navigation::DIST_SCALE_PACK;

Navigation::Navigation()
	: mapWidth(0)
	, mapHeight(0)
	, frameId(1)
	, cnode(0)
	, closest(0)
	  // no diagonal route - this should correspond to what AGS does
	, nodiag(true)
	, navLock(false) {
}

void Navigation::Resize(int width, int height) {
	mapWidth = width;
	mapHeight = height;

	int size = mapWidth * mapHeight;

	map.resize(mapHeight);
	mapNodes.resize(size);
}

void Navigation::IncFrameId() {
	if (++frameId == 0) {
		for (int i = 0; i < (int)mapNodes.size(); i++)
			mapNodes[i].frameId = 0;

		frameId = 1;
	}
}

inline int Navigation::PackSquare(int x, int y) {
	return (y << 16) + x;
}

inline void Navigation::UnpackSquare(int sq, int &x, int &y) {
	y = sq >> 16;
	x = sq & ((1 << 16) - 1);
}

inline bool Navigation::Outside(int x, int y) const {
	return
	    (unsigned)x >= (unsigned)mapWidth ||
	    (unsigned)y >= (unsigned)mapHeight;
}

inline bool Navigation::Walkable(int x, int y) const {
	// invert condition because of AGS
	return map[y][x] != 0;
}

bool Navigation::Passable(int x, int y) const {
	return !Outside(x, y) && Walkable(x, y);
}

bool Navigation::Reachable(int x0, int y0, int x1, int y1) const {
	assert(nodiag);

	return Passable(x1, y1) &&
	       (Passable(x1, y0) || Passable(x0, y1));
}

// A* using jump point search (JPS)
// reference: Online Graph Pruning for Pathfinding on Grid Maps
// https://users.cecs.anu.edu.au/~dharabor/data/papers/harabor-grastien-aaai11.pdf
void Navigation::AddPruned(int *buf, int &bcount, int x, int y) const {
	assert(buf && bcount < 8);

	if (Passable(x, y))
		buf[bcount++] = PackSquare(x, y);
}

bool Navigation::HasForcedNeighbor(int x, int y, int dx, int dy) const {
	if (!dy) {
		return (!Passable(x, y - 1) && Passable(x + dx, y - 1)) ||
		       (!Passable(x, y + 1) && Passable(x + dx, y + 1));
	}

	if (!dx) {
		return (!Passable(x - 1, y) && Passable(x - 1, y + dy)) ||
		       (!Passable(x + 1, y) && Passable(x + 1, y + dy));
	}

	return
	    (!Passable(x - dx, y) && Passable(x - dx, y + dy)) ||
	    (!Passable(x, y - dy) && Passable(x + dx, y - dy));
}

int Navigation::FindOrthoJump(int x, int y, int dx, int dy, int ex, int ey) {
	assert((!dx || !dy) && (dx || dy));

	for (;;) {
		x += dx;
		y += dy;

		if (!Passable(x, y))
			break;

		int edx = x - ex;
		int edy = y - ey;
		int edist = ClosestDist(edx, edy);

		if (edist < closest) {
			closest = edist;
			cnode = PackSquare(x, y);
		}

		if ((x == ex && y == ey) || HasForcedNeighbor(x, y, dx, dy))
			return PackSquare(x, y);
	}

	return -1;
}

int Navigation::FindJump(int x, int y, int dx, int dy, int ex, int ey) {
	if (!(dx && dy))
		return FindOrthoJump(x, y, dx, dy, ex, ey);

	if (nodiag && !Reachable(x, y, x + dx, y + dy))
		return -1;

	x += dx;
	y += dy;

	if (!Passable(x, y))
		return -1;

	int edx = x - ex;
	int edy = y - ey;
	int edist = ClosestDist(edx, edy);

	if (edist < closest) {
		closest = edist;
		cnode = PackSquare(x, y);
	}

	if ((x == ex && y == ey) || HasForcedNeighbor(x, y, dx, dy))
		return PackSquare(x, y);

	if (dx && dy) {
		if (FindOrthoJump(x, y, dx, 0, ex, ey) ||
		        FindOrthoJump(x, y, 0, dy, ex, ey))
			return PackSquare(x, y);
	}

	return nodiag ? -1 : FindJump(x, y, dx, dy, ex, ey);
}

Navigation::NavResult Navigation::Navigate(int sx, int sy, int ex, int ey, std::vector<int> &opath) {
	IncFrameId();

	if (!Passable(sx, sy)) {
		opath.clear();
		return NAV_UNREACHABLE;
	}

	// try ray first, if reachable, no need for A* at all
	if (!TraceLine(sx, sy, ex, ey, &opath))
		return NAV_STRAIGHT;

	{
		NodeInfo &node = mapNodes[sy * mapWidth + sx];
		node.dist = 0;
		node.frameId = frameId;
		node.prev = -1;
	}

	closest = 0x7fffffff;
	cnode = PackSquare(sx, sy);

	// no clear for priority queue, like, really?!
	while (!pq.empty())
		pq.pop();

	pq.push(Entry(0.0, cnode));

	while (!pq.empty()) {
		Entry e = pq.top();
		pq.pop();

		int x, y;
		UnpackSquare(e.index, x, y);

		{
			int edx = x - ex;
			int edy = y - ey;
			int edist = ClosestDist(edx, edy);

			if (edist < closest) {
				closest = edist;
				cnode = e.index;
			}
		}

		if (x == ex && y == ey) {
			// done
			break;
		}

		float dist;
		int prev;

		{
			const NodeInfo &node = mapNodes[y * mapWidth + x];
			dist = node.dist * DIST_SCALE_UNPACK;
			prev = node.prev;
		}

		int pneig[8];
		int ncount = 0;

		if (prev < 0) {
			for (int ny = y - 1; ny <= y + 1; ny++) {
				if ((unsigned)ny >= (unsigned)mapHeight)
					continue;

				for (int nx = x - 1; nx <= x + 1; nx++) {
					if (nx == x && ny == y)
						continue;

					if ((unsigned)nx >= (unsigned)mapWidth)
						continue;

					if (!Walkable(nx, ny))
						continue;

					if (nodiag && !Reachable(x, y, nx, ny))
						continue;

					pneig[ncount++] = PackSquare(nx, ny);
				}
			}
		} else {
			// filter
			int px, py;
			UnpackSquare(prev, px, py);
			int dx = sign(x - px);
			int dy = sign(y - py);
			assert(dx || dy);

			if (!dy) {
				AddPruned(pneig, ncount, x + dx, y);

				// add corners
				if (!nodiag || Passable(x + dx, y)) {
					if (!Passable(x, y + 1))
						AddPruned(pneig, ncount, x + dx, y + 1);

					if (!Passable(x, y - 1))
						AddPruned(pneig, ncount, x + dx, y - 1);
				}
			} else if (!dx) {
				// same as above but transposed
				AddPruned(pneig, ncount, x, y + dy);

				// add corners
				if (!nodiag || Passable(x, y + dy)) {
					if (!Passable(x + 1, y))
						AddPruned(pneig, ncount, x + 1, y + dy);

					if (!Passable(x - 1, y))
						AddPruned(pneig, ncount, x - 1, y + dy);
				}
			} else {
				// diagonal case
				AddPruned(pneig, ncount, x, y + dy);
				AddPruned(pneig, ncount, x + dx, y);

				if (!nodiag || Reachable(x, y, x + dx, y + dy))
					AddPruned(pneig, ncount, x + dx, y + dy);

				if (!Passable(x - dx, y) &&
					(nodiag || Reachable(x, y, x - dx, y + dy)))
					AddPruned(pneig, ncount, x - dx, y + dy);

				if (!Passable(x, y - dy) &&
					(nodiag || Reachable(x, y, x + dx, y - dy)))
					AddPruned(pneig, ncount, x + dx, y - dy);
			}
		}

		// sort by heuristics
		Entry sort[8];

		for (int ni = 0; ni < ncount; ni++) {
			int nx, ny;
			UnpackSquare(pneig[ni], nx, ny);
			float edx = (float)(nx - ex);
			float edy = (float)(ny - ey);
			sort[ni].cost = sqrt(edx * edx + edy * edy);
			sort[ni].index = pneig[ni];
		}

		std::sort(sort, sort + ncount);

		int succ[8];
		int nsucc = 0;

		for (int ni = 0; ni < ncount; ni++)
			pneig[ni] = sort[ni].index;

		for (int ni = 0; ni < ncount; ni++) {
			int nx, ny;
			UnpackSquare(pneig[ni], nx, ny);

			int dx = nx - x;
			int dy = ny - y;
			int j = FindJump(x, y, dx, dy, ex, ey);

			if (j < 0)
				continue;

			succ[nsucc++] = j;
		}

		for (int ni = 0; ni < nsucc; ni++) {
			int nx, ny;
			UnpackSquare(succ[ni], nx, ny);
			assert(Walkable(nx, ny));

			NodeInfo &node = mapNodes[ny * mapWidth + nx];

			float ndist = node.frameId != frameId ? INFINITY : node.dist * DIST_SCALE_UNPACK;

			float dx = (float)(nx - x);
			float dy = (float)(ny - y);
			// FIXME: can do better here
			float cost = sqrt(dx * dx + dy * dy);
			float ecost = dist + cost;

			float edx = (float)(nx - ex);
			float edy = (float)(ny - ey);
			float heur = sqrt(edx * edx + edy * edy);

			if (ecost < ndist) {
				ecost *= DIST_SCALE_PACK;

				// assert because we use 16-bit quantized min distance from start to save memory
				assert(ecost <= 65535.0f && "distance from start too large");

				if (ecost > 65535.0f)
					continue;

				node.dist = (unsigned short)(ecost + 0.5f);
				node.frameId = frameId;
				node.prev = PackSquare(x, y);
				pq.push(Entry(ecost + heur, PackSquare(nx, ny)));
			}
		}
	}

	opath.clear();

	// now since we allow approx routing even if dst
	// isn't directly reachable
	// note: not sure if this provides optimal results even if we update
	// cnode during jump search
	int nex, ney;
	UnpackSquare(cnode, nex, ney);

	if ((nex != sx || ney != sy) && (nex != ex || ney != ey)) {
		// target not directly reachable => move closer to target
		TraceLine(nex, ney, ex, ey, &opath);
		UnpackSquare(opath.back(), nex, ney);

		NavResult res = NAV_PATH;

		// note: navLock => better safe than sorry
		// infinite recursion should never happen but... better safe than sorry
		assert(!navLock);

		if (!navLock) {
			// and re-route
			opath.clear();

			navLock = true;
			res = Navigate(sx, sy, nex, ney, opath);
			navLock = false;
		}

		// refine this a bit further; find path point closest
		// to original target and truncate

		int best = 0x7fffffff;
		int bestSize = (int)opath.size();

		for (int i = 0; i < (int)opath.size(); i++) {
			int x, y;
			UnpackSquare(opath[i], x, y);
			int dx = x - ex, dy = y - ey;
			int cost = ClosestDist(dx, dy);

			if (cost < best) {
				best = cost;
				bestSize = i + 1;
			}
		}

		opath.resize(bestSize);

		return res;
	}

	if (ex < 0 || ex >= mapWidth || ey < 0 || ey >= mapHeight ||
		mapNodes[ey * mapWidth + ex].frameId != frameId) {
		// path not found
		return NAV_UNREACHABLE;
	}

	int tx = ex;
	int ty = ey;
	// add end
	opath.push_back(PackSquare(tx, ty));

	for (;;) {
		int prev = mapNodes[ty * mapWidth + tx].prev;

		if (prev < 0)
			break;

		// unpack because we use JPS
		int px, py;
		UnpackSquare(prev, px, py);
		int dx = sign(px - tx);
		int dy = sign(py - ty);

		while (tx != px || ty != py) {
			tx += dx;
			ty += dy;
			opath.push_back(PackSquare(tx, ty));
		}
	}

	std::reverse(opath.begin(), opath.end());
	return NAV_PATH;
}

Navigation::NavResult Navigation::NavigateRefined(int sx, int sy, int ex, int ey,
	std::vector<int> &opath, std::vector<int> &ncpath) {
	ncpath.clear();

	NavResult res = Navigate(sx, sy, ex, ey, opath);

	if (res != NAV_PATH) {
		if (res == NAV_STRAIGHT) {
			ncpath.push_back(opath[0]);
			ncpath.push_back(opath.back());
		}

		return res;
	}

	fpath.clear();
	ncpathIndex.clear();

	fpath.reserve(opath.size());
	fpath.push_back(opath[0]);
	ncpath.push_back(opath[0]);
	ncpathIndex.push_back(0);

	rayPath.clear();
	orayPath.clear();

	rayPath.reserve(opath.size());
	orayPath.reserve(opath.size());

	for (int i = 1, fx = sx, fy = sy; i < (int)opath.size(); i++) {
		// trying to optimize path
		int tx, ty;
		UnpackSquare(opath[i], tx, ty);

		bool last = i == (int)opath.size() - 1;

		if (!TraceLine(fx, fy, tx, ty, &rayPath)) {
			assert(rayPath.back() == opath[i]);
			std::swap(rayPath, orayPath);

			if (!last)
				continue;
		}

		// copy orayPath
		for (int j = 1; j < (int)orayPath.size(); j++)
			fpath.push_back(orayPath[j]);

		if (!orayPath.empty()) {
			assert(ncpath.back() == orayPath[0]);
			ncpath.push_back(orayPath.back());
			ncpathIndex.push_back((int)fpath.size() - 1);

			if (!last) {
				UnpackSquare(orayPath.back(), fx, fy);
				orayPath.clear();
				i--;
				continue;
			}
		}

		if (fpath.back() != opath[i])
			fpath.push_back(opath[i]);

		if (ncpath.back() != opath[i]) {
			ncpath.push_back(opath[i]);
			ncpathIndex.push_back((int)fpath.size() - 1);
		}

		fx = tx;
		fy = ty;
	}

	std::swap(opath, fpath);

	// validate cpath
	for (int i = 0; i < (int)ncpath.size() - 1; i++) {
		int fx, fy;
		int tx, ty;
		UnpackSquare(ncpath[i], fx, fy);
		UnpackSquare(ncpath[i + 1], tx, ty);
		assert(!TraceLine(fx, fy, tx, ty, &rayPath));
	}

	assert(ncpath.size() == ncpathIndex.size());

	// so now we have opath, ncpath and ncpathIndex
	// we want to gradually move ncpath node towards previous to see
	// if we can raycast from prev ncpath node to moved and from moved
	// to the end

	bool adjusted = false;

	for (int i = (int)ncpath.size() - 2; i > 0; i--) {
		int px, py;
		int nx, ny;

		int pidx = ncpathIndex[i - 1];
		int idx = ncpathIndex[i];

		UnpackSquare(ncpath[i - 1], px, py);
		UnpackSquare(ncpath[i + 1], nx, ny);

		for (int j = idx - 1; j >= pidx; j--) {
			int x, y;
			UnpackSquare(opath[j], x, y);

			// if we can raycast px,py => x,y and x,y => nx,ny,
			// we can move ncPath node!
			if (TraceLine(px, py, x, y))
				continue;

			if (TraceLine(x, y, nx, ny))
				continue;

			ncpath[i] = opath[j];
			ncpathIndex[i] = j;
			adjusted = true;
		}

		if (ncpath[i] == ncpath[i - 1]) {
			// if we get here, we need to remove ncpath[i]
			// because we reached the previous node
			ncpath.erase(ncpath.begin() + i);
			ncpathIndex.erase(ncpathIndex.begin() + i);
			adjusted = true;
		}
	}

	if (!adjusted)
		return NAV_PATH;

	// final step (if necessary) is to reconstruct path from compressed path

	opath.clear();
	opath.push_back(ncpath[0]);

	for (int i = 1; i < (int)ncpath.size(); i++) {
		int fx, fy;
		int tx, ty;

		UnpackSquare(ncpath[i - 1], fx, fy);
		UnpackSquare(ncpath[i], tx, ty);

		TraceLine(fx, fy, tx, ty, &rayPath);

		for (int j = 1; j < (int)rayPath.size(); j++)
			opath.push_back(rayPath[j]);
	}

	return NAV_PATH;
}

bool Navigation::TraceLine(int srcx, int srcy, int targx, int targy, int &lastValidX, int &lastValidY) const {
	lastValidX = srcx;
	lastValidY = srcy;

	bool res = TraceLine(srcx, srcy, targx, targy, &fpath);

	if (!fpath.empty())
		UnpackSquare(fpath.back(), lastValidX, lastValidY);

	return res;
}

bool Navigation::TraceLine(int srcx, int srcy, int targx, int targy, std::vector<int> *rpath) const {
	if (rpath)
		rpath->clear();

	// DDA
	int x0 = (srcx << 16) + 0x8000;
	int y0 = (srcy << 16) + 0x8000;
	int x1 = (targx << 16) + 0x8000;
	int y1 = (targy << 16) + 0x8000;

	int dx = x1 - x0;
	int dy = y1 - y0;

	if (!dx && !dy) {
		if (!Passable(srcx, srcy))
			return true;

		if (rpath)
			rpath->push_back(PackSquare(srcx, srcy));

		return false;
	}

	int xinc, yinc;

	if (iabs(dx) >= iabs(dy)) {
		// step along x
		xinc = sign(dx) * 65536;
		yinc = (int)((double)dy * 65536 / iabs(dx));
	} else {
		// step along y
		yinc = sign(dy) * 65536;
		xinc = (int)((double)dx * 65536 / iabs(dy));
	}

	int fx = x0;
	int fy = y0;
	int x = x0 >> 16;
	int y = y0 >> 16;
	int ex = x1 >> 16;
	int ey = y1 >> 16;

	while (x != ex || y != ey) {
		if (!Passable(x, y))
			return true;

		if (rpath)
			rpath->push_back(PackSquare(x, y));

		fx += xinc;
		fy += yinc;
		int ox = x;
		int oy = y;
		x = fx >> 16;
		y = fy >> 16;

		if (nodiag && !Reachable(ox, oy, x, y))
			return true;
	}

	assert(iabs(x - ex) <= 1 && iabs(y - ey) <= 1);

	if (nodiag && !Reachable(x, y, ex, ey))
		return false;

	if (!Passable(ex, ey))
		return true;

	int sq = PackSquare(ex, ey);

	if (rpath && (rpath->empty() || rpath->back() != sq))
		rpath->push_back(sq);

	return false;
}

} // namespace AGS3