// physics.cpp: no physics books were hurt nor consulted in the construction of
// this code. All physics computations and constants were invented on the fly
// and simply tweaked until they "felt right", and have no basis in reality.
// Collision detection is simplistic but very robust (uses discrete steps at
// fixed fps).

#include "cube.h"

bool
plcollide(dynent *d, dynent *o, float &headspace, float &hi,
    float &lo) // collide with player or monster
{
	if (o->state != CS_ALIVE)
		return true;
	const float r = o->radius + d->radius;
	if (fabs(o->o.x - d->o.x) < r && fabs(o->o.y - d->o.y) < r) {
		if (d->o.z - d->eyeheight < o->o.z - o->eyeheight) {
			if (o->o.z - o->eyeheight < hi)
				hi = o->o.z - o->eyeheight - 1;
		} else if (o->o.z + o->aboveeye > lo)
			lo = o->o.z + o->aboveeye + 1;

		if (fabs(o->o.z - d->o.z) < o->aboveeye + d->eyeheight)
			return false;
		if (d->monsterstate)
			return false; // hack
		headspace = d->o.z - o->o.z - o->aboveeye - d->eyeheight;
		if (headspace < 0)
			headspace = 10;
	};
	return true;
};

bool
cornertest(int mip, int x, int y, int dx, int dy, int &bx, int &by,
    int &bs) // recursively collide with a mipmapped corner cube
{
	sqr *w = wmip[mip];
	int sz = ssize >> mip;
	bool stest =
	    SOLID(SWS(w, x + dx, y, sz)) && SOLID(SWS(w, x, y + dy, sz));
	mip++;
	x /= 2;
	y /= 2;
	if (SWS(wmip[mip], x, y, ssize >> mip)->type == CORNER) {
		bx = x << mip;
		by = y << mip;
		bs = 1 << mip;
		return cornertest(mip, x, y, dx, dy, bx, by, bs);
	};
	return stest;
};

void
mmcollide(dynent *d, float &hi, float &lo) // collide with a mapmodel
{
	loopv(ents)
	{
		entity &e = ents[i];
		if (e.type != MAPMODEL)
			continue;
		mapmodelinfo &mmi = getmminfo(e.attr2);
		if (!&mmi || !mmi.h)
			continue;
		const float r = mmi.rad + d->radius;
		if (fabs(e.x - d->o.x) < r && fabs(e.y - d->o.y) < r) {
			float mmz =
			    (float)(S(e.x, e.y)->floor + mmi.zoff + e.attr3);
			if (d->o.z - d->eyeheight < mmz) {
				if (mmz < hi)
					hi = mmz;
			} else if (mmz + mmi.h > lo)
				lo = mmz + mmi.h;
		};
	};
};

// all collision happens here
// spawn is a dirty side effect used in spawning
// drop & rise are supplied by the physics below to indicate gravity/push for
// current mini-timestep

bool
collide(dynent *d, bool spawn, float drop, float rise)
{
	const float fx1 =
	    d->o.x - d->radius; // figure out integer cube rectangle this entity
	                        // covers in map
	const float fy1 = d->o.y - d->radius;
	const float fx2 = d->o.x + d->radius;
	const float fy2 = d->o.y + d->radius;
	const int x1 = fast_f2nat(fx1);
	const int y1 = fast_f2nat(fy1);
	const int x2 = fast_f2nat(fx2);
	const int y2 = fast_f2nat(fy2);
	float hi = 127, lo = -128;
	float minfloor = (d->monsterstate && !spawn && d->health > 100)
	                     ? d->o.z - d->eyeheight - 4.5f
	                     : -1000.0f; // big monsters are afraid of heights,
	                                 // unless angry :)

	for (int x = x1; x <= x2; x++)
		for (int y = y1; y <= y2; y++) // collide with map
		{
			if (OUTBORD(x, y))
				return false;
			sqr *s = S(x, y);
			float ceil = s->ceil;
			float floor = s->floor;
			switch (s->type) {
			case SOLID:
				return false;

			case CORNER: {
				int bx = x, by = y, bs = 1;
				if (x == x1 && y == y1 &&
				        cornertest(
				            0, x, y, -1, -1, bx, by, bs) &&
				        fx1 - bx + fy1 - by <= bs ||
				    x == x2 && y == y1 &&
				        cornertest(
				            0, x, y, 1, -1, bx, by, bs) &&
				        fx2 - bx >= fy1 - by ||
				    x == x1 && y == y2 &&
				        cornertest(
				            0, x, y, -1, 1, bx, by, bs) &&
				        fx1 - bx <= fy2 - by ||
				    x == x2 && y == y2 &&
				        cornertest(0, x, y, 1, 1, bx, by, bs) &&
				        fx2 - bx + fy2 - by >= bs)
					return false;
				break;
			};

			case FHF: // FIXME: too simplistic collision with
			          // slopes, makes it feels like tiny stairs
				floor -= (s->vdelta + S(x + 1, y)->vdelta +
				             S(x, y + 1)->vdelta +
				             S(x + 1, y + 1)->vdelta) /
				         16.0f;
				break;

			case CHF:
				ceil += (s->vdelta + S(x + 1, y)->vdelta +
				            S(x, y + 1)->vdelta +
				            S(x + 1, y + 1)->vdelta) /
				        16.0f;
			};
			if (ceil < hi)
				hi = ceil;
			if (floor > lo)
				lo = floor;
			if (floor < minfloor)
				return false;
		};

	if (hi - lo < d->eyeheight + d->aboveeye)
		return false;

	float headspace = 10;
	loopv(players) // collide with other players
	{
		dynent *o = players[i];
		if (!o || o == d)
			continue;
		if (!plcollide(d, o, headspace, hi, lo))
			return false;
	};
	if (d != player1)
		if (!plcollide(d, player1, headspace, hi, lo))
			return false;
	dvector &v = getmonsters();
	// this loop can be a performance bottleneck with many monster on a slow
	// cpu, should replace with a blockmap but seems mostly fast enough
	loopv(v) if (!vreject(d->o, v[i]->o, 7.0f) && d != v[i] &&
	             !plcollide(d, v[i], headspace, hi, lo)) return false;
	headspace -= 0.01f;

	mmcollide(d, hi, lo); // collide with map models

	if (spawn) {
		d->o.z = lo + d->eyeheight; // just drop to floor (sideeffect)
		d->onfloor = true;
	} else {
		const float space = d->o.z - d->eyeheight - lo;
		if (space < 0) {
			if (space > -0.01)
				d->o.z = lo + d->eyeheight; // stick on step
			else if (space > -1.26f)
				d->o.z += rise; // rise thru stair
			else
				return false;
		} else {
			d->o.z -= min(min(drop, space), headspace); // gravity
		};

		const float space2 = hi - (d->o.z + d->aboveeye);
		if (space2 < 0) {
			if (space2 < -0.1)
				return false;      // hack alert!
			d->o.z = hi - d->aboveeye; // glue to ceiling
			d->vel.z = 0; // cancel out jumping velocity
		};

		d->onfloor = d->o.z - d->eyeheight - lo < 0.001f;
	};
	return true;
}

float
rad(float x)
{
	return x * 3.14159f / 180;
};

VARP(maxroll, 0, 3, 20);

int physicsfraction = 0, physicsrepeat = 0;
const int MINFRAMETIME = 20; // physics always simulated at 50fps or better

void
physicsframe() // optimally schedule physics frames inside the graphics frames
{
	if (curtime >= MINFRAMETIME) {
		int faketime = curtime + physicsfraction;
		physicsrepeat = faketime / MINFRAMETIME;
		physicsfraction = faketime - physicsrepeat * MINFRAMETIME;
	} else {
		physicsrepeat = 1;
	};
};

// main physics routine, moves a player/monster for a curtime step
// moveres indicated the physics precision (which is lower for monsters and
// multiplayer prediction) local is false for multiplayer prediction

void
moveplayer(dynent *pl, int moveres, bool local, int curtime)
{
	const bool water = hdr.waterlevel > pl->o.z - 0.5f;
	const bool floating = (editmode && local) || pl->state == CS_EDITING;

	vec d; // vector of direction we ideally want to move in

	d.x = (float)(pl->move * cos(rad(pl->yaw - 90)));
	d.y = (float)(pl->move * sin(rad(pl->yaw - 90)));
	d.z = 0;

	if (floating || water) {
		d.x *= (float)cos(rad(pl->pitch));
		d.y *= (float)cos(rad(pl->pitch));
		d.z = (float)(pl->move * sin(rad(pl->pitch)));
	};

	d.x += (float)(pl->strafe * cos(rad(pl->yaw - 180)));
	d.y += (float)(pl->strafe * sin(rad(pl->yaw - 180)));

	const float speed =
	    curtime / (water ? 2000.0f : 1000.0f) * pl->maxspeed;
	const float friction =
	    water ? 20.0f : (pl->onfloor || floating ? 6.0f : 30.0f);

	const float fpsfric = friction / curtime * 20.0f;

	vmul(pl->vel, fpsfric - 1); // slowly apply friction and direction to
	                            // velocity, gives a smooth movement
	vadd(pl->vel, d);
	vdiv(pl->vel, fpsfric);
	d = pl->vel;
	vmul(d, speed); // d is now frametime based velocity vector

	pl->blocked = false;
	pl->moving = true;

	if (floating) // just apply velocity
	{
		vadd(pl->o, d);
		if (pl->jumpnext) {
			pl->jumpnext = false;
			pl->vel.z = 2;
		}
	} else // apply velocity with collision
	{
		if (pl->onfloor || water) {
			if (pl->jumpnext) {
				pl->jumpnext = false;
				pl->vel.z = 1.7f; // physics impulse upwards
				if (water) {
					pl->vel.x /= 8;
					pl->vel.y /= 8;
				}; // dampen velocity change even harder, gives
				   // correct water feel
				if (local)
					playsoundc(S_JUMP);
				else if (pl->monsterstate)
					playsound(S_JUMP, &pl->o);
			} else if (pl->timeinair >
			           800) // if we land after long time must have
			                // been a high jump, make thud sound
			{
				if (local)
					playsoundc(S_LAND);
				else if (pl->monsterstate)
					playsound(S_LAND, &pl->o);
			};
			pl->timeinair = 0;
		} else {
			pl->timeinair += curtime;
		};

		const float gravity = 20;
		const float f = 1.0f / moveres;
		float dropf =
		    ((gravity - 1) +
		        pl->timeinair / 15.0f); // incorrect, but works fine
		if (water) {
			dropf = 5;
			pl->timeinair = 0;
		}; // float slowly down in water
		const float drop =
		    dropf * curtime / gravity / 100 /
		    moveres; // at high fps, gravity kicks in too fast
		const float rise =
		    speed / moveres /
		    1.2f; // extra smoothness when lifting up stairs

		loopi(moveres) // discrete steps collision detection & sliding
		{
			// try move forward
			pl->o.x += f * d.x;
			pl->o.y += f * d.y;
			pl->o.z += f * d.z;
			if (collide(pl, false, drop, rise))
				continue;
			// player stuck, try slide along y axis
			pl->blocked = true;
			pl->o.x -= f * d.x;
			if (collide(pl, false, drop, rise)) {
				d.x = 0;
				continue;
			};
			pl->o.x += f * d.x;
			// still stuck, try x axis
			pl->o.y -= f * d.y;
			if (collide(pl, false, drop, rise)) {
				d.y = 0;
				continue;
			};
			pl->o.y += f * d.y;
			// try just dropping down
			pl->moving = false;
			pl->o.x -= f * d.x;
			pl->o.y -= f * d.y;
			if (collide(pl, false, drop, rise)) {
				d.y = d.x = 0;
				continue;
			};
			pl->o.z -= f * d.z;
			break;
		};
	};

	// detect wether player is outside map, used for skipping zbuffer clear
	// mostly

	if (pl->o.x < 0 || pl->o.x >= ssize || pl->o.y < 0 || pl->o.y > ssize) {
		pl->outsidemap = true;
	} else {
		sqr *s = S((int)pl->o.x, (int)pl->o.y);
		pl->outsidemap =
		    SOLID(s) ||
		    pl->o.z < s->floor - (s->type == FHF ? s->vdelta / 4 : 0) ||
		    pl->o.z > s->ceil + (s->type == CHF ? s->vdelta / 4 : 0);
	};

	// automatically apply smooth roll when strafing

	if (pl->strafe == 0) {
		pl->roll = pl->roll / (1 + (float)sqrt((float)curtime) / 25);
	} else {
		pl->roll += pl->strafe * curtime / -30.0f;
		if (pl->roll > maxroll)
			pl->roll = (float)maxroll;
		if (pl->roll < -maxroll)
			pl->roll = (float)-maxroll;
	};

	// play sounds on water transitions

	if (!pl->inwater && water) {
		playsound(S_SPLASH2, &pl->o);
		pl->vel.z = 0;
	} else if (pl->inwater && !water)
		playsound(S_SPLASH1, &pl->o);
	pl->inwater = water;
};

void
moveplayer(dynent *pl, int moveres, bool local)
{
	loopi(physicsrepeat) moveplayer(pl, moveres, local,
	    i ? curtime / physicsrepeat
	      : curtime - curtime / physicsrepeat * (physicsrepeat - 1));
};