#include <u.h>
#include <libc.h>
#include <thread.h>
#include <draw.h>
#include <memdraw.h>
#include <geometry.h>
#include "libobj/obj.h"
#include "graphics.h"
#include "internal.h"

Rectangle UR = {0,0,1,1};


static void
pixel(Memimage *dst, Point p, Memimage *src)
{
	if(dst == nil || src == nil)
		return;

	memimagedraw(dst, rectaddpt(UR, p), src, ZP, nil, ZP, SoverD);
}

static int
isvisible(Point3 p)
{
	if(p.x < -p.w || p.x > p.w ||
	   p.y < -p.w || p.y > p.w ||
	   p.z < -p.w || p.z > p.w)
		return 0;
	return 1;
}

static void
mulsdm(double r[6], double m[6][4], Point3 p)
{
	int i;

	for(i = 0; i < 6; i++)
		r[i] = m[i][0]*p.x + m[i][1]*p.y + m[i][2]*p.z + m[i][3]*p.w;
}

typedef struct
{
	Vertex *v;
	ulong n;
	ulong cap;
} Polygon;

static int
addvert(Polygon *p, Vertex v)
{
	if(++p->n > p->cap)
		p->v = erealloc(p->v, (p->cap = p->n)*sizeof(*p->v));
	p->v[p->n-1] = v;
	return p->n;
}

static void
swappoly(Polygon *a, Polygon *b)
{
	Polygon tmp;

	tmp = *a;
	*a = *b;
	*b = tmp;
}

/*
 * references:
 * 	- James F. Blinn, Martin E. Newell, “Clipping Using Homogeneous Coordinates”,
 * 	  SIGGRAPH '78, pp. 245-251
 * 	- https://cs418.cs.illinois.edu/website/text/clipping.html
 * 	- https://github.com/aap/librw/blob/14dab85dcae6f3762fb2b1eda4d58d8e67541330/tools/playground/tl_tests.cpp#L522
 */
static int
cliptriangle(Triangle *t)
{
	/* signed distance from each clipping plane */
	static double sdm[6][4] = {
		 1,  0,  0, 1,	/* l */
		-1,  0,  0, 1,	/* r */
		 0,  1,  0, 1,	/* b */
		 0, -1,  0, 1,	/* t */
		 0,  0,  1, 1,	/* f */
		 0,  0, -1, 1,	/* n */
	}, sd0[6], sd1[6];
	double d0, d1, perc;
	Polygon Vin, Vout;
	Vertex *v0, *v1, v;	/* edge verts and new vertex (line-plane intersection) */
	int i, j, nt;

	nt = 0;
	memset(&Vin, 0, sizeof Vin);
	memset(&Vout, 0, sizeof Vout);
	for(i = 0; i < 3; i++)
		addvert(&Vin, t[0][i]);

	for(j = 0; j < 6; j++){
		for(i = 0; i < Vin.n; i++){
			v0 = &Vin.v[i];
			v1 = &Vin.v[(i+1) % Vin.n];

			mulsdm(sd0, sdm, v0->p);
			mulsdm(sd1, sdm, v1->p);

			if(sd0[j] < 0 && sd1[j] < 0)
				continue;

			if(sd0[j] >= 0 && sd1[j] >= 0)
				goto allin;

			/* keep the discarded vertex attributes */
			v = sd0[j] < 0? *v0: *v1;

			d0 = (j&1) == 0? sd0[j]: -sd0[j];
			d1 = (j&1) == 0? sd1[j]: -sd1[j];
			perc = d0/(d0 - d1);
			v.p = lerp3(v0->p, v1->p, perc);
			v.uv = lerp2(v0->uv, v1->uv, perc);
			v.intensity = flerp(v0->intensity, v1->intensity, perc);
			addvert(&Vout, v);

			if(sd1[j] >= 0){
allin:
				addvert(&Vout, *v1);
			}
		}
		if(j < 6-1){
			swappoly(&Vin, &Vout);
			Vout.n = 0;
		}
	}

	if(Vout.n < 3){
		free(Vout.v);
		free(Vin.v);
		return 0;
	}

	/* triangulate */
	for(i = 0; i < Vout.n-2; i++, nt++){
		t[nt][0] = Vout.v[0];
		t[nt][1] = Vout.v[i+1];
		t[nt][2] = Vout.v[i+2];
	}
	free(Vout.v);
	free(Vin.v);

	return nt;
}

/*
 * transforms p from the world reference frame
 * to c's one (aka Viewing Coordinate System).
 */
Point3
world2vcs(Camera *c, Point3 p)
{
	return rframexform3(p, *c);
}

/*
 * projects p from the VCS to clip space, placing
 * p.[xyz] ∈ (-∞,-w)∪[-w,w]∪(w,∞) where [-w,w]
 * represents the visibility volume.
 *
 * the clipping planes are:
 *
 * 	|   -w   |   w   |
 *	+----------------+
 * 	| left   | right |
 * 	| bottom | top   |
 * 	| far    | near  |
 */
Point3
vcs2clip(Camera *c, Point3 p)
{
	return xform3(p, c->proj);
}

Point3
world2clip(Camera *c, Point3 p)
{
	return vcs2clip(c, world2vcs(c, p));
}

/*
 * performs the perspective division, placing
 * p.[xyz] ∈ [-1,1] and p.w = 1/z
 * (aka Normalized Device Coordinates).
 *
 * p.w is kept as z⁻¹ so we can later do
 * perspective-correct attribute interpolation.
 */
static Point3
clip2ndc(Point3 p)
{
	p.w = 1.0/p.w;
	p.x *= p.w;
	p.y *= p.w;
	p.z *= p.w;
	return p;
}

/*
 * scales p to fit the destination viewport,
 * placing p.x ∈ [0,width], p.y ∈ [0,height],
 * p.z ∈ [0,1] and leaving p.w intact.
 */
static Point3
ndc2viewport(Framebuf *fb, Point3 p)
{
	Matrix3 view = {
		Dx(fb->r)/2.0,             0,       0,       Dx(fb->r)/2.0,
		0,            -Dy(fb->r)/2.0,       0,       Dy(fb->r)/2.0,
		0,                         0, 1.0/2.0,             1.0/2.0,
		0,                         0,       0,                   1,
	};
	double w;

	w = p.w;
	p.w = 1;
	p = xform3(p, view);
	p.w = w;
	return p;
}

void
perspective(Matrix3 m, double fov, double a, double n, double f)
{
	double cotan;

	cotan = 1/tan(fov/2);
	identity3(m);
	m[0][0] =  cotan/a;
	m[1][1] =  cotan;
	m[2][2] =  (f+n)/(f-n);
	m[2][3] = -2*f*n/(f-n);
	m[3][2] = -1;
}

void
orthographic(Matrix3 m, double l, double r, double b, double t, double n, double f)
{
	identity3(m);
	m[0][0] =  2/(r - l);
	m[1][1] =  2/(t - b);
	m[2][2] = -2/(f - n);
	m[0][3] = -(r + l)/(r - l);
	m[1][3] = -(t + b)/(t - b);
	m[2][3] = -(f + n)/(f - n);
}

static void
rasterize(SUparams *params, Triangle t, Memimage *frag)
{
	FSparams fsp;
	Triangle2 t₂, tt₂;
	Rectangle bbox;
	Point p, tp;
	Point3 bc;
	double z, depth;
	uchar cbuf[4];

	t₂.p0 = Pt2(t[0].p.x, t[0].p.y, 1);
	t₂.p1 = Pt2(t[1].p.x, t[1].p.y, 1);
	t₂.p2 = Pt2(t[2].p.x, t[2].p.y, 1);
	/* find the triangle's bbox and clip it against the fb */
	bbox = Rect(
		min(min(t₂.p0.x, t₂.p1.x), t₂.p2.x), min(min(t₂.p0.y, t₂.p1.y), t₂.p2.y),
		max(max(t₂.p0.x, t₂.p1.x), t₂.p2.x)+1, max(max(t₂.p0.y, t₂.p1.y), t₂.p2.y)+1
	);
	bbox.min.x = max(bbox.min.x, params->fb->r.min.x);
	bbox.min.y = max(bbox.min.y, params->fb->r.min.y);
	bbox.max.x = min(bbox.max.x, params->fb->r.max.x);
	bbox.max.y = min(bbox.max.y, params->fb->r.max.y);
	cbuf[0] = 0xFF;
	fsp.su = params;
	fsp.frag = frag;
	fsp.cbuf = cbuf;

	/* perspective-divide the attributes */
//	t[0].c = mulpt3(t[0].c, t[0].p.w);
//	t[1].c = mulpt3(t[1].c, t[1].p.w);
//	t[2].c = mulpt3(t[2].c, t[2].p.w);
	t[0].uv = mulpt2(t[0].uv, t[0].p.w);
	t[1].uv = mulpt2(t[1].uv, t[1].p.w);
	t[2].uv = mulpt2(t[2].uv, t[2].p.w);

	for(p.y = bbox.min.y; p.y < bbox.max.y; p.y++)
		for(p.x = bbox.min.x; p.x < bbox.max.x; p.x++){
			bc = barycoords(t₂, Pt2(p.x,p.y,1));
			if(bc.x < 0 || bc.y < 0 || bc.z < 0)
				continue;

			z = t[0].p.z*bc.x + t[1].p.z*bc.y + t[2].p.z*bc.z;
			depth = fclamp(z, 0, 1);
			lock(&params->fb->zbuflk);
			if(depth <= params->fb->zbuf[p.x + p.y*Dx(params->fb->r)]){
				unlock(&params->fb->zbuflk);
				continue;
			}
			params->fb->zbuf[p.x + p.y*Dx(params->fb->r)] = depth;
			unlock(&params->fb->zbuflk);

			/* lerp z⁻¹ and get actual z */
			z = t[0].p.w*bc.x + t[1].p.w*bc.y + t[2].p.w*bc.z;
			z = 1.0/(z < 1e-5? 1e-5: z);

			/* lerp attribute and dissolve perspective */
//			t[0].c = mulpt3(t[0].c, bc.x*z);
//			t[1].c = mulpt3(t[1].c, bc.y*z);
//			t[2].c = mulpt3(t[2].c, bc.z*z);

			if((t[0].uv.w + t[1].uv.w + t[2].uv.w) != 0){
				tt₂.p0 = mulpt2(t[0].uv, bc.x*z);
				tt₂.p1 = mulpt2(t[1].uv, bc.y*z);
				tt₂.p2 = mulpt2(t[2].uv, bc.z*z);

				tp.x = (tt₂.p0.x + tt₂.p1.x + tt₂.p2.x)*Dx(params->model->tex->r);
				tp.y = (1 - (tt₂.p0.y + tt₂.p1.y + tt₂.p2.y))*Dy(params->model->tex->r);

				switch(params->model->tex->chan){
				case RGB24:
					unloadmemimage(params->model->tex, rectaddpt(UR, tp), cbuf+1, sizeof cbuf - 1);
					cbuf[0] = 0xFF;
					break;
				case RGBA32:
					unloadmemimage(params->model->tex, rectaddpt(UR, tp), cbuf, sizeof cbuf);
					break;
				case XRGB32:
					unloadmemimage(params->model->tex, rectaddpt(UR, tp), cbuf, sizeof cbuf);
					memmove(cbuf+1, cbuf, 3);
					cbuf[0] = 0xFF;
					break;
				}
			}else
				memset(cbuf, 0xFF, sizeof cbuf);

			params->var_intensity[0] = t[0].intensity;
			params->var_intensity[1] = t[1].intensity;
			params->var_intensity[2] = t[2].intensity;
			fsp.p = p;
			fsp.bc = bc;
			pixel(params->fb->cb, p, params->fshader(&fsp));
		}
}

static void
shaderunit(void *arg)
{
	SUparams *params;
	VSparams vsp;
	Memimage *frag;
	OBJVertex *verts, *tverts, *nverts;	/* geometric, texture and normals vertices */
	OBJIndexArray *idxtab;
	OBJElem **ep, **eb, **ee;
	Point3 n;				/* surface normal */
	Triangle *t;				/* triangles to raster */
	int nt;

	params = arg;
	vsp.su = params;
	frag = rgb(DBlack);

	threadsetname("shader unit #%d", params->id);

	t = emalloc(sizeof(*t)*16);
	verts = params->model->obj->vertdata[OBJVGeometric].verts;
	tverts = params->model->obj->vertdata[OBJVTexture].verts;
	nverts = params->model->obj->vertdata[OBJVNormal].verts;
	eb = params->model->elems;
	ee = eb + params->model->nelems;

	for(ep = eb; ep != ee; ep++){
		nt = 1;	/* start with one. after clipping it might change */

		idxtab = &(*ep)->indextab[OBJVGeometric];
		t[0][0].p = Pt3(verts[idxtab->indices[0]].x,verts[idxtab->indices[0]].y,verts[idxtab->indices[0]].z,verts[idxtab->indices[0]].w);
		t[0][1].p = Pt3(verts[idxtab->indices[1]].x,verts[idxtab->indices[1]].y,verts[idxtab->indices[1]].z,verts[idxtab->indices[1]].w);
		t[0][2].p = Pt3(verts[idxtab->indices[2]].x,verts[idxtab->indices[2]].y,verts[idxtab->indices[2]].z,verts[idxtab->indices[2]].w);

		idxtab = &(*ep)->indextab[OBJVNormal];
		if(idxtab->nindex == 3){
			t[0][0].n = Vec3(nverts[idxtab->indices[0]].i, nverts[idxtab->indices[0]].j, nverts[idxtab->indices[0]].k);
			t[0][0].n = normvec3(t[0][0].n);
			t[0][1].n = Vec3(nverts[idxtab->indices[1]].i, nverts[idxtab->indices[1]].j, nverts[idxtab->indices[1]].k);
			t[0][1].n = normvec3(t[0][1].n);
			t[0][2].n = Vec3(nverts[idxtab->indices[2]].i, nverts[idxtab->indices[2]].j, nverts[idxtab->indices[2]].k);
			t[0][2].n = normvec3(t[0][2].n);
		}else{
			/* TODO build a list of per-vertex normals earlier */
			n = normvec3(crossvec3(subpt3(t[0][2].p, t[0][0].p), subpt3(t[0][1].p, t[0][0].p)));
			t[0][0].n = t[0][1].n = t[0][2].n = mulpt3(n, -1);
		}

		idxtab = &(*ep)->indextab[OBJVTexture];
		if(params->model->tex != nil && idxtab->nindex == 3){
			t[0][0].uv = Pt2(tverts[idxtab->indices[0]].u, tverts[idxtab->indices[0]].v, 1);
			t[0][1].uv = Pt2(tverts[idxtab->indices[1]].u, tverts[idxtab->indices[1]].v, 1);
			t[0][2].uv = Pt2(tverts[idxtab->indices[2]].u, tverts[idxtab->indices[2]].v, 1);
		}else{
			t[0][0].uv = t[0][1].uv = t[0][2].uv = Vec2(0,0);
		}

		vsp.v = &t[0][0];
		vsp.idx = 0;
		t[0][0].p = params->vshader(&vsp);
		vsp.v = &t[0][1];
		vsp.idx = 1;
		t[0][1].p = params->vshader(&vsp);
		vsp.v = &t[0][2];
		vsp.idx = 2;
		t[0][2].p = params->vshader(&vsp);

		if(!isvisible(t[0][0].p) || !isvisible(t[0][1].p) || !isvisible(t[0][2].p))
			nt = cliptriangle(t);

		while(nt--){
			t[nt][0].p = ndc2viewport(params->fb, clip2ndc(t[nt][0].p));
			t[nt][1].p = ndc2viewport(params->fb, clip2ndc(t[nt][1].p));
			t[nt][2].p = ndc2viewport(params->fb, clip2ndc(t[nt][2].p));

			rasterize(params, t[nt], frag);
		}
	}

	free(t);
	freememimage(frag);
	sendp(params->donec, nil);
	free(params);
	threadexits(nil);
}

void
shade(Framebuf *fb, Scene *sc, Shader *s)
{
	int i;
	uvlong time;
	Entity *ent;
	SUparams *params;
	Channel *donec;

	time = nanosec();
	donec = chancreate(sizeof(void*), 0);

	/* TODO come up with an actual concurrent architecture */
	for(i = 0, ent = sc->ents.next; i < sc->nents; i++, ent = ent->next){
		params = emalloc(sizeof *params);
		params->fb = fb;
		params->id = i;
		params->donec = donec;
		params->model = ent->mdl;
		params->uni_time = time;
		params->vshader = s->vshader;
		params->fshader = s->fshader;
		proccreate(shaderunit, params, mainstacksize);
	}

	while(i--)
		recvp(donec);
	chanfree(donec);
}