#include "header.h"

typedef struct {
	long sx, sy, ex, ey;
} Line;

int LineCollision(Line a, Line b);


void TrackCollide(void) {
	Line a, b;
	VERTEX *v0, *v1, *v2, *v3;
	int i, loopAgain;
	
	// Get collision point segment numbers
	for (i=0; i<3; i++) {
		do {
			loopAgain = 0;
			v0 = &vertexLut[primitiveLut[racer.collisionSegment[i]].vert0];
			v1 = &vertexLut[primitiveLut[racer.collisionSegment[i]].vert1];
			v2 = &vertexLut[primitiveLut[racer.collisionSegment[i]].vert2];
			v3 = &vertexLut[primitiveLut[racer.collisionSegment[i]].vert3];
			a.sx = racer.pos.vx+racer.vel.vx+racer.collisionPoint[i].vx;
			a.sy = racer.pos.vz+racer.vel.vz+racer.collisionPoint[i].vz;
			a.ex = (v0->vx+v1->vx+v2->vx+v3->vx)>>2;
			a.ey = (v0->vz+v1->vz+v2->vz+v3->vz)>>2;
			
			b.sx = v2->vx;
			b.sy = v2->vz;
			b.ex = v3->vx;
			b.ey = v3->vz;
		
			if (LineCollision(a, b)) {
				racer.collisionSegment[i] = (racer.collisionSegment[i]+1)%rawTrack->numSegments;
				loopAgain = 1;
			}
			else {
				b.sx = v0->vx;
				b.sy = v0->vz;
				b.ex = v1->vx;
				b.ey = v1->vz;
				if (LineCollision(a, b)) {
					racer.collisionSegment[i]--;
					if (racer.collisionSegment[i] < 0)
						racer.collisionSegment[i] = rawTrack->numSegments-1;
					loopAgain = 1;
				}
	
			}
		} while (loopAgain);
	}
	// Get height point segment numbers
	for (i=0; i<4; i++) {
		do {
			loopAgain = 0;
			v0 = &vertexLut[primitiveLut[racer.heightSegment[i]].vert0];
			v1 = &vertexLut[primitiveLut[racer.heightSegment[i]].vert1];
			v2 = &vertexLut[primitiveLut[racer.heightSegment[i]].vert2];
			v3 = &vertexLut[primitiveLut[racer.heightSegment[i]].vert3];
			a.sx = racer.pos.vx+racer.vel.vx+racer.heightPoint[i].vx;
			a.sy = racer.pos.vz+racer.vel.vz+racer.heightPoint[i].vz;
			a.ex = (v0->vx+v1->vx+v2->vx+v3->vx)>>2;
			a.ey = (v0->vz+v1->vz+v2->vz+v3->vz)>>2;
			
			b.sx = v2->vx;
			b.sy = v2->vz;
			b.ex = v3->vx;
			b.ey = v3->vz;
		
			if (LineCollision(a, b)) {
				racer.heightSegment[i] = (racer.heightSegment[i]+1)%rawTrack->numSegments;
				loopAgain = 1;
			}
			else {
				b.sx = v0->vx;
				b.sy = v0->vz;
				b.ex = v1->vx;
				b.ey = v1->vz;
				if (LineCollision(a, b)) {
					racer.heightSegment[i]--;
					if (racer.heightSegment[i] < 0)
						racer.heightSegment[i] = rawTrack->numSegments-1;
					loopAgain = 1;
				}
	
			}
		} while (loopAgain);
		// Get which half of segment each point is on
		a.ex = (v0->vx+v1->vx)>>1;
		a.ey = (v0->vz+v1->vz)>>1;
		b.sx = v0->vx;
		b.sy = v0->vz;
		b.ex = v3->vx;
		b.ey = v3->vz;
		if (LineCollision(a, b))
			racer.half[i] = 1;
		else
			racer.half[i] = 0;
	}
}


int LineCollision(Line a, Line b) {
	long swapTemp;
	long ay, by, cy, dy;
	
	// Ensure coords are defined in correct order
	if (a.sx > a.ex) {
		swapTemp=a.sx; a.sx=a.ex; a.ex=swapTemp;
		swapTemp=a.sy; a.sy=a.ey; a.ey=swapTemp;
	}
	if (b.sx > b.ex) {
		swapTemp=b.sx; b.sx=b.ex; b.ex=swapTemp;
		swapTemp=b.sy; b.sy=b.ey; b.ey=swapTemp;
	}
	
	// Clip lines
	if (a.sx < b.sx) {
		if (a.ex <= b.sx)
			return 0;
		ay = ((a.ey-a.sy)*(b.sx-a.sx)) / (a.ex-a.sx) + a.sy;
		cy = b.sy;
		if (b.ex < a.ex) {
			by = ((a.ey-a.sy)*(b.ex-a.sx)) / (a.ex-a.sx) + a.sy;
			dy = b.ey;
		}
		else {
			by = a.ey;
			dy = ((b.ey-b.sy)*(a.ex-b.sx)) / (b.ex-b.sx) + b.sy;
		}
	}
	else {
		if (b.ex <= a.sx)
			return 0;
		ay = a.sy;
		cy = ((b.ey-b.sy)*(a.sx-b.sx)) / (b.ex-b.sx) + b.sy;
		if (a.ex < b.ex) {
			by = a.ey;
			dy = ((b.ey-b.sy)*(a.ex-b.sx)) / (b.ex-b.sx) + b.sy;
		}
		else {
			by = ((a.ey-a.sy)*(b.ex-a.sx)) / (a.ex-a.sx) + a.sy;
			dy = b.ey;
		}
	}
	
	// Don't accept collision if lines are touching
	if (ay==cy || by==dy)
		return 0;
	
	// Check that they cross
	return (Sgn(cy-ay) != Sgn(dy-by));
}