#include "tail.h"
#include "firefly.h"
#include "scene.h"

Tail::Tail(Firefly *_owner)
    : owner(_owner)
{
}

#define SET_COLOR(c, a)		glColor4f(c[0], c[1], c[2], a)
#define SET_VERTEX(v, dx)	glVertex3d(v[0]+dx, v[1], v[2])
#define DO_POINT(t, dx, a)\
    SET_COLOR((t).color, a); SET_VERTEX((t).pos, dx)

void Tail::draw()
{
    if (links.size() < 2) // need at least 2 links
	return;

    deque<Link>::iterator it = links.begin();
    double glow_width = scene.glow_factor*scene.tail_width;
    double stretch_factor = 2*scene.fsize*scene.wind[0];
    double dx1, dx2;

    dx2 = ((*it).glow ? glow_width : scene.tail_width);
    for (; (it+1) != links.end(); it++) {
	// half-width of the tail
	dx1 = dx2;
	dx2 = ((*(it+1)).glow ? glow_width : scene.tail_width);

	// have the wind stretch the tail (greater effect on ends)
	double age = (*it).age/scene.tail_length;
	double stretch = stretch_factor*age*age;
	double alpha = 0.9 - age;
	if (alpha > scene.tail_opaq)
	    alpha = scene.tail_opaq;

	// two rectangles: outer vertices have alpha=0, inner two have
	// alpha based on age. note: alpha goes negative, but opengl
	// should clamp it to 0.
	if (stretch > 0) { // stretch to the right
	    glBegin(GL_QUAD_STRIP);
	    DO_POINT(*it, -dx1, 0);
	    DO_POINT(*(it+1), -dx2, 0);

	    DO_POINT(*it, 0, alpha);
	    DO_POINT(*(it+1), 0, alpha);

	    DO_POINT(*it, dx1 + stretch, 0);
	    DO_POINT(*(it+1), dx2 + stretch, 0);
	}
	else { // stretch to the left
	    glBegin(GL_QUAD_STRIP);
	    DO_POINT(*it, -dx1 + stretch, 0);
	    DO_POINT(*(it+1), -dx2 + stretch, 0);

	    DO_POINT(*it, 0, alpha);
	    DO_POINT(*(it+1), 0, alpha);

	    DO_POINT(*it, dx1, 0);
	    DO_POINT(*(it+1), dx2, 0);
	}
	glEnd();
    }
}

bool Tail::elapse(double t)
{
    // pop off the dead ones.
    // note we only have to check the end, since that's where they're gonna
    // be dying from.  deque is very nice for this, because it has constant
    // time  insertion/removal from both ends.
    while (!links.empty() && links.back().age >= scene.tail_length)
	links.pop_back();

    deque<Link>::iterator it = links.begin();
    for (; it != links.end(); it++) {
	(*it).age += t;
	double age = (*it).age/scene.tail_length;
	(*it).pos += scene.wind*age*age;
    }

    if (owner == 0) // my owner died! grow no longer
	return links.empty(); // if we're empty, tell caller we're dead

    links.push_front(Link(owner->pos, owner->color, owner->bait->glow));

    return false;
}