/*** MIGRATE.C ***/

#include "header.h"

void DiffusePrey(Site *arena, double leftbias)
{
	int	i, dir;
	Site *origin, *nnabe;
	double	xxx, bias[4];

/* All sites have:
	Left:	nabes[0]	Top:	nabes[1]
	Bot:	nabes[2]	Right:	nabes[3]
*/
	bias[0] = 0.25 + leftbias;
	bias[3] = 0.25 - leftbias;
	bias[1] = bias[2] = 0.25;

	origin = arena;		/* this algorithm only allows uncontested moves */
	for(i=0;i<NSITES;i++,origin++)
	{
		if(origin->prey==1)   				/* consider move if present */
		{
			xxx = drand48()-bias[0];		/* choose step direction */
			dir = 0;
			while(xxx>0.0)
			{
				dir++;
				xxx -= bias[dir];
			}
			nnabe = origin->nabes[dir];

			if(nnabe->flag==0 && nnabe->prey==0)	/* empty and not tried before */
			{
				nnabe->indirect = 3 - dir;	/* incoming direction */
				nnabe->flag = 1;		/* set flag to note attempt */
				origin->flag = 2;		/* individual has moved */
			}
			else if(nnabe->flag==1)			/* site previously stepped on */
			{
				nnabe->flag = 3;			 /* flag multiple attempts */
				nnabe->nabes[nnabe->indirect]->flag = 0; /* reset previous stepper */
			}
		}
	}

	origin = arena;
	for(i=0;i<NSITES;i++)
	{
		if(origin->flag>0)
		{
			if(origin->flag==1) origin->prey = 1;
			else if(origin->flag==2) origin->prey = 0;
			origin->flag = 0;
		}
		origin++;
	}
}