#define _POSIX_C_SOURCE 200809L	// for strnlen
#include <stdio.h>
#include <string.h>

char s[4] = "0000";
char f = 'A';
unsigned fi = 0;
unsigned sp = 1;
unsigned max = 0;
unsigned sk = 1;
unsigned mdl = 0;

// recursion is fun
int advance_sprite( int idx );
int advance_sprite( int idx )
{
	if ( idx < 0 ) return 0;	// we reached the limit, bail out
	if ( s[idx] == '9' ) s[idx] = 'A';	// from 9 to A
	else if ( s[idx] == 'Z' )	// at limit
	{
		// advance the previous char
		if ( !advance_sprite(idx-1) ) return 0;	// no more, bail out
		s[idx] = '0';	// restart
	}
	else s[idx]++;	// just increment
	return 1;
}

int advance_frame( void )
{
	printf("\tFrameIndex %.4s %c %d %d\n",s,f,mdl,fi);
	fi+=sk;	// advance frame in model
	f++;	// advance frame in sprite
	if ( f > 'Z' )	// note that [,\ and ] are not used. this is personal preference, really
	{
		// we need to change the sprite name
		if ( !advance_sprite(3) ) return 0;	// can't advance further
		f = 'A';	// restart
	}
	return 1;
}

int main( int argc, char **argv )
{
	if ( argc < 5 )
	{
		fprintf(stderr,"usage: pframes <sprite name> <start frame> <max frames> [frame step] [model index] [first sprite frame]\n"
			"\n"
			" - sprite name: must be 4 characters.\n"
			" - start frame: frame offset within the model to start from.\n"
			" - max frames: limit on frames advanced.\n"
			" - frame step: how many frames to move each step (default:1, must be higher than zero).\n"
			" - model index: which model to assign (default: 0).\n"
			" - first sprite frame: which sprite frame to start from (default: A).\n"
			"\n"
			"   Frames advance from A to Z, wrapping around.\n"
			"   Each wrap, the fourth char of the sprite name will be cycled, from 0 to 9, then A to Z.\n"
			"   After ###Z is reached, the third character will by cycled instead.\n"
			"   And so on for the second, then the first...\n"
			"   If you somehow run out of sprite names, you need to be more reasonable. (^^;\n");
		return 1;
	}
	strncpy(s,argv[1],4);
	if ( strnlen(s,4) < 4 )
	{
		fprintf(stderr,"fatal: sprite name must be 4 characters.\n");
		return 2;
	}
	sscanf(argv[2],"%u",&fi);
	sscanf(argv[3],"%u",&max);
	if ( max == 0 )
	{
		fprintf(stderr,"fatal: max frames must be higher than zero.\n");
		return 4;
	}
	if ( argc > 4 ) sscanf(argv[4],"%u",&sk);
	if ( sk == 0 )
	{
		fprintf(stderr,"fatal: frame step must be higher than zero.\n");
		return 8;
	}
	if ( argc > 5 ) sscanf(argv[5],"%u",&mdl);
	if ( argc > 6 ) sscanf(argv[6],"%c",&f);
	if ( (f < 'A') || (f > 'Z') )
	{
		fprintf(stderr,"fatal: first sprite frame must be between A and Z (inclusive).\n");
		return 16;
	}
	for ( unsigned i=0; i<max; i+=sk )
	{
		if ( !advance_frame() )
		{
			fprintf(stderr,"fatal: ran out of sprite names. please be reasonable.\n");
			return 32;
		}
	}
	return 0;
}