#include <stdio.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>

/*
 * Read a P6 PPM file on standard input, and write a P6 PPM file on standard output.
 * The output file will have the object centered, with the assumption that any
 * pixels with values >= 10% R/G/B are part of the object, and elsewise are background
 */

Usage()
	{
	fprintf(stderr,"ppmcentre [infile] [outfile]\n");
	fprintf(stderr,"Infile is either a PPM file or '-' for standard input. \n");
	fprintf(stderr,"Outfile is a PPM file.\n");
	fprintf(stderr,"If outfile is omitted, standard output is used.\n");
	fprintf(stderr,"If both Infile and Outfile are omitted, standard input and output are used\n");
	}


main(int argc, char *argv[])
	{
	int width,height,depth,colourmax;
	char type[10];
	FILE *in = stdin;
	FILE *out = stdout;
	int i,err;
	int bufsize = 0;
	char *buffer,*outbuffer;
	
#ifdef WIN32
	// Make stdout/stdin binary mode
	setmode(fileno(stdin), O_BINARY);
	setmode(fileno(stdout), O_BINARY);
#endif

	// how many ways are there of asking for help??
	if (argc == 2) {
	   if (!strcmp(argv[1],"--help") || !strcmp(argv[1],"-?") || !strcmp(argv[1],"-h") || !strcmp(argv[1],"/?")) {
		Usage();
		exit(0);
		}

	   // 1 argument, must be input file
	   if (!strcmp(argv[1],"-")) in = stdin;
	   else in = fopen(argv[1],"rb");

	   out = fdopen(1,"wb");
	   }
	else if (argc == 3) {
	   // Both input and output are specified
	   if (!strcmp(argv[1] ,"-")) in = stdin;
	   else in = fopen(argv[1],"rb");

	   out = fopen(argv[2],"wb");

	   }
	   
	if (in == NULL) {
	   fprintf(stderr,"ppmcenter: cannot open input file\n");
	   Usage();
	   exit(1);
	   }

	if (out == NULL) {
	   fprintf(stderr,"ppmcenter: cannot open output file\n");
	   Usage();
	   exit(1);
	   }

	/*
	 * Read the input
	 */
	type[0] = 0;
	ppm_header(in,type,&width,&height,&colourmax);

	if (strcmp(type,"P6")) {
	   fprintf(stderr,"Type '%s' not understood\n",type);
	   Usage();
	   exit(1);
	   }

	fprintf(stderr,"Image is %dx%d\n",width,height);

	/*
	 * Allocate the buffer and load the data
	 */
	bufsize = width * height * 3;
	buffer = (char *)malloc(bufsize);
	if (buffer == NULL) {
		fprintf(stderr,"Cannot malloc buffer of %d bytes\n",bufsize);
		exit(1);
		}

	err = fread(buffer,1,bufsize,in);
	if (err != bufsize) {
	   fprintf(stderr,"Error in reading data, only read %d bytes of %d\n",err,bufsize);
	   exit(1);
	   }

	outbuffer = (char *)malloc(bufsize);
	if (outbuffer == NULL) {
		fprintf(stderr,"Cannot malloc outbuffer of %d bytes\n",bufsize);
		exit(1);
		}

	if (! process(width,height,buffer,outbuffer)) {
		fprintf(stderr,"Error in processing, no output generated\n");
		exit(1);
		}

fprintf(out,"P6\n%d %d\n%d\n",width,height,colourmax);
fwrite(outbuffer,1,bufsize,out);
fflush(out);

	exit(0);
	}

int process(int width, int height, char *in, char *out)
	{
	int x,y;
	int count;	// count of significant pixels
	int x_total, y_total;
	int x_avg,y_avg,xc,yc;
	int size = width * height * 3;
	char *ptr = in;
	int i,r,g,b;

	count=0;
	x_total = y_total = 0;
	for(y=0; y<height; ++y) {
	   for (x=0; x<width; ++x) {
		r = *(ptr++);
		g = *(ptr++);
		b = *(ptr++);

		if (r+g+b > 50) {
		   x_total += x;
		   y_total += y;
		   count++;
		   }
	      }
	   }

	if (count == 0) {
	   fprintf(stderr,"Could not find anything in the frame\n");
	   return(0);
	   }

	if (count < 250) {
	   fprintf(stderr,"Not enough pixels found. Found %d\n",count);
	   return(0);
	   }

	x_avg = x_total / count;
	y_avg = y_total / count;

fprintf(stderr,"Object centre at (%d,%d), size %d pixels\n",x_avg,y_avg,count);

	// Fill the buffer with zeroes
	for(i=0; i<size; ++i) out[i] = 0;

	// Centre location in output buffer
	xc = width/2; yc=height/2;
	
	// cut out image +/- 200 pixels from that spot
	count=0;
	for(y = -200; y <= 200; ++y) {

	   int yi = y + y_avg;
	   if (yi<0 || yi>=height) continue;

	   for (x=-200; x<=200; ++x) {
		int xi,xo,yo,oi,oo;

		xi = x + x_avg; 
		// Skip if source off the image
		if (xi<0 || xi>=width) continue;

		// Input Offset
		oi = (yi * width + xi) * 3;

		// Output Offset
		xo = x + xc;
		yo = y + yc;
		oo = (yo * width + xo) * 3;

		// It's an error if the dest is off the image
		if (xo<0 || xo>=width || yo<0 || yo>=height) {
			fprintf(stderr, "Oops - dest (%d,%d) is off the image!\n",xo,yo);
			return(0);
			}

	//printf("(%d,%d) -> (%d,%d)\n",xi,yi,xo,yo);

		out[oo] = in[oi];
		out[oo+1] = in[oi+1];
		out[oo+2] = in[oi+2];
	   	}
	   }

	return(1);
	}


int ppm_header(FILE *in,char *type, int *width, int *height, int *colours)
	{
	int ch,i,incomment;
	char buf[32];

	type[0]=0; *width=0; *height=0; *colours=0;
	incomment=0; i=0;
	while(1)
	   {
	   switch(ch=getc(in))
		{
		case EOF: return 1;
		case '#': incomment=1; break;
		case ' ': case '\t':
			if (incomment) break;
		case '\n': case '\r':
			if (incomment) {incomment=0; break;}
			if (type[0]==0)
			   {
			   strcpy(type,buf);
			   if (type[0]!='P') return 1;
			   if (type[1]!='3' && type[1]!='6') return 1;
			   i=0; buf[0]=0; break;
			   }
			if (*width==0) {*width=atoi(buf); i=0; buf[0]=0; break;}
			if (*height==0) {*height=atoi(buf); i=0; buf[0]=0; break;}
			if (*colours==0) {*colours=atoi(buf); return(0); break;}
		default:
			buf[i++]=ch; buf[i]=0; break;
	   	}
	   }
	return 1;
	}