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

#define MAX_PRINT_THRESHOLD 20

typedef struct {
	int start;
	int end;
	int length;
}Longest;

/*find the longest interval where mx is max mn is min*/
int LongestInterval(FILE* input, int m, Longest* pos) {

	int mx = 0; //max value
	int mn = 0; //min value
	int value;
	int k; //to store end value
	int j; //to store start value
	long int filepos; //current file position


	if((fscanf(input, "%d", &value) == EOF)) {
		fprintf(stderr, "There is nothing in the file to process\n");
		return 1;
	}

	//initialise variables
	mx = mn = value;
	j = 0; //start
	k = 0; //end
  	pos->length = 1;
	pos->start = 0;=20
	pos->end = 0;
	filepos = ftell(input); //first element

	while((fscanf(input, "%d", &value) != EOF)) {

		//test condition: value > mx = mx -- maxvalue  value < mn = mn -- min=
value
		if(value > mx){
			mx = value;
		}=20=20
		if(value < mn){
			mn = value;
		}

		/*Condition : mx-mn <= m*/
		if(mx - mn <= m) {
			/*When mx-mn is satisfied k++(end)*/
			/*increment end counter as satisfy condition*/
			k++;=20
	//		printf("%d ", value);

		} else {
			// printf(" %d -- start: %d end %d length %d\n", value, j, k, k-j+1);
			/*   does not satisfy condition*/

			/*  When mx-mn fails (value of startpos= j, endpos = k, leng = (k-=
j))
				-compare to previous length:=20
					if(current lenght > previous Length)
						let the previous Length = current Lenght NB: first occurrence
					reset k
					jump the pointer to j+1
					increment j (the start value)
 			*/
			if(((k-j)+1) > pos->length){
				pos->start = j;
				pos->end   = k;
				pos->length = (k-j)+1;

			}
			j++; //goes to next value in file.
			k = j;
			//jump the file pointer to j+1 -- from previously recorded position
			fseek(input, filepos, SEEK_SET);
			//so u know what value to initialise mx and mn
			if(fscanf(input, "%d", &value) == EOF) break;
			mx = mn = value;
			filepos = ftell(input);
		}


	}


	if(((k-j)+1) > pos->length) {
		pos->start = j;
		pos->end = k;
		pos->length = (k-j)+1;

	}
	return 0;
}

/*=20
   longest 2 inp.txt
   argc = 2
   argv[0] = longest
   argv[1] = 2
   argv[2] = inp.txt=20
*/
int main(int argc, char** argv) {

	int m,i,v;
	FILE* inp = NULL;
	Longest lpos ;

	if(argc != 3) {
		fprintf(stderr, "Usage: %s <m> <filename>\n", argv[0]);
		return 1;
	}

	//Open file from command line, mode "r" to read text
	if((inp = fopen(argv[2], "r")) == NULL) {
		fprintf(stderr, "Could not open %s\n", argv[2]);
		return 1;
	}

	//to get value m and convert to integer
	m = atoi(argv[1]);

	if(m<0) {
		fprintf(stderr, "The value m has to be a non negative integer\n");
		return 1;
	}

	//Find the result
 	if((LongestInterval(inp, m,&lpos)) ) {
		fprintf(stderr, "Could not open file %s\n", argv[2]);
		fclose(inp);
		return 1;
	}
	//Output results
	/*if(lpos.length <= MAX_PRINT_THRESHOLD) {
		rewind(inp);

		printf("\n\n\n\nPrinting the Longest interval\n");
		for(i=0;i<= lpos.end;i++) {
			if((fscanf(inp,"%d",&v)) == EOF) break;

			if(i == lpos.start) printf("%d",v);
			else if(i >= lpos.start) printf(" %d", v);
		}
	} else {
		printf("The result is over %d numbers long, no numbers printed.",MAX_PRIN=
T_THRESHOLD);
	}*/

	if(lpos.length) {
		printf("\nLongest: %d %d %d\n", lpos.start, lpos.end, lpos.length);
	}else {
		printf("\nNO longest interval that satisfy mx-mn <= m\n");
	}

	fclose(inp);
	return 0;
}