/*

 *  prog3A.c

 *	

 *	Calculates the integral of cos^2(x).

 *

 *  Input command line argument of upper limit between 0 and Pi/2.

 *  Lower limit is set by default to 0.

 */



#include <stdio.h>

#include <stdlib.h>

#include <math.h>

#define NODATA "There was not one argument entered. Exiting...\n"

#define INVALID "The data entered was not valid. Entered value must be between 0 and Pi/2\n"

#define LOWERLIMIT 0

#define MAXLIMIT M_PI/2

#define FILENAME "px270prog3a.dat"

#define RESULT "The integral of (Cos(x))^2 between %lf and %lf is %lf\n"

#define DEBUG 0



void integrate(double *xvalues, double *fvalues, int count, double low , double high, double *integral);



int main(int argc, char* argv[]) {

	/*Values*/

	double a,b,value,dummy;

	double *xvalues, *fvalues,integral;

	/*Counts*/

	int size=0,count=0,entrycount=0;

	/*Flags*/

	int rightnumber=0,validInput;

	/*File*/

	FILE* input;

	

	/*Set Lower Limit*/

	a = LOWERLIMIT;

	/*Check and then read command line arguments */

	if ((argc < 2)||(argc > 2)){

		printf(NODATA);

		exit(EXIT_FAILURE);

	}

	else {

		sscanf(argv[1],"%lf", &b);

	}

	/*Test for valid input. If not valid, exit*/

	validInput = ((b > LOWERLIMIT) && (b < MAXLIMIT) && (b != EOF));

	if(!validInput){

		printf(INVALID);

		exit(EXIT_FAILURE);

	}

	/*Open file, read data from file*/

	input = fopen(FILENAME,"r");

	/*Scan through the file once, to help work out size of array needed*/

	while (rightnumber == 0){

		fscanf(input," %lf ",&value);

		fscanf(input," %lf ",&dummy);

		count++;
		printf("Count = %d \n",count);

		/*If the value read for x is greater than the upper limit, stop counting data*/

		if (value >= b) {

			rightnumber = 1;

			rewind(input);

		}

	}

	/*Set the size of the arrays*/

	size = (count+1)*(sizeof(double));

	xvalues = (double*)malloc(size);

	fvalues = (double*)malloc(size);

	/*Use fscanf to fill arrays with values*/

	while (entrycount<=count) {

		fscanf(input,"%lf",&xvalues[entrycount]);

		fscanf(input,"%lf",&fvalues[entrycount]);

		entrycount++;
		//printf("Entrycount = %lf, Xvalues = %lf, FXVALues = %lf \n",entrycount,xvalues[entrycount],fvalues[entrycount]);

	}

	fclose(input);

	/*Call integrate function, using pointer for integral, print result*/

	integrate(xvalues,fvalues,count+1,a,b,&integral);

	printf(RESULT,a,b,integral);

	

	return 0;

}

		

void integrate(double *xvalues, double *fvalues, int length, double lowlim , double uplim, double *integral){

	double workinginteg;

	int count=0;

	int firstpoint=0;

	

	while (count<length) {

		/*Check if values within integration limits*/

		if (xvalues[count] <= uplim){

			if (xvalues[count] >= lowlim) {

				if (firstpoint == 0) {

					/*If the lower limit is not zero, add in the first part. If it is, this part will be zero anyway*/

					if (count != 0) *integral += (xvalues[count]-lowlim)*(fvalues[count-1]);

					firstpoint = 1;

				}

				else {

					/*Add the next part of the integral*/

					*integral += (xvalues[count]-xvalues[count-1])*(fvalues[count-1]);

				}

			}

		}

		count++;

	}

}