//=========================================================================
#define PROGRAMMER "SOLUTIONS, NoFrills"
#define PROG_CODE  "soln"
#define COURSE     "ECE-1021"
#define YEAR       (2003)
#define TERM       "Fall"
#define SECTION    (0)
#define ASSIGNMENT "HW #2B"
#define REVISION   (0)
#define TITLE      "Printing a Calendar"
#define SUBTITLE   "Programming Exercise #4.6"
#define EMAIL      "wbahn@eas.uccs.edu"
#define FILENAME   "02b0soln.c"
//=========================================================================
// PROBLEM:
//
// Modify an existing program (Section 4.6) to print a calendar in a two
// column format to a file and only requiring a year from the user.
//
// The steps to be followed to perform the modification are as follows:
//
// TASK #1: Implement the program as it presently exists in Sec 4.6.
//          The code is available on the course website in the
//          text book section.
// TASK #2: Modify it to require only a year from the yser.
//          Using the formula given in the problem, compute the
//          day_code for Jan 1st and whether it is a leap year.
// TASK #3: Modify it to print a second image shifted right.
//          This should be a simple matter of dublicating some printf()
//          statements.
// TASK #4: Modify it to use a constant number of lines per month.
//          Just need to print a line of blank dates if necessary.
// TASK #5: Modify it to prints only six months in a column.
//          Trivial (should be, anyway).
// TASK #6: Identify which variables must be split between columns.
//          Probably daycode, month, and day - perhaps others.
// TASK #7: Modify it to print the complete calendar.
//          Should just be a matter of using the new variables.
// TASK #8: Modify it to print to a file instead of the screen.
//          Open and check the file and convert all of the printf()
//          statements to fprintf() statements using a search and
//          replace - or perhaps a macro.
// TASK #9: OPTIONAL - pretty up the printout.

//== RECORD OF MODIFICATIONS ==============================================

// TASK #1: Implement the program as it presently exists in Sec 4.6.
//
// From the website, got the zip file containing the source code for all
// of the problems in the text and copied the body into the Source Code
// template. Inserted the PrintHeader() call at the proper place. Cleaned
// up the formatting to being it into compliance with the course standards.
//
// Ran program and it works as expected.
//
// Time to perform Task #1: 6 minutes.

// TASK #2: Modify it to require only a year from the yser.
//
// Replace the code for the user input with the code to compute these
// items from the year alone.
//
// Time to perform Task #2: 7 minutes.

// TASK #3: Modify it to print a second image shifted right.
//
// The goal is just to print the same contents shifted to the right so
// that it is lined up in a second column. This will be done in to steps.
// First, spaces will be printed to flesh out the line to column 40. Then
// the same content will be reprinted.
//
// Had to modify code so that the month was printed out one week at a time
// and that the month always contained exactly six printed weeks.
//
// Time to perform Task #3: 37 minutes.

// TASK #4: Modify it to use a constant number of lines per month.
//
// This was done as part of Task #3
//
// Time to perform Task #4: 0 minutes.

// TASK #5: Modify it to prints only six months in a column.
// TASK #6: Identify which variables must be split between columns.
// TASK #7: Modify it to print the complete calendar.
//
// While performing Task #3, the details of how to do these three
// tasks because apparent. The switch statement will respond to the
// first six months but will set up the variable for both that month
// and the month (siz months later) that will be printed in the right
// column. A second set of variables is needed for the right hand
// column consisting of R_day_code, R_day, R_days_in_month.
//
// Time to perform Tasks #5-#7: 15 minutes.

// TASK #8: Modify it to print to a file instead of the screen.
//
// This is just a matter of opening the file calendar.dat, verifying
// that it opened, and changing the printf() statements to fprintf()
// statements.
//
// Time to perform Tasks #8: 5 minutes.

//== INCLUDE FILES ========================================================
#include <stdio.h> // printf()

//== MACROS ===============================================================

//== FUNCTION PROTOTYPES ==================================================
void PrintHeader(void);

//== MAIN FUNCTION ========================================================
int main(void)
{
	int day_code,      // day_code = 0 means the month starts on Sun
		 days_in_month, // number of days in month currently 																  being printed */
		 leap_year,     // 1 means leap year; 0 means no leap year
		 day,           // counter for day of month
		 month;         // month = 1 is Jan, month = 2 is Feb, etc.
	int year;	  		 // Year of the calandar.
	int week;          // The week of the month 0 to 5
	int i;             // dummy counter;

	int R_day, R_day_code, R_days_in_month; // Variable set for RH column.

	FILE *fp;

	PrintHeader();
	printf("\n"); // Print a blank line

	printf( "Enter the year for which you want the calendar printed: ");
	scanf( "%i", &year);

	// Using integer division intentionally:
	day_code = ( year + (year-1)/4 - (year-1)/100 + (year-1)/400 )%7;

	if(year%4) // TRUE if x is NOT divisible by 4
		leap_year = 0;
	else
		if(year%100) // TRUE if x is divisible by 4 but NOT 100
			leap_year = 1;
		else
			if(year%400) // TRUE if x is divisible by 100 but NOT 400
				leap_year = 0;
			else
				leap_year = 1;

	if(leap_year)
		R_day_code = day_code;
	else
		R_day_code = (day_code + 6)%7;

	if(NULL == (fp = fopen("calendar.dat", "wt")))
	{
		printf("Error opening calendar.dat for writing - aborting!\n");
		return(1);
	}

	fprintf(fp, "\n");
	fprintf(fp,  "                             Calendar for Year %4i\n", year);

	for( month = 1; month <= 6; month++ )
	{
		switch ( month )
		{  // print name and set days_in_month
			case 1:
				fprintf(fp,  "\n  January                               " );
				days_in_month = 31;
				fprintf(fp,  "  July" );
				R_days_in_month = 31;
				break;
			case 2:
				fprintf(fp,  "\n  February                              " );
				days_in_month = leap_year ? 29 : 28;
				fprintf(fp,  "  August" );
				R_days_in_month = 31;
				break;
			case 3:
				fprintf(fp,  "\n  March                                 " );
				days_in_month = 31;
				fprintf(fp,  "  September" );
				R_days_in_month = 30;
				break;
			case 4:
				fprintf(fp,  "\n  April                                 " );
				days_in_month = 30;
				fprintf(fp,  "  October" );
				R_days_in_month = 31;
				break;
			case 5:
				fprintf(fp,  "\n  May                                   " );
				days_in_month = 31;
				fprintf(fp,  "  November" );
				R_days_in_month = 30;
				break;
			case 6:
				fprintf(fp,  "\n  June                                  " );
				days_in_month = 30;
				fprintf(fp,  "  December" );
				R_days_in_month = 31;
				break;
		}
		fprintf(fp,  "\n  Sun  Mon  Tue  Wed  Thu  Fri  Sat     " );
		fprintf(fp,  "  Sun  Mon  Tue  Wed  Thu  Fri  Sat" );
		fprintf(fp, "\n");

		// We will print six full weeks of numbers. If the "number" for
		// a given location is not within the current month, we will
		// print two blank spaces in the number's place.
		//
		// We can assign "dates" to the days of the first week prior
		// to the actual start of the month by just numbering them
		// backward.
		//
		// If the week starts on Sunday (day_code = 0) then Sunday is 1
		// If the week starts on Monday, (day_code = 1) then Sunday is 0
		// If the week starts on Saturday, (day_code = 6) then Sunday is -5
		//
		// So the first Sunday's "date" is 1 - day_code
		// The dates for the succeeding Sundays can be obtained by adding
		// multiples of 7.

		for(week = 0; week <6; week++)
		{
			// Left Hand Month
			fprintf(fp, "  "); // Left Margin
			day = (1 - day_code) + 7*week;
			for(i = 0; i < 7; i++, day++)
			{
				if( (1 > day) || (days_in_month < day) )
					fprintf(fp, "     ");
				else
					fprintf(fp, " %2i  ", day);
			}

			fprintf(fp, "   "); // Finish the 40 spaces on left side.

			// Right Hand Month
			fprintf(fp, "  "); // Left Margin
			R_day = (1 - R_day_code) + 7*week;
			for(i = 0; i < 7; i++, R_day++)
			{
				if( (1 > R_day) || (R_days_in_month < R_day) )
					fprintf(fp, "     ");
				else
					fprintf(fp, " %2i  ", R_day);
			}

			fprintf(fp, "\n"); // Go on to next week;

		}

		// set day_code for next month to begin
		day_code = ( day_code + days_in_month ) % 7;
		R_day_code = ( R_day_code + R_days_in_month ) % 7;
	}

	fclose(fp);
	return(0);
}

//== SUPPORT FUNCTIONS ====================================================
void PrintHeader(void)
{
	printf("========================================"
			 "=======================================\n");
	printf("Course....... %s-%i (%s %i)\n", COURSE, SECTION, TERM, YEAR);
	printf("Programmer... %s (%s)\n", PROGRAMMER, PROG_CODE);
	printf("Assignment... %s (Rev %i) (Source Code in %s)\n",
		ASSIGNMENT, REVISION, FILENAME);
	printf("Description.. %s\n", TITLE);
	printf("              %s\n", SUBTITLE);
	printf("========================================"
			 "=======================================\n");

	return;
}