#include "date.h"
#include <time.h>

static int DaysInMonth(int,int);             // # of days in month in year

string dayNames [] = {"Sunday",  "Monday", "Tuesday","Wednesday",
                      "Thursday","Friday", "Saturday"};

string monthNames [] = {"January","February","March","April",
			"May","June","July","August",
			"September","October","November","December"};

Date::Date()
// postcondition: date initialized to default date (today)
{
    static struct tm timeHolder;
    static struct tm *date = &timeHolder;
    time_t tloc;
    
    time(&tloc);

    date = localtime(&tloc);
    
    myMonth = date->tm_mon+1;
    myDay   = date->tm_mday;
    myYear  = date->tm_year+1900;             // struct tm based on 1900
}

Date::Date(int m, int d, int y)
// postcondition: date properly initialized for date m/d/y (american style)
// exception:  if m isn't between 1 and 12, converted to 1
//             if d out of range for month, converted to 1     
{
    CheckDate(m,d,y);    
}

Date::Date(long int days)
// postcondition: date initialized corresponding to absolute days
//                after 1 A.D.
{
        // this code is taken from "Calendrical Calculations, II"
        // Reingold and Dershowitz and Clamen
        // Software Practice and Experience, V. 23(4) 383-404 (april 1993)

    int prior = days - 1;                  // prior days
    int years400 = prior / 146097;         // # of 400 year cycles
    int days400 = prior % 146097;          // days NOT in years400

    int years100 = days400 / 36524;        // # 100 yr. cycles not checked
    int days100 =  days400 % 36524;        // days NOT already included

    int years4 = days100 / 1461;           // # 4 yr cycles not checked
    int days4 = days100 % 1461;            // days NOT already included

    int year1 = days4 / 365;                // # years not already checked
    int day1  = days4 % 365;                // days NOT already included


        // use "magic formula" from SP&E article
    int finalDay;
    int finalYear = 400*years400 + 100*years100 + 4*years4 + year1;
    
    if (years100 == 4 || year1 == 4){      // December 31 of leap year
        finalDay = 366;
    }
    else{
        finalDay = day1 + 1;
        finalYear += 1;
    }

        // now have year and day #, find month and day in month
    myMonth = 1;
    while (myMonth <= 12 && 0 < finalDay){
        finalDay -= DaysInMonth(myMonth,finalYear);
        myMonth += 1;
    }
    myMonth -= 1;                              // went one to far
    finalDay += DaysInMonth(myMonth,finalYear);

    myDay = finalDay;
    myYear = finalYear;
}
     

void Date::SetDate(int m, int d, int y)
// postcondition: date properly initialized for date m/d/y (american style)
{
    CheckDate(m,d,y);
}

int Date::Month() const
// postcondition: returns month of Date     
{
    return myMonth;
}

int Date::Day() const
// postcondition: returns day of Date     
{
    return myDay;
}

int Date::Year() const
// postcondition: returns year of Date     
{
    return myYear;
}

string Date::Ascii() const
// postcondition: returns string (ascii) for date: day, month, year
{
    const int BUFSIZE = 50;
    char buf[BUFSIZE];
    struct tm timeHolder;
    struct tm *date = &timeHolder;

        // set parameters for use of strftime
    
    date->tm_mday = myDay;
    date->tm_mon = myMonth-1;
    date->tm_year = myYear-1900;
    
    strftime(buf,BUFSIZE,"%B %d %Y",date);

    return buf;
}

string Date::DateAscii() const
// postcondition: returns string (ascii) for date: day, month, year
{
    return Ascii();
}

static bool IsLeap(int year)
// postcondition: returns 1 if year is a leap year, else returns 0     
{
    int leapValue = 0;             // default is NOT leap year

    if (year % 400 == 0){
        leapValue = 1;
    }
    else if (year % 100 == 0){
        leapValue = 0;
    }
    else if (year % 4 == 0){
        leapValue = 1;
    }

    return leapValue;
}

static int DaysInMonth(int month,int year)
// postcondition: returns # of days in month in year     
{
    int days = 30;

        // 30 days hath september, april, june, and november
        // other months have 31 as below (except February)
    
    if (month == 1 || month == 3 || month == 5 || month == 7 ||
        month == 8 || month == 10 || month == 12){
        days = 31;
    }
    else if (month == 2){          // treat February differently
        days = 28;
        if (IsLeap(year) == 1){        // add 1 for leap years
            days += 1;
        }
    }
    return days;
}


int Date::DaysIn() const
{
    return DaysInMonth(myMonth,myYear);
}

long int Date::Absolute() const
// postcondition: returns absolute # days corresponding to Date
//                assuming January 1, 1 B.C is day 1
{
    int m = 1;               // start in January;
    int daysBefore = 0;      // count # days before month

    while (m < myMonth){       // tally # of days in preceding months
        daysBefore += DaysInMonth(m,myYear);
        m += 1;
    }

    long int dayYears = 365 * (myYear - 1);    // days before this year

        // add 1 extra day for each leap year
    
    int leapYears = (myYear - 1) / 4;     // initial # of leap years

    leapYears -= (myYear - 1) / 100;      // subtract years divisible by 100
    leapYears += (myYear - 1) / 400;      // add back years divisibly by 400

    return myDay + daysBefore + dayYears + leapYears;
}

string Date::DayName() const
{
    return dayNames[Absolute() % 7];
}

string Date::MonthName() const
{
    return monthNames[myMonth-1];
}

Date& Date::operator +=(int dx)
{
    *this = Date(Absolute()+dx);
    return *this;
}

Date& Date::operator -=(int dx)
{
    *this = Date(Absolute()-dx);
    return *this;
}

Date Date::operator ++(int)
{
    Date hold = *this;
    *this += 1;
    return hold;
}

Date Date::operator --(int)
{
    Date hold = *this;
    *this -= 1;
    return hold;
}

Date operator + (const Date & d, int dx)
{
    Date copy(d);
    copy += dx;
    return copy;
}

Date operator + (int dx, const Date & d)
{
    return d+dx;
}

Date operator - (const Date & d, int dx)
{
    Date copy(d);
    copy -= dx;
    return copy;
}

void Date::CheckDate(int m, int d, int y)
{
    if (m < 1 || 12 < m)              // month out of range?
    {
        m = 1;
    }
    myMonth = m;
    
    if (d < 1 || DaysInMonth(m,y) < d)   // day out of range?
    {
        d = 1;
    }
    myDay = d;
    myYear = y;   
}