#include "Date.hpp"

#include <cassert>

  ////////////////////////////
 // Private static helpers //
////////////////////////////

// Determine whether the specified year is a leap year.
bool Date::is_leap_year( unsigned int const year ) {
  // February 1582 occurred before the Gregorian-calendar
  // transition, so 1582 uses the Julian rule here.
  if ( year <= 1582 ) {
    return year%4 == 0;
  }

  return (year%400 == 0)
      || ((year%4 == 0) && (year%100 != 0));
}

// Return the number of days in the specified month.
unsigned int Date::days_in_month( unsigned int const year,
                                  unsigned int const month ) {
  assert( month >= 1 );
  assert( month <= 12 );

  if ( month == 2 ) {
    return is_leap_year( year ) ? 29 : 28;
  }

  if ( (month == 4)
    || (month == 6)
    || (month == 9)
    || (month == 11) ) {
    return 30;
  }

  return 31;
}

// Determine whether the specified values form a valid date.
bool Date::is_valid( unsigned int const year,
                     unsigned int const month,
                     unsigned int const day ) {
  if ( year == 0 ) {
    return false;
  }

  if ( (month < 1) || (month > 12) ) {
    return false;
  }

  if ( (day < 1) || (day > days_in_month( year, month )) ) {
    return false;
  }

  // The Gregorian calendar followed October 4, 1582,
  // with October 15, 1582.
  if ( (year == 1582)
    && (month == 10)
    && (day >= 5)
    && (day <= 14) ) {
    return false;
  }

  return true;
}

  /////////////////
 // Constructor //
/////////////////

// Construct the specified date.
Date::Date( unsigned int const year,
            unsigned int const month,
            unsigned int const day ):
year_{ year },
month_{ month },
day_{ day } {
  assert( is_valid( year_, month_, day_ ) );
}

  /////////////////////
 // Date components //
/////////////////////

// Return the year.
unsigned int Date::year() const {
  return year_;
}

// Return the month.
unsigned int Date::month() const {
  return month_;
}

// Return the day.
unsigned int Date::day() const {
  return day_;
}

  ///////////////////////////
 // Incrementing the date //
///////////////////////////

// Move to the next date and return this object.
Date &Date::operator++() {
  // The Gregorian calendar followed October 4, 1582,
  // with October 15, 1582.
  if ( (year_ == 1582)
    && (month_ == 10)
    && (day_ == 4) ) {
    day_ = 15;
  } else if ( day_ < days_in_month( year_, month_ ) ) {
    ++day_;
  } else if ( month_ < 12 ) {
    day_ = 1;
    ++month_;
  } else {
    day_ = 1;
    month_ = 1;
    ++year_;
  }

  return *this;
}

// Move to the next date and return the previous value.
Date Date::operator++( int ) {
  Date old_date{ *this };

  ++(*this);

  return old_date;
}

  ///////////////////////////
 // Decrementing the date //
///////////////////////////

// Move to the previous date and return this object.
Date &Date::operator--() {
  // There is no supported date before January 1, 1.
  assert( (year_ != 1) || (month_ != 1) || (day_ != 1) );

  // The Julian calendar ended on October 4, 1582.
  if ( (year_ == 1582)
    && (month_ == 10)
    && (day_ == 15) ) {
    day_ = 4;
  } else if ( day_ > 1 ) {
    --day_;
  } else if ( month_ > 1 ) {
    --month_;
    day_ = days_in_month( year_, month_ );
  } else {
    --year_;
    month_ = 12;
    day_ = 31;
  }

  return *this;
}

// Move to the previous date and return the previous value.
Date Date::operator--( int ) {
  Date old_date{ *this };

  --(*this);

  return old_date;
}

  ///////////////////////////
 // String representation //
///////////////////////////

// Return a string representation of this date.
std::string Date::to_string() const {
  std::string result{ std::to_string( year_ ) + "-" };

  if ( month_ < 10 ) {
    result += "0";
  }

  result += std::to_string( month_ ) + "-";

  if ( day_ < 10 ) {
    result += "0";
  }

  result += std::to_string( day_ );

  return result;
}

  ///////////////////
 // Stream output //
///////////////////

// Insert date into an output stream.
std::ostream &operator<<( std::ostream &out,
                          Date const   &date ) {
  out << date.to_string();

  return out;
}