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package DateTime::Indic::Utils;

use base 'Exporter';
use warnings;
use strict;
use Carp qw/ carp croak /;
use DateTime::Util::Calc qw/ mod revolution sin_deg /;
use POSIX qw/ ceil floor /;
use Math::Trig qw( pi pi2 atan deg2rad tan );

our @EXPORT_OK = qw/
  epoch
  anomalistic_year
  anomalistic_month
  J0
  J1900
  sidereal_year
  sidereal_month
  synodic_month
  creation
  ayanamsha
  lunar_longitude
  lunar_on_or_before
  newmoon
  saura_rashi
  saura_varsha
  solar_longitude
  tithi_at_dt
  /;

=head1 NAME

DateTime::Indic::Utils - Utility functions for Indian calendar calculation

=head1 VERSION

Version 0.3

=cut

our $VERSION = '0.3';

=head1 SYNOPSIS

  my $dt = DateTime->now;
  
  my $ayanamsha = ayanamsha(J1900);

  my $moon = lunar_longitude($J1900);
  
  my $d1 = DateTime::Calendar::VikramaSamvata::Gujarati->new(
    varsha => 2064,
    masa   => 7,
    paksha => 1,
    tithi  => 30,
  );
  my $d2 = DateTime::Calendar::VikramaSamvata::Gujarati->new(
    varsha => 2065,
    masa   => 1,
    paksha => 0,
    tithi  => 15,
  );
  my $bool = lunar_on_or_before($d1, $d2);
  
  my $previous_newmoon = newmoon(J1900, 0);
  my $next_newmoon     = newmoon(J1900, 1);
  
  my $sun = solar_longitude(J1900);

  my $rashi = saura_rashi(J1900);
  
  my $year = saura_varsha($dt);
  
  my $lunar_day = tithi_at_dt($dt);


=head1 ABSTRACT

A collection of utility functions and constants helpful in creating Indian 
calendars.

=head1 DESCRIPTION

Note:  In this document, Sanskrit words are transliterated using the ITRANS
scheme.

These functions and constants were not included directly in 
L<DateTime::Indic::Chandramana> as they are more useful stand-alone. None of 
them are exported by default.

=head1 CONSTANTS

=head2 epoch

Fixed date of the beginning of the Kali Yuga.

=cut

## no critic 'ProhibitConstantPragma'

use constant epoch => -1_132_959;

=head2 anomalistic_year

Mean time from aphelion to aphelion.

=cut

use constant anomalistic_year => 1_577_917_828_000 / ( 4_320_000_000 - 387 );

=head2 anomalistic_month

Mean time from apogee to apogee with bija correction.

=cut

use constant anomalistic_month => 1_577_917_828 / ( 57_753_336 - 488_199 );

=head2 J0

The fixed (RD) date of Julian date 0

=cut

use constant J0 => -1_721_425;

=head2 J1900

The Julian date at noon on Jan 1, 1900.

=cut

use constant J1900 => 2_415_020.0;

=head2 sidereal_year

Mean length of Hindu sidereal year.

=cut