+sub _delta_units {
+ my ( $date1, $date2, $unit ) = @_;
+ # date1 and date2 are array refs in the form [ yy, mm, dd ]
+
+ if( $unit eq 'day' ) {
+ return Delta_Days( @$date1, @$date2 );
+ } elsif( $unit eq 'week' ) {
+ return int( Delta_Days( @$date1, @$date2 ) / 7 );
+ }
+
+ # In case of months or years, this is a wrapper around N_Delta_YMD.
+ # Note that N_Delta_YMD returns 29 days between e.g. 22-2-72 and 22-3-72
+ # while we expect 1 month.
+ my @delta = N_Delta_YMD( @$date1, @$date2 );
+ if( $delta[2] > 27 ) {
+ # Check if we could add a month
+ my @jump = Add_Delta_YM( @$date1, $delta[0], 1 + $delta[1] );
+ if( Delta_Days( @jump, @$date2 ) >= 0 ) {
+ $delta[1]++;
+ }
+ }
+ if( $delta[1] >= 12 ) {
+ $delta[0]++;
+ $delta[1] -= 12;
+ }
+ # if unit is year, we only return full years
+ return $unit eq 'month' ? $delta[0] * 12 + $delta[1] : $delta[0];
+}
+
+sub _get_next_date_day {
+ my ($subscription, $freqdata, $year, $month, $day) = @_;
+
+ my @newissue; # ( yy, mm, dd )
+ # We do not need $delta_days here, since it would be zero where used
+
+ if( $freqdata->{issuesperunit} == 1 ) {
+ # Add full days
+ @newissue = Add_Delta_Days(
+ $year, $month, $day, $freqdata->{"unitsperissue"} );
+ } elsif ( $subscription->{countissuesperunit} < $freqdata->{issuesperunit} ) {
+ # Add zero days
+ @newissue = ( $year, $month, $day );
+ $subscription->{countissuesperunit}++;
+ } else {
+ # We finished a cycle of issues within a unit.
+ # No subtraction of zero needed, just add one day
+ @newissue = Add_Delta_Days( $year, $month, $day, 1 );
+ $subscription->{countissuesperunit} = 1;
+ }
+ return @newissue;
+}
+
+sub _get_next_date_week {
+ my ($subscription, $freqdata, $year, $month, $day) = @_;
+
+ my @newissue; # ( yy, mm, dd )
+ my $delta_days = int( 7 / $freqdata->{issuesperunit} );
+
+ if( $freqdata->{issuesperunit} == 1 ) {
+ # Add full weeks (of 7 days)
+ @newissue = Add_Delta_Days(
+ $year, $month, $day, 7 * $freqdata->{"unitsperissue"} );
+ } elsif ( $subscription->{countissuesperunit} < $freqdata->{issuesperunit} ) {
+ # Add rounded number of days based on frequency.
+ @newissue = Add_Delta_Days( $year, $month, $day, $delta_days );
+ $subscription->{countissuesperunit}++;
+ } else {
+ # We finished a cycle of issues within a unit.
+ # Subtract delta * (issues - 1), add 1 week
+ @newissue = Add_Delta_Days( $year, $month, $day,
+ -$delta_days * ($freqdata->{issuesperunit} - 1) );
+ @newissue = Add_Delta_Days( @newissue, 7 );
+ $subscription->{countissuesperunit} = 1;
+ }
+ return @newissue;
+}
+
+sub _get_next_date_month {
+ my ($subscription, $freqdata, $year, $month, $day) = @_;
+
+ my @newissue; # ( yy, mm, dd )
+ my $delta_days = int( 30 / $freqdata->{issuesperunit} );
+
+ if( $freqdata->{issuesperunit} == 1 ) {
+ # Add full months
+ @newissue = Add_Delta_YM(
+ $year, $month, $day, 0, $freqdata->{"unitsperissue"} );
+ } elsif ( $subscription->{countissuesperunit} < $freqdata->{issuesperunit} ) {
+ # Add rounded number of days based on frequency.
+ @newissue = Add_Delta_Days( $year, $month, $day, $delta_days );
+ $subscription->{countissuesperunit}++;
+ } else {
+ # We finished a cycle of issues within a unit.
+ # Subtract delta * (issues - 1), add 1 month
+ @newissue = Add_Delta_Days( $year, $month, $day,
+ -$delta_days * ($freqdata->{issuesperunit} - 1) );
+ @newissue = Add_Delta_YM( @newissue, 0, 1 );
+ $subscription->{countissuesperunit} = 1;
+ }
+ return @newissue;
+}
+
+sub _get_next_date_year {
+ my ($subscription, $freqdata, $year, $month, $day) = @_;
+
+ my @newissue; # ( yy, mm, dd )
+ my $delta_days = int( 365 / $freqdata->{issuesperunit} );
+
+ if( $freqdata->{issuesperunit} == 1 ) {
+ # Add full years
+ @newissue = Add_Delta_YM( $year, $month, $day, $freqdata->{"unitsperissue"}, 0 );
+ } elsif ( $subscription->{countissuesperunit} < $freqdata->{issuesperunit} ) {
+ # Add rounded number of days based on frequency.
+ @newissue = Add_Delta_Days( $year, $month, $day, $delta_days );
+ $subscription->{countissuesperunit}++;
+ } else {
+ # We finished a cycle of issues within a unit.
+ # Subtract delta * (issues - 1), add 1 year
+ @newissue = Add_Delta_Days( $year, $month, $day, -$delta_days * ($freqdata->{issuesperunit} - 1) );
+ @newissue = Add_Delta_YM( @newissue, 1, 0 );
+ $subscription->{countissuesperunit} = 1;
+ }
+ return @newissue;
+}
+