From 08e8660ad9a031ed7e2dc739e01c646ab79f5662 Mon Sep 17 00:00:00 2001
From: "Peter J. Holzer" <hjp@hjp.at>
Date: Sat, 4 Jun 2016 13:17:19 +0200
Subject: [PATCH] Extend usable time range to about 200 years

Previously the maximum grid spacing was 3 months which became
impractical with more than about 10 years of data. Now there are also
1 year and 5 year grid spacings.
Also worked around timelocal() DWIMery which would return wrong values
for much of the 20th century.
---
 TimeSeries.pm | 45 +++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 41 insertions(+), 4 deletions(-)

diff --git a/TimeSeries.pm b/TimeSeries.pm
index d2a8070..1206403 100644
--- a/TimeSeries.pm
+++ b/TimeSeries.pm
@@ -31,7 +31,7 @@ use Time::Local;
 use Data::Dumper;
 use HTTP::Date qw(parse_date);
 use Time::Local qw(timegm_nocheck);
-use POSIX qw(strftime);
+use POSIX qw(floor strftime);
 
 our $VERSION = do { my @r=(q$Revision: 1.24 $=~/\d+/g);sprintf "%d."."%02d"x$#r,@r};
 
@@ -404,8 +404,10 @@ sub plot {
 
     my @tics = get_ticks($firsttime, $lasttime);
 
+    # force tick values to look like fp numbers to avoid warnings about
+    # exceeding the int range from gnuplot
     print $ctlfh "set xtics rotate (",
-	    join(", ", map sprintf(qq|"%s" %d|, $_->[1], $_->[0]), @tics),
+	    join(", ", map sprintf(qq|"%s" %.16e|, $_->[1], $_->[0]), @tics),
 	    ")\n";
 
     # what to plot
@@ -499,7 +501,32 @@ sub get_ticks {
     my $label;
     my $nexttime;
 
-    if ($lasttime - $firsttime > 3 * 365 * 24 * 3600) {
+    if ($lasttime - $firsttime > 50 * 365 * 24 * 3600) {
+	# more than 50 years: 1 tick/5 years
+
+	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($firsttime);
+	$sec = $min = $hour = 0;
+	$mday = 1;
+	$mon = 0;
+        $year = floor($year / 5) * 5;
+	$firsttime = timelocal($sec,$min,$hour,$mday,$mon,$year);
+
+	$label = '%Y-%m-%d';
+
+	$nexttime = sub { return add_years($_[0], 5) };
+    } elsif ($lasttime - $firsttime > 10 * 365 * 24 * 3600) {
+	# more than 10 years: 1 tick/year
+
+	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($firsttime);
+	$sec = $min = $hour = 0;
+	$mday = 1;
+	$mon = 0;
+	$firsttime = timelocal($sec,$min,$hour,$mday,$mon,$year);
+
+	$label = '%Y-%m-%d';
+
+	$nexttime = sub { return add_years($_[0], 1) };
+    } elsif ($lasttime - $firsttime > 3 * 365 * 24 * 3600) {
 	# more than 3 years: 4 ticks/year
 
 	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($firsttime);
@@ -601,11 +628,21 @@ sub add_months {
     my ($time, $d_mon) = @_;
     my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst)
 	= localtime($time);
+    $year += 1900; # localtime/timelocal mismatch
     $mon += $d_mon;
     if ($mon >= 12) {
 	$mon -= 12; $year++;
     }
     $time = timelocal($sec,$min,$hour,$mday,$mon,$year);
-};
+}
+
+sub add_years {
+    my ($time, $d_year) = @_;
+    my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst)
+	= localtime($time);
+    $year += 1900; # localtime/timelocal mismatch
+    $year += $d_year;
+    $time = timelocal($sec,$min,$hour,$mday,$mon,$year);
+}
 
 1;