#!/usr/bin/perl

# List of general TODO
# * autodetect optimal frequency depending on date range for commits
# * default to something else than "the whole history", probably
# * if no commits are specified and a commit grouping step is specified,
#   limit commits proportionally (e.g. --daily => one week worth of commits)
# * find a better way to group commits, the current is a little too inaccurate
#
# Most of the mentioned TODOs require either some peeking at the commits
# or some other form of pre/post-processing. For both it's probably better
# to just slurp them at once and then think about the grouping

use strict;
use warnings;
use POSIX qw(ceil);
use Getopt::Long;
use Date::Parse;

my $SECS_PER_DAY = 24*3600;

my %steps = (
	hourly => 3600,
	daily => $SECS_PER_DAY,
	weekly => 7*$SECS_PER_DAY,
	monthly => 30*$SECS_PER_DAY,
	yearly => 12*30*$SECS_PER_DAY,
);

sub usage() {
	# TODO
	print "Usage: git chart\n";
}

sub gather_data($) {
	my $options = shift;
	my %dataset;

	print "Gathering data ...\n";

	my $groups = 0;
	my $commits = 0;

	my $step=$options->{step};

	open my $fd, '-|', qw(git log --date=raw), '--pretty=%ad %s', @{$options->{cmdline}};
	die "failed to get revs" unless $fd;
	while (<$fd>) {
		chomp;
		$commits += 1;
		my ($date, $tz, $sub) = split ' ', $_, 3;
		# TODO use $tz

		my $key = $date - ($date % $step);
		if (exists $dataset{$key}) {
			$dataset{$key} += 1;
		} else {
			$dataset{$key} = 1;
			$groups += 1;
		}
	}
	close $fd;

	print "...done, $commits commits in $groups groups.\n";

	# fill missing steps and find max
	my @keys = sort keys %dataset;
	my $last = pop @keys;
	my $max = 0;
	while (my $key = shift @keys) {
		$max = $dataset{$key} if $max < $dataset{$key};
		my $next = $key + $step;
		while (! exists $dataset{$next}) {
			$dataset{$next} = 0;
			$next += $step;
			last if $next >= $last;
		}
	}

	$options->{max} = $max;
	return \%dataset;
}

# functions to plot the datasets.
# each function can be called with either one or two parameters.
# when called with two parameters, the first is assumed to be the dataset, and the second the options
# (array and hash ref respectively).
# when called with a single parameter, it is assumed to be an options hash ref, and the dataset is 
# created by calling gather_data with the passed options.

# google chart API
# TODO needs a lot of customization
sub google_chart($;$) {
	my $dataset = shift;
	my $options = shift;
	if (! defined $options) {
		$options = $dataset;
		$dataset = gather_data($options);
	}

	my $height=$options->{chart_height};
	my $max = $options->{max};

	my @keys = sort keys %$dataset;
	my $from = $keys[0];
	my $to = $keys[@keys-1];

	my @data;
	while (my $key = shift @keys) {
		push @data, $dataset->{$key};
	}

	my $width=ceil(4*$height/3);

	my $url="https://chart.googleapis.com/chart?chs=${width}x${height}&cht=bvg&chd=t:%s&chds=0,$max&chbh=a&chxt=y&chxr=0,0,$max";

	my $launch = sprintf $url, join(",",@data);
	print $launch, "\n";
	# `git web--browse "$launch"`
}

# gnuplot
sub gnuplot_chart($;$) {
	my $dataset = shift;
	my $options = shift;
	if (! defined $options) {
		$options = $dataset;
		$dataset = gather_data($options);
	}

	my @keys = sort keys %$dataset;
	my $step=$options->{step};
	my $from = $keys[0];
	my $to = $keys[@keys-1];
	my $data = '';
	while (my $key = shift @keys) {
		$data .= "$key $dataset->{$key}\n";
	}
	my $max = $options->{max};

	# TODO allow customization
	# in particular, detect (lack of) display and set term to dumb accordingly
	my $termcmd = $options->{gnuplot_term};

	my $plotsetup = $options->{gnuplot_setup};
	$plotsetup .= "\nset yrange [0:$max]\n";
	$plotsetup .= "set xrange ['$from':'$to']\n";
	my ($formatx, $ticks);
	if ($to - $from > $steps{yearly}) {
		$formatx = "%Y";
		$ticks = $steps{yearly};
	} elsif ($to - $from > $steps{monthly}) {
		$formatx = "%b\\n%Y";
		$ticks = $steps{monthly};
	} elsif ($to - $from > 2*$steps{daily}) {
		$formatx = "%d\\n%b";
		$ticks = $steps{daily};
	} else {
		$formatx = "%H:%M";
		$ticks = $steps{hourly};
	}
	$plotsetup .= "set format x \"$formatx\"\n";
	$plotsetup .= "set xtics $ticks\n";
	my $plotstyle = $options->{gnuplot_style};
	my $plotoptions = $options->{gnuplot_plotwith};

	open my $gp, "|gnuplot -persist";

	my $gp_script = <<GPCMD
$termcmd
set xdata time
set timefmt "%s"
$plotsetup
$plotstyle
plot "-" using 1:2 $plotoptions
$data
GPCMD
	;

	print STDOUT $gp_script;
	print $gp $gp_script;
	close $gp;
}

# some defaults
my %options = (
	step => $SECS_PER_DAY,
	cmdline => [],
	# charting/plotting options
	plotter => \&gnuplot_chart,
	chart_height => 144,
	gnuplot_term => '',
	gnuplot_setup => "set nokey",
	gnuplot_style => 'set style data histeps',
	gnuplot_plotwith => '',
);

sub parse_step(@) {
	my $key = shift;
	my $step = shift;
	if (exists $steps{$key}) {
		$options{step} = $steps{$key};
		return;
	}
	die "this can't happen ($key)" unless $key eq 'step';

	if ($step =~/^\d+$/) {
		$options{step} = 0 + $step;
		return
	} else {
		if (exists $steps{$step}) {
			$options{step} = $steps{$step};
			return;
		}
		die "unknown step $step";
	}
}

# read our options first
Getopt::Long::Configure('pass_through');
GetOptions(
	'hourly' => \&parse_step,
	'daily' => \&parse_step,
	'weekly' => \&parse_step,
	'monthly' => \&parse_step,
	'yearly' => \&parse_step,
	'step=s' => sub { parse_step(@_) },
	'chart-height=i' => sub { $options{chart_height} = $_[1]},
	google => sub { $options{plotter} = \&google_chart },
	gnuplot => sub { $options{plotter} = \&gnuplot_chart },
);

# if anything was left, check for log options
if (@ARGV) {
	$options{cmdline} = \@ARGV;
}

die "step must be strictly positive!" unless $options{step} > 0;

$options{plotter}->(\%options);