#!/usr/bin/perl
#
# Peteris Krumins (peter@catonmat.net)
# http://www.catonmat.net  --  good coders code, great reuse
#
# Feedburner graph generator
# More info at: http://www.catonmat.net/blog/generating-feedburner-graphs
#
# Version 1.0
#

use warnings;
use strict;

use WWW::Mechanize;
use List::Util 'max';
use XML::Simple;
use POSIX;
use GD;

# This is the API URL that returns XML data with feed statistics by day.
my $feedburner_url = "http://feedburner.google.com/api/awareness/1.0/GetFeedData?uri=%s&dates=%s,%s";

# This function prints the usage and terminates the program.
sub usage {
    printf "Usage: %s <feed name> [<start date> [<end date>]]\n", $0;
    print "Parameters:\n";
    print "<feed name>  - your feed name, for example 'catonmat'\n";
    print "<start date> - start date (YYYY-MM-DD)\n";
    print "<end date>   - end date (YYYY-MM-DD), today if not specified\n";
    exit(1);
}

# This function checks if DejaVuSans font is present, if not
# it prints the instructions on how to download and terminates the program.
sub check_dejavu_sans {
    unless (-e 'DejaVuSans.ttf') {
        print "Please download DejaVu fonts and put DejaVuSans.ttf file in\n";
        print "the same directory as this program.\n";
        print "http://dejavu-fonts.org/wiki/index.php?title=Download\n";
        exit(1);
    }
}

# Given year, month, day from `struct tm` (man 3 mktime),
# it constructs a YYYY-MM-DD string.
sub format_date {
    my ($y, $m, $d) = @_;
    return sprintf("%04d-%02d-%02d", $y+1900, $m+1, $d);
}

# Given the `struct tm` (man 3 mktime) as a 9-list (perldoc -f localtime),
# it constructs a YYYY-MM-DD string.
sub yyyymmdd_from_9list {
    my ($y, $m, $d) = @_[5,4,3];
    return format_date $y, $m, $d;
}

# This function returns a YYYY-MM-DD string for today.
sub today {
    return yyyymmdd_from_9list localtime
}

# This function constructs the 9-list (perldoc -f localtime) for a 
# date that was $months_ago months ago.
sub months_ago {
    my $months_ago = shift;
    my @date = @_;
    $date[4] -= $months_ago;
    return localtime mktime @date;
}

# Given feed data from feedburner's api (array of hashrefs), it finds
# the first date that had non-zero circulation.
# If no such date exists, it returns undef.
sub find_first_nonzero {
    my @feed_data = @_;
    return if $feed_data[0]->{circulation} != 0;
    my $prev_item;
    for my $item (@feed_data) {
        return $prev_item if $item->{circulation};
        $prev_item = $item;
    }
    return
}

# Given feed's name, this function finds the first date the
# feed had some subscribers, i.e., feed's start date.
sub find_start_date {
    my $feed = shift;
    print "Finding feed's start date...\n";
    my @ago = months_ago 6, localtime;
    my $end_date = today();
    while (1) {
        my $start_date = format_date @ago[5,4,3];

        print "Trying $start_date as start date...\n";
        my @feed_data = get_feed_data($feed, $start_date, $end_date);
        my $non_zero = find_first_nonzero(@feed_data);
        if ($non_zero) {
            print "Found $non_zero->{date} as start date!\n";
            return $non_zero->{date};
        }

        $end_date = yyyymmdd_from_9list @ago;
        @ago = months_ago 6, @ago;
    }
}

# This function returns an array of hashrefs of feeds data.
# Each hash contains 'reach', 'hits', 'date', and 'circulation' keys.
sub get_feed_data {
    my $raw_feed_data = get_raw_feed_data(@_);
    my $feed_data = XML::Simple->new->XMLin($raw_feed_data);
    if ($feed_data->{stat} ne "ok") {
        die $feed_data->{err}{msg}
    }
    return @{$feed_data->{'feed'}{'entry'}};
}

# This function formats the $feedburner_url and uses WWW::Mechanize
# to get the feed data via feedburner's API.
sub get_raw_feed_data {
    my ($feed, $start_date, $end_date) = @_;
    my $url = sprintf($feedburner_url, $feed, $start_date, $end_date);
    return WWW::Mechanize->new(agent => 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.5) Gecko/20091102 Firefox/3.5.5')->get($url)->content;
}

# This function drops feed items when they can't fit in graph's width.
sub drop_data {
    my ($width, @data) = @_;
    my $len = $#data;
    my $delta = @data - $width;
    my @drop = map { int($len / $delta * $_) } 1..$delta;
    splice @data, $_, 1 for reverse @drop;
    return @data;
}

# This function duplicates feed items when there are not enough items
# to fill the whole graph.
sub dupe_data {
    my ($width, @data) = @_;
    my $len = $#data;
    my $delta = $width - @data;
    my @dupe = map { int($len / $delta * $_) } 1..$delta;
    splice @data, $_, 0, $data[$_] for reverse @dupe;
    return @data;
}

# This function draws the outline of the graph box where the green
# lines are drawn.
sub draw_outline {
    my ($gd, $grid, $xy, $bg) = @_;
    $gd->rectangle(40, 4, 482, 100, $grid);
    $gd->filledRectangle(41, 5, 481, 99, $bg);
    $gd->line(40, 4, 40, 100, $xy);
    $gd->line(38, 100, 482, 100, $xy);
}

# This function draws the grid lines.
sub draw_grid {
    my ($gd, $xy, $grid) = @_;

    # horizontal
    $gd->line(41, 26, 482, 26, $grid);
    $gd->line(38, 26, 40, 26, $xy);
    $gd->line(41, 63, 482, 63, $grid);
    $gd->line(38, 63, 40, 63, $xy);

    # vertical
    for (my $x = 77; $x <= 442; $x += 73) {
        $gd->line($x, 4, $x, 99, $grid);
        $gd->line($x, 100, $x, 102, $xy);
    }
}

# This function saves the $gd image to a file named
# "feed_name-start_date-end_date.png"
sub save_image {
    my ($gd, $feed, $start_date, $end_date, @data) = @_;

    my $filename = "$feed-$start_date-$end_date.png";
    $filename =~ s|/|_|g;

    open my $fh, '>', $filename or die $!;
    print $fh $gd->png;
    close $fh;

    print "Done. Image written to $filename\n";
}

# This function draws the date thingies on the x axis.
sub draw_date {
    my ($gd, $item, $text_color, $x) = @_;
    my @mons = qw/Nul Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec/;

    my ($y, $m, $d) = $item->{date} =~ /(\d{4})-(\d{2})-(\d{2})/;
    $m = $mons[$m];
    my $text1 = sprintf("%s-", $m);
    my $text2 = sprintf("%s-%d", $m, $y);

    my @bounds = GD::Image->stringTTF($text_color, './DejaVuSans.ttf', 7, 0, 0, 0, $text1);
    my $offset = $bounds[4];

    $gd->stringTTF($text_color, './DejaVuSans.ttf', 7, 0, $x-$offset+2, 114, $text2);
}

# This function draws the feed usage numbers on the y axis.
sub draw_count {
    my ($gd, $count, $text_color, $y) = @_;

    my $text = int $count;

    my @bounds = GD::Image->stringTTF($text_color, './DejaVuSans.ttf', 7, 0, 0, 0, $text);
    my $width = $bounds[4] - $bounds[6];

    $gd->stringTTF($text_color, './DejaVuSans.ttf', 7, 0, 34-$width, $y+4, $text);
}

# This function creates the GD image and draws everything.
sub draw_feedburner_image {
    my ($feed, $start_date, $end_date, @data) = @_;

    print "Creating the awesome feedburner image.\n";

    my $gd = GD::Image->new(490, 120, 1);
    my $white  = $gd->colorAllocate(0xff, 0xff, 0xff);
    my $green  = $gd->colorAllocate(0x95, 0xcf, 0x9c);
    my $bg     = $gd->colorAllocate(0xf2, 0xf8, 0xfc);
    my $grid   = $gd->colorAllocate(0xcc, 0xce, 0xce);
    my $xy     = $gd->colorAllocate(0x80, 0x80, 0x80);
    my $alphagrid = $gd->colorAllocateAlpha(0xcc, 0xce, 0xce, 0x30);
    my $border = $gd->colorAllocate(0x68, 0x72, 0x79);
    my $text   = $gd->colorAllocate(0, 0 , 0);

    $gd->alphaBlending(1);
    $gd->filledRectangle(0, 0, 489, 119, $white);
    $gd->setAntiAliased($border);

    draw_outline($gd, $grid, $xy, $bg);

    my $t_height = 90;
    my $t_width = 441;
    my $max_circulation = max map { $_->{circulation} } @data;

    my $compress_factor = @data/$t_width;

    if ($compress_factor > 1) {
        @data = drop_data($t_width, @data);
    }
    elsif ($compress_factor < 1) {
        @data = dupe_data($t_width, @data);
    }

    my ($prev_x1, $prev_y1);
    my $x = 41;
    my %x_markers = (77 => 1, 150 => 1, 223 => 1, 296 => 1, 369 => 1, 442 => 1);
    for my $item (@data) {
        my $height = int($item->{circulation}/$max_circulation * $t_height);
        my ($x1, $y1, $x2, $y2) = ($x, 99, $x, 99-$height);
        $gd->line($x1, $y1, $x2, $y2, $green);
        if ($prev_x1) {
            $gd->line($prev_x1, $prev_y1, $x2, $y2, gdAntiAliased);
        }
        ($prev_x1, $prev_y1) = ($x1, $y2);

        if (exists $x_markers{$x}) {
            draw_date($gd, $item, $text, $x)
        }

        $x++;
    }

    draw_grid($gd, $xy, $alphagrid);
    draw_count($gd, 0,  $text, 100);
    draw_count($gd, $max_circulation * 74/90, $text, 26);
    draw_count($gd, $max_circulation * 37/90, $text, 63);
    save_image($gd, $feed, $start_date, $end_date);
}

# The main function, does everything.
sub main {
    check_dejavu_sans;

    my $feed = shift || usage();
    my $start_date = shift || find_start_date($feed);
    my $end_date = shift || today();

    unless ($start_date =~ /^\d{4}-\d{2}-\d{2}$/) {
        die "Invalid start date. Format: YYYY-MM-DD."
    }
    unless ($end_date =~ /^\d{4}-\d{2}-\d{2}$/) {
        die "Invalid end date. Format: YYYY-MM-DD."
    }

    print "Getting feed data for $feed from $start_date to $end_date\n";
    my @feed_data = get_feed_data($feed, $start_date, $end_date);

    draw_feedburner_image($feed, $start_date, $end_date, @feed_data);
}

main @ARGV;