#!/usr/bin/perl

use strict;
use warnings;

use File::Slurp qw( slurp );
use Getopt::Long;
use POSIX qw( mktime strftime );
use POSIX::strptime qw( strptime );
use Text::Balanced qw( extract_bracketed );
use YAML qw( LoadFile );

GetOptions(
   'timestamp|t=s' => \(my $TIMESTAMP = "%Y/%m/%d %H:%M:%S"),
   'theme=s' => \(my $THEME = "../circle-fe-term/share/circle-fe-term.theme"), # TODO
) or exit 1;

my $filename = shift @ARGV; defined $filename or die "Require a filename\n";

my %theme;
{
   foreach ( slurp $THEME ) {
      next unless m/^(.*?)=(.*)$/;
      $theme{$1} = $2;
   }
}

open my $inh, "<", $filename or
   die "Cannot read $filename - $!";

my $headline = <$inh>;
my ( $start, $items, $timefmt ) = $headline =~ m/^!LOG START="([^"]+)" ITEMS="([^"]+)" TIMESTAMP_FMT="([^"]+)"$/ or
   die "Unable to parse headline - is this a yamllog file?\n";

# The first string part of each log line is formatted as per $timefmt, but
#   we'll need to know how many spaces it contains in order to strip it
my $timere = join " +", ( "\\S+" ) x ( 1 + ( () = $timefmt =~ m/ +/g ) );
$timere = qr/$timere/;

my @startt = ( strptime $start, "%Y/%m/%d %H:%M:%S" )[0..5];

while( <$inh> ) {
   my $line = $_; chomp $line;
   my ( $time, $type, $data ) = $line =~ m/^($timere) +(\S+) +(.*)$/ or
      die "Unparseable line> $line\n";

   my @thist = strptime $time, $timefmt;
   $thist[$_] //= $startt[$_] for 0 .. 5;
   $time = mktime @thist[0..5];

   # YAML::Load doesn't like flow forms at toplevel. Lets cheat
   $data = YAML::Load( "data: $data" )->{data};

   my $timestamp = strftime $TIMESTAMP, localtime $time;

   my $template = $theme{$type} or (print "<<unrecognised event $type>>\n"), next;

   my $text = process( $template, $data );

   print "$timestamp: $text\n";
}

sub process
{
   my ( $template, $args ) = @_;

   my $ret = "";
   while( length $template ) {
      if( $template =~ s/^\$(\w+)// ) {
         my $val = $args->{$1};
         my @parts = ref $val eq "ARRAY" ? @$val : ( $val );
         foreach my $part ( @parts ) {
            $ret .= ref $part eq "ARRAY" ? $part->[0] : $part;
         }
      }
      elsif( $template =~ m/^{/ ) {
         my $piece = extract_bracketed( $template, "{}" );
         s/^{//, s/}$// for $piece;

         my ( $code, $content ) = split( m/ /, $piece, 2 );
         $ret .= process( $content, $args );
      }
      else {
         $template =~ s/^([^\$\{]+)//;
         $ret .= $1;
      }
   }

   return $ret;
}