package folder;

BEGIN { *slog = \&::slog };

use Digest::SHA1;

use constant MDIFVERSION => 1;

sub new {
   my $class = shift;
   my %arg = @_;
   bless {
      path => "$::PREFIX/$arg{name}",
      %arg,
   }, $class;
}

sub dirty {
   $_[0]{dirty} = 1;
}

sub DESTROY {
   $_[0]->write_mdif;
}

# parse_mbox(mbox-file-path, callback)
# callback gets called with \$header and \$body,
# $header includes the mbox From_ line without
# the leading From_ itself.
sub parse_mbox {
  my ($path, $cb) = @_;

  open my $fh, "<", $path
     or die "$path: $!";

  local $/ = "\n\n";

  my ($head, $body, $offs);

  5 == read $fh, $head, 5
     or return;

  $head eq "From "
     or return;

  $offs = 0;
  while (defined ($head = <$fh>)) {
     $head =~ /^.*? [A-Z][a-z][a-z] [A-Z][a-z][a-z] [ 0-9][0-9] \d\d:\d\d:\d\d(?: [+-]\d\d\d\d)? \d\d(?:\d\d)\n/
        or die "$path: not standard mbox format header:\n$head\n";

     local $/ = "\nFrom ";
     # NEVER enable this. content-length simply is broken by design
     #if ($head =~ /^Content-Length:\s+(\d+)$/im) {
     #   $1 <= read $fh, $body, $1 + 5
     #      or die "$path: partial message in mbox";
     #} else {
        $body = <$fh>;
     #}
     chomp $body;
     $cb->($offs, \$head, \$body);
     $offs = (tell $fh) - 5;
     ::give unless ++$ecnt & 1023;
  }

  1;
}

sub conf_path {
   (my $conf = $_[0]{path}) =~ s%([^/]+$)%.$1.mdif%;
   $conf;
}

sub read_mdif {
   my $self = shift;
   my $path = $self->conf_path;

   return if $self->{idx};

   open my $fh, "<", $path
      or return;

   defined ($_ = <$fh>)
      or die "$path: empty mdif file\n";

   do {
      if ($_ eq "[SYNCMAIL]\n") {
         while (<$fh>) {
            last unless /^([a-z]+)\s*=\s*(.*)\n$/;
            $self->{$1} = $2;
         }
      } elsif ($_ eq "[HOSTS]\n") {
         while (<$fh>) {
            last unless /^([^[].*)=(.*)\n$/;
            $self->{host}{$1} = $2;
         }
      } elsif (/^\[DIFF (\d+)\]\n$/) {
         my $mtime = $1;
         my (@add, @del);
         while (<$fh>) {
            last unless /^([+-])(.*)\n$/;
            if ($1 eq "+") {
               push @add, $2;
            } else {
               push @del, $2;
            }
         }
         unshift @{$self->{diff}}, [$mtime, \@add, \@del];
      } elsif ($_ eq "[INDEX]\n") {
         my @idx;
         while (<$fh>) {
            last unless /^(\d+)=(.*)\n$/;
            push @idx, [$1, $2];
         }
         $self->{idx} = \@idx;
      } elsif (/^#/) {
         $_ = <$fh>;
         # nop
      } else {
         die "$path: unparseable section '$_'\n";
      }
   } while defined $_;

   $self->{version} <= MDIFVERSION
      or die "$path: version mismatch ($self->{version} found, <".MDIFVERSION." expected)\n";
}

sub write_mdif {
   my $self = shift;
   my $path = $self->conf_path;

   return unless $self->{dirty};

   open my $fh, ">", "$path~"
      or die "$path~: $!";

   print $fh "# automatically generated, do NOT edit\n";

   print $fh "[SYNCMAIL]\n";
   print $fh "$_=$self->{$_}\n" for (qw(fsize mtime version));

   print $fh "[HOSTS]\n";
   while (my ($k,$v) = each %{$self->{host}}) {
      print $fh "$k=$v\n";
   }

   print $fh "[INDEX]\n";
   print $fh "$_->[0]=$_->[1]\n" for @{$self->{idx}};

   for (reverse @{$self->{diff}}) {
      print $fh "[DIFF $_->[0]]\n";
      print $fh "+$_\n" for @{$_->[1]};
      print $fh "-$_\n" for @{$_->[2]};
   }

   close $fh
      or die "$path~: unable to create updated .mdif: $!";

   rename "$path~", $path;

   delete $self->{dirty};
}

if (1) {
   use OpenSSL ();
   *hash = \&OpenSSL::Digest::sha1_hex;
} elsif (0) {
   # use Digest::SHA1;
   my $digest = new Digest::SHA1;
   *hash = sub {
      $digest->reset;
      $digest->add(@_);
      $mid = $digest->hexdigest;
   };
} 

sub gendiff {
   my ($d1, $d2) = @_;

   my (@add, @del);
   my (%d1, %d2);

   for (@$d2) {
      undef $d2{$_->[1]};
   }

   # delete msgs in d1 but not in d2
   for (@$d1) {
      undef $d1{$_->[1]};
      push @del, $_->[1] unless exists $d2{$_->[1]};
   }
   %d2 = (); # conserve memory

   # add msgs in d2 but not in d1
   for (@$d2) {
      push @add, $_->[1] unless exists $d1{$_->[1]};
   }

   (\@add, \@del);
}

sub check {
   my $self = shift;
   my $path = $self->{path};
   my $conf = $self->conf_path;
   my $guard = $::lockdisk->guard;

   slog 3, "checking $path\n";

   if (stat $path) {
      my ($fsize, $mtime) = (stat _)[7, 9];

      if (open my $fh, "<", $conf) {
         my %conf;
         <$fh>; # skip initial comment
         <$fh> eq "[SYNCMAIL]\n"
            or die "$conf: format error";
         while (<$fh> =~ /^([a-z]+)\s*=\s*(.*)$/) {
            $conf{$1} = $2;
         }
         return 1 if $fsize == $conf{fsize}
                  && $mtime == $conf{mtime};

         $conf{mtime} <= $mtime
            or die "$path: folder older than mdif";
      }

      slog 2, "updating $path\n";

      my @idx;

      parse_mbox $path, sub {
         my ($offs, $head, $body) = @_;
         push @idx, [$offs, hash($$head, "\0", $$body)];
      } or return ();

      $self->read_mdif;

      $self->{version} ||= MDIFVERSION;
      my ($add, $del) = gendiff $self->{idx}, \@idx;
      push @{$self->{diff}}, [
         $mtime,
         $add, $del,
      ] if @$add || @$del;

      $self->{fsize} = $fsize;
      $self->{mtime} = $mtime;
      $self->{idx}   = \@idx;

      $self->dirty;

      return 2;
   } else {
      slog 2, "$path: no longer exists\n";
      unlink $conf;

      return ();
   }
}

1;