+sub closed {
+  my ($self) = @_;
+  return $self->paid >= $self->amount;
+}
+
+sub new_from {
+  my ($class, $source, %params) = @_;
+
+  croak("Unsupported source object type '" . ref($source) . "'") unless ref($source) =~ m/^ SL::DB:: (?: Order | DeliveryOrder ) $/x;
+  croak("Cannot create invoices for purchase records")           unless $source->customer_id;
+
+  my $terms = $source->can('payment_id') && $source->payment_id ? $source->payment_terms->terms_netto : 0;
+
+  my %args = ( map({ ( $_ => $source->$_ ) } qw(customer_id taxincluded shippingpoint shipvia notes intnotes salesman_id cusordnumber ordnumber quonumber
+                                                department_id cp_id language_id payment_id delivery_customer_id delivery_vendor_id taxzone_id shipto_id
+                                                globalproject_id transaction_description currency_id)),
+               transdate   => DateTime->today_local,
+               gldate      => DateTime->today_local,
+               duedate     => DateTime->today_local->add(days => $terms * 1),
+               invoice     => 1,
+               type        => 'invoice',
+               storno      => 0,
+               paid        => 0,
+               employee_id => (SL::DB::Manager::Employee->current || SL::DB::Employee->new(id => $source->employee_id))->id,
+            );
+
+  if ($source->type =~ /_order$/) {
+    $args{deliverydate} = $source->reqdate;
+    $args{orddate}      = $source->transdate;
+  } else {
+    $args{quodate}      = $source->transdate;
+  }
+
+  my $invoice = $class->new(%args, %params);
+
+  my @items = map {
+    my $source_item = $_;
+    SL::DB::InvoiceItem->new(map({ ( $_ => $source_item->$_ ) }
+                                 qw(parts_id description qty sellprice discount project_id
+                                    serialnumber pricegroup_id ordnumber transdate cusordnumber unit
+                                    base_qty subtotal longdescription lastcost price_factor_id)),
+                            deliverydate => $source_item->reqdate,
+                            fxsellprice  => $source_item->sellprice,);
+  } @{ $source->items };
+
+  $invoice->invoiceitems(\@items);
+
+  return $invoice;
+}
+
+sub post {
+  my ($self, %params) = @_;
+
+  if (!$params{ar_id}) {
+    my $chart = SL::DB::Manager::Chart->get_all(query   => [ SL::DB::Manager::Chart->link_filter('AR') ],
+                                                sort_by => 'id ASC',
+                                                limit   => 1)->[0];
+    croak("No AR chart found and no parameter `ar_id' given") unless $chart;
+    $params{ar_id} = $chart->id;
+  }
+
+  my $worker = sub {
+    my %data = $self->calculate_prices_and_taxes;
+
+    $self->_post_create_assemblyitem_entries($data{assembly_items});
+    $self->create_trans_number;
+    $self->save;
+
+    $self->_post_add_acctrans($data{amounts_cogs});
+    $self->_post_add_acctrans($data{amounts});
+    $self->_post_add_acctrans($data{taxes});
+
+    $self->_post_add_acctrans({ $params{ar_id} => $self->amount * -1 });
+
+    $self->_post_update_allocated($data{allocated});
+  };
+
+  if ($self->db->in_transaction) {
+    $worker->();
+  } elsif (!$self->db->do_transaction($worker)) {
+    $::lxdebug->message(LXDebug->WARN(), "convert_to_invoice failed: " . join("\n", (split(/\n/, $self->db->error))[0..2]));
+    return undef;
+  }
+
+  return $self;
+}
+
+sub _post_add_acctrans {
+  my ($self, $entries) = @_;
+
+  my $default_tax_id = SL::DB::Manager::Tax->find_by(taxkey => 0)->id;
+  my $chart_link;
+
+  while (my ($chart_id, $spec) = each %{ $entries }) {
+    $spec = { taxkey => 0, tax_id => $default_tax_id, amount => $spec } unless ref $spec;
+    $chart_link = SL::DB::Manager::Chart->find_by(id => $chart_id)->{'link'};
+    $chart_link ||= '';
+
+    SL::DB::AccTransaction->new(trans_id   => $self->id,
+                                chart_id   => $chart_id,
+                                amount     => $spec->{amount},
+                                tax_id     => $spec->{tax_id},
+                                taxkey     => $spec->{taxkey},
+                                project_id => $self->globalproject_id,
+                                transdate  => $self->transdate,
+                                chart_link => $chart_link)->save;
+  }
+}
+
+sub _post_create_assemblyitem_entries {
+  my ($self, $assembly_entries) = @_;
+
+  my $items = $self->invoiceitems;
+  my @new_items;
+
+  my $item_idx = 0;
+  foreach my $item (@{ $items }) {
+    next if $item->assemblyitem;
+
+    push @new_items, $item;
+    $item_idx++;
+
+    foreach my $assembly_item (@{ $assembly_entries->[$item_idx] || [ ] }) {
+      push @new_items, SL::DB::InvoiceItem->new(parts_id     => $assembly_item->{part},
+                                                description  => $assembly_item->{part}->description,
+                                                unit         => $assembly_item->{part}->unit,
+                                                qty          => $assembly_item->{qty},
+                                                allocated    => $assembly_item->{allocated},
+                                                sellprice    => 0,
+                                                fxsellprice  => 0,
+                                                assemblyitem => 't');
+    }
+  }
+
+  $self->invoiceitems(\@new_items);
+}
+
+sub _post_update_allocated {
+  my ($self, $allocated) = @_;
+
+  while (my ($invoice_id, $diff) = each %{ $allocated }) {
+    SL::DB::Manager::InvoiceItem->update_all(set   => { allocated => { sql => "allocated + $diff" } },
+                                             where => [ id        => $invoice_id ]);
+  }
+}
+
+sub invoice_type {
+  my ($self) = @_;
+
+  return 'ar_transaction'     if !$self->invoice;
+  return 'credit_note'        if $self->type eq 'credit_note' && $self->amount < 0 && !$self->storno;
+  return 'invoice_storno'     if $self->type ne 'credit_note' && $self->amount < 0 &&  $self->storno;
+  return 'credit_note_storno' if $self->type eq 'credit_note' && $self->amount > 0 &&  $self->storno;
+  return 'invoice';
+}
+
+sub displayable_state {
+  my $self = shift;
+
+  return $self->closed ? $::locale->text('closed') : $::locale->text('open');
+}
+
+sub date {
+  goto &transdate;
+}
+