package Slic3r::Print::GCode;
use Moo;

has 'print'     => (is => 'ro', required => 1, handles => [qw(objects placeholder_parser config)]);
has 'fh'        => (is => 'ro', required => 1);

has '_gcodegen'                      => (is => 'rw');
has '_cooling_buffer'                => (is => 'rw');
has '_spiral_vase'                   => (is => 'rw');
has '_arc_fitting'                   => (is => 'rw');
has '_pressure_regulator'            => (is => 'rw');
has '_pressure_equalizer'            => (is => 'rw');
has '_skirt_done'                    => (is => 'rw', default => sub { {} });  # print_z => 1
has '_brim_done'                     => (is => 'rw');
has '_second_layer_things_done'      => (is => 'rw');
has '_last_obj_copy'                 => (is => 'rw');

use List::Util qw(first sum min max);
use Slic3r::ExtrusionPath ':roles';
use Slic3r::Flow ':roles';
use Slic3r::Geometry qw(X Y scale unscale chained_path convex_hull);
use Slic3r::Geometry::Clipper qw(JT_SQUARE union_ex offset);

sub BUILD {
    my ($self) = @_;
    
    {
        # estimate the total number of layer changes
        # TODO: only do this when M73 is enabled
        my $layer_count;
        if ($self->config->complete_objects) {
            $layer_count = sum(map { $_->total_layer_count * @{$_->copies} } @{$self->objects});
        } else {
            # if sequential printing is not enable, all copies of the same object share the same layer change command(s)
            $layer_count = sum(map { $_->total_layer_count } @{$self->objects});
        }
    
        # set up our helper object: This is a C++ Slic3r::GCode instance.
        my $gcodegen = Slic3r::GCode->new;
        $self->_gcodegen($gcodegen);
        $gcodegen->set_placeholder_parser($self->placeholder_parser);
        # Tell the G-code generator, how many times the $gcodegen->change_layer() will be called.
        # $gcodegen->change_layer() in turn increments the progress bar status. 
        $gcodegen->set_layer_count($layer_count);
        $gcodegen->set_enable_cooling_markers(1);
        $gcodegen->apply_print_config($self->config);
        $gcodegen->set_extruders($self->print->extruders);
        
        # initialize autospeed
        {
            # get the minimum cross-section used in the print
            my @mm3_per_mm = ();
            foreach my $object (@{$self->print->objects}) {
                foreach my $region_id (0..$#{$self->print->regions}) {
                    my $region = $self->print->get_region($region_id);
                    foreach my $layer (@{$object->layers}) {
                        my $layerm = $layer->get_region($region_id);
                        if ($region->config->get_abs_value('perimeter_speed') == 0
                            || $region->config->get_abs_value('small_perimeter_speed') == 0
                            || $region->config->get_abs_value('external_perimeter_speed') == 0
                            || $region->config->get_abs_value('bridge_speed') == 0) {
                            push @mm3_per_mm, $layerm->perimeters->min_mm3_per_mm;
                        }
                        if ($region->config->get_abs_value('infill_speed') == 0
                            || $region->config->get_abs_value('solid_infill_speed') == 0
                            || $region->config->get_abs_value('top_solid_infill_speed') == 0
                            || $region->config->get_abs_value('bridge_speed') == 0) {
                            push @mm3_per_mm, $layerm->fills->min_mm3_per_mm;
                        }
                    }
                }
                if ($object->config->get_abs_value('support_material_speed') == 0
                    || $object->config->get_abs_value('support_material_interface_speed') == 0) {
                    foreach my $layer (@{$object->support_layers}) {
                        push @mm3_per_mm, $layer->support_fills->min_mm3_per_mm;
                        push @mm3_per_mm, $layer->support_interface_fills->min_mm3_per_mm;
                    }
                }
            }
            # filter out 0-width segments
            @mm3_per_mm = grep $_ > 0.000001, @mm3_per_mm;
            if (@mm3_per_mm) {
                my $min_mm3_per_mm = min(@mm3_per_mm);
                # In order to honor max_print_speed we need to find a target volumetric
                # speed that we can use throughout the print. So we define this target 
                # volumetric speed as the volumetric speed produced by printing the 
                # smallest cross-section at the maximum speed: any larger cross-section
                # will need slower feedrates.
                my $volumetric_speed = $min_mm3_per_mm * $self->config->max_print_speed;
                
                # limit such volumetric speed with max_volumetric_speed if set
                if ($self->config->max_volumetric_speed > 0) {
                    $volumetric_speed = min(
                        $volumetric_speed,
                        $self->config->max_volumetric_speed,
                    );
                }
                $gcodegen->set_volumetric_speed($volumetric_speed);
            }
        }
    }
    
    $self->_cooling_buffer(Slic3r::GCode::CoolingBuffer->new(
        config      => $self->config,
        gcodegen    => $self->_gcodegen,
    ));
    
    $self->_spiral_vase(Slic3r::GCode::SpiralVase->new(config => $self->config))
        if $self->config->spiral_vase;
    
    $self->_arc_fitting(Slic3r::GCode::ArcFitting->new(config => $self->config))
        if $self->config->gcode_arcs;
    
    $self->_pressure_regulator(Slic3r::GCode::PressureRegulator->new(config => $self->config))
        if $self->config->pressure_advance > 0;

    $self->_pressure_equalizer(Slic3r::GCode::PressureEqualizer->new($self->config))
        if ($self->config->max_volumetric_extrusion_rate_slope_positive > 0 ||
            $self->config->max_volumetric_extrusion_rate_slope_negative > 0);

    $self->_gcodegen->set_enable_extrusion_role_markers(defined $self->_pressure_equalizer);
}

# Export a G-code for the complete print.
sub export {
    my ($self) = @_;
    
    my $fh          = $self->fh;
    my $gcodegen    = $self->_gcodegen;
    
    # Write information on the generator.
    my @lt = localtime;
    printf $fh "; generated by Slic3r $Slic3r::VERSION on %04d-%02d-%02d at %02d:%02d:%02d\n\n",
        $lt[5] + 1900, $lt[4]+1, $lt[3], $lt[2], $lt[1], $lt[0];
    # Write notes (content of the Print Settings tab -> Notes)
    print $fh "; $_\n" foreach split /\R/, $self->config->notes;
    print $fh "\n" if $self->config->notes;
    # Write some terse information on the slicing parameters.
    my $first_object = $self->objects->[0];
    my $layer_height = $first_object->config->layer_height;
    for my $region_id (0..$#{$self->print->regions}) {
        my $region = $self->print->regions->[$region_id];
        printf $fh "; external perimeters extrusion width = %.2fmm\n",
            $region->flow(FLOW_ROLE_EXTERNAL_PERIMETER, $layer_height, 0, 0, -1, $first_object)->width;
        printf $fh "; perimeters extrusion width = %.2fmm\n",
            $region->flow(FLOW_ROLE_PERIMETER, $layer_height, 0, 0, -1, $first_object)->width;
        printf $fh "; infill extrusion width = %.2fmm\n",
            $region->flow(FLOW_ROLE_INFILL, $layer_height, 0, 0, -1, $first_object)->width;
        printf $fh "; solid infill extrusion width = %.2fmm\n",
            $region->flow(FLOW_ROLE_SOLID_INFILL, $layer_height, 0, 0, -1, $first_object)->width;
        printf $fh "; top infill extrusion width = %.2fmm\n",
            $region->flow(FLOW_ROLE_TOP_SOLID_INFILL, $layer_height, 0, 0, -1, $first_object)->width;
        printf $fh "; support material extrusion width = %.2fmm\n",
            $self->objects->[0]->support_material_flow->width
            if $self->print->has_support_material;
        printf $fh "; first layer extrusion width = %.2fmm\n",
            $region->flow(FLOW_ROLE_PERIMETER, $layer_height, 0, 1, -1, $self->objects->[0])->width
            if $region->config->first_layer_extrusion_width;
        print  $fh "\n";
    }
    
    # prepare the helper object for replacing placeholders in custom G-code and output filename
    $self->placeholder_parser->update_timestamp;
    
    # disable fan
    print $fh $gcodegen->writer->set_fan(0, 1)
        if $self->config->cooling && $self->config->disable_fan_first_layers;
    
    # set bed temperature
    if ((my $temp = $self->config->first_layer_bed_temperature) && $self->config->start_gcode !~ /M(?:190|140)/i) {
        printf $fh $gcodegen->writer->set_bed_temperature($temp, 1);
    }
    
    # set extruder(s) temperature before and after start G-code
    $self->_print_first_layer_temperature(0);
    printf $fh "%s\n", $gcodegen->placeholder_parser->process($self->config->start_gcode);
    $self->_print_first_layer_temperature(1);
    
    # set other general things
    print $fh $gcodegen->preamble;
    
    # initialize a motion planner for object-to-object travel moves
    if ($self->config->avoid_crossing_perimeters) {
        my $distance_from_objects = scale 1;
        
        # compute the offsetted convex hull for each object and repeat it for each copy.
        my @islands_p = ();
        foreach my $object (@{$self->objects}) {
            # discard objects only containing thin walls (offset would fail on an empty polygon)
            my @polygons = map $_->contour, map @{$_->slices}, @{$object->layers};
            next if !@polygons;
            
            # translate convex hull for each object copy and append it to the islands array
            foreach my $copy (@{ $object->_shifted_copies }) {
                my @copy_islands_p = map $_->clone, @polygons;
                $_->translate(@$copy) for @copy_islands_p;
                push @islands_p, @copy_islands_p;
            }
        }
        $gcodegen->avoid_crossing_perimeters->init_external_mp(union_ex(\@islands_p));
    }
    
    # calculate wiping points if needed
    if ($self->config->ooze_prevention) {
        my @skirt_points = map @$_, map @$_, @{$self->print->skirt};
        if (@skirt_points) {
            my $outer_skirt = convex_hull(\@skirt_points);
            my @skirts = ();
            foreach my $extruder_id (@{$self->print->extruders}) {
                my $extruder_offset = $self->config->get_at('extruder_offset', $extruder_id);
                push @skirts, my $s = $outer_skirt->clone;
                $s->translate(-scale($extruder_offset->x), -scale($extruder_offset->y));  #)
            }
            my $convex_hull = convex_hull([ map @$_, @skirts ]);
            
            $gcodegen->ooze_prevention->set_enable(1);
            $gcodegen->ooze_prevention->set_standby_points(
                [ map @{$_->equally_spaced_points(scale 10)}, @{offset([$convex_hull], scale 3)} ]
            );
            
            if (0) {
                require "Slic3r/SVG.pm";
                Slic3r::SVG::output(
                    "ooze_prevention.svg",
                    red_polygons    => \@skirts,
                    polygons        => [$outer_skirt],
                    points          => $gcodegen->ooze_prevention->standby_points,
                );
            }
        }
    }
    
    # set initial extruder only after custom start G-code
    print $fh $gcodegen->set_extruder($self->print->extruders->[0]);
    
    # do all objects for each layer
    if ($self->config->complete_objects) {
        # print objects from the smallest to the tallest to avoid collisions
        # when moving onto next object starting point
        my @obj_idx = sort { $self->objects->[$a]->size->z <=> $self->objects->[$b]->size->z } 0..($self->print->object_count - 1);
        
        my $finished_objects = 0;
        for my $obj_idx (@obj_idx) {
            my $object = $self->objects->[$obj_idx];
            for my $copy (@{ $self->objects->[$obj_idx]->_shifted_copies }) {
                # move to the origin position for the copy we're going to print.
                # this happens before Z goes down to layer 0 again, so that 
                # no collision happens hopefully.
                if ($finished_objects > 0) {
                    $gcodegen->set_origin(Slic3r::Pointf->new(map unscale $copy->[$_], X,Y));
                    $gcodegen->set_enable_cooling_markers(0);  # we're not filtering these moves through CoolingBuffer
                    $gcodegen->avoid_crossing_perimeters->set_use_external_mp_once(1);
                    print $fh $gcodegen->retract;
                    print $fh $gcodegen->travel_to(
                        Slic3r::Point->new(0,0),
                        EXTR_ROLE_NONE,
                        'move to origin position for next object',
                    );
                    $gcodegen->set_enable_cooling_markers(1);
                    
                    # disable motion planner when traveling to first object point
                    $gcodegen->avoid_crossing_perimeters->set_disable_once(1);
                }
                
                # Order layers by print_z, support layers preceding the object layers.
                my @layers = sort 
                    { ($a->print_z == $b->print_z) ? ($a->isa('Slic3r::Layer::Support') ? -1 : 0) : $a->print_z <=> $b->print_z }
                    @{$object->layers}, @{$object->support_layers};
                for my $layer (@layers) {
                    # if we are printing the bottom layer of an object, and we have already finished
                    # another one, set first layer temperatures. this happens before the Z move
                    # is triggered, so machine has more time to reach such temperatures
                    if ($layer->id == 0 && $finished_objects > 0) {
                        printf $fh $gcodegen->writer->set_bed_temperature($self->config->first_layer_bed_temperature),
                            if $self->config->first_layer_bed_temperature;
                        $self->_print_first_layer_temperature(0);
                    }
                    $self->process_layer($layer, [$copy]);
                }
                $self->flush_filters;
                $finished_objects++;
                $self->_second_layer_things_done(0);
            }
        }
    } else {
        # order objects using a nearest neighbor search
        my @obj_idx = @{chained_path([ map Slic3r::Point->new(@{$_->_shifted_copies->[0]}), @{$self->objects} ])};
        
        # sort layers by Z
        # All extrusion moves with the same top layer height are extruded uninterrupted,
        # object extrusion moves are performed first, then the support.
        my %layers = ();  # print_z => [ [layers], [layers], [layers] ]  by obj_idx
        foreach my $obj_idx (0 .. ($self->print->object_count - 1)) {
            my $object = $self->objects->[$obj_idx];
            # Collect the object layers by z, support layers first, object layers second.
            foreach my $layer (@{$object->support_layers}, @{$object->layers}) {
                $layers{ $layer->print_z } ||= [];
                $layers{ $layer->print_z }[$obj_idx] ||= [];
                push @{$layers{ $layer->print_z }[$obj_idx]}, $layer;
            }
        }
        
        foreach my $print_z (sort { $a <=> $b } keys %layers) {
            foreach my $obj_idx (@obj_idx) {
                foreach my $layer (@{ $layers{$print_z}[$obj_idx] // [] }) {
                    $self->process_layer($layer, $layer->object->_shifted_copies);
                }
            }
        }
        $self->flush_filters;
    }
    
    # write end commands to file
    print $fh $gcodegen->retract;   # TODO: process this retract through PressureRegulator in order to discharge fully
    print $fh $gcodegen->writer->set_fan(0);
    printf $fh "%s\n", $gcodegen->placeholder_parser->process($self->config->end_gcode);
    print $fh $gcodegen->writer->update_progress($gcodegen->layer_count, $gcodegen->layer_count, 1);  # 100%
    print $fh $gcodegen->writer->postamble;
    
    # get filament stats
    $self->print->clear_filament_stats;
    $self->print->total_used_filament(0);
    $self->print->total_extruded_volume(0);
    foreach my $extruder (@{$gcodegen->writer->extruders}) {
        my $used_filament = $extruder->used_filament;
        my $extruded_volume = $extruder->extruded_volume;
        $self->print->set_filament_stats($extruder->id, $used_filament);
        
        printf $fh "; filament used = %.1fmm (%.1fcm3)\n",
            $used_filament, $extruded_volume/1000;
        
        $self->print->total_used_filament($self->print->total_used_filament + $used_filament);
        $self->print->total_extruded_volume($self->print->total_extruded_volume + $extruded_volume);
    }
    
    # append full config
    print $fh "\n";
    foreach my $config ($self->print->config, $self->print->default_object_config, $self->print->default_region_config) {
        foreach my $opt_key (sort @{$config->get_keys}) {
            next if $Slic3r::Config::Options->{$opt_key}{shortcut};
            printf $fh "; %s = %s\n", $opt_key, $config->serialize($opt_key);
        }
    }
}

sub _print_first_layer_temperature {
    my ($self, $wait) = @_;
    
    return if $self->config->start_gcode =~ /M(?:109|104)/i;
    for my $t (@{$self->print->extruders}) {
        my $temp = $self->config->get_at('first_layer_temperature', $t);
        $temp += $self->config->standby_temperature_delta if $self->config->ooze_prevention;
        printf {$self->fh} $self->_gcodegen->writer->set_temperature($temp, $wait, $t) if $temp > 0;
    }
}

# Called per object's layer.
# First a $gcode string is collected,
# then filtered and finally written to a file $fh.
#FIXME If printing multiple objects at once, this incorrectly applies cooling logic to a single object's layer instead
# of all the objects printed.
sub process_layer {
    my $self = shift;
    my ($layer, $object_copies) = @_;
    my $gcode = "";
    
    my $object = $layer->object;
    $self->_gcodegen->config->apply_static($object->config);
    
    # check whether we're going to apply spiralvase logic
    if (defined $self->_spiral_vase) {
        $self->_spiral_vase->enable(
            ($layer->id > 0 || $self->print->config->brim_width == 0)
                && ($layer->id >= $self->print->config->skirt_height && !$self->print->has_infinite_skirt)
                && !defined(first { $_->region->config->bottom_solid_layers > $layer->id } @{$layer->regions})
                && !defined(first { $_->perimeters->items_count > 1 } @{$layer->regions})
                && !defined(first { $_->fills->items_count > 0 } @{$layer->regions})
        );
    }
    
    # if we're going to apply spiralvase to this layer, disable loop clipping
    $self->_gcodegen->set_enable_loop_clipping(!defined $self->_spiral_vase || !$self->_spiral_vase->enable);
    
    if (!$self->_second_layer_things_done && $layer->id == 1) {
        for my $extruder (@{$self->_gcodegen->writer->extruders}) {
            my $temperature = $self->config->get_at('temperature', $extruder->id);
            $gcode .= $self->_gcodegen->writer->set_temperature($temperature, 0, $extruder->id)
                if $temperature && $temperature != $self->config->get_at('first_layer_temperature', $extruder->id);
        }
        $gcode .= $self->_gcodegen->writer->set_bed_temperature($self->print->config->bed_temperature)
            if $self->print->config->bed_temperature && $self->print->config->bed_temperature != $self->print->config->first_layer_bed_temperature;
        $self->_second_layer_things_done(1);
    }
    
    # set new layer - this will change Z and force a retraction if retract_layer_change is enabled
    if ($self->print->config->before_layer_gcode) {
        my $pp = $self->_gcodegen->placeholder_parser->clone;
        $pp->set('layer_num' => $self->_gcodegen->layer_index + 1);
        $pp->set('layer_z'   => $layer->print_z);
        $gcode .= $pp->process($self->print->config->before_layer_gcode) . "\n";
    }
    $gcode .= $self->_gcodegen->change_layer($layer->as_layer);  # this will increase $self->_gcodegen->layer_index
    if ($self->print->config->layer_gcode) {
        my $pp = $self->_gcodegen->placeholder_parser->clone;
        $pp->set('layer_num' => $self->_gcodegen->layer_index);
        $pp->set('layer_z'   => $layer->print_z);
        $gcode .= $pp->process($self->print->config->layer_gcode) . "\n";
    }
    
    # extrude skirt along raft layers and normal object layers
    # (not along interlaced support material layers)
    if (((values %{$self->_skirt_done}) < $self->print->config->skirt_height || $self->print->has_infinite_skirt)
        && !$self->_skirt_done->{$layer->print_z}
        && (!$layer->isa('Slic3r::Layer::Support') || $layer->id < $object->config->raft_layers)) {
        $self->_gcodegen->set_origin(Slic3r::Pointf->new(0,0));
        $self->_gcodegen->avoid_crossing_perimeters->set_use_external_mp(1);
        my @extruder_ids = map { $_->id } @{$self->_gcodegen->writer->extruders};
        $gcode .= $self->_gcodegen->set_extruder($extruder_ids[0]);
        # skip skirt if we have a large brim
        if ($layer->id < $self->print->config->skirt_height || $self->print->has_infinite_skirt) {
            my $skirt_flow = $self->print->skirt_flow;
            
            # distribute skirt loops across all extruders
            my @skirt_loops = @{$self->print->skirt};
            for my $i (0 .. $#skirt_loops) {
                # when printing layers > 0 ignore 'min_skirt_length' and 
                # just use the 'skirts' setting; also just use the current extruder
                last if ($layer->id > 0) && ($i >= $self->print->config->skirts);
                my $extruder_id = $extruder_ids[($i/@extruder_ids) % @extruder_ids];
                $gcode .= $self->_gcodegen->set_extruder($extruder_id)
                    if $layer->id == 0;
                
                # adjust flow according to this layer's layer height
                my $loop = $skirt_loops[$i]->clone;
                {
                    my $layer_skirt_flow = $skirt_flow->clone;
                    $layer_skirt_flow->set_height($layer->height);
                    my $mm3_per_mm = $layer_skirt_flow->mm3_per_mm;
                    foreach my $path (@$loop) {
                        $path->height($layer->height);
                        $path->mm3_per_mm($mm3_per_mm);
                    }
                }
                
                $gcode .= $self->_gcodegen->extrude_loop($loop, 'skirt', $object->config->support_material_speed);
            }
        }
        $self->_skirt_done->{$layer->print_z} = 1;
        $self->_gcodegen->avoid_crossing_perimeters->set_use_external_mp(0);
        
        # allow a straight travel move to the first object point if this is the first layer
        # (but don't in next layers)
        if ($layer->id == 0) {
            $self->_gcodegen->avoid_crossing_perimeters->set_disable_once(1);
        }
    }
    
    # extrude brim
    if (!$self->_brim_done) {
        $gcode .= $self->_gcodegen->set_extruder($self->print->regions->[0]->config->perimeter_extruder-1);
        $self->_gcodegen->set_origin(Slic3r::Pointf->new(0,0));
        $self->_gcodegen->avoid_crossing_perimeters->set_use_external_mp(1);
        $gcode .= $self->_gcodegen->extrude_loop($_, 'brim', $object->config->support_material_speed)
            for @{$self->print->brim};
        $self->_brim_done(1);
        $self->_gcodegen->avoid_crossing_perimeters->set_use_external_mp(0);
        
        # allow a straight travel move to the first object point
        $self->_gcodegen->avoid_crossing_perimeters->set_disable_once(1);
    }
    
    for my $copy (@$object_copies) {
        # when starting a new object, use the external motion planner for the first travel move
        $self->_gcodegen->avoid_crossing_perimeters->set_use_external_mp_once(1) if ($self->_last_obj_copy // '') ne "$copy";
        $self->_last_obj_copy("$copy");
        
        $self->_gcodegen->set_origin(Slic3r::Pointf->new(map unscale $copy->[$_], X,Y));
        
        # extrude support material before other things because it might use a lower Z
        # and also because we avoid travelling on other things when printing it
        if ($layer->isa('Slic3r::Layer::Support')) {
            if ($layer->support_interface_fills->count > 0) {
                $gcode .= $self->_gcodegen->set_extruder($object->config->support_material_interface_extruder-1);
                $gcode .= $self->_gcodegen->extrude_path($_, 'support material interface', $object->config->get_abs_value('support_material_interface_speed')) 
                    for @{$layer->support_interface_fills->chained_path_from($self->_gcodegen->last_pos, 0)}; 
            }
            if ($layer->support_fills->count > 0) {
                $gcode .= $self->_gcodegen->set_extruder($object->config->support_material_extruder-1);
                $gcode .= $self->_gcodegen->extrude_path($_, 'support material', $object->config->get_abs_value('support_material_speed')) 
                    for @{$layer->support_fills->chained_path_from($self->_gcodegen->last_pos, 0)};
            }
        }
        
        # We now define a strategy for building perimeters and fills. The separation 
        # between regions doesn't matter in terms of printing order, as we follow 
        # another logic instead:
        # - we group all extrusions by extruder so that we minimize toolchanges
        # - we start from the last used extruder
        # - for each extruder, we group extrusions by island
        # - for each island, we extrude perimeters first, unless user set the infill_first
        #   option
        # (Still, we have to keep track of regions because we need to apply their config)
        
        # group extrusions by extruder and then by island
        my %by_extruder = ();  # extruder_id => [ { perimeters => \@perimeters, infill => \@infill } ]

        my $n_slices = $#{$layer->slices};
        my @layer_surface_bboxes = ();
        for my $i (0 .. $n_slices) {
            push @layer_surface_bboxes, $layer->slices->[$i]->contour->bounding_box;
        }
        my $point_inside_surface = sub { 
            my ($i, $point) = @_;
            my $bbox = $layer_surface_bboxes[$i];
            return 
                $point->x >= $bbox->x_min && $point->x < $bbox->x_max &&
                $point->y >= $bbox->y_min && $point->y < $bbox->y_max &&
                $layer->slices->[$i]->contour->contains_point($point);
        };

        foreach my $region_id (0..($self->print->region_count-1)) {
            my $layerm = $layer->regions->[$region_id] or next;
            my $region = $self->print->get_region($region_id);
            
            # process perimeters
            {
                my $extruder_id = $region->config->perimeter_extruder-1;
                foreach my $perimeter_coll (@{$layerm->perimeters}) {
                    next if $perimeter_coll->empty;  # this shouldn't happen but first_point() would fail
                    
                    # init by_extruder item only if we actually use the extruder
                    $by_extruder{$extruder_id} //= [];
                    
                    # $perimeter_coll is an ExtrusionPath::Collection object representing a single slice
                    for my $i (0 .. $n_slices) {
                        if (
                            # $perimeter_coll->first_point does not fit inside any slice
                            $i == $n_slices 
                            # $perimeter_coll->first_point fits inside ith slice
                            || $point_inside_surface->($i, $perimeter_coll->first_point)) {
                            $by_extruder{$extruder_id}[$i] //= { perimeters => {} };
                            $by_extruder{$extruder_id}[$i]{perimeters}{$region_id} //= [];
                            push @{ $by_extruder{$extruder_id}[$i]{perimeters}{$region_id} }, @$perimeter_coll;
                            last;
                        }
                    }
                }
            }
            
            # process infill
            # $layerm->fills is a collection of Slic3r::ExtrusionPath::Collection objects (C++ class ExtrusionEntityCollection), 
            # each one containing the ExtrusionPath objects of a certain infill "group" (also called "surface"
            # throughout the code). We can redefine the order of such Collections but we have to 
            # do each one completely at once.
            foreach my $fill (@{$layerm->fills}) {
                next if $fill->empty;  # this shouldn't happen but first_point() would fail
                
                # init by_extruder item only if we actually use the extruder
                my $extruder_id = $fill->[0]->is_solid_infill
                    ? $region->config->solid_infill_extruder-1
                    : $region->config->infill_extruder-1;
                
                $by_extruder{$extruder_id} //= [];
                
                # $fill is an ExtrusionPath::Collection object
                for my $i (0 .. $n_slices) {
                    if ($i == $n_slices
                        || $point_inside_surface->($i, $fill->first_point)) {
                        $by_extruder{$extruder_id}[$i] //= { infill => {} };
                        $by_extruder{$extruder_id}[$i]{infill}{$region_id} //= [];
                        push @{ $by_extruder{$extruder_id}[$i]{infill}{$region_id} }, $fill;
                        last;
                    }
                }
            }
        } # for regions
        
        # tweak extruder ordering to save toolchanges
        my @extruders = sort keys %by_extruder;
        if (@extruders > 1) {
            my $last_extruder_id = $self->_gcodegen->writer->extruder->id;
            if (exists $by_extruder{$last_extruder_id}) {
                @extruders = (
                    $last_extruder_id,
                    grep $_ != $last_extruder_id, @extruders,
                );
            }
        }
        
        foreach my $extruder_id (@extruders) {
            $gcode .= $self->_gcodegen->set_extruder($extruder_id);
            foreach my $island (@{ $by_extruder{$extruder_id} }) {
                if ($self->print->config->infill_first) {
                    $gcode .= $self->_extrude_infill($island->{infill} // {});
                    $gcode .= $self->_extrude_perimeters($island->{perimeters} // {});
                } else {
                    $gcode .= $self->_extrude_perimeters($island->{perimeters} // {});
                    $gcode .= $self->_extrude_infill($island->{infill} // {});
                }
            }
        }
    } # for object copies
    
    # apply spiral vase post-processing if this layer contains suitable geometry
    # (we must feed all the G-code into the post-processor, including the first 
    # bottom non-spiral layers otherwise it will mess with positions)
    # we apply spiral vase at this stage because it requires a full layer
    $gcode = $self->_spiral_vase->process_layer($gcode)
        if defined $self->_spiral_vase;
    
    # apply cooling logic; this may alter speeds
    $gcode = $self->_cooling_buffer->append(
        $gcode,
        $layer->object->ptr . ref($layer),  # differentiate $obj_id between normal layers and support layers
        $layer->id,
        $layer->print_z,
    ) if defined $self->_cooling_buffer;
    
    $gcode = $self->filter($gcode);
    print {$self->fh} $gcode if defined($gcode);
}

# Extrude perimeters: Decide where to put seams (hide or align seams).
sub _extrude_perimeters {
    my ($self, $entities_by_region) = @_;
    
    my $gcode = "";
    foreach my $region_id (sort keys %$entities_by_region) {
        $self->_gcodegen->config->apply_static($self->print->get_region($region_id)->config);
        $gcode .= $self->_gcodegen->extrude($_, 'perimeter', -1)
            for @{ $entities_by_region->{$region_id} };
    }
    return $gcode;
}

# Chain the paths hierarchically by a greedy algorithm to minimize a travel distance.
sub _extrude_infill {
    my ($self, $entities_by_region) = @_;
    
    my $gcode = "";
    foreach my $region_id (sort keys %$entities_by_region) {
        $self->_gcodegen->config->apply_static($self->print->get_region($region_id)->config);
        
        my $collection = Slic3r::ExtrusionPath::Collection->new(@{ $entities_by_region->{$region_id} });
        for my $fill (@{$collection->chained_path_from($self->_gcodegen->last_pos, 0)}) {
            if ($fill->isa('Slic3r::ExtrusionPath::Collection')) {
                $gcode .= $self->_gcodegen->extrude($_, 'infill', -1) 
                    for @{$fill->chained_path_from($self->_gcodegen->last_pos, 0)};
            } else {
                $gcode .= $self->_gcodegen->extrude($fill, 'infill', -1) ;
            }
        }
    }
    return $gcode;
}

sub flush_filters {
    my ($self) = @_;
    
    print {$self->fh} $self->filter($self->_cooling_buffer->flush, 1);
}

sub filter {
    my ($self, $gcode, $flush) = @_;
    $flush //= 0;
    
    # apply pressure regulation if enabled;
    # this depends on actual speeds
    $gcode = $self->_pressure_regulator->process($gcode, $flush)
        if defined $self->_pressure_regulator;

    # apply pressure equalization if enabled;
#    print "G-code before filter:\n", $gcode;
    $gcode = $self->_pressure_equalizer->process($gcode, $flush)
        if defined $self->_pressure_equalizer;
#    print "G-code after filter:\n", $gcode;

    # apply arc fitting if enabled;
    # this does not depend on speeds but changes G1 XY commands into G2/G2 IJ
    $gcode = $self->_arc_fitting->process($gcode)
        if defined $self->_arc_fitting;
    
    return $gcode;
}

1;