class SvgIconBuilder

class SvgIconBuilder implements IconBuilderInterface {
    
    /**
     * The machine name of the layout.
     *
     * @var string
     */
    protected $id;
    
    /**
     * The label of the layout.
     *
     * @var string
     */
    protected $label;
    
    /**
     * The width of the SVG.
     *
     * @var int
     */
    protected $width = 125;
    
    /**
     * The height of the SVG.
     *
     * @var int
     */
    protected $height = 150;
    
    /**
     * The padding between regions.
     *
     * @var int
     */
    protected $padding = 4;
    
    /**
     * The width of region borders.
     *
     * @var int|null
     */
    protected $strokeWidth = 1;
    
    /**
     * {@inheritdoc}
     */
    public function build(array $icon_map) {
        $regions = $this->calculateSvgValues($icon_map, $this->width, $this->height, $this->strokeWidth, $this->padding);
        return $this->buildRenderArray($regions, $this->width, $this->height, $this->strokeWidth);
    }
    
    /**
     * Builds a render array representation of an SVG.
     *
     * @param mixed[] $regions
     *   An array keyed by region name, with each element containing the 'height',
     *   'width', and 'x' and 'y' offsets of each region.
     * @param int $width
     *   The width of the SVG.
     * @param int $height
     *   The height of the SVG.
     * @param int|null $stroke_width
     *   The width of region borders.
     *
     * @return array
     *   A render array representing a SVG icon.
     */
    protected function buildRenderArray(array $regions, $width, $height, $stroke_width) {
        $build = [
            '#type' => 'html_tag',
            '#tag' => 'svg',
            '#attributes' => [
                'width' => $width,
                'height' => $height,
                'class' => [
                    'layout-icon',
                ],
            ],
        ];
        if ($this->id) {
            $build['#attributes']['class'][] = Html::getClass('layout-icon--' . $this->id);
        }
        if ($this->label) {
            $build['title'] = [
                '#type' => 'html_tag',
                '#tag' => 'title',
                '#value' => $this->label,
            ];
        }
        // Append each polygon to the SVG.
        foreach ($regions as $region => $attributes) {
            // Wrapping with a <g> element allows for metadata to exist alongside the
            // rectangle.
            $build['region'][$region] = [
                '#type' => 'html_tag',
                '#tag' => 'g',
            ];
            $build['region'][$region]['title'] = [
                '#type' => 'html_tag',
                '#tag' => 'title',
                '#value' => $region,
            ];
            // Assemble the rectangle SVG element.
            $build['region'][$region]['rect'] = [
                '#type' => 'html_tag',
                '#tag' => 'rect',
                '#attributes' => [
                    'x' => $attributes['x'],
                    'y' => $attributes['y'],
                    'width' => $attributes['width'],
                    'height' => $attributes['height'],
                    'stroke-width' => $stroke_width,
                    'class' => [
                        'layout-icon__region',
                        Html::getClass('layout-icon__region--' . $region),
                    ],
                ],
            ];
        }
        return $build;
    }
    
    /**
     * Calculates the dimensions and offsets of all regions.
     *
     * @param string[][] $rows
     *   A two-dimensional array representing the visual output of the layout. See
     *   the documentation for the $icon_map parameter of
     *   \Drupal\Core\Layout\Icon\IconBuilderInterface::build().
     * @param int $width
     *   The width of the SVG.
     * @param int $height
     *   The height of the SVG.
     * @param int $stroke_width
     *   The width of region borders.
     * @param int $padding
     *   The padding between regions.
     *
     * @return mixed[][]
     *   An array keyed by region name, with each element containing the 'height',
     *   'width', and 'x' and 'y' offsets of each region.
     */
    protected function calculateSvgValues(array $rows, $width, $height, $stroke_width, $padding) {
        $region_rects = [];
        $row_height = $this->getLength(count($rows), $height, $stroke_width, $padding);
        foreach ($rows as $row => $cols) {
            $column_width = $this->getLength(count($cols), $width, $stroke_width, $padding);
            $vertical_offset = $this->getOffset($row, $row_height, $stroke_width, $padding);
            foreach ($cols as $col => $region) {
                $horizontal_offset = $this->getOffset($col, $column_width, $stroke_width, $padding);
                // Check if this region is new, or already exists in the rectangle.
                if (!isset($region_rects[$region])) {
                    $region_rects[$region] = [
                        'x' => $horizontal_offset,
                        'y' => $vertical_offset,
                        'width' => $column_width,
                        'height' => $row_height,
                    ];
                }
                else {
                    // In order to include the area of the previous region and any padding
                    // or border, subtract the calculated offset from the original offset.
                    $region_rects[$region]['width'] = $column_width + ($horizontal_offset - $region_rects[$region]['x']);
                    $region_rects[$region]['height'] = $row_height + ($vertical_offset - $region_rects[$region]['y']);
                }
            }
        }
        return $region_rects;
    }
    
    /**
     * Gets the offset for this region.
     *
     * @param int $delta
     *   The zero-based delta of the region.
     * @param int $length
     *   The height or width of the region.
     * @param int $stroke_width
     *   The width of the region borders.
     * @param int $padding
     *   The padding between regions.
     *
     * @return int
     *   The offset for this region.
     */
    protected function getOffset($delta, $length, $stroke_width, $padding) {
        // Half of the stroke width is drawn outside the dimensions.
        $stroke_width /= 2;
        // For every region in front of this add two strokes, as well as one
        // directly in front.
        $num_of_strokes = 2 * $delta + 1;
        return $num_of_strokes * $stroke_width + $delta * ($length + $padding);
    }
    
    /**
     * Gets the height or width of a region.
     *
     * @param int $number_of_regions
     *   The total number of regions.
     * @param int $length
     *   The total height or width of the icon.
     * @param int $stroke_width
     *   The width of the region borders.
     * @param int $padding
     *   The padding between regions.
     *
     * @return float|int
     *   The height or width of a region.
     */
    protected function getLength($number_of_regions, $length, $stroke_width, $padding) {
        if ($number_of_regions === 0) {
            return 0;
        }
        // Half of the stroke width is drawn outside the dimensions.
        $total_stroke = $number_of_regions * $stroke_width;
        // Padding does not precede the first region.
        $total_padding = ($number_of_regions - 1) * $padding;
        // Divide the remaining length by the number of regions.
        return ($length - $total_padding - $total_stroke) / $number_of_regions;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setId($id) {
        $this->id = $id;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setLabel($label) {
        $this->label = $label;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setWidth($width) {
        $this->width = $width;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setHeight($height) {
        $this->height = $height;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setPadding($padding) {
        $this->padding = $padding;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setStrokeWidth($stroke_width) {
        $this->strokeWidth = $stroke_width;
        return $this;
    }

}