trait SectionListTrait

trait SectionListTrait {
    
    /**
     * Stores the information for all sections.
     *
     * Implementations of this method are expected to call array_values() to rekey
     * the list of sections.
     *
     * @param \Drupal\layout_builder\Section[] $sections
     *   An array of section objects.
     *
     * @return $this
     */
    protected abstract function setSections(array $sections);
    
    /**
     * {@inheritdoc}
     */
    public function count() : int {
        if ($this->hasBlankSection()) {
            return 0;
        }
        return count($this->getSections());
    }
    
    /**
     * {@inheritdoc}
     */
    public function getSection($delta) {
        if (!$this->hasSection($delta)) {
            throw new \OutOfBoundsException(sprintf('Invalid delta "%s"', $delta));
        }
        return $this->getSections()[$delta];
    }
    
    /**
     * Sets the section for the given delta on the display.
     *
     * @param int $delta
     *   The delta of the section.
     * @param \Drupal\layout_builder\Section $section
     *   The layout section.
     *
     * @return $this
     */
    protected function setSection($delta, Section $section) {
        $sections = $this->getSections();
        $sections[$delta] = $section;
        $this->setSections($sections);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function appendSection(Section $section) {
        $delta = $this->count();
        $this->setSection($delta, $section);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function insertSection($delta, Section $section) {
        // Clear the section list if there is currently a blank section.
        if ($this->hasBlankSection()) {
            $this->removeAllSections();
        }
        if ($this->hasSection($delta)) {
            // @todo Use https://www.drupal.org/node/66183 once resolved.
            $start = array_slice($this->getSections(), 0, $delta);
            $end = array_slice($this->getSections(), $delta);
            $this->setSections(array_merge($start, [
                $section,
            ], $end));
        }
        else {
            $this->appendSection($section);
        }
        return $this;
    }
    
    /**
     * Adds a blank section to the list.
     *
     * @return $this
     *
     * @see \Drupal\layout_builder\Plugin\Layout\BlankLayout
     */
    protected function addBlankSection() {
        if ($this->hasSection(0)) {
            throw new \Exception('A blank section must only be added to an empty list');
        }
        $this->appendSection(new Section('layout_builder_blank'));
        return $this;
    }
    
    /**
     * Indicates if this section list contains a blank section.
     *
     * A blank section is used to differentiate the difference between a layout
     * that has never been instantiated and one that has purposefully had all
     * sections removed.
     *
     * @return bool
     *   TRUE if the section list contains a blank section, FALSE otherwise.
     *
     * @see \Drupal\layout_builder\Plugin\Layout\BlankLayout
     */
    protected function hasBlankSection() {
        // A blank section will only ever exist when the delta is 0, as added by
        // ::removeSection().
        return $this->hasSection(0) && $this->getSection(0)
            ->getLayoutId() === 'layout_builder_blank';
    }
    
    /**
     * {@inheritdoc}
     */
    public function removeSection($delta) {
        // Clear the section list if there is currently a blank section.
        if ($this->hasBlankSection()) {
            $this->removeAllSections();
        }
        $sections = $this->getSections();
        unset($sections[$delta]);
        $this->setSections($sections);
        // Add a blank section when the last section is removed.
        if (empty($sections)) {
            $this->addBlankSection();
        }
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function removeAllSections($set_blank = FALSE) {
        $this->setSections([]);
        if ($set_blank) {
            $this->addBlankSection();
        }
        return $this;
    }
    
    /**
     * Indicates if there is a section at the specified delta.
     *
     * @param int $delta
     *   The delta of the section.
     *
     * @return bool
     *   TRUE if there is a section for this delta, FALSE otherwise.
     */
    protected function hasSection($delta) {
        return isset($this->getSections()[$delta]);
    }
    
    /**
     * Magic method: Implements a deep clone.
     */
    public function __clone() {
        $sections = $this->getSections();
        foreach ($sections as $delta => $item) {
            $sections[$delta] = clone $item;
        }
        $this->setSections($sections);
    }

}