class Section

class Section implements ThirdPartySettingsInterface {
    
    /**
     * The layout plugin ID.
     *
     * @var string
     */
    protected $layoutId;
    
    /**
     * The layout plugin settings.
     *
     * @var array
     */
    protected $layoutSettings = [];
    
    /**
     * An array of components, keyed by UUID.
     *
     * @var \Drupal\layout_builder\SectionComponent[]
     */
    protected $components = [];
    
    /**
     * Third party settings.
     *
     * An array of key/value pairs keyed by provider.
     *
     * @var array[]
     */
    protected $thirdPartySettings = [];
    
    /**
     * Constructs a new Section.
     *
     * @param string $layout_id
     *   The layout plugin ID.
     * @param array $layout_settings
     *   (optional) The layout plugin settings.
     * @param \Drupal\layout_builder\SectionComponent[] $components
     *   (optional) The components.
     * @param array[] $third_party_settings
     *   (optional) Any third party settings.
     */
    public function __construct($layout_id, array $layout_settings = [], array $components = [], array $third_party_settings = []) {
        $this->layoutId = $layout_id;
        $this->layoutSettings = $layout_settings;
        foreach ($components as $component) {
            $this->setComponent($component);
        }
        $this->thirdPartySettings = $third_party_settings;
    }
    
    /**
     * Returns the renderable array for this section.
     *
     * @param \Drupal\Core\Plugin\Context\ContextInterface[] $contexts
     *   An array of available contexts.
     * @param bool $in_preview
     *   TRUE if the section is being previewed, FALSE otherwise.
     *
     * @return array
     *   A renderable array representing the content of the section.
     */
    public function toRenderArray(array $contexts = [], $in_preview = FALSE) {
        $regions = [];
        foreach ($this->getComponents() as $component) {
            if ($output = $component->toRenderArray($contexts, $in_preview)) {
                $regions[$component->getRegion()][$component->getUuid()] = $output;
            }
        }
        $layout = $this->getLayout($contexts);
        if ($layout instanceof PreviewAwarePluginInterface) {
            $layout->setInPreview($in_preview);
        }
        $build = $layout->build($regions);
        // If an entity was used to build the layout, store it on the build.
        if (!Element::isEmpty($build) && isset($contexts['layout_builder.entity'])) {
            $build['#entity'] = $contexts['layout_builder.entity']->getContextValue();
        }
        return $build;
    }
    
    /**
     * Gets the layout plugin for this section.
     *
     * @param \Drupal\Core\Plugin\Context\ContextInterface[] $contexts
     *   An array of available contexts.
     *
     * @return \Drupal\Core\Layout\LayoutInterface
     *   The layout plugin.
     */
    public function getLayout(array $contexts = []) {
        $layout = $this->layoutPluginManager()
            ->createInstance($this->getLayoutId(), $this->layoutSettings);
        if ($contexts) {
            $this->contextHandler()
                ->applyContextMapping($layout, $contexts);
        }
        return $layout;
    }
    
    /**
     * Gets the layout plugin ID for this section.
     *
     * @return string
     *   The layout plugin ID.
     *
     * @internal
     *   This method should only be used by code responsible for storing the data.
     */
    public function getLayoutId() {
        return $this->layoutId;
    }
    
    /**
     * Gets the layout plugin settings for this section.
     *
     * @return mixed[]
     *   The layout plugin settings.
     *
     * @internal
     *   This method should only be used by code responsible for storing the data.
     */
    public function getLayoutSettings() {
        return $this->getLayout()
            ->getConfiguration();
    }
    
    /**
     * Sets the layout plugin settings for this section.
     *
     * @param mixed[] $layout_settings
     *   The layout plugin settings.
     *
     * @return $this
     */
    public function setLayoutSettings(array $layout_settings) {
        $this->layoutSettings = $layout_settings;
        return $this;
    }
    
    /**
     * Gets the default region.
     *
     * @return string
     *   The machine-readable name of the default region.
     */
    public function getDefaultRegion() {
        return $this->layoutPluginManager()
            ->getDefinition($this->getLayoutId())
            ->getDefaultRegion();
    }
    
    /**
     * Returns the components of the section.
     *
     * @return \Drupal\layout_builder\SectionComponent[]
     *   An array of components, keyed by the component UUID.
     */
    public function getComponents() {
        return $this->components;
    }
    
    /**
     * Gets the component for a given UUID.
     *
     * @param string $uuid
     *   The UUID of the component to retrieve.
     *
     * @return \Drupal\layout_builder\SectionComponent
     *   The component.
     *
     * @throws \InvalidArgumentException
     *   Thrown when the expected UUID does not exist.
     */
    public function getComponent($uuid) {
        if (!isset($this->components[$uuid])) {
            throw new \InvalidArgumentException(sprintf('Invalid UUID "%s"', $uuid));
        }
        return $this->components[$uuid];
    }
    
    /**
     * Helper method to set a component.
     *
     * @param \Drupal\layout_builder\SectionComponent $component
     *   The component.
     *
     * @return $this
     */
    protected function setComponent(SectionComponent $component) {
        $this->components[$component->getUuid()] = $component;
        return $this;
    }
    
    /**
     * Removes a given component from a region.
     *
     * @param string $uuid
     *   The UUID of the component to remove.
     *
     * @return $this
     */
    public function removeComponent($uuid) {
        unset($this->components[$uuid]);
        return $this;
    }
    
    /**
     * Appends a component to the end of a region.
     *
     * @param \Drupal\layout_builder\SectionComponent $component
     *   The component being appended.
     *
     * @return $this
     */
    public function appendComponent(SectionComponent $component) {
        $component->setWeight($this->getNextHighestWeight($component->getRegion()));
        $this->setComponent($component);
        return $this;
    }
    
    /**
     * Returns the next highest weight of the component in a region.
     *
     * @param string $region
     *   The region name.
     *
     * @return int
     *   A number higher than the highest weight of the component in the region.
     */
    protected function getNextHighestWeight($region) {
        $components = $this->getComponentsByRegion($region);
        $weights = array_map(function (SectionComponent $component) {
            return $component->getWeight();
        }, $components);
        return $weights ? max($weights) + 1 : 0;
    }
    
    /**
     * Gets the components for a specific region.
     *
     * @param string $region
     *   The region name.
     *
     * @return \Drupal\layout_builder\SectionComponent[]
     *   An array of components in the specified region, sorted by weight.
     */
    public function getComponentsByRegion($region) {
        $components = array_filter($this->getComponents(), function (SectionComponent $component) use ($region) {
            return $component->getRegion() === $region;
        });
        uasort($components, function (SectionComponent $a, SectionComponent $b) {
            return $a->getWeight() <=> $b->getWeight();
        });
        return $components;
    }
    
    /**
     * Inserts a component after a specified existing component.
     *
     * @param string $preceding_uuid
     *   The UUID of the existing component to insert after.
     * @param \Drupal\layout_builder\SectionComponent $component
     *   The component being inserted.
     *
     * @return $this
     *
     * @throws \InvalidArgumentException
     *   Thrown when the expected UUID does not exist.
     */
    public function insertAfterComponent($preceding_uuid, SectionComponent $component) {
        // Find the delta of the specified UUID.
        $uuids = array_keys($this->getComponentsByRegion($component->getRegion()));
        $delta = array_search($preceding_uuid, $uuids, TRUE);
        if ($delta === FALSE) {
            throw new \InvalidArgumentException(sprintf('Invalid preceding UUID "%s"', $preceding_uuid));
        }
        return $this->insertComponent($delta + 1, $component);
    }
    
    /**
     * Inserts a component at a specified delta.
     *
     * @param int $delta
     *   The zero-based delta in which to insert the component.
     * @param \Drupal\layout_builder\SectionComponent $new_component
     *   The component being inserted.
     *
     * @return $this
     *
     * @throws \OutOfBoundsException
     *   Thrown when the specified delta is invalid.
     */
    public function insertComponent($delta, SectionComponent $new_component) {
        $components = $this->getComponentsByRegion($new_component->getRegion());
        $count = count($components);
        if ($delta > $count) {
            throw new \OutOfBoundsException(sprintf('Invalid delta "%s" for the "%s" component', $delta, $new_component->getUuid()));
        }
        // If the delta is the end of the list, append the component instead.
        if ($delta === $count) {
            return $this->appendComponent($new_component);
        }
        // Find the weight of the component that exists at the specified delta.
        $weight = array_values($components)[$delta]->getWeight();
        $this->setComponent($new_component->setWeight($weight++));
        // Increase the weight of every subsequent component.
        foreach (array_slice($components, $delta) as $component) {
            $component->setWeight($weight++);
        }
        return $this;
    }
    
    /**
     * Wraps the layout plugin manager.
     *
     * @return \Drupal\Core\Layout\LayoutPluginManagerInterface
     *   The layout plugin manager.
     */
    protected function layoutPluginManager() {
        return \Drupal::service('plugin.manager.core.layout');
    }
    
    /**
     * Returns an array representation of the section.
     *
     * Only use this method if you are implementing custom storage for sections.
     *
     * @return array
     *   An array representation of the section component.
     */
    public function toArray() {
        return [
            'layout_id' => $this->getLayoutId(),
            'layout_settings' => $this->getLayoutSettings(),
            'components' => array_map(function (SectionComponent $component) {
                return $component->toArray();
            }, $this->getComponents()),
            'third_party_settings' => $this->thirdPartySettings,
        ];
    }
    
    /**
     * Creates an object from an array representation of the section.
     *
     * Only use this method if you are implementing custom storage for sections.
     *
     * @param array $section
     *   An array of section data in the format returned by ::toArray().
     *
     * @return static
     *   The section object.
     */
    public static function fromArray(array $section) {
        // Ensure expected array keys are present.
        $section += [
            'layout_id' => '',
            'layout_settings' => [],
            'components' => [],
            'third_party_settings' => [],
        ];
        return new static($section['layout_id'], $section['layout_settings'], array_map([
            SectionComponent::class,
            'fromArray',
        ], $section['components']), $section['third_party_settings']);
    }
    
    /**
     * Magic method: Implements a deep clone.
     */
    public function __clone() {
        foreach ($this->components as $uuid => $component) {
            $this->components[$uuid] = clone $component;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getThirdPartySetting($provider, $key, $default = NULL) {
        return $this->thirdPartySettings[$provider][$key] ?? $default;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getThirdPartySettings($provider) {
        return $this->thirdPartySettings[$provider] ?? [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function setThirdPartySetting($provider, $key, $value) {
        $this->thirdPartySettings[$provider][$key] = $value;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function unsetThirdPartySetting($provider, $key) {
        unset($this->thirdPartySettings[$provider][$key]);
        // If the third party is no longer storing any information, completely
        // remove the array holding the settings for this provider.
        if (empty($this->thirdPartySettings[$provider])) {
            unset($this->thirdPartySettings[$provider]);
        }
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getThirdPartyProviders() {
        return array_keys($this->thirdPartySettings);
    }
    
    /**
     * Wraps the context handler.
     *
     * @return \Drupal\Core\Plugin\Context\ContextHandlerInterface
     *   The context handler.
     */
    protected function contextHandler() {
        return \Drupal::service('context.handler');
    }

}