--- /dev/null
+<?php
+
+namespace Drupal\layout_builder;
+
+/**
+ * Provides a domain object for layout sections.
+ *
+ * A section consists of three parts:
+ * - The layout plugin ID for the layout applied to the section (for example,
+ * 'layout_onecol').
+ * - An array of settings for the layout plugin.
+ * - An array of components that can be rendered in the section.
+ *
+ * @internal
+ * Layout Builder is currently experimental and should only be leveraged by
+ * experimental modules and development releases of contributed modules.
+ * See https://www.drupal.org/core/experimental for more information.
+ *
+ * @see \Drupal\Core\Layout\LayoutDefinition
+ * @see \Drupal\layout_builder\SectionComponent
+ *
+ * @todo Determine whether an interface will be provided for this in
+ * https://www.drupal.org/project/drupal/issues/2930334.
+ */
+class Section {
+
+ /**
+ * 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 = [];
+
+ /**
+ * 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[] $components
+ * (optional) The components.
+ */
+ public function __construct($layout_id, array $layout_settings = [], array $components = []) {
+ $this->layoutId = $layout_id;
+ $this->layoutSettings = $layout_settings;
+ foreach ($components as $component) {
+ $this->setComponent($component);
+ }
+ }
+
+ /**
+ * 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;
+ }
+ }
+
+ return $this->getLayout()->build($regions);
+ }
+
+ /**
+ * Gets the layout plugin for this section.
+ *
+ * @return \Drupal\Core\Layout\LayoutInterface
+ * The layout plugin.
+ */
+ public function getLayout() {
+ return $this->layoutPluginManager()->createInstance($this->getLayoutId(), $this->getLayoutSettings());
+ }
+
+ /**
+ * 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->layoutSettings;
+ }
+
+ /**
+ * 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[]
+ * The components.
+ */
+ 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 $region
+ * The region name.
+ *
+ * @return \Drupal\layout_builder\SectionComponent[]
+ * An array of components in the specified region, sorted by weight.
+ */
+ protected function getComponentsByRegion($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() ? 1 : -1;
+ });
+ 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.
+ *
+ * @internal
+ * This is intended for use by a storage mechanism 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()),
+ ];
+ }
+
+}