Drupal 8.x Search API processor plugin for boosting search items by term reference field

TermReferenceBoost.php

<?php

// This plugin allows the administrator to boost items in an index based on a taxonomy term. 
// 
// Drop into an existing plugin module or create a new one, ex. create an info.yml file as 
//   modules/custom/search_api_boost_term_reference/search_api_boost_term_reference.info.yml
// 
// name: 'Search API Boost by Term Reference'
// description: 'Define custom boost priority in Search API index by term reference field'
// core: 8.x
// package: Search
// type: module
// dependencies:
//  - search_api:search_api
// version: '8.x-1.0'
// core: '8.x'
// project: 'search_api_boost_term_reference'
//
// and then save in your module folder as:
//
// modules/custom/search_api_boost_term_reference/src/Plugin/search_api/processor/TermReferenceBoost.php
//
// Enable the module and configure 

namespace Drupal\search_api_boost_term_reference\Plugin\search_api\processor;

use Drupal\comment\CommentInterface;
use Drupal\Component\Utility\Html;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Plugin\PluginFormInterface;
use Drupal\Core\TypedData\ComplexDataInterface;
use Drupal\node\NodeInterface;
use Drupal\search_api\Plugin\PluginFormTrait;
use Drupal\search_api\Processor\ProcessorPluginBase;

/**
 * Adds a boost to indexed items based on a taxonomy term
 *
 * @SearchApiProcessor(
 *   id = "search_api_boost_term_reference",
 *   label = @Translation("Add boost processor based on term reference field"),
 *   description = @Translation("Adds search_api processor to allow weighted boosting for a term reference field."),
 *   stages = {
 *     "preprocess_index" = 0,
 *   }
 * )
 */
class TermReferenceBoost extends ProcessorPluginBase implements PluginFormInterface {

  use PluginFormTrait;

  /**
   * The available boost factors.
   *
   * @var string[]
   */
  protected static $boostFactors = [
    '0.0' => '0.0',
    '0.1' => '0.1',
    '0.2' => '0.2',
    '0.3' => '0.3',
    '0.5' => '0.5',
    '0.8' => '0.8',
    '1.0' => '1.0',
    '2.0' => '2.0',
    '3.0' => '3.0',
    '5.0' => '5.0',
    '8.0' => '8.0',
    '13.0' => '13.0',
    '21.0' => '21.0',
  ];

  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
      'boost_table' => [
        'weight' => '0.0',
      ],
    ];
  }

  /**
   * {@inheritdoc}
   */
  public function buildConfigurationForm(array $form, FormStateInterface $formState) {
    $form['boost_table'] = [
      '#type' => 'table',
      '#header' => [
        $this->t('## FIELD LABEL ##'),
        $this->t('Boost'),
      ],
    ];

    // add the name of the vocabulary I am trying to load
    $vid = '## VOCABULARY MACHINE NAME ##';
    $terms =\Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadTree($vid);

    foreach ($terms as $term) {
      
      // load values from existing configuration if they exist
      if (isset($this->configuration['boost_table'][$term->tid]['weight'])) {
        $weight = $this->configuration['boost_table'][$term->tid]['weight'];
      } else { 
        $key =array_rand(static::$boostFactors);
        //$weight = static::$boostFactors[$key];
        $weight = 0;
      }
      $term_data[] = array(
        'tid' => $term->tid,
        'name' => $term->name,
        'weight' => $weight
      );
    }

    // Sort weights, with heaviest items dropping down in the list.
    uasort($term_data, ['Drupal\Component\Utility\SortArray', 'sortByWeightElement']);
    
    // Create our configuration table
    foreach ($term_data as $term) {
      $form['boost_table'][$term["tid"]]['label']['#plain_text'] = $term["name"];

      // Weight column element.
      $form['boost_table'][$term["tid"]]['weight'] = [
        '#type' => 'select',
        '#title' => t('Weight for @title', ['@title' => $term["name"]]),
        '#title_display' => 'invisible',
        '#default_value' => $term["weight"],
        '#options' => static::$boostFactors,
      ];
    }

    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
    $values = $form_state->getValues();
    // add the name of the vocabulary I am trying to load
    $vid = '## VOCABULARY MACHINE NAME ##';
    $terms =\Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadTree($vid);

    foreach ($terms as $term) {
      if (!empty($values['boost_table'][$term->tid]['weight'])) {
        $weight = $values['boost_table'][$term->tid]['weight'];
        if ($weight === '') {
          unset($values['boost_table'][$term->tid]);
        }
      }
    }
    $form_state->setValues($values);
    $this->setConfiguration($values);
  }

  /**
   * {@inheritdoc}
   */
  public function preprocessIndexItems(array $items) {
    foreach ($items as $item) {
      $entityTypeId = $item->getDatasource()->getEntityTypeId();

      switch ($entityTypeId) {
        case 'node':
          // Get the node object.
          $node = $this->getNode($item->getOriginalObject());
          $boost = $this->getBoostFromNode($node);
          break;

        // pass on all other entity types
        default:
          $boost = 0;
          break;
      }

      $item->setBoost($boost);
    }
  }

  /**
   * Retrieves the node related to an indexed search object.
   *
   * Will be either the node itself, or the node the comment is attached to.
   *
   * @param \Drupal\Core\TypedData\ComplexDataInterface $item
   *   A search object that is being indexed.
   *
   * @return \Drupal\node\NodeInterface|null
   *   The node related to that search object.
   */
  protected function getNode(ComplexDataInterface $item) {
    $item = $item->getValue();
    if ($item instanceof CommentInterface) {
      $item = $item->getCommentedEntity();
    }
    if ($item instanceof NodeInterface) {
      return $item;
    }

    return NULL;
  }

  /**
   * Retrieves the boost related to a node.
   *
   * @return float
   *   Boost Value.
   */
  protected function getBoostFromNode($node) {

    $node_type = $node->getType();
    switch($node_type) {
      case "professional":
        $tid = $node->get('## NODE TERM REFERENCE FIELD')->target_id;
        $boost = $this->configuration['boost_table'][$tid]['weight'];
      break;

      default:
        $boost = 1.0;
    }
    return $boost;
  }

}