OverrideInterface.php

<?php
namespace Drupal\sps;
interface OverrideInterface {
  /**
   * construct an array of override arrays
   *
   * @return an array of override arrays
   */
  public function getOverrides();
}

PreviewForm.php

<?php
namespace Drupal\sps

/**
 * a helper class for the PreviewForm
 * this wrap up the methods around each condition
 */
class Condition {
  protected $widget;
  protected $override;
  protected $title;
  public function __constuct($config) {
    $override = $config['override'];
    $widget = $config['widget'];

    $this->widget = $config['widget'];
    $this->override = $config['override'];
    $this->title = $config['title'];
  }
  public getWidget() {
    $this->getPlugin("widget", $this->widget);
  }
  public getOverride() {
    $this->getPlugin("override", $this->override);
  }
  protected Plugin($type, $name) {
    return "cool stuff"
  }
}

/**
 * PreviewForm is used for constructing and processing the form used to set the site state
 */
class PreviewForm {
  protected $conditions;
  protected $override;
  /**
   * Set the configuration for the PreviewForm
   *
   * @param $config
   *   an array of the following form
   *   array (
   *     'conditions' => array(
   *       'collection' => array(
   *         'title' => 'Collection',
   *         'widget' => 'collection_select', (widget plugin)
   *         'override' => 'view_collection_override', (override plugin)
   *       ),
   *       'date' => array(
   *         'title' => 'Live Date',
   *         'widget' => 'live_date', (widget plugin)
   *         'override' => 'view_live_date_override', (override plugin)
   *      ),
   *    ),
   *   );
   */
   public function setConfig($config) { 
     $this->conditions = array_map(function($data) { return new Condition($data);}, $config['conditions']);

   /**
   * Construct the Form using the conditions
   *
   * @param $form
   *   the form structure array passed in by drupal_get_form().
   * @param $form_state 
   *   the array of state data for the form.
   *
   * @return 
   *   a FAPI render array
   */
  function getPreviewForm($form, $form_state) {
    return $form;
  }

  /**
   * Validates the preview form.
   * 
   * @param $form
   *   The FAPI form to validate 
   * @param $form_state
   *   The state for the form
   *
   * @return
   *   self
   */
  function validatePreviewForm($form, $form_state) {
    return $this;
  }

  /**
   * Extracts the values for the conditions from the FormAPI array.
   *  
   * @param $form
   *   The FAPI form to validate 
   * @param $form_state
   *   The state for the form
   * @return
   *   self
   */
  function sumbitPreviewForm($form, $form_state) {
    return $this;
  }

  /**
   * retrieve the Conditions override object
   *
   * @return a \Drupal\sps\Override object
   */
  function getOverride() {
    return $this->override;
  }
}

PreviewFormInterface.php

<?php
namespace Drupal\sps

interface PreviewFormInterface {

   /**
   * Set the configuration for the PreviewForm
   *
   * @param $config
   *   an array of the following form
   *   array (
   *     'conditions' => array(
   *       'collection' => array(
   *         'title' => 'Collection',
   *         'widget' => 'collection_select', (widget plugin)
   *         'override' => 'view_collection_override', (override plugin)
   *       ),
   *       'date' => array(
   *         'title' => 'Live Date',
   *         'widget' => 'live_date', (widget plugin)
   *         'override' => 'view_live_date_override', (override plugin)
   *      ),
   *    ),
   *   );
   */
   public function setConfig($config);

  /**
   * Get the FormAPI preview form for the condition.
   *
   * @param $form
   *   the form structure array passed in by drupal_get_form().
   * @param $form_state 
   *   the array of state data for the form.
   *
   * @return 
   *   a FAPI render array
   */
  function getPreviewForm($form, $form_state);

  /**
   * retrieve the Conditions override object
   *
   * @return a \Drupal\sps\Override object
   */
  public function getOverride();

  /**
   * Validates the preview form.
   * 
   * @param $form
   *   The FAPI form to validate 
   * @param $form_state
   *   The state for the form
   *
   * @return
   *   self
   */
  public function validatePreviewForm($form, $form_state);

  /**
   * Extracts the values for the conditions from the FormAPI array.
   *  
   * @param $form
   *   The FAPI form to validate 
   * @param $form_state
   *   The state for the form
   * @return
   *   self
   */
  public function sumbitPreviewForm($form, $form_state);
}

SiteState.php

<?php
interface StorageController {}

  public function save($table);
  public function getRevisionID($id);
  public function getMap();
}

class SiteState {
  protected $cacheController;
  protected $conditions = array();
  /**
   *
   */
  public function __constuct($cacheController) {
    $this->$cacheController = $cacheController
  }
  /**
   * SiteState::addCondition
   *
   */
  public addCondition($condition) {
    if( $condition instanceof ConditionInterface) {
      $this->$conditions[] = $condition;
    }
    else {
      throw ....
    }
  }
  /*
   * SiteState:getOverrides
   *
   * RETURN array of assoc arrays
   */
  public function getOverrides() {
    if(!$this->cacheController->hasCache()) {
      $this->buildOverrides();
    }
    return $this->cacheController->getMap();
  }
  /*
   * SiteState:buildOverrides()
   *
   * Construct and Cache Overrides for the current state;
   */
  protected function buildOverrides() {
    $ss_of_overrides = array();
    foreach($this->conditions as $condition) {
      $set_of_overrides[] = $condition->setter()->getOverrides();
    }
    $overrides = $this->combineOverrides($set_of_overrides);
    $this->save($overrides);
  }
  /**
   * SiteState::combineOverrides
   *
   * PARAM set_of_overrides: an array of override arrays
   * RETURN : an override array
   */
  protected function combineOverrides($setOfOverrides) {
    var $final_overrides = array();
    foreach(array_reverse($setOfOverrides) as $overrides) {
      foreach($overrides as $override) {
        var $key = "{$override->type}.{$override->id}";
        $final_overrides[$key] = $overrides;
      }
    }
    return array_values($final_overrides);
  }
}

WidgetInterface.php

<?php
namespace Drupal\sps\Condition;

interface WidgetInterface {

  /**
   * Get the FormAPI preview form for the condition.
   *
   * @param $form
   *   the form structure array passed in by drupal_get_form().
   * @param $form_state 
   *   the array of state data for the form.
   *
   * @return 
   *   a FAPI render array
   */
  function getPreviewForm($form, $form_state, $element);

  /**
   * Validates the preview form.
   * 
   * @param $form
   *   The FAPI form to validate 
   * @param $form_state
   *   The state for the form
   *
   * @return
   *   self
   */
  function validatePreviewForm($form, $form_state, $element);

  /**
   * Extracts the values for the conditions from the FormAPI array.
   *  
   * @param $values
   *   The values key from the $form_state of a submitted condition form
   *
   * @return
   *   An associative array of values
   */
  function extractValues($values, $form, $form_state);
}