Explore a WP entity export iterator

packages/playground/data-liberation/bootstrap.php

@@ -68,6 +68,7 @@
 require_once __DIR__ . '/src/import/WP_Retry_Frontloading_Iterator.php';
 require_once __DIR__ . '/src/entity-readers/WP_Entity_Reader.php';
 require_once __DIR__ . '/src/entity-readers/WP_HTML_Entity_Reader.php';
+require_once __DIR__ . '/src/export/WP_Entity_Export_Iterator.php';
 
 require_once __DIR__ . '/src/utf8_decoder.php';
 

packages/playground/data-liberation/src/export/WP_Entity_Export_Iterator.php

@@ -0,0 +1,241 @@
+<?php
+
+// @TODO: This is just a hack for easy manual testing. Remove it before merge.
+add_action('plugins_loaded', function() {
+	if (!str_starts_with($_SERVER['REQUEST_URI'], '/_test_export_entities')) {
+		return;
+	}
+
+	header('Content-Type: text/plain');
+	$export_iterator = new WP_Entity_Export_Iterator();
+	foreach ($export_iterator as $key => $entity) {
+		echo "Key: $key\n";
+		var_dump($entity);
+	}
+	die();
+});
+
+// @TODO: Move to dedicated file
+class WP_Export_Entity {
+	// @TODO: If we want to naively stream entities, perhaps sites should be able
+	//        run a process that cleans up cruft like orphaned term relationships.
+	//        Then that process could be run before attempting export.
+	// @TODO: Is there any reason we need to model specific concepts like
+	//       "category" rather than just exporting terms and taxonomy
+	//       relationships?
+	//       Intuition: Directly representing terms, taxonomies,
+	//       and relationships will be more flexible at this level.
+	const TYPE_TERM              = 'term';
+	// @TODO: Counts likely will need regenerated after import
+	const TYPE_TERM_TAXONOMY     = 'term_taxonomy';
+	const TYPE_USER              = 'user';
+	const TYPE_POST              = 'post';
+	const TYPE_POST_META         = 'post_meta';
+	const TYPE_TERM_RELATIONSHIP = 'term_relationship';
+	const TYPE_COMMENT           = 'comment';
+	const TYPE_COMMENT_META      = 'comment_meta';
+	const TYPE_OPTION            = 'option';
+
+	private $type;
+	private $data;
+
+	public function __construct($type, $data) {
+		$this->type = $type;
+		$this->data = $data;
+	}
+
+	public function get_type() {
+		return $this->type;
+	}
+
+	public function get_data() {
+		return $this->data;
+	}
+
+	public function set_data($data) {
+		$this->data = $data;
+	}
+}
+
+// TODO: Maybe this can work for all primary key types
+class WP_Entity_Iterator_For_Table_With_Incrementing_IDs implements Iterator {
+	protected $entity_type;
+	protected $table_name;
+	protected $primary_key;
+	protected $current_entity;
+	protected $current_id;
+
+	public function __construct($entity_type, $table_name, $primary_key) {
+		$this->entity_type = $entity_type;
+		$this->table_name = $table_name;
+		$this->primary_key = $primary_key;
+		$this->current_id = 0;
+		$this->current_entity = null;
+	}
+
+	#[\ReturnTypeWillChange]
+	public function rewind() {
+		$this->current_id = 0;
+		$this->next();
+	}
+
+	#[\ReturnTypeWillChange]
+	public function current() {
+		return $this->current_entity;
+	}
+
+	#[\ReturnTypeWillChange]
+	public function key() {
+		return $this->current_id;
+	}
+
+	#[\ReturnTypeWillChange]
+	public function next() {
+		global $wpdb;
+		$current_row = $wpdb->get_row(
+			$wpdb->prepare(
+				// @TODO: Consider selecting more than 1 row at a time for possibly-better performance.
+				"SELECT * FROM {$this->table_name} WHERE {$this->primary_key} > %d ORDER BY {$this->primary_key} ASC LIMIT 1",
+				$this->current_id
+			),
+			ARRAY_A
+		);
+		// @TODO: How to handle errors?
+
+		$this->current_entity = null;
+		if ($current_row) {
+			$this->current_id = $current_row[$this->primary_key];
+			$this->current_entity = new WP_Export_Entity($this->entity_type, $current_row);
+		}
+	}
+
+	#[\ReturnTypeWillChange]
+	public function valid() {
+		return $this->current_entity !== null;
+	}
+}
+
+// @TODO: Maybe this is the same as incrementing ID iterator, but maybe should should handle other kinds of tables as well.
+// class WP_Custom_Table_Entity_Iterator implements Iterator {
+// 	// @TODO: Implement
+// }
+
+class WP_Entity_Export_Iterator implements Iterator {
+	protected $entity_iterator_iterator = null;
+
+	#[\ReturnTypeWillChange]
+	public function rewind() {
+		$entity_export_strategies = $this->create_entity_export_strategies();
+		$this->entity_iterator_iterator = new ArrayIterator($entity_export_strategies);
+		$this->next();
+	}
+
+	#[\ReturnTypeWillChange]
+	public function current() {
+		return $this->entity_iterator_iterator->current()->current();
+	}
+
+	#[\ReturnTypeWillChange]
+	public function next() {
+		if (!$this->entity_iterator_iterator->valid()) {
+			return;
+		}
+
+		$this->entity_iterator_iterator->current()->next();
+		while (
+			! $this->entity_iterator_iterator->current()->valid() &&
+			$this->entity_iterator_iterator->valid()
+		) {
+			$this->entity_iterator_iterator->next();
+			$this->entity_iterator_iterator->current()->rewind();
+		}
+	}
+
+	#[\ReturnTypeWillChange]
+	public function key() {
+
+		if (!$this->entity_iterator_iterator->valid()) {
+			return null;
+		}
+
+		if (!$this->entity_iterator_iterator->current()->valid()) {
+			return null;
+		}
+
+		$entity_iterator_iterator_key = $this->entity_iterator_iterator->key();
+		$entity_iterator_key = $this->entity_iterator_iterator->current()->key();
+
+		// @TODO: Return reentrancy cursor which can also be the cursor for the current item?
+		// NOTE: For reentrancy, should we prefer including table name instead of table iterator index?
+		return implode(
+			',',
+			array(
+				$entity_iterator_iterator_key,
+				$entity_iterator_key,
+			)
+		);
+	}
+
+	#[\ReturnTypeWillChange]
+	public function valid() {
+		return $this->entity_iterator_iterator->valid();
+	}
+
+	// TODO: Maybe simplify this if we stick with just iterating over rows for all tables.
+	protected function create_entity_export_strategies() {
+		global $wpdb;
+		return array(
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'term',
+				$wpdb->terms,
+				'term_id'
+			),
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'termmeta',
+				$wpdb->terms,
+				'term_id'
+			),
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'term_taxonomy',
+				$wpdb->term_taxonomy,
+				'term_id'
+			),
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'term_relationship',
+				$wpdb->term_relationships,
+				'term_taxonomy_id'
+			),
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'user',
+				$wpdb->users,
+				'ID'
+			),
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'post',
+				$wpdb->posts,
+				'ID'
+			),
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'post_meta',
+				$wpdb->postmeta,
+				'meta_id'
+			),
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'comment',
+				$wpdb->comments,
+				'comment_ID'
+			),
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'comment_meta',
+				$wpdb->commentmeta,
+				'meta_id'
+			),
+			new WP_Entity_Iterator_For_Table_With_Incrementing_IDs(
+				'option',
+				$wpdb->options,
+				'option_id'
+			),
+			// @TODO: Support export of custom tables, maybe allowing plugins to choose entity iterator via filter
+		);
+	}
+}