Source

File: wp-admin/includes/class-wp-screen.php

public static function get( $hook_name = '' ) {
		if ( $hook_name instanceof WP_Screen ) {
			return $hook_name;
		}

		$post_type       = null;
		$taxonomy        = null;
		$in_admin        = false;
		$action          = '';
		$is_block_editor = false;

		if ( $hook_name ) {
			$id = $hook_name;
		} else {
			$id = $GLOBALS['hook_suffix'];
		}

		// For those pesky meta boxes.
		if ( $hook_name && post_type_exists( $hook_name ) ) {
			$post_type = $id;
			$id        = 'post'; // Changes later. Ends up being $base.
		} else {
			if ( '.php' === substr( $id, -4 ) ) {
				$id = substr( $id, 0, -4 );
			}

			if ( in_array( $id, array( 'post-new', 'link-add', 'media-new', 'user-new' ), true ) ) {
				$id     = substr( $id, 0, -4 );
				$action = 'add';
			}
		}

		if ( ! $post_type && $hook_name ) {
			if ( '-network' === substr( $id, -8 ) ) {
				$id       = substr( $id, 0, -8 );
				$in_admin = 'network';
			} elseif ( '-user' === substr( $id, -5 ) ) {
				$id       = substr( $id, 0, -5 );
				$in_admin = 'user';
			}

			$id = sanitize_key( $id );
			if ( 'edit-comments' !== $id && 'edit-tags' !== $id && 'edit-' === substr( $id, 0, 5 ) ) {
				$maybe = substr( $id, 5 );
				if ( taxonomy_exists( $maybe ) ) {
					$id       = 'edit-tags';
					$taxonomy = $maybe;
				} elseif ( post_type_exists( $maybe ) ) {
					$id        = 'edit';
					$post_type = $maybe;
				}
			}

			if ( ! $in_admin ) {
				$in_admin = 'site';
			}
		} else {
			if ( defined( 'WP_NETWORK_ADMIN' ) && WP_NETWORK_ADMIN ) {
				$in_admin = 'network';
			} elseif ( defined( 'WP_USER_ADMIN' ) && WP_USER_ADMIN ) {
				$in_admin = 'user';
			} else {
				$in_admin = 'site';
			}
		}

		if ( 'index' === $id ) {
			$id = 'dashboard';
		} elseif ( 'front' === $id ) {
			$in_admin = false;
		}

		$base = $id;

		// If this is the current screen, see if we can be more accurate for post types and taxonomies.
		if ( ! $hook_name ) {
			if ( isset( $_REQUEST['post_type'] ) ) {
				$post_type = post_type_exists( $_REQUEST['post_type'] ) ? $_REQUEST['post_type'] : false;
			}
			if ( isset( $_REQUEST['taxonomy'] ) ) {
				$taxonomy = taxonomy_exists( $_REQUEST['taxonomy'] ) ? $_REQUEST['taxonomy'] : false;
			}

			switch ( $base ) {
				case 'post':
					if ( isset( $_GET['post'] ) && isset( $_POST['post_ID'] ) && (int) $_GET['post'] !== (int) $_POST['post_ID'] ) {
						wp_die( __( 'A post ID mismatch has been detected.' ), __( 'Sorry, you are not allowed to edit this item.' ), 400 );
					} elseif ( isset( $_GET['post'] ) ) {
						$post_id = (int) $_GET['post'];
					} elseif ( isset( $_POST['post_ID'] ) ) {
						$post_id = (int) $_POST['post_ID'];
					} else {
						$post_id = 0;
					}

					if ( $post_id ) {
						$post = get_post( $post_id );
						if ( $post ) {
							$post_type = $post->post_type;

							/** This filter is documented in wp-admin/post.php */
							$replace_editor = apply_filters( 'replace_editor', false, $post );

							if ( ! $replace_editor ) {
								$is_block_editor = use_block_editor_for_post( $post );
							}
						}
					}
					break;
				case 'edit-tags':
				case 'term':
					if ( null === $post_type && is_object_in_taxonomy( 'post', $taxonomy ? $taxonomy : 'post_tag' ) ) {
						$post_type = 'post';
					}
					break;
				case 'upload':
					$post_type = 'attachment';
					break;
			}
		}

		switch ( $base ) {
			case 'post':
				if ( null === $post_type ) {
					$post_type = 'post';
				}

				// When creating a new post, use the default block editor support value for the post type.
				if ( empty( $post_id ) ) {
					$is_block_editor = use_block_editor_for_post_type( $post_type );
				}

				$id = $post_type;
				break;
			case 'edit':
				if ( null === $post_type ) {
					$post_type = 'post';
				}
				$id .= '-' . $post_type;
				break;
			case 'edit-tags':
			case 'term':
				if ( null === $taxonomy ) {
					$taxonomy = 'post_tag';
				}
				// The edit-tags ID does not contain the post type. Look for it in the request.
				if ( null === $post_type ) {
					$post_type = 'post';
					if ( isset( $_REQUEST['post_type'] ) && post_type_exists( $_REQUEST['post_type'] ) ) {
						$post_type = $_REQUEST['post_type'];
					}
				}

				$id = 'edit-' . $taxonomy;
				break;
		}

		if ( 'network' === $in_admin ) {
			$id   .= '-network';
			$base .= '-network';
		} elseif ( 'user' === $in_admin ) {
			$id   .= '-user';
			$base .= '-user';
		}

		if ( isset( self::$_registry[ $id ] ) ) {
			$screen = self::$_registry[ $id ];
			if ( get_current_screen() === $screen ) {
				return $screen;
			}
		} else {
			$screen     = new WP_Screen();
			$screen->id = $id;
		}

		$screen->base            = $base;
		$screen->action          = $action;
		$screen->post_type       = (string) $post_type;
		$screen->taxonomy        = (string) $taxonomy;
		$screen->is_user         = ( 'user' === $in_admin );
		$screen->is_network      = ( 'network' === $in_admin );
		$screen->in_admin        = $in_admin;
		$screen->is_block_editor = $is_block_editor;

		self::$_registry[ $id ] = $screen;

		return $screen;
	}