<?php

/**

 * Block Serialization Parser

 *

 * @package WordPress

 */

/**

 * Class WP_Block_Parser

 *

 * Parses a document and constructs a list of parsed block objects

 *

 * @since 5.0.0

 * @since 4.0.0 returns arrays not objects, all attributes are arrays

 */

class WP_Block_Parser {

	/**

	 * Input document being parsed

	 *

	 * @example "Pre-text\n<!-- wp:paragraph -->This is inside a block!<!-- /wp:paragraph -->"

	 *

	 * @since 5.0.0

	 * @var string

	 */

	public $document;

	/**

	 * Tracks parsing progress through document

	 *

	 * @since 5.0.0

	 * @var int

	 */

	public $offset;

	/**

	 * List of parsed blocks

	 *

	 * @since 5.0.0

	 * @var WP_Block_Parser_Block[]

	 */

	public $output;

	/**

	 * Stack of partially-parsed structures in memory during parse

	 *

	 * @since 5.0.0

	 * @var WP_Block_Parser_Frame[]

	 */

	public $stack;

	/**

	 * Parses a document and returns a list of block structures

	 *

	 * When encountering an invalid parse will return a best-effort

	 * parse. In contrast to the specification parser this does not

	 * return an error on invalid inputs.

	 *

	 * @since 5.0.0

	 *

	 * @param string $document Input document being parsed.

	 */

		return $this->output;

	}

	/**

	 * Processes the next token from the input document

	 * and returns whether to proceed eating more tokens

	 *

	 * This is the "next step" function that essentially

	 * takes a token as its input and decides what to do

	 * with that token before descending deeper into a

	 * nested block tree or continuing along the document

	 * or breaking out of a level of nesting.

	 *

	 * @internal

	 * @since 5.0.0

	 * @return bool

	 */

		$next_token = $this->next_token();

		list( $token_type, $block_name, $attrs, $start_offset, $token_length ) = $next_token;

		$stack_depth = count( $this->stack );

		// we may have some HTML soup before the next block.

		$leading_html_start = $start_offset > $this->offset ? $this->offset : null;

		switch ( $token_type ) {

			case 'no-more-tokens':

				// if not in a block then flush output.

				if ( 0 === $stack_depth ) {

					$this->add_freeform();

					return false;

				}

				/*

				 * Otherwise we have a problem

				 * This is an error

				 *

				 * we have options

				 * - treat it all as freeform text

				 * - assume an implicit closer (easiest when not nesting)

				 */

				// for the easy case we'll assume an implicit closer.

				if ( 1 === $stack_depth ) {

					$this->add_block_from_stack();

					return false;

				}

				/*

				 * for the nested case where it's more difficult we'll

				 * have to assume that multiple closers are missing

				 * and so we'll collapse the whole stack piecewise

				 */

				while ( 0 < count( $this->stack ) ) {

					$this->add_block_from_stack();

				}

				return false;

			case 'void-block':

				/*

				 * easy case is if we stumbled upon a void block

				 * in the top-level of the document

				 */

				if ( 0 === $stack_depth ) {

					if ( isset( $leading_html_start ) ) {

						$this->output[] = (array) $this->freeform(

							substr(

								$this->document,

								$leading_html_start,

								$start_offset - $leading_html_start

							)

						);

					}

					$this->output[] = (array) new WP_Block_Parser_Block( $block_name, $attrs, array(), '', array() );

					$this->offset   = $start_offset + $token_length;

					return true;

				}

				// otherwise we found an inner block.

				$this->add_inner_block(

					new WP_Block_Parser_Block( $block_name, $attrs, array(), '', array() ),

					$start_offset,

					$token_length

				);

				$this->offset = $start_offset + $token_length;

				return true;

			case 'block-opener':

				// track all newly-opened blocks on the stack.

				array_push(

					$this->stack,

					new WP_Block_Parser_Frame(

						new WP_Block_Parser_Block( $block_name, $attrs, array(), '', array() ),

						$start_offset,

						$token_length,

						$start_offset + $token_length,

						$leading_html_start

					)

				);

				$this->offset = $start_offset + $token_length;

				return true;

			case 'block-closer':

				/*

				 * if we're missing an opener we're in trouble

				 * This is an error

				 */

				if ( 0 === $stack_depth ) {

					/*

					 * we have options

					 * - assume an implicit opener

					 * - assume _this_ is the opener

					 * - give up and close out the document

					 */

					$this->add_freeform();

					return false;

				}

				// if we're not nesting then this is easy - close the block.

				if ( 1 === $stack_depth ) {

					$this->add_block_from_stack( $start_offset );

					$this->offset = $start_offset + $token_length;

					return true;

				}

				/*

				 * otherwise we're nested and we have to close out the current

				 * block and add it as a new innerBlock to the parent

				 */

				$stack_top                        = array_pop( $this->stack );

				$html                             = substr( $this->document, $stack_top->prev_offset, $start_offset - $stack_top->prev_offset );

				$stack_top->block->innerHTML     .= $html;

				$stack_top->block->innerContent[] = $html;

				$stack_top->prev_offset           = $start_offset + $token_length;

				$this->add_inner_block(

					$stack_top->block,

					$stack_top->token_start,

					$stack_top->token_length,

					$start_offset + $token_length

				);

				$this->offset = $start_offset + $token_length;

				return true;

			default:

				// This is an error.

				$this->add_freeform();

				return false;

		}

	}

	/**

	 * Scans the document from where we last left off

	 * and finds the next valid token to parse if it exists

	 *

	 * Returns the type of the find: kind of find, block information, attributes

	 *

	 * @internal

	 * @since 5.0.0

	 * @since 4.6.1 fixed a bug in attribute parsing which caused catastrophic backtracking on invalid block comments

	 * @return array

	 */

		$matches = null;

		/*

		 * aye the magic

		 * we're using a single RegExp to tokenize the block comment delimiters

		 * we're also using a trick here because the only difference between a

		 * block opener and a block closer is the leading `/` before `wp:` (and

		 * a closer has no attributes). we can trap them both and process the

		 * match back in PHP to see which one it was.

		 */

		$has_match = preg_match(

			'/<!--\s+(?P<closer>\/)?wp:(?P<namespace>[a-z][a-z0-9_-]*\/)?(?P<name>[a-z][a-z0-9_-]*)\s+(?P<attrs>{(?:(?:[^}]+|}+(?=})|(?!}\s+\/?-->).)*+)?}\s+)?(?P<void>\/)?-->/s',

			$this->document,

			$matches,

			PREG_OFFSET_CAPTURE,

			$this->offset

		);

		// if we get here we probably have catastrophic backtracking or out-of-memory in the PCRE.

		if ( false === $has_match ) {

			return array( 'no-more-tokens', null, null, null, null );

		}

		// we have no more tokens.

		if ( 0 === $has_match ) {

			return array( 'no-more-tokens', null, null, null, null );

		}

		list( $match, $started_at ) = $matches[0];

		$length    = strlen( $match );

		$is_closer = isset( $matches['closer'] ) && -1 !== $matches['closer'][1];

		$is_void   = isset( $matches['void'] ) && -1 !== $matches['void'][1];

		$namespace = $matches['namespace'];

		$namespace = ( isset( $namespace ) && -1 !== $namespace[1] ) ? $namespace[0] : 'core/';

		$name      = $namespace . $matches['name'][0];

		$has_attrs = isset( $matches['attrs'] ) && -1 !== $matches['attrs'][1];

		/*

		 * Fun fact! It's not trivial in PHP to create "an empty associative array" since all arrays

		 * are associative arrays. If we use `array()` we get a JSON `[]`

		 */

		$attrs = $has_attrs

			? json_decode( $matches['attrs'][0], /* as-associative */ true )

		/*

		 * This state isn't allowed

		 * This is an error

		 */

		if ( $is_closer && ( $is_void || $has_attrs ) ) {

			// we can ignore them since they don't hurt anything.

		}

		if ( $is_void ) {

			return array( 'void-block', $name, $attrs, $started_at, $length );

		}

		if ( $is_closer ) {

			return array( 'block-closer', $name, null, $started_at, $length );

		}

		return array( 'block-opener', $name, $attrs, $started_at, $length );

	}

	/**

	 * Returns a new block object for freeform HTML

	 *

	 * @internal

	 * @since 3.9.0

	 *

	 * @return WP_Block_Parser_Block freeform block object.

	 */

	}

	/**

	 * Pushes a length of text from the input document

	 * to the output list as a freeform block.

	 *

	 * @internal

	 * @since 5.0.0

	 * @param null $length how many bytes of document text to output.

	 */

		$length = $length ? $length : strlen( $this->document ) - $this->offset;

		if ( 0 === $length ) {

			return;

		}

		$this->output[] = (array) $this->freeform( substr( $this->document, $this->offset, $length ) );

	}

	/**

	 * Given a block structure from memory pushes

	 * a new block to the output list.

	 *

	 * @internal

	 * @since 5.0.0

	 * @param WP_Block_Parser_Block $block        The block to add to the output.

	 * @param int                   $token_start  Byte offset into the document where the first token for the block starts.

	 * @param int                   $token_length Byte length of entire block from start of opening token to end of closing token.

	 * @param int|null              $last_offset  Last byte offset into document if continuing form earlier output.

	 */

		$parent                       = $this->stack[ count( $this->stack ) - 1 ];

		$parent->block->innerBlocks[] = (array) $block;

		$html                         = substr( $this->document, $parent->prev_offset, $token_start - $parent->prev_offset );

		if ( ! empty( $html ) ) {

			$parent->block->innerHTML     .= $html;

			$parent->block->innerContent[] = $html;

		}

		$parent->block->innerContent[] = null;

		$parent->prev_offset           = $last_offset ? $last_offset : $token_start + $token_length;

	}

	/**

	 * Pushes the top block from the parsing stack to the output list.

	 *

	 * @internal

	 * @since 5.0.0

	 * @param int|null $end_offset byte offset into document for where we should stop sending text output as HTML.

	 */

		$stack_top   = array_pop( $this->stack );

		$prev_offset = $stack_top->prev_offset;

		$html = isset( $end_offset )

			? substr( $this->document, $prev_offset, $end_offset - $prev_offset )

			: substr( $this->document, $prev_offset );

		if ( ! empty( $html ) ) {

			$stack_top->block->innerHTML     .= $html;

			$stack_top->block->innerContent[] = $html;

		}

		if ( isset( $stack_top->leading_html_start ) ) {

			$this->output[] = (array) $this->freeform(

				substr(

					$this->document,

					$stack_top->leading_html_start,

					$stack_top->token_start - $stack_top->leading_html_start

				)

			);

		}

		$this->output[] = (array) $stack_top->block;

	}

}