<?php
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}
// phpcs:disable WordPress.WP.AlternativeFunctions -- Cache plugin: direct file operations are limited to wp-content/cache/velox, its own config/drop-in and the site .htaccess; WP_Filesystem is unsuitable for per-request cache writes.

/**
 * CSS engine for "critical CSS" and "remove unused CSS".
 *
 * How it works (no headless browser needed): every stylesheet is parsed into rules, and a rule is
 * kept when all parts of at least one of its selectors (tags, .classes, #ids, [attributes]) exist in
 * the page HTML. Pseudo-classes are ignored (so :hover rules of present elements are kept).
 * Anything the matcher cannot understand is kept, never dropped. @font-face / @import are always kept,
 * @keyframes are kept when an animation uses them.
 *
 * Critical CSS = rules matching the top of the page (head + first part of the body).
 * Used CSS     = rules matching the whole page.
 */
class Velox_CSS {

	const FOLD_BYTES = 30000;

	public static function dir() {
		return Velox_Cache::dir() . 'css/';
	}

	/* ---------- parser ---------- */

	public static function parse( $css ) {
		$css = preg_replace( '!/\*.*?\*/!s', '', (string) $css );
		$i   = 0;
		return self::parse_block( $css, $i, strlen( $css ) );
	}

	private static function parse_block( $css, &$i, $len ) {
		$nodes = array();
		while ( $i < $len ) {
			$start = $i;
			$j     = $i;
			$in    = false;
			$q     = '';
			$paren = 0;
			for ( ; $j < $len; $j++ ) {
				$c = $css[ $j ];
				if ( $in ) {
					if ( '\\' === $c ) {
						++$j;
						continue;
					}
					if ( $c === $q ) {
						$in = false;
					}
					continue;
				}
				if ( '"' === $c || "'" === $c ) {
					$in = true;
					$q  = $c;
					continue;
				}
				if ( '(' === $c ) {
					++$paren;
					continue;
				}
				if ( ')' === $c ) {
					--$paren;
					continue;
				}
				if ( $paren > 0 ) {
					continue;
				}
				if ( '{' === $c || ';' === $c || '}' === $c ) {
					break;
				}
			}
			$prelude = trim( substr( $css, $start, $j - $start ) );
			if ( $j >= $len ) {
				break;
			}
			$c = $css[ $j ];
			$i = $j + 1;
			if ( '}' === $c ) {
				return $nodes;
			}
			if ( ';' === $c ) {
				if ( '' !== $prelude ) {
					$nodes[] = array(
						'type' => 'stmt',
						'text' => $prelude . ';',
					);
				}
				continue;
			}
			if ( '' !== $prelude && '@' === $prelude[0] ) {
				$name = strtolower( preg_replace( '/^@([a-zA-Z-]+).*/s', '$1', $prelude ) );
				if ( in_array( $name, array( 'media', 'supports', 'layer', 'container', 'document', '-moz-document' ), true ) ) {
					$nodes[] = array(
						'type'     => 'at',
						'name'     => $name,
						'prelude'  => $prelude,
						'children' => self::parse_block( $css, $i, $len ),
					);
				} else {
					$body    = self::raw_block( $css, $i, $len );
					$nodes[] = array(
						'type'    => 'raw',
						'name'    => $name,
						'prelude' => $prelude,
						'text'    => $prelude . '{' . $body . '}',
					);
				}
			} else {
				$body    = self::raw_block( $css, $i, $len );
				$nodes[] = array(
					'type' => 'rule',
					'sel'  => $prelude,
					'body' => $body,
				);
			}
		}
		return $nodes;
	}

	private static function raw_block( $css, &$i, $len ) {
		$depth = 1;
		$start = $i;
		$in    = false;
		$q     = '';
		for ( ; $i < $len; $i++ ) {
			$c = $css[ $i ];
			if ( $in ) {
				if ( '\\' === $c ) {
					++$i;
					continue;
				}
				if ( $c === $q ) {
					$in = false;
				}
				continue;
			}
			if ( '"' === $c || "'" === $c ) {
				$in = true;
				$q  = $c;
				continue;
			}
			if ( '{' === $c ) {
				++$depth;
			} elseif ( '}' === $c ) {
				--$depth;
				if ( 0 === $depth ) {
					$inner = substr( $css, $start, $i - $start );
					++$i;
					return $inner;
				}
			}
		}
		return substr( $css, $start );
	}

	public static function render( $nodes ) {
		$out = '';
		foreach ( $nodes as $n ) {
			switch ( $n['type'] ) {
				case 'rule':
					$out .= $n['sel'] . '{' . trim( $n['body'] ) . '}';
					break;
				case 'at':
					$inner = self::render( $n['children'] );
					if ( '' !== $inner ) {
						$out .= $n['prelude'] . '{' . $inner . '}';
					}
					break;
				case 'raw':
					$out .= $n['text'];
					break;
				case 'stmt':
					$out .= $n['text'];
					break;
			}
		}
		return $out;
	}

	/* ---------- HTML index ---------- */

	public static function index( $html ) {
		$idx = array(
			'tags'    => array(
				'html' => 1,
				'body' => 1,
			),
			'classes' => array(),
			'ids'     => array(),
			'attrs'   => array(),
		);
		if ( ! preg_match_all( '/<([a-zA-Z][\w-]*)([^>]*)>/', $html, $m, PREG_SET_ORDER ) ) {
			return $idx;
		}
		foreach ( $m as $t ) {
			$idx['tags'][ strtolower( $t[1] ) ] = 1;
			if ( '' === trim( $t[2] ) ) {
				continue;
			}
			if ( ! preg_match_all( '/\s([a-zA-Z_:][\w:.-]*)(?:\s*=\s*(?:"([^"]*)"|\'([^\']*)\'|([^\s"\'>]+)))?/', $t[2], $am, PREG_SET_ORDER ) ) {
				continue;
			}
			foreach ( $am as $a ) {
				$name                  = strtolower( $a[1] );
				$idx['attrs'][ $name ] = 1;
				$val                   = isset( $a[2] ) && '' !== $a[2] ? $a[2] : ( isset( $a[3] ) && '' !== $a[3] ? $a[3] : ( isset( $a[4] ) ? $a[4] : '' ) );
				if ( 'class' === $name ) {
					foreach ( preg_split( '/\s+/', trim( html_entity_decode( $val ) ) ) as $c ) {
						if ( '' !== $c ) {
							$idx['classes'][ $c ] = 1;
						}
					}
				} elseif ( 'id' === $name ) {
					$val = trim( $val );
					if ( '' !== $val ) {
						$idx['ids'][ $val ] = 1;
					}
				}
			}
		}
		// Class names that scripts toggle at runtime ("classList.add('open')", "addClass('is-active')").
		// Also catches aliases such as "var b = document.body.classList; b.add('x')" (extra classes only keep more CSS).
		if ( preg_match_all( '/(?:\.(?:add|toggle|replace)|addClass|toggleClass)\(\s*[\'"]([^\'"]+)[\'"]/', $html, $jm ) ) {
			foreach ( $jm[1] as $list ) {
				foreach ( preg_split( '/\s+/', trim( $list ) ) as $c ) {
					if ( '' !== $c ) {
						$idx['classes'][ $c ] = 1;
					}
				}
			}
		}
		return $idx;
	}

	/* ---------- selector matching ---------- */

	private static function split_top( $s, $sep ) {
		if ( false === strpbrk( $s, '([\\' ) ) {
			return explode( $sep, $s );
		}
		$out   = array();
		$depth = 0;
		$cur   = '';
		$len   = strlen( $s );
		for ( $i = 0; $i < $len; $i++ ) {
			$c = $s[ $i ];
			if ( '\\' === $c ) {
				$cur .= $c . ( $i + 1 < $len ? $s[ ++$i ] : '' );
				continue;
			}
			if ( '(' === $c || '[' === $c ) {
				++$depth;
			} elseif ( ')' === $c || ']' === $c ) {
				--$depth;
			}
			if ( $c === $sep && 0 === $depth ) {
				$out[] = $cur;
				$cur   = '';
				continue;
			}
			$cur .= $c;
		}
		$out[] = $cur;
		return $out;
	}

	public static function selector_used( $sel, $idx, $safelist ) {
		if ( ! $safelist && false === strpos( $sel, ',' ) ) {
			return self::single_used( trim( $sel ), $idx );
		}
		foreach ( $safelist as $s ) {
			if ( '' !== $s && false !== stripos( $sel, $s ) ) {
				return true;
			}
		}
		foreach ( self::split_top( $sel, ',' ) as $single ) {
			if ( self::single_used( trim( $single ), $idx ) ) {
				return true;
			}
		}
		return false;
	}

	private static function single_used( $s, $idx ) {
		if ( '' === $s ) {
			return true;
		}
		// Fast path for plain selectors (tags, classes, ids, combinators): no regex replacements needed.
		if ( strpbrk( $s, ':[\\(' ) === false ) {
			foreach ( preg_split( '/[\s>~+]+/', $s, -1, PREG_SPLIT_NO_EMPTY ) as $comp ) {
				$parts = preg_split( '/(?=[.#])/', $comp, -1, PREG_SPLIT_NO_EMPTY );
				foreach ( $parts as $k => $x ) {
					if ( '*' === $x ) {
						continue;
					}
					if ( '.' === $x[0] ) {
						if ( ! isset( $idx['classes'][ substr( $x, 1 ) ] ) ) {
							return false;
						}
					} elseif ( '#' === $x[0] ) {
						if ( ! isset( $idx['ids'][ substr( $x, 1 ) ] ) ) {
							return false;
						}
					} elseif ( 0 === $k && ! isset( $idx['tags'][ strtolower( $x ) ] ) ) {
						if ( ! preg_match( '/^[a-zA-Z][\w-]*$/', $x ) ) {
							return true; // Unknown syntax: keep.
						}
						return false;
					}
				}
			}
			return true;
		}
		if ( preg_match( '/\\\\[0-9a-fA-F]/', $s ) ) {
			return true; // Hex escapes: cannot resolve safely, keep.
		}
		// Drop pseudo-classes / pseudo-elements, with or without parentheses (escaped colons are class chars).
		if ( false !== strpos( $s, '(' ) ) {
			$s = preg_replace( '/(?<!\\\\)::?[a-zA-Z-]+\((?:[^()]|\([^()]*\))*\)/', '', $s );
		}
		if ( null !== $s && false !== strpos( $s, ':' ) ) {
			$s = preg_replace( '/(?<!\\\\)::?[a-zA-Z-]+/', '', $s );
		}
		if ( null === $s ) {
			return true;
		}
		if ( false === strpbrk( $s, ':[\\(' ) ) {
			return '' === trim( $s ) ? true : self::single_used( $s, $idx );
		}
		// Attribute selectors: only the attribute name needs to exist.
		$attrs_ok = true;
		$s        = preg_replace_callback(
			'/\[\s*([a-zA-Z_:][\w:.-]*)[^\]]*\]/',
			function ( $m ) use ( &$attrs_ok, $idx ) {
				if ( ! isset( $idx['attrs'][ strtolower( $m[1] ) ] ) ) {
					$attrs_ok = false;
				}
				return '';
			},
			$s
		);
		if ( ! $attrs_ok ) {
			return false;
		}
		$s = preg_replace( '/\\\\(.)/', '$1', $s );
		$s = trim( preg_replace( '/\s*[>~+]\s*|\s+/', ' ', $s ) );
		if ( '' === $s ) {
			return true;
		}
		foreach ( explode( ' ', $s ) as $comp ) {
			if ( '' === $comp || '*' === $comp ) {
				continue;
			}
			if ( ! preg_match( '/^([a-zA-Z][\w-]*|\*)?((?:[.#][^.#\s]+)*)$/', $comp, $m ) ) {
				return true; // Unparsable: keep.
			}
			$tag = strtolower( $m[1] );
			if ( '' !== $tag && '*' !== $tag && ! isset( $idx['tags'][ $tag ] ) ) {
				return false;
			}
			if ( '' !== $m[2] && preg_match_all( '/([.#])([^.#]+)/', $m[2], $mm, PREG_SET_ORDER ) ) {
				foreach ( $mm as $x ) {
					if ( '.' === $x[1] ) {
						if ( ! isset( $idx['classes'][ $x[2] ] ) ) {
							return false;
						}
					} elseif ( ! isset( $idx['ids'][ $x[2] ] ) ) {
						return false;
					}
				}
			}
		}
		return true;
	}

	/* ---------- filtering ---------- */

	/** Selector parts that only style an interaction state (not visible on first paint). */
	private static function interaction_only( $single ) {
		if ( false === strpos( $single, ':' ) ) {
			return false;
		}
		return (bool) preg_match( '/(?<!\\\\):(?:hover|focus|focus-within|focus-visible|active|visited)\b|::?selection\b/i', $single );
	}

	/**
	 * Keeps used rules. Selector groups are trimmed to the parts that match, so "h1,.unused,.x:hover"
	 * becomes "h1". In critical mode, print media and pure interaction states are left for the full CSS.
	 */
	public static function filter( $nodes, $idx, $safelist, &$keyframes, $critical = false ) {
		$out = array();
		foreach ( $nodes as $n ) {
			switch ( $n['type'] ) {
				case 'rule':
					$parts = array();
					foreach ( self::split_top( $n['sel'], ',' ) as $single ) {
						$single = trim( $single );
						if ( $critical && self::interaction_only( $single ) ) {
							continue;
						}
						if ( self::selector_used( $single, $idx, $safelist ) ) {
							$parts[] = $single;
						}
					}
					if ( $parts ) {
						$n['sel'] = implode( ',', $parts );
						$out[]    = $n;
					}
					break;
				case 'at':
					if ( $critical && 'media' === $n['name'] && preg_match( '/^@media\s+print\b/i', $n['prelude'] ) ) {
						break;
					}
					$kids = self::filter( $n['children'], $idx, $safelist, $keyframes, $critical );
					if ( ! empty( $kids ) ) {
						$n['children'] = $kids;
						$out[]         = $n;
					}
					break;
				case 'raw':
					if ( false !== strpos( $n['name'], 'keyframes' ) ) {
						$keyframes[] = $n;
					} else {
						$out[] = $n;
					}
					break;
				default:
					$out[] = $n;
			}
		}
		return $out;
	}

	/** Splits a declaration block at top-level semicolons (values may contain ; inside strings or brackets). */
	private static function declarations( $body ) {
		if ( false === strpbrk( $body, '("\'[{' ) ) {
			return explode( ';', $body );
		}
		$out   = array();
		$cur   = '';
		$depth = 0;
		$q     = '';
		$len   = strlen( $body );
		for ( $i = 0; $i < $len; $i++ ) {
			$c = $body[ $i ];
			if ( '' !== $q ) {
				$cur .= $c;
				if ( '\\' === $c && $i + 1 < $len ) {
					$cur .= $body[ ++$i ];
				} elseif ( $c === $q ) {
					$q = '';
				}
				continue;
			}
			if ( '"' === $c || "'" === $c ) {
				$q = $c;
			} elseif ( '(' === $c || '[' === $c || '{' === $c ) {
				++$depth;
			} elseif ( ')' === $c || ']' === $c || '}' === $c ) {
				--$depth;
			} elseif ( ';' === $c && 0 === $depth ) {
				$out[] = $cur;
				$cur   = '';
				continue;
			}
			$cur .= $c;
		}
		if ( '' !== trim( $cur ) ) {
			$out[] = $cur;
		}
		return $out;
	}

	/** Collects every custom property referenced with var(), following variables that use other variables. */
	private static function used_vars( $nodes ) {
		$defs = array();
		$refs = array();
		$walk = function ( $list ) use ( &$walk, &$defs, &$refs ) {
			foreach ( $list as $n ) {
				if ( 'at' === $n['type'] ) {
					$walk( $n['children'] );
				} elseif ( 'rule' === $n['type'] && false !== strpos( $n['body'], '--' ) ) {
					foreach ( self::declarations( $n['body'] ) as $d ) {
						$d = trim( $d );
						if ( 0 === strpos( $d, '--' ) && false !== ( $p = strpos( $d, ':' ) ) ) {
							$defs[ trim( substr( $d, 0, $p ) ) ][] = substr( $d, $p + 1 );
						} elseif ( preg_match_all( '/var\(\s*(--[\w-]+)/', $d, $m ) ) {
							foreach ( $m[1] as $v ) {
								$refs[ $v ] = 1;
							}
						}
					}
				} elseif ( 'raw' === $n['type'] && preg_match_all( '/var\(\s*(--[\w-]+)/', $n['text'], $m ) ) {
					foreach ( $m[1] as $v ) {
						$refs[ $v ] = 1;
					}
				}
			}
		};
		$walk( $nodes );
		$queue = array_keys( $refs );
		while ( $queue ) {
			$v = array_pop( $queue );
			foreach ( isset( $defs[ $v ] ) ? $defs[ $v ] : array() as $val ) {
				if ( preg_match_all( '/var\(\s*(--[\w-]+)/', $val, $m ) ) {
					foreach ( $m[1] as $w ) {
						if ( ! isset( $refs[ $w ] ) ) {
							$refs[ $w ] = 1;
							$queue[]    = $w;
						}
					}
				}
			}
		}
		return $refs;
	}

	/** Removes custom property declarations nothing refers to (themes often define hundreds). */
	private static function prune_vars( $nodes, $used ) {
		$out = array();
		foreach ( $nodes as $n ) {
			if ( 'at' === $n['type'] ) {
				$n['children'] = self::prune_vars( $n['children'], $used );
				if ( empty( $n['children'] ) ) {
					continue;
				}
			} elseif ( 'rule' === $n['type'] && false !== strpos( $n['body'], '--' ) ) {
				$keep = array();
				foreach ( self::declarations( $n['body'] ) as $d ) {
					$t = trim( $d );
					if ( 0 === strpos( $t, '--' ) && false !== ( $p = strpos( $t, ':' ) ) && ! isset( $used[ trim( substr( $t, 0, $p ) ) ] ) ) {
						continue;
					}
					if ( '' !== $t ) {
						$keep[] = $t;
					}
				}
				if ( ! $keep ) {
					continue;
				}
				$n['body'] = implode( ';', $keep );
			}
			$out[] = $n;
		}
		return $out;
	}

	public static function reduce( $nodes, $idx, $safelist, $critical = false ) {
		$keyframes = array();
		$kept      = self::filter( $nodes, $idx, $safelist, $keyframes, $critical );
		if ( $critical ) {
			// The full stylesheets load right after first paint, so unused variables can wait for them.
			$kept = self::prune_vars( $kept, self::used_vars( $kept ) );
		}
		$css = self::render( $kept );
		foreach ( $keyframes as $k ) {
			$name = trim( preg_replace( '/^@[a-zA-Z-]*keyframes\s+/i', '', $k['prelude'] ), " \"'" );
			if ( '' !== $name && preg_match( '/animation(?:-name)?\s*:[^;}]*(?<![\w-])' . preg_quote( $name, '/' ) . '(?![\w-])/i', $css ) ) {
				$css .= $k['text'];
			}
		}
		return $css;
	}

	/* ---------- stylesheet access with disk cache ---------- */

	public static function nodes_for_file( $path, $base_url ) {
		$key  = md5( $path . filemtime( $path ) . VELOX_VERSION );
		$file = self::dir() . 'p-' . $key . '.json';
		if ( is_file( $file ) ) {
			$data = json_decode( (string) file_get_contents( $file ), true );
			if ( is_array( $data ) ) {
				return $data;
			}
		}
		$css = file_get_contents( $path );
		if ( false === $css ) {
			return array();
		}
		$css   = Velox_Optimizer::absolutize_css( $css, $base_url );
		$nodes = self::parse( $css );
		wp_mkdir_p( self::dir() );
		// Parsed stylesheet, stored as plain JSON data (never as executable code).
		@file_put_contents( $file, wp_json_encode( $nodes ), LOCK_EX );
		return $nodes;
	}

	/**
	 * Builds the reduced CSS for the given stylesheet files.
	 *
	 * @param array  $sheets   [ [path, base_url], ... ]
	 * @param string $html     HTML used for matching.
	 * @param array  $safelist Selector fragments that are always kept.
	 * @param string $mode     'critical' or 'used' (cache key only).
	 * @return string
	 */
	/**
	 * Cache key for a page's CSS. Critical CSS is shared by pages built from the same template and
	 * stylesheets (body classes without IDs, e.g. all single posts), so only the first page of each
	 * template pays for it after a purge. Used CSS stays per URL because it covers the whole page.
	 */
	private static function page_key( $html, $mode ) {
		if ( 'critical' === $mode && preg_match( '/<body\b[^>]*\bclass\s*=\s*(["\'])(.*?)\1/is', $html, $m ) ) {
			$classes = array_filter(
				preg_split( '/\s+/', strtolower( trim( $m[2] ) ) ),
				function ( $c ) {
					return '' !== $c && ! preg_match( '/\d/', $c );
				}
			);
			sort( $classes );
			return 't:' . implode( ' ', $classes );
		}
		$uri = isset( $_SERVER['REQUEST_URI'] ) ? (string) wp_parse_url( sanitize_text_field( wp_unslash( $_SERVER['REQUEST_URI'] ) ), PHP_URL_PATH ) : '/';
		return 'u:' . $uri;
	}

	public static function build( $sheets, $html, $safelist, $mode ) {
		$sig = $mode . '|' . implode( '|', $safelist );
		foreach ( $sheets as $s ) {
			$sig .= '|' . $s[0] . filemtime( $s[0] );
		}
		$key  = md5( $sig . '|' . self::page_key( $html, $mode ) . '|' . ( Velox_Cache::is_mobile_ua() ? 'm' : 'd' ) . VELOX_VERSION );
		$file = self::dir() . 'r-' . $key . '.css';
		if ( is_file( $file ) && time() - filemtime( $file ) < DAY_IN_SECONDS ) {
			$css = file_get_contents( $file );
			if ( false !== $css ) {
				return $css;
			}
		}
		$idx   = self::index( $html );
		$nodes = array();
		foreach ( $sheets as $s ) {
			$nodes = array_merge( $nodes, self::nodes_for_file( $s[0], $s[1] ) );
		}
		$css = self::reduce( $nodes, $idx, $safelist, 'critical' === $mode );
		wp_mkdir_p( self::dir() );
		@file_put_contents( $file, $css, LOCK_EX );
		return $css;
	}

	/* ---------- per page / template record: the CSS that wp_add_inline_style() prints ---------- */

	/** Stored record, or null when missing, older than a day or built from changed stylesheets. */
	public static function load_record( $key ) {
		$file = self::dir() . 's-' . $key . '.json';
		if ( ! is_file( $file ) || time() - filemtime( $file ) > DAY_IN_SECONDS ) {
			return null;
		}
		$rec = json_decode( (string) file_get_contents( $file ), true );
		if ( ! is_array( $rec ) || empty( $rec['css'] ) || empty( $rec['handles'] ) || ! in_array( $rec['mode'] ?? '', array( 'critical', 'used' ), true ) ) {
			return null;
		}
		foreach ( (array) ( $rec['files'] ?? array() ) as $f ) {
			if ( ! is_array( $f ) || ! is_file( (string) $f[0] ) || filemtime( (string) $f[0] ) !== (int) $f[1] ) {
				return null;
			}
		}
		return $rec;
	}

	public static function save_record( $key, $rec ) {
		wp_mkdir_p( self::dir() );
		@file_put_contents( self::dir() . 's-' . $key . '.json', wp_json_encode( $rec ), LOCK_EX );
	}

	public static function purge() {
		if ( is_dir( self::dir() ) ) {
			foreach ( array_merge( glob( self::dir() . 'r-*.css' ) ?: array(), glob( self::dir() . 's-*.json' ) ?: array(), glob( self::dir() . 'p-*.php' ) ?: array() ) as $f ) {
				wp_delete_file( $f );
			}
		}
	}
}