<?php
namespace QWSpeedCache\Preload;

defined( 'ABSPATH' ) || exit;

/**
 * Persistent preload URL queue (option-backed).
 * Pure helpers for unit testing without WordPress where noted.
 */
class Queue {

	const OPTION = 'qwsc_preload_queue';
	const MAX_QUEUE = 500;
	const MAX_URL_LENGTH = 2048;

	/**
	 * Normalize and validate a candidate URL (string-only; host check done by caller with WP).
	 *
	 * @param string $url Raw URL.
	 * @return string Empty string if invalid.
	 */
	public static function normalize_url( $url ) {
		$url = trim( (string) $url );
		if ( '' === $url || strlen( $url ) > self::MAX_URL_LENGTH ) {
			return '';
		}
		// Only enqueue public, same-site HTTP(S) URLs. Do not allow userinfo,
		// non-standard ports or protocol-relative URLs into the HTTP worker.
		$parts = wp_parse_url( $url );
		if ( ! is_array( $parts ) || empty( $parts['scheme'] ) || empty( $parts['host'] )
			|| ! in_array( strtolower( $parts['scheme'] ), array( 'http', 'https' ), true )
			|| isset( $parts['user'] ) || isset( $parts['pass'] ) || isset( $parts['port'] )
			|| isset( $parts['fragment'] ) ) {
			return '';
		}
		if ( function_exists( 'home_url' ) ) {
			$home = wp_parse_url( home_url( '/' ) );
			if ( ! is_array( $home ) || empty( $home['host'] )
				|| strtolower( $parts['host'] ) !== strtolower( $home['host'] )
				|| strtolower( $parts['scheme'] ) !== strtolower( $home['scheme'] ) ) {
				return '';
			}
		}
		if ( filter_var( $parts['host'], FILTER_VALIDATE_IP ) ) {
			return '';
		}
		return $url;
	}

	/**
	 * Merge new URLs into an existing queue list (unique, capped).
	 *
	 * @param string[] $current Current queue.
	 * @param string[] $incoming New URLs.
	 * @return string[]
	 */
	public static function merge( array $current, array $incoming ) {
		$seen = array();
		$out  = array();
		foreach ( array_merge( $current, $incoming ) as $url ) {
			$url = self::normalize_url( $url );
			if ( '' === $url ) {
				continue;
			}
			$key = strtolower( $url );
			if ( isset( $seen[ $key ] ) ) {
				continue;
			}
			$seen[ $key ] = true;
			$out[]        = $url;
			if ( count( $out ) >= self::MAX_QUEUE ) {
				break;
			}
		}
		return $out;
	}

	/**
	 * Take up to $n URLs from the front of the queue.
	 *
	 * @param string[] $queue Queue.
	 * @param int      $n     Batch size.
	 * @return array{0: string[], 1: string[]} [ batch, remaining ]
	 */
	public static function take( array $queue, $n ) {
		$n = max( 1, (int) $n );
		$batch = array_slice( $queue, 0, $n );
		$rest  = array_slice( $queue, count( $batch ) );
		return array( $batch, $rest );
	}

	/** @return string[] */
	public static function get() {
		$q = get_option( self::OPTION, array() );
		return is_array( $q ) ? array_values( $q ) : array();
	}

	/** @param string[] $urls */
	public static function set( array $urls ) {
		update_option( self::OPTION, array_values( $urls ), false );
	}

	/** @param string[] $urls */
	public static function enqueue( array $urls ) {
		self::set( self::merge( self::get(), $urls ) );
	}

	/**
	 * Put URLs at the front of the queue (homepage / priority).
	 *
	 * @param string[] $urls URLs.
	 */
	public static function enqueue_priority( array $urls ) {
		$norm = array();
		foreach ( $urls as $u ) {
			$u = self::normalize_url( $u );
			if ( '' !== $u ) {
				$norm[] = $u;
			}
		}
		if ( ! $norm ) {
			return;
		}
		// Priority first, then existing (deduped).
		self::set( self::merge( $norm, self::get() ) );
	}

	/**
	 * Re-queue failed URLs at the end (capped).
	 *
	 * @param string[] $urls Failed URLs.
	 */
	public static function requeue_failed( array $urls ) {
		if ( ! $urls ) {
			return;
		}
		self::enqueue( $urls );
	}

	public static function clear() {
		delete_option( self::OPTION );
	}

	public static function count() {
		return count( self::get() );
	}
}