<?php
/**
 * Content Signals Policy.
 *
 * @package AIBlackout
 */

namespace AIBlackout\Declarations;

use AIBlackout\Core\Settings;

defined( 'ABSPATH' ) || exit;

/**
 * Emits the Content Signals Policy block into robots.txt.
 *
 * @since 1.0.0
 */
class ContentSignals {

	/**
	 * Directive name, capitalised as Cloudflare documents it.
	 *
	 * @var string
	 */
	const DIRECTIVE = 'Content-signal';

	/**
	 * Declaration type recorded in history.
	 *
	 * @var string
	 */
	const TYPE = 'content_signals';

	/**
	 * Plugin settings.
	 *
	 * @var Settings
	 */
	private $settings;

	/**
	 * Declaration history.
	 *
	 * @var History
	 */
	private $history;

	/**
	 * Constructor.
	 *
	 * @param Settings $settings Plugin settings.
	 * @param History  $history  Declaration history.
	 */
	public function __construct( Settings $settings, History $history ) {
		$this->settings = $settings;
		$this->history  = $history;
	}

	/**
	 * Whether the policy block is switched on.
	 *
	 * @return bool True when signals should be published.
	 */
	public function is_enabled(): bool {
		return ! aiblackout_is_disabled() && (bool) $this->settings->get_declaration( 'content_signals', false );
	}

	/**
	 * Returns the configured signals, omitting any set to "unset".
	 *
	 * @return array Signal name => value.
	 */
	public function get_signals(): array {
		$map = array(
			'search'   => 'signal_search',
			'ai-input' => 'signal_ai_input',
			'ai-train' => 'signal_ai_train',
		);

		$signals = array();

		foreach ( $map as $signal => $key ) {
			$value = (string) $this->settings->get_declaration( $key, Settings::SIGNAL_UNSET );

			if ( Settings::SIGNAL_YES !== $value && Settings::SIGNAL_NO !== $value ) {
				continue;
			}

			$signals[ $signal ] = $value;
		}

		return $signals;
	}

	/**
	 * Builds the robots.txt block.
	 *
	 * @return string The block, or an empty string when nothing is declared.
	 */
	public function build_block(): string {
		if ( ! $this->is_enabled() ) {
			return '';
		}

		$signals = $this->get_signals();

		if ( empty( $signals ) ) {
			return '';
		}

		$pairs = array();

		foreach ( $signals as $signal => $value ) {
			$pairs[] = $signal . '=' . $value;
		}

		$lines = array(
			'# As a condition of accessing this website, you agree to abide by the',
			'# following content signals:',
			'#',
			'# (a) If a content-signal = yes, you may collect content for the',
			'#     corresponding use.',
			'# (b) If a content-signal = no, you may not collect content for the',
			'#     corresponding use.',
			'# (c) If the website operator does not include a content signal for a',
			'#     corresponding use, the website operator neither grants nor restricts',
			'#     permission via content signal with respect to the corresponding use.',
			'#',
			'# The content signals and their meanings are:',
			'#',
			'# search:   building a search index and providing search results (e.g.,',
			'#           returning hyperlinks and short excerpts from this website\'s',
			'#           contents). Search does not include providing AI-generated',
			'#           search summaries.',
			'# ai-input: inputting content into one or more AI models (e.g., retrieval',
			'#           augmented generation, grounding, or other real-time taking of',
			'#           content for generative AI search answers).',
			'# ai-train: training or fine-tuning AI models.',
			'#',
			'# ANY RESTRICTIONS EXPRESSED VIA CONTENT SIGNALS ARE EXPRESS RESERVATIONS',
			'# OF RIGHTS UNDER ARTICLE 4 OF THE EUROPEAN UNION DIRECTIVE 2019/790 ON',
			'# COPYRIGHT AND RELATED RIGHTS IN THE DIGITAL SINGLE MARKET.',
			'',
			'User-agent: *',
			self::DIRECTIVE . ': ' . implode( ', ', $pairs ),
		);

		return implode( "\n", $lines );
	}

	/**
	 * Returns a plain-language description of what is currently declared.
	 *
	 * @return string Human-readable summary.
	 */
	public function describe(): string {
		$signals = $this->get_signals();

		if ( ! $this->is_enabled() || empty( $signals ) ) {
			return __( 'No content signals are being published.', 'ai-blackout' );
		}

		$parts = array();

		if ( isset( $signals['search'] ) ) {
			$parts[] = Settings::SIGNAL_YES === $signals['search']
				? __( 'search engines may index this site', 'ai-blackout' )
				: __( 'search engines may not index this site', 'ai-blackout' );
		}

		if ( isset( $signals['ai-input'] ) ) {
			$parts[] = Settings::SIGNAL_YES === $signals['ai-input']
				? __( 'AI systems may use this content to answer questions', 'ai-blackout' )
				: __( 'AI systems may not use this content to answer questions', 'ai-blackout' );
		}

		if ( isset( $signals['ai-train'] ) ) {
			$parts[] = Settings::SIGNAL_YES === $signals['ai-train']
				? __( 'this content may be used to train AI models', 'ai-blackout' )
				: __( 'this content may not be used to train AI models', 'ai-blackout' );
		}

		return ucfirst( implode( ', ', $parts ) ) . '.';
	}

	/**
	 * Records the current declaration in the history log.
	 *
	 * @return void
	 */
	public function record(): void {
		$this->history->record(
			self::TYPE,
			$this->describe(),
			$this->get_signals()
		);
	}
}