<?php
/**
 * How many try-ons may start, and how much may be spent.
 *
 * @package Fitzaro
 */

namespace Fitzaro\Limits;

use Fitzaro\Job\Requests;

defined( 'ABSPATH' ) || exit;

/**
 * Counts come from the requests table, so they are exact across PHP workers. Windows are rolling
 * 24 hours; the budget is per calendar month in UTC. Every limit can be 0 for "no limit".
 *
 * The budget check adds an estimate for each request that may still cost money (queued, running,
 * or sent to a provider that reports no cost), so a burst of starts cannot overshoot it.
 */
final class Limits {

	public const VISITOR = 'visitor';
	public const IP      = 'ip';
	public const SITE    = 'site';
	public const BUDGET  = 'budget';
	public const UPLOADS = 'uploads';

	public const WINDOW = 86400;

	public const DEFAULTS = array(
		'per_visitor'    => 10,
		'per_ip'         => 30,
		'per_site'       => 300,
		'uploads_per_ip' => 60,
		'monthly_budget' => '10',
		'estimate'       => '0.07',
	);

	/**
	 * Request storage.
	 *
	 * @var Requests
	 */
	private $requests;

	/**
	 * Upload counter.
	 *
	 * @var Throttle
	 */
	private $throttle;

	/**
	 * Normalised settings.
	 *
	 * @var array<string, int>
	 */
	private $config;

	/**
	 * Returns the current Unix time.
	 *
	 * @var callable
	 */
	private $clock;

	/**
	 * Creates the limits.
	 *
	 * @param Requests           $requests Request storage.
	 * @param Throttle           $throttle Upload counter.
	 * @param array<string, int> $config   From normalize().
	 * @param callable           $clock    Returns the current Unix time.
	 */
	public function __construct( Requests $requests, Throttle $throttle, array $config, callable $clock ) {
		$this->requests = $requests;
		$this->throttle = $throttle;
		$this->config   = $config;
		$this->clock    = $clock;
	}

	/**
	 * Settings with defaults for anything missing or unreadable.
	 *
	 * @param mixed $config Saved or filtered settings.
	 * @return array{per_visitor: int, per_ip: int, per_site: int, uploads_per_ip: int, monthly_budget_micros: int, estimate_micros: int}
	 */
	public static function normalize( $config ): array {
		$config = is_array( $config ) ? $config : array();

		$count = static function ( string $key ) use ( $config ): int {
			$value = $config[ $key ] ?? self::DEFAULTS[ $key ];

			return is_numeric( $value ) ? max( 0, (int) $value ) : (int) self::DEFAULTS[ $key ];
		};

		$money = static function ( string $key ) use ( $config ): int {
			$value = $config[ $key ] ?? self::DEFAULTS[ $key ];

			return is_numeric( $value ) ? Money::to_micros( is_string( $value ) ? $value : (float) $value ) : Money::to_micros( self::DEFAULTS[ $key ] );
		};

		return array(
			'per_visitor'           => $count( 'per_visitor' ),
			'per_ip'                => $count( 'per_ip' ),
			'per_site'              => $count( 'per_site' ),
			'uploads_per_ip'        => $count( 'uploads_per_ip' ),
			'monthly_budget_micros' => $money( 'monthly_budget' ),
			'estimate_micros'       => $money( 'estimate' ),
		);
	}

	/**
	 * Why a new try-on may not start, or null when it may.
	 *
	 * @param string $visitor Visitor hash.
	 * @param string $ip      IP hash, '' when unknown.
	 */
	public function tryon_problem( string $visitor, string $ip ): ?string {
		$now   = $this->now();
		$since = gmdate( 'Y-m-d H:i:s', $now - self::WINDOW );

		if ( $this->reached( ( $this->config['per_visitor'] ?? 0 ), $this->requests->count_created_since( $since, 'visitor_hash', $visitor ) ) ) {
			return self::VISITOR;
		}

		if ( '' !== $ip && $this->reached( ( $this->config['per_ip'] ?? 0 ), $this->requests->count_created_since( $since, 'ip_hash', $ip ) ) ) {
			return self::IP;
		}

		if ( $this->reached( ( $this->config['per_site'] ?? 0 ), $this->requests->count_created_since( $since ) ) ) {
			return self::SITE;
		}

		$budget = $this->config['monthly_budget_micros'] ?? 0;
		if ( $budget > 0 ) {
			$spend    = $this->requests->spend_since( self::month_start( $now ) );
			$estimate = $this->config['estimate_micros'] ?? 0;

			if ( $spend['micros'] + ( $spend['unpriced'] + 1 ) * $estimate > $budget ) {
				return self::BUDGET;
			}
		}

		return null;
	}

	/**
	 * Counts a photo upload; false when this IP uploaded too many in the window.
	 *
	 * @param string $ip IP hash, '' when unknown.
	 */
	public function allow_upload( string $ip ): bool {
		if ( '' === $ip ) {
			return true;
		}

		return $this->throttle->hit( 'fitzaro_up_' . substr( $ip, 0, 40 ), $this->config['uploads_per_ip'] ?? 0, self::WINDOW );
	}

	/**
	 * Start of the calendar month of $now, in UTC.
	 *
	 * @param int $now Unix time.
	 */
	public static function month_start( int $now ): string {
		return gmdate( 'Y-m-01 00:00:00', $now );
	}

	/**
	 * Whether a count reached a limit (0 = unlimited).
	 *
	 * @param int $limit Limit.
	 * @param int $count Current count.
	 */
	private function reached( int $limit, int $count ): bool {
		return $limit > 0 && $count >= $limit;
	}

	/**
	 * Current Unix time.
	 */
	private function now(): int {
		return (int) ( $this->clock )();
	}
}