<?php
/**
 * Issues personal codes: one per e-mail address and campaign.
 *
 * @package CNWS\Coupons
 */

namespace CNWS\Coupons;

use WP_Error;

defined( 'ABSPATH' ) || exit;

final class Issuer {

	private const ATTEMPTS = 5;

	public function __construct(
		private CampaignRepository $campaigns,
		private CodeRepository $codes
	) {}

	/**
	 * The recipient's code in a campaign. Asking again for the same e-mail returns the same code, so
	 * resends and retries never hand out a second code.
	 *
	 * @param string $slug   Campaign slug.
	 * @param string $email  Recipient.
	 * @param string $source Who asked, e.g. 'admin', 'cli', 'cnws-mail'.
	 * @return string|WP_Error The code.
	 */
	public function issue( string $slug, string $email, string $source = '' ) {
		$email = CodeRepository::normalize_email( $email );

		if ( ! is_email( $email ) ) {
			return new WP_Error( 'cnwscoupons_email', __( 'A valid e-mail address is required.', 'webstyle-coupons' ) );
		}

		$campaign = $this->campaigns->find_by_slug( $slug );

		if ( ! $campaign ) {
			return new WP_Error( 'cnwscoupons_campaign_missing', __( 'The campaign does not exist.', 'webstyle-coupons' ) );
		}

		if ( $campaign->is_shared() ) {
			return new WP_Error( 'cnwscoupons_campaign_shared', __( 'This campaign has one shared code and issues no personal codes.', 'webstyle-coupons' ) );
		}

		$existing = $this->codes->find_for( $campaign->id, $email );

		if ( $existing ) {
			return (string) $existing->code;
		}

		if ( ! $campaign->is_active() ) {
			return new WP_Error( 'cnwscoupons_campaign_ended', __( 'The campaign has ended and issues no new codes.', 'webstyle-coupons' ) );
		}

		if ( $campaign->max_codes > 0 && $this->codes->count_personal( $campaign->id ) >= $campaign->max_codes ) {
			return new WP_Error( 'cnwscoupons_campaign_full', __( 'The campaign has issued all its codes.', 'webstyle-coupons' ) );
		}

		$expires_at = self::expires_at( $campaign, time() );

		for ( $attempt = 0; $attempt < self::ATTEMPTS; $attempt++ ) {
			$code = CodeGenerator::generate( $campaign->code_prefix );

			if ( $this->taken( $code ) ) {
				continue;
			}

			if ( $this->codes->insert( $campaign->id, $code, $email, $source, $expires_at ) ) {
				return $code;
			}

			// A parallel request may have issued this recipient's code in the meantime.
			$existing = $this->codes->find_for( $campaign->id, $email );

			if ( $existing ) {
				return (string) $existing->code;
			}
		}

		return new WP_Error( 'cnwscoupons_issue_failed', __( 'No code could be issued. Try again.', 'webstyle-coupons' ) );
	}

	/**
	 * When a code issued now expires, in UTC (Y-m-d H:i:s), or null for never.
	 *
	 * A code is valid to the end of its last day in the site's time zone. With both an end date and
	 * a number of days, the earlier one wins.
	 *
	 * @param Campaign $campaign Campaign.
	 * @param int      $now      Unix timestamp of issue.
	 */
	public static function expires_at( Campaign $campaign, int $now ): ?string {
		$zone  = wp_timezone();
		$dates = array();

		if ( '' !== $campaign->expires_on ) {
			$dates[] = new \DateTimeImmutable( $campaign->expires_on . ' 23:59:59', $zone );
		}

		if ( $campaign->valid_days > 0 ) {
			$dates[] = ( new \DateTimeImmutable( '@' . $now ) )->setTimezone( $zone )->modify( '+' . $campaign->valid_days . ' days' )->setTime( 23, 59, 59 );
		}

		if ( ! $dates ) {
			return null;
		}

		return min( $dates )->setTimezone( new \DateTimeZone( 'UTC' ) )->format( 'Y-m-d H:i:s' );
	}

	/**
	 * A code must be unique among our codes and among the shop's own WooCommerce coupons.
	 *
	 * @param string $code Candidate code.
	 */
	private function taken( string $code ): bool {
		return $this->codes->code_exists( $code ) || ( function_exists( 'wc_get_coupon_id_by_code' ) && wc_get_coupon_id_by_code( $code ) );
	}
}