<?php
/**
 * enabled -> draining -> disabled state machine.
 *
 * Disabling must never strand mail that is already queued: the interceptor
 * stops queueing immediately, but the worker keeps draining what is there.
 *
 * @package studiou-wc-mail-queue
 * @copyright 2026 QUADARAX
 * @author    Dalibor Votruba <dvotruba@quadarax.com>
 * @license   GPL-2.0-or-later
 */

defined( 'ABSPATH' ) || exit;

/**
 * Class Studiou_WCMQ_State
 */
class Studiou_WCMQ_State {

	/**
	 * Register hooks.
	 */
	public static function init() {
		// A queue emptied by retention or by manual deletion still needs to settle.
		add_action( 'admin_init', array( __CLASS__, 'maybe_settle' ) );
	}

	/**
	 * Current state.
	 *
	 * @return string
	 */
	public static function get() {
		return Studiou_WCMQ_Settings::state();
	}

	/**
	 * Whether new mail should be queued right now.
	 *
	 * @return bool
	 */
	public static function is_queueing() {
		return Studiou_WCMQ_Settings::STATE_ENABLED === self::get();
	}

	/**
	 * Turn queueing on.
	 */
	public static function enable() {
		Studiou_WCMQ_Settings::set_state( Studiou_WCMQ_Settings::STATE_ENABLED );
		Studiou_WCMQ_DB::log( 'info', 'Queue enabled.' );
	}

	/**
	 * Turn queueing off, draining first if anything is in flight.
	 */
	public static function disable() {
		if ( Studiou_WCMQ_DB::count_unfinished() > 0 ) {
			Studiou_WCMQ_Settings::set_state( Studiou_WCMQ_Settings::STATE_DRAINING );
			Studiou_WCMQ_DB::log( 'info', 'Queue draining; new mail sends synchronously.' );
			return;
		}
		Studiou_WCMQ_Settings::set_state( Studiou_WCMQ_Settings::STATE_DISABLED );
		Studiou_WCMQ_DB::log( 'info', 'Queue disabled.' );
	}

	/**
	 * Move draining -> disabled once nothing is left in flight.
	 *
	 * Called by the worker after each send and on admin_init.
	 */
	public static function maybe_settle() {
		if ( Studiou_WCMQ_Settings::STATE_DRAINING !== self::get() ) {
			return;
		}
		if ( Studiou_WCMQ_DB::count_unfinished() > 0 ) {
			return;
		}
		Studiou_WCMQ_Settings::set_state( Studiou_WCMQ_Settings::STATE_DISABLED );
		Studiou_WCMQ_DB::log( 'info', 'Queue drained; now disabled.' );
	}
}