<?php
/**
 * Call Window
 *
 * @package Aisentic\Voice
 */

declare( strict_types = 1 );

namespace Aisentic\Voice;

defined( 'ABSPATH' ) || exit;

/**
 * Server-side clock for one caller's voice call.
 *
 * It enforces `voice.maxCallMinutes` on the server.
 * Why: the browser check alone can be skipped by posting to /voice/turn.
 *
 * A call is not saved anywhere. We only store when it started, in a
 * transient (a WordPress value that expires). Each turn keeps it alive for
 * IDLE seconds. After IDLE seconds with no turn, the next turn starts a new call.
 */
class Call_Window {

	/**
	 * Transient name, with the caller's id on the end.
	 */
	private const PREFIX = 'aisentic_voice_call_';

	/**
	 * Quiet time that ends a call.
	 *
	 * While someone talks, a turn comes every 20 to 30 seconds.
	 * `voice.silenceEndSeconds` hangs up after 30 seconds of silence.
	 * So 5 minutes with no turn means the call has ended.
	 */
	private const IDLE = 5 * MINUTE_IN_SECONDS;

	/**
	 * Begin a call, or begin it again.
	 *
	 * @param int      $user_id Caller.
	 * @param int|null $at      When it began. Now when not given.
	 * @return void
	 */
	public static function start( int $user_id, ?int $at = null ): void {
		set_transient( self::key( $user_id ), $at ?? time(), self::IDLE );
	}

	/**
	 * Check if this caller's call is past the time limit.
	 *
	 * If no call is open, this starts one. So skipping the greeting does
	 * not skip the limit.
	 *
	 * @param int $user_id     Caller.
	 * @param int $max_minutes From `voice.maxCallMinutes`. Zero turns it off.
	 * @return bool True when this turn should be refused.
	 */
	public static function too_long( int $user_id, int $max_minutes ): bool {
		if ( 1 > $max_minutes ) {
			return false;
		}

		$began = get_transient( self::key( $user_id ) );

		if ( false === $began ) {
			self::start( $user_id );

			return false;
		}

		$began = (int) $began;

		if ( time() - $began <= $max_minutes * MINUTE_IN_SECONDS ) {
			// Still inside the limit. Reset the idle timer, but keep the
			// start time.
			set_transient( self::key( $user_id ), $began, self::IDLE );

			return false;
		}

		// Out of time. End the call so the caller can call again.
		// The monthly plan limits total spend, not this setting.
		self::end( $user_id );

		return true;
	}

	/**
	 * When this caller's call must stop, as a Unix time.
	 *
	 * too_long() is checked once, when a turn starts. A turn can then run
	 * for a long time (speech to text, model, tools, retry, speech). So the
	 * turn checks this time again before each paid step.
	 *
	 * @param int $user_id     Caller.
	 * @param int $max_minutes From `voice.maxCallMinutes`. Zero turns it off.
	 * @return int 0 when there is no limit or no open call.
	 */
	public static function ends_at( int $user_id, int $max_minutes ): int {
		if ( 1 > $max_minutes ) {
			return 0;
		}

		$began = get_transient( self::key( $user_id ) );

		if ( false === $began ) {
			return 0;
		}

		return (int) $began + $max_minutes * MINUTE_IN_SECONDS;
	}

	/**
	 * Forget this caller's call.
	 *
	 * @param int $user_id Caller.
	 * @return void
	 */
	public static function end( int $user_id ): void {
		delete_transient( self::key( $user_id ) );
	}

	/**
	 * Transient name for one caller.
	 *
	 * @param int $user_id Caller.
	 * @return string
	 */
	private static function key( int $user_id ): string {
		return self::PREFIX . $user_id;
	}
}