<?php
/** Pure elapsed-time window calculation over normalized UTC opening intervals. */
namespace Abientot\Support;
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}
final class NotificationWindow {
	/** Intervals are [start_timestamp,end_timestamp]; callers must supply preceding openings. */
	public static function since( int $now, int $hours, array $open_intervals, bool $extend = true ): int {
		$since = $now - max( 1, min( 720, $hours ) ) * 3600;
		if ( ! $extend ) {
			return $since;
		}
		$intervals = array();
		foreach ( $open_intervals as $interval ) {
			if ( is_array( $interval ) && isset( $interval[0], $interval[1] ) && is_numeric( $interval[0] ) && is_numeric( $interval[1] ) && $interval[1] > $interval[0] ) {
				$intervals[] = array( (int) $interval[0], (int) $interval[1] );
			}
		}
		usort( $intervals, static fn( array $a, array $b ): int => $a[0] <=> $b[0] );
		$merged = array();
		foreach ( $intervals as $interval ) {
			$last = count( $merged ) - 1;
			if ( $last >= 0 && $interval[0] <= $merged[ $last ][1] ) {
				$merged[ $last ][1] = max( $merged[ $last ][1], $interval[1] );
			} else {
				$merged[] = $interval;
			}
		}
		$previous_end  = null;
		$last_start    = null;
		$closure_start = null;
		foreach ( $merged as $interval ) {
			if ( $interval[0] > $now ) {
				break;
			}
			$last_start    = $interval[0];
			$closure_start = $previous_end;
			if ( $interval[1] > $now ) {
				return $last_start >= $since && $closure_start !== null ? min( $since, $closure_start ) : $since;
			}
			$previous_end = $interval[1];
		}
		// Currently closed: include the current closure, even when older than the base window.
		if ( $last_start !== null && $last_start >= $since && $closure_start !== null ) {
			$since = min( $since, $closure_start );
		}
		return $previous_end === null ? $since : min( $since, $previous_end );
	}
}