<?php

namespace AcademicCrew\Courses;

/**
 * Calculates the current academic year and teaching period.
 *
 * Convention: "2025/26" is stored as int 2025 (start year). The academic
 * year rolls over on period 1's configured start month (September by
 * default) regardless of which period a course belongs to, so with the
 * default windows May 2026 → A.Y. 2025 ("2025/26"), October 2026 → A.Y. 2026.
 */
class AcademicYearCalculator {

    /**
     * Returns the academic start-year for $reference (defaults to now).
     *
     * The rollover point is period 1's configured start month (September
     * when unconfigured), independent of which period $period refers to —
     * period 2 in, say, February is still part of the A.Y. that started the
     * previous September.
     */
    public function calculate( int $period = 1, ?\DateTimeImmutable $reference = null ): int {
        $now   = $reference ?? new \DateTimeImmutable( 'now', wp_timezone() );
        $month = (int) $now->format( 'm' );
        $year  = (int) $now->format( 'Y' );

        $windows        = $this->configured_windows();
        $rollover_month = $windows[1]['start']['month'] ?? 9;

        return $month >= $rollover_month ? $year : $year - 1;
    }

    /**
     * Returns the teaching period currently running for $reference (defaults
     * to now), based on Settings → Academic Year Period Windows.
     *
     * Falls back to the legacy Sep–Jan / Feb–Aug split when no window is
     * configured for any period (e.g. a fresh install, or a cadence whose
     * windows the admin hasn't set yet).
     */
    public function current_period( ?\DateTimeImmutable $reference = null ): int {
        $now   = $reference ?? new \DateTimeImmutable( 'now', wp_timezone() );
        $today = (int) $now->format( 'n' ) * 100 + (int) $now->format( 'j' );

        foreach ( $this->configured_windows() as $period => $window ) {
            if ( $this->in_window( $today, $window ) ) {
                return $period;
            }
        }

        $month = (int) $now->format( 'm' );
        return ( $month >= 9 || 1 === $month ) ? 1 : 2;
    }

    /**
     * Formats a start-year as e.g. 2025 → "2025/26".
     */
    public function format( int $academic_year ): string {
        $short_next = substr( (string) ( $academic_year + 1 ), -2 );
        return "{$academic_year}/{$short_next}";
    }

    /**
     * @return array<int,array{start:array{month:int,day:int},end:array{month:int,day:int}}>
     *         Only periods the admin has actually configured a window for.
     */
    private function configured_windows(): array {
        $settings = get_option( 'academiccrew_settings', [] );
        $windows  = $settings['period_windows'] ?? [];
        $result   = [];

        foreach ( $windows as $period => $window ) {
            if ( ! empty( $window['start']['month'] ) && ! empty( $window['end']['month'] ) ) {
                $result[ (int) $period ] = $window;
            }
        }

        ksort( $result );
        return $result;
    }

    /** Whether $today (an n*100+j "month-day" int) falls inside $window, handling year wraparound. */
    private function in_window( int $today, array $window ): bool {
        $start = (int) $window['start']['month'] * 100 + (int) $window['start']['day'];
        $end   = (int) $window['end']['month']   * 100 + (int) $window['end']['day'];

        return $start <= $end
            ? ( $today >= $start && $today <= $end )
            : ( $today >= $start || $today <= $end ); // window crosses the new year
    }
}