<?php
/**
 * Figures for the overview: codes issued and redeemed, savings and revenue in a period, per
 * campaign and category, with a series per day or week for the chart.
 *
 * Codes count on the day they were issued and uses on the day the order was placed; released uses
 * (cancelled, refunded, failed orders) do not count. Days follow the site's time zone.
 *
 * @package CNWS\Coupons
 */

namespace CNWS\Coupons;

defined( 'ABSPATH' ) || exit;

// phpcs:disable WordPress.DB.DirectDatabaseQuery -- Aggregates over the plugin's own tables, named through %i; cached in the object cache.

final class Dashboard {

	public const PERIODS     = array( 'week', 'month', '3months', 'custom' );
	public const CACHE_GROUP = 'cnwscoupons';

	/**
	 * Longest custom period, so one request never aggregates years of hourly rows.
	 */
	public const MAX_DAYS = 731;

	public function __construct(
		private CampaignRepository $campaigns,
		private CategoryRepository $categories
	) {}

	/**
	 * The report for a period, a category (0 = all, -1 = none) and a campaign (0 = all).
	 *
	 * @param string $period   One of PERIODS.
	 * @param string $from     Custom start, Y-m-d.
	 * @param string $to       Custom end, Y-m-d.
	 * @param int    $category Category ID.
	 * @param int    $campaign Campaign ID.
	 * @return array|null Null for an invalid custom period.
	 */
	public function filtered( string $period, string $from, string $to, int $category, int $campaign ): ?array {
		$days = self::period( in_array( $period, self::PERIODS, true ) ? $period : 'month', $from, $to, wp_date( 'Y-m-d' ) );

		if ( ! $days ) {
			return null;
		}

		$campaigns = array_filter(
			$this->campaigns->all(),
			static fn( Campaign $c ) => ( ! $campaign || $c->id === $campaign )
				&& ( ! $category || ( -1 === $category ? ! $c->category_id : (int) $c->category_id === $category ) )
		);

		return $this->report( $days[0], $days[1], array_values( $campaigns ), $this->categories->all() );
	}

	/**
	 * Mark the figures as changed, so cached reports are not reused.
	 */
	public static function changed(): void {
		wp_cache_set( 'last_changed', microtime(), self::CACHE_GROUP );
	}

	/**
	 * First and last day (site time, Y-m-d) of a period: week = 7, month = 30 and 3 months = 90 days up to today.
	 *
	 * @param string $period One of PERIODS.
	 * @param string $from   Custom start, Y-m-d.
	 * @param string $to     Custom end, Y-m-d.
	 * @param string $today  Today in site time, Y-m-d.
	 * @return array{0: string, 1: string}|null Null for an invalid custom period.
	 */
	public static function period( string $period, string $from, string $to, string $today ): ?array {
		$end = new \DateTimeImmutable( $today );

		switch ( $period ) {
			case 'week':
				return array( $end->modify( '-6 days' )->format( 'Y-m-d' ), $today );
			case '3months':
				return array( $end->modify( '-89 days' )->format( 'Y-m-d' ), $today );
			case 'custom':
				if ( ! self::is_date( $from ) || ! self::is_date( $to ) || $from > $to ) {
					return null;
				}

				$days = (int) ( new \DateTimeImmutable( $from ) )->diff( new \DateTimeImmutable( $to ) )->days + 1;

				return $days > self::MAX_DAYS ? null : array( $from, $to );
			default:
				return array( $end->modify( '-29 days' )->format( 'Y-m-d' ), $today );
		}
	}

	/**
	 * Up to 62 days the chart shows days, after that weeks starting on Monday.
	 *
	 * @param string $from First day, Y-m-d.
	 * @param string $to   Last day, Y-m-d.
	 * @return array{bucket: string, keys: string[]}
	 */
	public static function buckets( string $from, string $to ): array {
		$start = new \DateTimeImmutable( $from );
		$end   = new \DateTimeImmutable( $to );
		$days  = (int) $start->diff( $end )->days + 1;
		$week  = $days > 62;
		$keys  = array();

		for ( $day = $week ? self::monday( $start ) : $start; $day <= $end; $day = $day->modify( $week ? '+7 days' : '+1 day' ) ) {
			$keys[] = $day->format( 'Y-m-d' );
		}

		return array(
			'bucket' => $week ? 'week' : 'day',
			'keys'   => $keys,
		);
	}

	/**
	 * The report for a period. $campaigns are the campaigns the filter allows.
	 *
	 * @param string     $from       First day, Y-m-d (site time).
	 * @param string     $to         Last day, Y-m-d (site time).
	 * @param Campaign[] $campaigns  Campaigns to include.
	 * @param array      $categories Category ID => name.
	 */
	public function report( string $from, string $to, array $campaigns, array $categories ): array {
		$key    = md5( wp_json_encode( array( $from, $to, array_map( static fn( Campaign $c ) => $c->id, $campaigns ) ) ) ) . ':' . wp_cache_get( 'last_changed', self::CACHE_GROUP );
		$cached = wp_cache_get( 'report:' . $key, self::CACHE_GROUP );

		if ( is_array( $cached ) ) {
			$rows = $cached;
		} else {
			$rows = $this->query( self::utc( $from . ' 00:00:00' ), self::utc( $to . ' 23:59:59' ) );
			wp_cache_set( 'report:' . $key, $rows, self::CACHE_GROUP, 5 * MINUTE_IN_SECONDS );
		}

		return self::build( $from, $to, $campaigns, $categories, $rows['issued'], $rows['hours'] );
	}

	/**
	 * Put the queried rows together. Kept free of the database so it can be tested.
	 *
	 * @param string     $from       First day, Y-m-d.
	 * @param string     $to         Last day, Y-m-d.
	 * @param Campaign[] $campaigns  Campaigns to include.
	 * @param array      $categories Category ID => name.
	 * @param array      $issued     Rows: campaign_id, issued, used (personal codes issued in the period).
	 * @param array      $hours      Rows: campaign_id, hour (UTC, Y-m-d H:00:00), redemptions, saved, revenue.
	 */
	public static function build( string $from, string $to, array $campaigns, array $categories, array $issued, array $hours ): array {
		$buckets = self::buckets( $from, $to );
		$series  = array_fill_keys(
			$buckets['keys'],
			array(
				'redemptions' => 0,
				'saved'       => 0.0,
			)
		);
		$rows    = array();

		foreach ( $campaigns as $campaign ) {
			$rows[ $campaign->id ] = array(
				'id'          => $campaign->id,
				'name'        => $campaign->name,
				'category_id' => (int) $campaign->category_id,
				'type'        => $campaign->type,
				'status'      => $campaign->status,
			) + self::zero();
		}

		foreach ( $issued as $row ) {
			$id = (int) $row->campaign_id;

			if ( isset( $rows[ $id ] ) ) {
				$rows[ $id ]['issued'] = (int) $row->issued;
				$rows[ $id ]['used']   = (int) $row->used;
			}
		}

		$zone = wp_timezone();
		$utc  = new \DateTimeZone( 'UTC' );

		foreach ( $hours as $row ) {
			$id = (int) $row->campaign_id;

			if ( ! isset( $rows[ $id ] ) ) {
				continue;
			}

			$rows[ $id ]['redemptions'] += (int) $row->redemptions;
			$rows[ $id ]['saved']       += (float) $row->saved;
			$rows[ $id ]['revenue']     += (float) $row->revenue;

			$day    = ( new \DateTimeImmutable( (string) $row->hour, $utc ) )->setTimezone( $zone );
			$bucket = ( 'week' === $buckets['bucket'] ? self::monday( $day ) : $day )->format( 'Y-m-d' );

			if ( isset( $series[ $bucket ] ) ) {
				$series[ $bucket ]['redemptions'] += (int) $row->redemptions;
				$series[ $bucket ]['saved']       += (float) $row->saved;
			}
		}

		// Campaigns with nothing in the period are left out unless they are running.
		$rows = array_values(
			array_filter(
				array_map( array( self::class, 'finish' ), $rows ),
				static fn( array $row ) => 'active' === $row['status'] || $row['issued'] || $row['redemptions']
			)
		);

		$groups = array();

		foreach ( $rows as $row ) {
			$id = isset( $categories[ $row['category_id'] ] ) ? $row['category_id'] : 0;

			if ( ! isset( $groups[ $id ] ) ) {
				$groups[ $id ] = array(
					'id'   => $id,
					'name' => $categories[ $id ] ?? '',
				) + self::zero();
			}

			foreach ( array_keys( self::zero() ) as $field ) {
				$groups[ $id ][ $field ] += $row[ $field ];
			}
		}

		$totals = self::zero();
		$shared = count( array_filter( $rows, static fn( array $row ) => Campaign::TYPE_SHARED === $row['type'] ) );

		foreach ( $rows as $row ) {
			foreach ( array_keys( $totals ) as $field ) {
				$totals[ $field ] += $row[ $field ];
			}
		}

		$points = array();

		foreach ( $series as $date => $point ) {
			$points[] = array(
				'date'        => $date,
				'redemptions' => $point['redemptions'],
				'saved'       => round( $point['saved'], 2 ),
			);
		}

		return array(
			'from'       => $from,
			'to'         => $to,
			'bucket'     => $buckets['bucket'],
			'totals'     => self::finish( $totals ) + array( 'shared_campaigns' => $shared ),
			'series'     => $points,
			'categories' => array_values( array_map( array( self::class, 'finish' ), $groups ) ),
			'campaigns'  => $rows,
		);
	}

	/**
	 * @param string $from UTC start, Y-m-d H:i:s.
	 * @param string $to   UTC end, Y-m-d H:i:s.
	 * @return array{issued: array, hours: array}
	 */
	private function query( string $from, string $to ): array {
		global $wpdb;

		$issued = (array) $wpdb->get_results(
			$wpdb->prepare(
				"SELECT campaign_id, COUNT(*) AS issued, SUM( uses > 0 ) AS used FROM %i WHERE email <> '' AND created_at BETWEEN %s AND %s GROUP BY campaign_id",
				Tables::codes(),
				$from,
				$to
			)
		);

		// Grouped per UTC hour, so PHP can place each hour on the right local day across DST changes.
		$hours = (array) $wpdb->get_results(
			$wpdb->prepare(
				"SELECT campaign_id, DATE_FORMAT( redeemed_at, '%%Y-%%m-%%d %%H:00:00' ) AS hour, COUNT(*) AS redemptions, SUM( discount_amount ) AS saved, SUM( order_total ) AS revenue FROM %i WHERE released_at IS NULL AND redeemed_at BETWEEN %s AND %s GROUP BY campaign_id, hour",
				Tables::redemptions(),
				$from,
				$to
			)
		);

		return array(
			'issued' => $issued,
			'hours'  => $hours,
		);
	}

	/**
	 * @param array $row Figures.
	 */
	private static function finish( array $row ): array {
		$row['saved']   = round( $row['saved'], 2 );
		$row['revenue'] = round( $row['revenue'], 2 );
		$row['rate']    = $row['issued'] ? round( 100 * $row['used'] / $row['issued'], 1 ) : null;

		return $row;
	}

	private static function zero(): array {
		return array(
			'issued'      => 0,
			'used'        => 0,
			'redemptions' => 0,
			'saved'       => 0.0,
			'revenue'     => 0.0,
		);
	}

	/**
	 * @param string $local Site time, Y-m-d H:i:s.
	 */
	private static function utc( string $local ): string {
		return ( new \DateTimeImmutable( $local, wp_timezone() ) )->setTimezone( new \DateTimeZone( 'UTC' ) )->format( 'Y-m-d H:i:s' );
	}

	private static function monday( \DateTimeImmutable $day ): \DateTimeImmutable {
		return $day->modify( '-' . ( (int) $day->format( 'N' ) - 1 ) . ' days' );
	}

	private static function is_date( string $date ): bool {
		$parsed = \DateTimeImmutable::createFromFormat( '!Y-m-d', $date );

		return $parsed && $parsed->format( 'Y-m-d' ) === $date;
	}
}