<?php
/**
 * The availability rule (tech spec §4). Core stock is read, never written.
 *
 * owned          = units not retired (when the item tracks units), else max(0, inventory_quantity)
 * available_now  = owned − out-of-service units − outstanding quantity on open loans
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

class WPIMLend_Availability {

	/**
	 * Is this item lendable? Per item flag, "all items", or a lendable category.
	 *
	 * @param object      $core_item Row with inventory_id and category_id.
	 * @param object|null $settings  Lending item settings row (optional, fetched if NULL).
	 */
	public static function is_lendable( $core_item, $settings = NULL ) {
		if ( ! $core_item ) {
			return FALSE;
		}
		if ( WPIMLend_Settings::get( 'lend_all_items' ) ) {
			return TRUE;
		}
		if ( NULL === $settings ) {
			$settings = WPIMLend_Repo::get_item_settings( $core_item->inventory_id );
		}
		if ( ! empty( $settings->lendable ) ) {
			return TRUE;
		}
		$cats = (array) WPIMLend_Settings::get( 'lendable_categories' );

		return $cats && in_array( (int) $core_item->category_id, $cats, TRUE );
	}

	/**
	 * Peak number in use on any single day of [from, to], per item (tech spec §9).
	 *
	 * @return array inventory_id => int
	 */
	public static function peak_usage( array $ids, $from, $to, $exclude_booking = 0 ) {
		$events = [];
		foreach ( WPIMLend_Repo::occupancy( $ids, $from, $to, self::today(), $exclude_booking ) as $row ) {
			$s = max( $row->s, $from );
			$e = min( $row->e, $to );
			if ( $s > $e || (int) $row->q < 1 ) {
				continue;
			}
			$id                      = (int) $row->inventory_id;
			$events[ $id ][]         = [ $s, 1, (int) $row->q ];                 // starts on $s
			$events[ $id ][]         = [ self::next_day( $e ), 0, - (int) $row->q ]; // free again the day after $e
		}

		$peak = [];
		foreach ( $events as $id => $list ) {
			// Same date: releases (0) before starts (1), so back-to-back ranges do not overlap.
			usort( $list, function ( $a, $b ) {
				return strcmp( $a[0], $b[0] ) ?: ( $a[1] - $b[1] );
			} );
			$running = 0;
			$max     = 0;
			foreach ( $list as $ev ) {
				$running += $ev[2];
				$max      = max( $max, $running );
			}
			$peak[ $id ] = $max;
		}

		return $peak;
	}

	/**
	 * Number in use on each day of [from, to], per item, from one occupancy query (calendar).
	 *
	 * @return array inventory_id => [ 'Y-m-d' => int ]
	 */
	public static function daily_usage( array $ids, $from, $to ) {
		$days = [];
		for ( $d = $from; $d <= $to; $d = self::next_day( $d ) ) {
			$days[] = $d;
		}
		$out = [];
		foreach ( $ids as $id ) {
			$out[ (int) $id ] = array_fill_keys( $days, 0 );
		}
		foreach ( WPIMLend_Repo::occupancy( $ids, $from, $to, self::today() ) as $row ) {
			$id = (int) $row->inventory_id;
			for ( $d = max( $row->s, $from ), $end = min( $row->e, $to ); $d <= $end; $d = self::next_day( $d ) ) {
				$out[ $id ][ $d ] += (int) $row->q;
			}
		}

		return $out;
	}

	public static function next_day( $ymd ) {
		return gmdate( 'Y-m-d', strtotime( $ymd . ' 00:00:00 UTC' ) + DAY_IN_SECONDS );
	}

	/**
	 * Availability for many items. Without dates this is "right now" (today..today), which is
	 * exactly the M1 rule when there are no bookings.
	 *
	 * @param string|null $from Site-local Y-m-d.
	 * @param string|null $to   Site-local Y-m-d.
	 *
	 * @return array inventory_id => [ owned, out_of_service, on_loan, available, track_units, lendable ]
	 */
	public static function for_items( array $ids, $from = NULL, $to = NULL, $exclude_booking = 0 ) {
		$ids = array_values( array_unique( array_filter( array_map( 'absint', $ids ) ) ) );
		if ( ! $ids ) {
			return [];
		}
		$from = $from ? $from : self::today();
		$to   = $to ? $to : $from;
		if ( $to < $from ) {
			list( $from, $to ) = [ $to, $from ];
		}

		$core     = WPIMLend_Repo::get_core_items( $ids );
		$settings = WPIMLend_Repo::get_item_settings_map( $ids );
		$units    = WPIMLend_Repo::unit_counts( $ids );
		$open     = WPIMLend_Repo::open_quantities( $ids );
		$peak     = self::peak_usage( $ids, $from, $to, $exclude_booking );

		$out = [];
		foreach ( $ids as $id ) {
			if ( ! isset( $core[ $id ] ) ) {
				continue;
			}
			$s           = isset( $settings[ $id ] ) ? $settings[ $id ] : NULL;
			$track_units = $s && ! empty( $s->track_units );
			$counts      = isset( $units[ $id ] ) ? $units[ $id ] : [];

			if ( $track_units ) {
				$owned = array_sum( $counts ) - ( isset( $counts['retired'] ) ? $counts['retired'] : 0 );
				$oos   = isset( $counts['out_of_service'] ) ? $counts['out_of_service'] : 0;
			} else {
				$owned = max( 0, (int) $core[ $id ]->inventory_quantity );
				$oos   = 0;
			}

			$on_loan = isset( $open[ $id ] ) ? $open[ $id ] : 0;
			$in_use  = isset( $peak[ $id ] ) ? $peak[ $id ] : 0;

			$available = (int) apply_filters( 'wpim_lending_available_now', $owned - $oos - $in_use, $id, $from, $to );

			$out[ $id ] = [
				'owned'          => $owned,
				'out_of_service' => $oos,
				'on_loan'        => $on_loan,
				'available'      => $available,
				'track_units'    => $track_units,
				'lendable'       => self::is_lendable( $core[ $id ], $s ? $s : (object) [ 'lendable' => 0 ] ),
			];
		}

		return $out;
	}

	public static function for_item( $inventory_id, $from = NULL, $to = NULL, $exclude_booking = 0 ) {
		$all = self::for_items( [ $inventory_id ], $from, $to, $exclude_booking );

		return isset( $all[ $inventory_id ] ) ? $all[ $inventory_id ] : NULL;
	}

	/**
	 * Site-local "today" as Y-m-d.
	 */
	public static function today() {
		return wp_date( 'Y-m-d' );
	}

	/**
	 * Default due date for an item, site-local Y-m-d.
	 */
	public static function default_due_date( $inventory_id = 0 ) {
		$days = (int) WPIMLend_Settings::get( 'default_days' );
		if ( $inventory_id ) {
			$s = WPIMLend_Repo::get_item_settings( $inventory_id );
			if ( ! empty( $s->default_days ) ) {
				$days = (int) $s->default_days;
			}
		}

		return wp_date( 'Y-m-d', time() + max( 1, $days ) * DAY_IN_SECONDS );
	}
}