<?php
/**
 * Data function get_stock_runway.
 *
 * @package Askshelf
 */

declare( strict_types = 1 );

namespace Askshelf\Tools;

use Askshelf\Data\Analytics;
use Askshelf\Data\Period;
use Askshelf\Settings;
use DateTimeImmutable;

defined( 'ABSPATH' ) || exit;

/**
 * Days of stock left = stock on hand / average units sold per day.
 *
 * Stock can be managed on the product (covering all its variations) or on each
 * variation; the sales rate is taken at the same level as the stock.
 */
final class StockRunway implements Tool {

	/** Most sold products/variations read for the rate (pages of 100). */
	private const MAX_ROWS = 500;

	/** {@inheritDoc} */
	public function name(): string {
		return 'get_stock_runway';
	}

	/** {@inheritDoc} */
	public function scopes(): array {
		return array( Settings::SCOPE_ORDERS, Settings::SCOPE_PRODUCTS );
	}

	/** {@inheritDoc} */
	public function schema(): array {
		return Schema::object(
			array(
				'within_days'   => array(
					'type'    => 'integer',
					'minimum' => 1,
					'maximum' => 120,
					'default' => 14,
				),
				'lookback_days' => array(
					'type'    => 'integer',
					'minimum' => 7,
					'maximum' => 90,
					'default' => 30,
				),
				'limit'         => array(
					'type'    => 'integer',
					'minimum' => 1,
					'maximum' => 50,
					'default' => 20,
				),
			)
		);
	}

	/**
	 * Runs the data function.
	 *
	 * @param array<string, mixed> $args Validated arguments.
	 * @return array<string, mixed>
	 */
	public function run( array $args ): array {
		$within   = (int) ( $args['within_days'] ?? 14 );
		$lookback = (int) ( $args['lookback_days'] ?? 30 );
		$limit    = (int) ( $args['limit'] ?? 20 );

		// Lookback ends yesterday so a part-day does not drag the rate down.
		$yesterday = ( new DateTimeImmutable( 'yesterday', wp_timezone() ) );
		$period    = Period::from_dates( $yesterday->modify( '-' . ( $lookback - 1 ) . ' days' )->format( 'Y-m-d' ), $yesterday->format( 'Y-m-d' ) );

		$product_sales   = self::sold( '/reports/products', 'product_id', $period );
		$variation_sales = self::sold( '/reports/variations', 'variation_id', $period );

		$candidates = array();

		// Stock managed per variation.
		foreach ( $variation_sales as $variation_id => $sold ) {
			$variation = wc_get_product( $variation_id );
			if ( ! $variation || true !== $variation->managing_stock() ) {
				continue;
				// false, or 'parent' when the parent product manages stock.
			}
			$candidates[] = self::row( $variation, $sold, $lookback );
		}

		// Stock managed on the product itself (simple products, or variable products with parent-level stock).
		foreach ( $product_sales as $product_id => $sold ) {
			$product = wc_get_product( $product_id );
			if ( ! $product || ! $product->get_manage_stock() ) {
				continue;
			}
			$candidates[] = self::row( $product, $sold, $lookback );
		}

		$soon = array_values(
			array_filter(
				$candidates,
				static fn( array $row ): bool => null !== $row['days_left'] && $row['days_left'] <= $within
			)
		);
		usort( $soon, static fn( array $a, array $b ): int => $a['days_left'] <=> $b['days_left'] );
		$total_soon = count( $soon );
		$soon       = array_slice( $soon, 0, $limit );

		return array(
			'lookback_period'   => $period->to_array(),
			'within_days'       => $within,
			'products_checked'  => count( $candidates ),
			'running_out'       => $soon,
			'running_out_count' => $total_soon,
			'rows_read'         => count( $product_sales ) + count( $variation_sales ),
			'notes'             => array( 'Only products with managed stock that sold in the lookback period are included. Days left = stock / average units sold per day.' ),
			'chart'             => array(
				'type'   => 'bar',
				'title'  => __( 'Days of stock left', 'askshelf' ),
				'format' => 'days',
				'points' => array_map(
					static fn( array $r ): array => array(
						'label' => $r['name'],
						'value' => $r['days_left'],
					),
					$soon
				),
			),
		);
	}

	/**
	 * Units sold per id over the period, most sold first.
	 *
	 * @param string $route  Analytics route.
	 * @param string $id_key Id field in the rows.
	 * @param Period $period Period.
	 * @return array<int, int>
	 */
	private static function sold( string $route, string $id_key, Period $period ): array {
		$sold  = array();
		$pages = (int) ceil( self::MAX_ROWS / 100 );
		for ( $page = 1; $page <= $pages; $page++ ) {
			$response = Analytics::get(
				$route,
				array(
					'after'    => $period->after(),
					'before'   => $period->before(),
					'orderby'  => 'items_sold',
					'order'    => 'desc',
					'per_page' => 100,
					'page'     => $page,
				)
			);
			$rows     = is_array( $response['data'] ) ? $response['data'] : array();
			foreach ( $rows as $row ) {
				if ( (int) $row['items_sold'] > 0 ) {
					$sold[ (int) $row[ $id_key ] ] = (int) $row['items_sold'];
				}
			}
			if ( count( $rows ) < 100 ) {
				break;
			}
		}//end for
		return $sold;
	}

	/**
	 * One result row.
	 *
	 * @param \WC_Product $product  Product or variation.
	 * @param int         $sold     Units sold in the lookback.
	 * @param int         $lookback Lookback days.
	 * @return array<string, mixed>
	 */
	private static function row( \WC_Product $product, int $sold, int $lookback ): array {
		$stock   = (int) $product->get_stock_quantity();
		$per_day = $sold / $lookback;
		$days    = $per_day > 0 ? max( 0.0, round( $stock / $per_day, 1 ) ) : null;
		return array(
			'product_id'   => $product->get_id(),
			'name'         => wp_strip_all_tags( $product->get_name() ),
			'sku'          => (string) $product->get_sku(),
			'stock'        => $stock,
			'sold_per_day' => round( $per_day, 2 ),
			'units_sold'   => $sold,
			'days_left'    => $days,
			'backorders'   => $product->backorders_allowed(),
		);
	}
}