<?php
/**
 * Normalises WooCommerce products into "purchasable units".
 *
 * @package ProfitEngine
 */

declare( strict_types=1 );

namespace ProfitEngine\Support;

use WC_Product;

defined( 'ABSPATH' ) || exit;

/**
 * A "purchasable unit" is the thing you actually buy and hold stock for:
 * a variation for variable products, or the product itself for simple products.
 *
 * All PPE purchasing/cost data attaches to purchasable units, while the Products
 * UI groups them under their parent product. This resolver is the single place
 * that understands that mapping so the rest of the codebase never has to branch
 * on product type.
 */
class ProductResolver {

	/**
	 * Load a WC product object, or null.
	 *
	 * @param int $product_id Product or variation ID.
	 */
	public function product( int $product_id ): ?WC_Product {
		if ( ! function_exists( 'wc_get_product' ) ) {
			return null;
		}
		$product = wc_get_product( $product_id );
		return $product instanceof WC_Product ? $product : null;
	}

	/**
	 * Whether the given ID refers to a product variation.
	 *
	 * @param int $product_id Product ID.
	 */
	public function is_variation( int $product_id ): bool {
		$product = $this->product( $product_id );
		return $product && $product->is_type( 'variation' );
	}

	/**
	 * Whether the given ID refers to a variable (parent) product.
	 *
	 * @param int $product_id Product ID.
	 */
	public function is_variable( int $product_id ): bool {
		$product = $this->product( $product_id );
		return $product && $product->is_type( 'variable' );
	}

	/**
	 * Return the purchasable-unit IDs for a product.
	 *
	 * Variable products expand to their variation IDs; everything else returns
	 * its own ID. Variations passed directly return themselves.
	 *
	 * @param int $product_id Product ID.
	 * @return int[]
	 */
	public function purchasable_units( int $product_id ): array {
		$product = $this->product( $product_id );
		if ( ! $product ) {
			return array();
		}

		if ( $product->is_type( 'variable' ) ) {
			return array_map( 'intval', $product->get_children() );
		}

		return array( $product_id );
	}

	/**
	 * A human-readable label for a purchasable unit (parent name + attributes).
	 *
	 * @param int $unit_id Purchasable-unit ID.
	 */
	public function unit_label( int $unit_id ): string {
		$product = $this->product( $unit_id );
		if ( ! $product ) {
			return '#' . $unit_id;
		}

		if ( $product->is_type( 'variation' ) ) {
			$name = $product->get_name(); // Includes attribute summary.
			return $name ? $name : ( '#' . $unit_id );
		}

		return $product->get_name();
	}

	/**
	 * Current managed stock quantity for a unit (null when stock isn't managed).
	 *
	 * IMPORTANT: a variation whose stock is managed at the PARENT level reports
	 * manage_stock === 'parent' and WooCommerce returns the PARENT's full
	 * quantity from get_stock_quantity(). Summing that across variations would
	 * multiply the parent stock by the number of variations, so such variations
	 * are treated as having no own quantity (null) here. Parent-level totals are
	 * read from the parent product instead (see manages_stock_at_parent()).
	 *
	 * @param int $unit_id Purchasable-unit ID.
	 */
	public function stock_quantity( int $unit_id ): ?float {
		$product = $this->product( $unit_id );
		if ( ! $product ) {
			return null;
		}

		// Variation deferring stock to its parent has no independent quantity.
		if ( $product->is_type( 'variation' ) && true !== $product->get_manage_stock() ) {
			return null;
		}

		$qty = $product->get_stock_quantity();
		return null === $qty ? null : (float) $qty;
	}

	/**
	 * Whether a variable product manages stock at the parent level (one pooled
	 * quantity) rather than per variation.
	 *
	 * @param int $product_id Product ID.
	 */
	public function manages_stock_at_parent( int $product_id ): bool {
		$product = $this->product( $product_id );
		return $product && $product->is_type( 'variable' ) && true === $product->get_manage_stock();
	}

	/**
	 * The parent holding a variation's stock when it draws from a shared
	 * (product-level) quantity, or null when the variation has its own stock or
	 * nobody tracks it.
	 *
	 * @param int $unit_id Variation ID.
	 */
	public function shared_stock_parent( int $unit_id ): ?WC_Product {
		$product = $this->product( $unit_id );
		if ( ! $product || ! $product->is_type( 'variation' ) || true === $product->get_manage_stock() ) {
			return null;
		}
		$parent = $this->product( (int) $product->get_parent_id() );
		return $parent && true === $parent->get_manage_stock() ? $parent : null;
	}

	/**
	 * Variations that draw from a parent's shared stock (those without their own
	 * stock management).
	 *
	 * @param WC_Product $variable Variable product.
	 * @return int[]
	 */
	public function shared_stock_variations( WC_Product $variable ): array {
		$ids = array();
		foreach ( $variable->get_children() as $child_id ) {
			$child = $this->product( (int) $child_id );
			if ( $child && true !== $child->get_manage_stock() ) {
				$ids[] = (int) $child_id;
			}
		}
		return $ids;
	}

	/**
	 * The true total stock for any product, avoiding the parent-deferral
	 * multiplication: parent-managed variable products return the parent's
	 * quantity; per-variation ones sum each variation's own stock; simple
	 * products return their own.
	 *
	 * @param int $product_id Product (parent or simple) ID.
	 */
	public function total_stock( int $product_id ): ?float {
		$product = $this->product( $product_id );
		if ( ! $product ) {
			return null;
		}

		if ( $product->is_type( 'variable' ) ) {
			if ( true === $product->get_manage_stock() ) {
				$qty = $product->get_stock_quantity();
				return null === $qty ? null : (float) $qty;
			}

			$total = 0.0;
			$found = false;
			foreach ( $product->get_children() as $child_id ) {
				$qty = $this->stock_quantity( (int) $child_id );
				if ( null !== $qty ) {
					$total += $qty;
					$found  = true;
				}
			}
			return $found ? $total : null;
		}

		return $this->stock_quantity( $product_id );
	}

	/**
	 * Thumbnail URL for a product or variation, or '' when it has no image.
	 *
	 * A variation without its own image uses its parent's (WooCommerce does this
	 * in the "view" context). No placeholder: callers show no image instead.
	 *
	 * @param int $unit_id Product or variation ID.
	 */
	public function image_url( int $unit_id ): string {
		$product  = $this->product( $unit_id );
		$image_id = $product ? (int) $product->get_image_id() : 0;
		$url      = $image_id > 0 ? wp_get_attachment_image_url( $image_id, 'thumbnail' ) : false;
		return $url ? (string) $url : '';
	}

	/**
	 * The unit's SKU.
	 *
	 * @param int $unit_id Purchasable-unit ID.
	 */
	public function sku( int $unit_id ): string {
		$product = $this->product( $unit_id );
		return $product ? (string) $product->get_sku() : '';
	}

	/**
	 * The unit's current selling price as a float.
	 *
	 * @param int $unit_id Purchasable-unit ID.
	 */
	public function price( int $unit_id ): float {
		$product = $this->product( $unit_id );
		return $product ? (float) $product->get_price() : 0.0;
	}

	/**
	 * Days since the unit (or its parent) was created — for forecast confidence.
	 *
	 * @param int $unit_id Purchasable-unit ID.
	 * @return int Days, or a large number when unknown.
	 */
	public function created_days( int $unit_id ): int {
		$product = $this->product( $unit_id );
		if ( ! $product ) {
			return PHP_INT_MAX;
		}

		$created = $product->get_date_created();
		if ( ! $created && $product->get_parent_id() ) {
			$parent  = $this->product( (int) $product->get_parent_id() );
			$created = $parent ? $parent->get_date_created() : null;
		}
		if ( ! $created ) {
			return PHP_INT_MAX;
		}

		$seconds = time() - $created->getTimestamp();
		return (int) max( 0, floor( $seconds / DAY_IN_SECONDS ) );
	}

	/**
	 * A compact summary array describing a purchasable unit for the UI.
	 *
	 * @param int $unit_id Purchasable-unit ID.
	 * @return array<string,mixed>|null
	 */
	public function unit_summary( int $unit_id ): ?array {
		$product = $this->product( $unit_id );
		if ( ! $product ) {
			return null;
		}

		return array(
			'id'           => $unit_id,
			'parent_id'    => (int) $product->get_parent_id(),
			'label'        => $this->unit_label( $unit_id ),
			'sku'          => (string) $product->get_sku(),
			'type'         => $product->get_type(),
			'price'        => (float) $product->get_price(),
			'manage_stock' => true === $product->get_manage_stock(),
			'stock'        => $this->stock_quantity( $unit_id ),
			'image'        => $this->image_url( $unit_id ),
		);
	}
}