<?php
/**
 * Discount Integration for displaying customer-specific discounts.
 *
 * Handles price display modifications on product pages and in cart
 * based on customer discount data from Genius Commerce backend.
 *
 * @package GeniusCommerce
 */

namespace GeniusCommerce;

defined( 'ABSPATH' ) || exit;

/**
 * GC_Discount_Integration class.
 *
 * Integrates customer discount display into WooCommerce frontend.
 */
class GC_Discount_Integration {

	/**
	 * Cache TTL in seconds (5 minutes).
	 */
	private const CACHE_TTL = 300;

	/**
	 * API Client instance.
	 *
	 * @var GC_API_Client
	 */
	private GC_API_Client $api_client;

	/**
	 * Template engine instance.
	 *
	 * @var GC_Template_Engine
	 */
	private GC_Template_Engine $template_engine;

	/**
	 * Constructor.
	 */
	public function __construct() {
		$this->api_client      = new GC_API_Client();
		$this->template_engine = new GC_Template_Engine();

		$this->init_hooks();
	}

	/**
	 * Initialize hooks.
	 *
	 * @return void
	 */
	private function init_hooks(): void {
		// Only load on frontend.
		if ( is_admin() ) {
			return;
		}

		// Price display filter.
		add_filter( 'woocommerce_get_price_html', array( $this, 'maybe_show_discount_price' ), 10, 2 );

		// Cart discount fee.
		add_action( 'woocommerce_cart_calculate_fees', array( $this, 'apply_cart_discount' ) );

		// Invalidate cart discount cache on cart update.
		add_action( 'woocommerce_cart_updated', array( $this, 'invalidate_cart_discount_cache' ) );

		// Enqueue frontend assets.
		add_action( 'wp_enqueue_scripts', array( $this, 'enqueue_assets' ) );

		// Clear cache on logout.
		add_action( 'wp_logout', array( $this, 'clear_user_discount_cache' ) );
	}

	/**
	 * Check if discount display should be shown.
	 *
	 * @return bool
	 */
	private function should_show_discount(): bool {
		// Must be logged in.
		if ( ! is_user_logged_in() ) {
			return false;
		}

		// Check if discount display is enabled.
		if ( 'no' === get_option( 'genius_commerce_enable_discount_display', 'yes' ) ) {
			return false;
		}

		return true;
	}

	/**
	 * Maybe show discount price HTML.
	 *
	 * Filters the price HTML to show customer-specific discount.
	 *
	 * @param string      $price_html Original price HTML.
	 * @param \WC_Product $product    Product object.
	 * @return string Modified price HTML.
	 */
	public function maybe_show_discount_price( string $price_html, \WC_Product $product ): string {
		// Check if we should show discount.
		if ( ! $this->should_show_discount() ) {
			return $price_html;
		}

		// Skip variable products (handled by variations).
		if ( $product->is_type( 'variable' ) ) {
			return $price_html;
		}

		// Get discount data.
		$discount_data = $this->get_product_discount( $product );

		// No discount available, return original.
		// Backend response format: originalPriceIncVAT, discountedPriceIncVAT, discountPercentage, discountReason
		$has_discount = ! empty( $discount_data['discountPercentage'] ) && $discount_data['discountPercentage'] > 0;
		if ( ! $discount_data || ! $has_discount ) {
			return $price_html;
		}

		// Render discount price template.
		return $this->render_discount_price( $product, $discount_data, $price_html );
	}

	/**
	 * Get discount data for a product.
	 *
	 * @param \WC_Product $product Product object.
	 * @return array|null Discount data or null if not available.
	 */
	private function get_product_discount( \WC_Product $product ): ?array {
		$user_id    = get_current_user_id();
		$product_id = $product->get_id();
		$sku        = $product->get_sku();

		// SKU is required.
		if ( empty( $sku ) ) {
			return null;
		}

		// Check cache first.
		$cache_key = $this->get_cache_key( $user_id, $product_id );
		$cached    = get_transient( $cache_key );

		if ( false !== $cached ) {
			return $cached;
		}

		// Fetch from API.
		$discount_data = $this->fetch_discount_from_api( $user_id, $sku, (float) $product->get_price() );

		// Cache the result (even if null to prevent repeated failed calls).
		set_transient( $cache_key, $discount_data ?? array(), self::CACHE_TTL );

		return $discount_data;
	}

	/**
	 * Fetch discount data from Genius Commerce API.
	 *
	 * @param int    $user_id       WordPress user ID.
	 * @param string $sku           Product SKU.
	 * @param float  $original_price Original product price.
	 * @return array|null Discount data or null on failure.
	 */
	private function fetch_discount_from_api( int $user_id, string $sku, float $original_price ): ?array {
		$result = $this->api_client->request(
			'POST',
			'/calculate-prices',
			array(
				'wcUserId' => $user_id,
				'products' => array(
					array(
						'sku'      => $sku,
						'quantity' => 1,
						'price'    => $original_price,
					),
				),
			)
		);

		// API call failed - graceful fallback.
		if ( ! $result['success'] ) {
			Genius_Commerce::log(
				sprintf( 'Failed to fetch discount for SKU %s: %s', $sku, $result['error'] ?? 'Unknown error' ),
				'warning'
			);
			return null;
		}

		// Extract price data from response.
		$data = $result['data'] ?? array();

		// Handle direct response format.
		if ( isset( $data['prices'] ) && is_array( $data['prices'] ) ) {
			foreach ( $data['prices'] as $price_data ) {
				if ( isset( $price_data['sku'] ) && $price_data['sku'] === $sku ) {
					return $price_data;
				}
			}
		}

		// Handle single product response.
		if ( isset( $data['sku'] ) && $data['sku'] === $sku ) {
			return $data;
		}

		return null;
	}

	/**
	 * Render discount price HTML.
	 *
	 * @param \WC_Product $product        Product object.
	 * @param array       $discount_data  Discount data from API.
	 * @param string      $original_html  Original price HTML.
	 * @return string Rendered discount price HTML.
	 */
	private function render_discount_price( \WC_Product $product, array $discount_data, string $original_html ): string {
		// Backend response format: originalPriceIncVAT, discountedPriceIncVAT, discountPercentage, discountReason
		$original_price      = $discount_data['originalPriceIncVAT'] ?? (float) $product->get_price();
		$discount_price      = $discount_data['discountedPriceIncVAT'] ?? $original_price;
		$discount_percentage = $discount_data['discountPercentage'] ?? 0;
		$discount_amount     = $original_price - $discount_price;
		$discount_reason     = $discount_data['discountReason'] ?? '';

		// Format prices for display.
		$formatted_original = wc_price( $original_price );
		$formatted_discount = wc_price( $discount_price );

		// Build template arguments.
		$template_args = array(
			'original_price'      => $formatted_original,
			'discount_price'      => $formatted_discount,
			'discount_percentage' => round( $discount_percentage ),
			'discount_amount'     => wc_price( $discount_amount ),
			'discount_reason'     => $discount_reason,
			'product'             => $product,
			'original_html'       => $original_html,
		);

		/**
		 * Filter the discount price template arguments.
		 *
		 * Allows themes to modify or add template variables.
		 *
		 * @since 1.0.0
		 *
		 * @param array       $template_args  Template arguments.
		 * @param \WC_Product $product        The product object.
		 * @param array       $discount_data  Raw discount data from API.
		 */
		$template_args = apply_filters( 'genius_commerce_discount_price_template_args', $template_args, $product, $discount_data );

		// Render using template engine.
		return $this->template_engine->render( 'discount-price.php', $template_args );
	}

	/**
	 * Get cache key for user/product discount.
	 *
	 * @param int $user_id    User ID.
	 * @param int $product_id Product ID.
	 * @return string Cache key.
	 */
	private function get_cache_key( int $user_id, int $product_id ): string {
		return sprintf( 'genius_commerce_discount_%d_%d', $user_id, $product_id );
	}

	/**
	 * Clear discount cache for current user.
	 *
	 * @return void
	 */
	public function clear_user_discount_cache(): void {
		$user_id = get_current_user_id();

		if ( ! $user_id ) {
			return;
		}

		// We can't easily clear all product caches, but the 5 minute TTL
		// ensures they expire naturally. For immediate clearing on logout,
		// we rely on the new session not having cached data.
		Genius_Commerce::log(
			sprintf( 'User %d logged out, discount cache will expire naturally', $user_id ),
			'debug'
		);
	}

	/**
	 * Enqueue frontend assets.
	 *
	 * @return void
	 */
	public function enqueue_assets(): void {
		// Only on WooCommerce pages.
		if ( ! is_woocommerce() && ! is_cart() && ! is_checkout() ) {
			return;
		}

		wp_enqueue_style(
			'genius-commerce-frontend',
			GENIUS_COMMERCE_PLUGIN_URL . 'assets/css/frontend.css',
			array(),
			GENIUS_COMMERCE_VERSION
		);
	}

	/**
	 * Get discounts for multiple products (for cart integration).
	 *
	 * @param array $products Array of products with sku and quantity.
	 * @return array|null Discount data for all products.
	 */
	public function get_cart_discounts( array $products ): ?array {
		if ( ! is_user_logged_in() ) {
			return null;
		}

		$user_id = get_current_user_id();

		// Build cache key from all products.
		$products_hash = md5( wp_json_encode( $products ) );
		$cache_key     = sprintf( 'genius_commerce_cart_discount_%d_%s', $user_id, $products_hash );

		// Check cache.
		$cached = get_transient( $cache_key );
		if ( false !== $cached ) {
			return $cached;
		}

		// Fetch from API.
		$result = $this->api_client->request(
			'POST',
			'/calculate-prices',
			array(
				'wcUserId' => $user_id,
				'products' => $products,
			)
		);

		if ( ! $result['success'] ) {
			Genius_Commerce::log(
				sprintf( 'Failed to fetch cart discounts: %s', $result['error'] ?? 'Unknown error' ),
				'warning'
			);
			return null;
		}

		$data = $result['data'] ?? array();

		// Cache the result.
		set_transient( $cache_key, $data, self::CACHE_TTL );

		return $data;
	}

	/**
	 * Apply customer discount as negative fee to cart.
	 *
	 * Hooked to woocommerce_cart_calculate_fees.
	 *
	 * @param \WC_Cart $cart Cart object.
	 * @return void
	 */
	public function apply_cart_discount( \WC_Cart $cart ): void {
		// Must be logged in.
		if ( ! is_user_logged_in() ) {
			return;
		}

		// Check if discount display is enabled.
		if ( 'no' === get_option( 'genius_commerce_enable_discount_display', 'yes' ) ) {
			return;
		}

		// Avoid running during admin AJAX calls for cart fragments.
		if ( is_admin() && ! defined( 'DOING_AJAX' ) ) {
			return;
		}

		// Get cart products.
		$products = $this->get_cart_products();

		if ( empty( $products ) ) {
			return;
		}

		// Get discount data from API.
		$discount_data = $this->get_cart_discounts( $products );

		if ( ! $discount_data || empty( $discount_data['prices'] ) ) {
			return;
		}

		// Calculate total discount from individual product discounts.
		$discount_result = $this->calculate_total_discount( $discount_data, $products );

		if ( $discount_result['total'] <= 0 ) {
			return;
		}

		// Add negative fee for discount.
		$fee_name = $discount_result['reason'] ?: __( 'Klantkorting', 'genius-commerce' );

		// WooCommerce bug: negative fees ignore taxable=false and always calculate tax
		// See: https://github.com/woocommerce/woocommerce/issues/25719
		// Workaround: Pass ex-VAT amount with taxable=true, so WooCommerce adds VAT correctly
		// Our API calculates discounts on incl-VAT prices, so we need to convert to ex-VAT
		$discount_incl_vat = $discount_result['total'];
		$vat_rate          = 0.21; // Standard Dutch VAT rate
		$discount_excl_vat = $discount_incl_vat / ( 1 + $vat_rate );

		$cart->add_fee(
			$fee_name,
			-$discount_excl_vat,
			true  // Taxable - WooCommerce will add VAT to reach the correct incl-VAT amount
		);

		Genius_Commerce::log(
			sprintf(
				'Applied cart discount: %s (-%s)',
				$fee_name,
				wc_price( $discount_result['total'] )
			),
			'debug'
		);
	}

	/**
	 * Get all products from cart for API request.
	 *
	 * @return array Array of products with sku and quantity.
	 */
	private function get_cart_products(): array {
		$products = array();

		if ( ! WC()->cart ) {
			return $products;
		}

		foreach ( WC()->cart->get_cart() as $cart_item ) {
			/** @var \WC_Product $product */
			$product = $cart_item['data'];
			$sku     = $product->get_sku();

			// Skip products without SKU.
			if ( empty( $sku ) ) {
				continue;
			}

			$products[] = array(
				'sku'      => $sku,
				'quantity' => (int) $cart_item['quantity'],
			);
		}

		return $products;
	}

	/**
	 * Calculate total discount from API response.
	 *
	 * @param array $discount_data API response with prices array.
	 * @param array $products      Cart products with quantities.
	 * @return array{total: float, reason: string} Total discount and reason.
	 */
	private function calculate_total_discount( array $discount_data, array $products ): array {
		$total_discount  = 0.0;
		$discount_reason = '';

		// Build quantity lookup by SKU.
		$quantity_by_sku = array();
		foreach ( $products as $product ) {
			$quantity_by_sku[ $product['sku'] ] = $product['quantity'];
		}

		// Calculate discount for each product.
		foreach ( $discount_data['prices'] as $price_data ) {
			$sku = $price_data['sku'] ?? '';

			if ( empty( $sku ) || ! isset( $quantity_by_sku[ $sku ] ) ) {
				continue;
			}

			// Backend response format: originalPriceIncVAT, discountedPriceIncVAT
			$original_price   = (float) ( $price_data['originalPriceIncVAT'] ?? 0 );
			$discounted_price = (float) ( $price_data['discountedPriceIncVAT'] ?? $original_price );
			$quantity         = $quantity_by_sku[ $sku ];

			// Calculate discount per unit and multiply by quantity.
			$discount_per_unit = $original_price - $discounted_price;
			$total_discount   += $discount_per_unit * $quantity;

			// Capture first discount reason.
			if ( empty( $discount_reason ) && ! empty( $price_data['discountReason'] ) ) {
				$discount_reason = $price_data['discountReason'];
			}
		}

		// Also check for customerGroup in response for reason fallback.
		if ( empty( $discount_reason ) && ! empty( $discount_data['customerGroup'] ) ) {
			$discount_reason = sprintf(
				/* translators: %s: customer group name */
				__( 'Klantgroep: %s', 'genius-commerce' ),
				$discount_data['customerGroup']
			);
		}

		return array(
			'total'  => $total_discount,
			'reason' => $discount_reason,
		);
	}

	/**
	 * Invalidate cart discount cache.
	 *
	 * Hooked to woocommerce_cart_updated.
	 *
	 * @return void
	 */
	public function invalidate_cart_discount_cache(): void {
		if ( ! is_user_logged_in() ) {
			return;
		}

		$user_id = get_current_user_id();

		// We can't easily delete specific transients without knowing the hash,
		// but we can delete based on a pattern using a global transient list.
		// For simplicity, we rely on the hash-based cache key which automatically
		// invalidates when cart contents change (different hash = different key).

		Genius_Commerce::log(
			sprintf( 'Cart updated for user %d, discount cache will be recalculated', $user_id ),
			'debug'
		);
	}
}