<?php
/**
 * AKSRT Discount Engine
 *
 * 优惠活动计算引擎 — reduction 立减 / discount 打折 / gift 买赠。
 * scope: item / product / author / order。
 * 绑定在 shop_discount taxonomy 上，商品可挂多个活动。
 *
 * @package AKSRT
 */

defined('ABSPATH') || exit;

class AKSRT_Discount {

    private static $instance = null;

    public static function get_instance(): self {
        if (null === self::$instance) {
            self::$instance = new self();
        }
        return self::$instance;
    }

    /**
     * Get all active discount campaigns for a product.
     *
     * @param int $product_id
     * @return array<int, array> Sorted by priority desc.
     */
    public function get_active_discounts(int $product_id): array {
        $terms = wp_get_object_terms($product_id, 'shop_discount', ['fields' => 'all']);
        if (is_wp_error($terms) || empty($terms)) {
            return [];
        }

        $now = current_time('timestamp');
        $active = [];

        foreach ($terms as $term) {
            $meta = AKSRT_Shop_Term_Meta::get_discount_meta($term->term_id);

            // Time limit check
            if (!empty($meta['start']) && strtotime($meta['start']) > $now) {
                continue;
            }
            if (!empty($meta['end']) && strtotime($meta['end']) < $now) {
                continue;
            }

            $meta['term_id'] = $term->term_id;
            $meta['name'] = $term->name;
            $active[] = $meta;
        }

        // Sort by priority desc
        usort($active, function ($a, $b) {
            return ((int) $b['priority']) - ((int) $a['priority']);
        });

        return $active;
    }

    /**
     * Calculate discount for a single line item.
     *
     * @param float $unit_price  Unit price
     * @param int   $quantity    Quantity
     * @param int   $product_id  Product ID
     * @param int   $user_id     User ID (for user_limit checks)
     * @return array{
     *   original: float,
     *   discount_amount: float,
     *   final_price: float,
     *   gifts: array,
     *   applied: array<int, array>
     * }
     */
    public function calculate(float $unit_price, int $quantity, int $product_id, int $user_id = 0): array {
        $original = $unit_price * $quantity;
        $discount_amount = 0.0;
        $gifts = [];
        $applied = [];

        $discounts = $this->get_active_discounts($product_id);

        foreach ($discounts as $d) {
            // User limit check
            if (!empty($d['user_limit']) && $user_id > 0) {
                if (!$this->check_user_limit($d['user_limit'], $user_id)) {
                    continue;
                }
            }

            // Price limit check
            if ((float) $d['price_limit'] > 0 && $original < (float) $d['price_limit']) {
                continue;
            }

            $type = $d['type'] ?? 'reduction';
            $value = (float) ($d['value'] ?? 0);

            switch ($type) {
                case 'reduction':
                    // 立减
                    $discount_amount += min($value * $quantity, $original - $discount_amount);
                    break;

                case 'discount':
                    // 打折 (value = 折扣系数 e.g. 8.5 = 85折)
                    if ($value > 0 && $value < 10) {
                        $rate = $value / 10.0;
                        $save = ($original - $discount_amount) * (1 - $rate);
                        $discount_amount += $save;
                    }
                    break;

                case 'gift':
                    // 买赠 — collect gift config, no price reduction
                    if (!empty($d['gift_config'])) {
                        $gift_data = json_decode($d['gift_config'], true);
                        if (is_array($gift_data)) {
                            $gifts[] = $gift_data;
                        }
                    }
                    break;
            }

            $applied[] = [
                'term_id' => $d['term_id'],
                'name'    => $d['name'] ?? '',
                'type'    => $type,
                'value'   => $value,
            ];
        }

        $discount_amount = min($discount_amount, $original);

        return [
            'original'        => $original,
            'discount_amount' => round($discount_amount, 2),
            'final_price'     => round($original - $discount_amount, 2),
            'gifts'           => $gifts,
            'applied'         => $applied,
        ];
    }

    /**
     * Check if a user meets the user_limit requirement.
     *
     * @param string $limit  'vip' / 'vip_2' / 'auth'
     * @param int    $user_id
     * @return bool
     */
    private function check_user_limit(string $limit, int $user_id): bool {
        if (empty($limit)) {
            return true;
        }

        switch ($limit) {
            case 'vip':
                return function_exists('aksrt_is_vip') ? aksrt_is_vip($user_id) : false;
            case 'vip_2':
                return function_exists('aksrt_is_vip2') ? aksrt_is_vip2($user_id) : false;
            case 'auth':
                return function_exists('aksrt_is_verified') ? aksrt_is_verified($user_id) : false;
            default:
                return true;
        }
    }
}