import { Injectable, inject } from '@angular/core';
import { Meta, Title } from '@angular/platform-browser';
import { environment } from '../../environments/environment';
import { Item } from '../models';
import { getDiscountedPrice, getMainImage } from '../utils/item.utils';

@Injectable({
  providedIn: 'root'
})
export class SeoService {
  private meta = inject(Meta);
  private title = inject(Title);

  private readonly siteUrl = `https://${environment.domain}`;
  private readonly siteName = environment.brandFullName;

  /**
   * Set Open Graph & Twitter Card meta tags for a product/item page.
   */
  setItemMeta(item: Item): void {
    const price = item.discount > 0 ? getDiscountedPrice(item) : item.price;
    const imageUrl = this.resolveUrl(getMainImage(item));
    const itemUrl = `${this.siteUrl}/item/${item.itemID}`;
    const description = this.truncate(this.stripHtml(item.description), 160);
    const titleText = `${item.name} — ${this.siteName}`;

    this.title.setTitle(titleText);

    this.setOrUpdate([
      // Open Graph
      { property: 'og:type', content: 'product' },
      { property: 'og:title', content: item.name },
      { property: 'og:description', content: description },
      { property: 'og:image', content: imageUrl },
      { property: 'og:url', content: itemUrl },
      { property: 'og:site_name', content: this.siteName },
      { property: 'og:locale', content: 'ru_RU' },

      // Product-specific OG tags
      { property: 'product:price:amount', content: price.toFixed(2) },
      { property: 'product:price:currency', content: item.currency || 'RUB' },

      // Twitter Card
      { name: 'twitter:card', content: 'summary_large_image' },
      { name: 'twitter:title', content: item.name },
      { name: 'twitter:description', content: description },
      { name: 'twitter:image', content: imageUrl },

      // Standard meta
      { name: 'description', content: description },
    ]);
  }

  /**
   * Reset meta tags back to defaults (call on navigation away from item page).
   */
  resetToDefaults(): void {
    const defaultTitle = `${this.siteName} — Маркетплейс товаров и услуг`;
    const defaultDescription = 'Современный маркетплейс для покупки цифровых товаров. Широкий выбор товаров, удобный поиск, быстрая доставка.';
    const defaultImage = `${this.siteUrl}/og-image.jpg`;

    this.title.setTitle(defaultTitle);

    this.setOrUpdate([
      { property: 'og:type', content: 'website' },
      { property: 'og:title', content: defaultTitle },
      { property: 'og:description', content: defaultDescription },
      { property: 'og:image', content: defaultImage },
      { property: 'og:url', content: this.siteUrl },
      { property: 'og:site_name', content: this.siteName },
      { property: 'og:locale', content: 'ru_RU' },

      { name: 'twitter:card', content: 'summary_large_image' },
      { name: 'twitter:title', content: defaultTitle },
      { name: 'twitter:description', content: defaultDescription },
      { name: 'twitter:image', content: defaultImage },

      { name: 'description', content: defaultDescription },
    ]);

    // Remove product-specific tags
    this.meta.removeTag("property='product:price:amount'");
    this.meta.removeTag("property='product:price:currency'");
  }

  private setOrUpdate(tags: Array<{ property?: string; name?: string; content: string }>): void {
    for (const tag of tags) {
      const selector = tag.property
        ? `property='${tag.property}'`
        : `name='${tag.name}'`;

      const existing = this.meta.getTag(selector);
      if (existing) {
        this.meta.updateTag(tag as any, selector);
      } else {
        this.meta.addTag(tag as any);
      }
    }
  }

  /** Convert relative URLs to absolute */
  private resolveUrl(url: string): string {
    if (!url || url.startsWith('http')) return url;
    return `${this.siteUrl}${url.startsWith('/') ? '' : '/'}${url}`;
  }

  /** Strip HTML tags from a string */
  private stripHtml(html: string): string {
    return html?.replace(/<[^>]*>/g, '') || '';
  }

  /** Truncate text to maxLength, adding ellipsis */
  private truncate(text: string, maxLength: number): string {
    if (!text || text.length <= maxLength) return text || '';
    return text.substring(0, maxLength - 1) + '…';
  }
}