import type { Media } from "@/payload-types";
import { mediaUrl } from "@/lib/payload/media";

type MediaRef = Media | number | null | undefined;

type SeoGroup =
  | {
      title?: string | null;
      description?: string | null;
      keywords?: string | null;
      ogImage?: MediaRef;
    }
  | null
  | undefined;

export type ResolvedSeo = {
  title: string;
  description: string;
  keywords?: string;
  ogImageUrl?: string;
};

/**
 * Priority chain used everywhere on the site (see section 32 of the SEO
 * brief): manual CMS field → content-derived fallback → nothing invented.
 * `fallbackDescription` may be a thunk so callers only pay for building an
 * excerpt (walking richText) when the manual field is actually empty.
 */
export function resolveSeo(args: {
  seo?: SeoGroup;
  fallbackTitle: string;
  fallbackDescription: string | (() => string);
  fallbackImage?: MediaRef;
  defaultOgImage?: MediaRef;
}): ResolvedSeo {
  const title = args.seo?.title?.trim() || args.fallbackTitle;
  const description =
    args.seo?.description?.trim() ||
    (typeof args.fallbackDescription === "function" ? args.fallbackDescription() : args.fallbackDescription);

  const ogImageUrl =
    mediaUrl(args.seo?.ogImage, "hero") ?? mediaUrl(args.fallbackImage, "hero") ?? mediaUrl(args.defaultOgImage, "hero");

  return {
    title,
    description,
    keywords: args.seo?.keywords?.trim() || undefined,
    ogImageUrl,
  };
}