/**
 * Pure metadata derivation for `PageHead`.
 *
 * Intentionally imports NOTHING from solid-js / @solidjs/router / @solidjs/meta
 * so it can be unit-tested in `bun:test` without spinning up the SolidJS
 * router + MetaProvider + DOM (which this repo does not configure). The
 * `PageHead` component is a thin render layer over this function.
 *
 * Rules:
 *  - `title` → `props.title + site.titleSuffix`
 *  - `canonical` → explicit `props.canonical` override wins; otherwise
 *    `https://${site.domain}${pathname}` where `pathname` is the *public*
 *    browser path. Subdomain routing is host-aware (root routes dispatch by
 *    `useSite()`, see `src/routes/index.tsx`/`privacy.tsx`/`deletion.tsx`),
 *    so `useLocation()` already reports the public path. The defensive
 *    prefix-strip below also handles any legacy prefixed form, so the canonical
 *    is always the public URL.
 *  - `ogImage` → explicit `props.ogImage` wins; otherwise `site.ogDefaultImage`.
 *    Either way it is resolved to an **absolute** URL against the site's
 *    domain — OG consumers (X, Slack, Discord, iMessage) require an absolute
 *    URL, and a site-relative path in `ogDefaultImage` would 404 otherwise.
 *  - `ogTitle` / `ogDescription` → explicit override wins; otherwise fall
 *    back to the base title (no suffix) / description (existing behavior).
 */
import type { Site } from "~/lib/site-context";

export interface PageHeadProps {
  title: string;
  description?: string;
  ogImage?: string;
  ogTitle?: string;
  ogDescription?: string;
  canonical?: string;
}

/**
 * Fully-resolved metadata computed by {@link resolvePageHeadMeta}. `PageHead`
 * renders these verbatim. Kept as an exported type so call sites / tests can
 * assert against the exact values without a DOM render.
 */
export interface ResolvedPageHeadMeta {
  /** Page title with the active site's `titleSuffix` appended. */
  title: string;
  description?: string;
  /** Canonical absolute URL for the current route. */
  canonical: string;
  /** OpenGraph title (falls back to the page title without suffix). */
  ogTitle: string;
  /** OpenGraph description (falls back to `description`). */
  ogDescription?: string;
  /** OpenGraph image (defaults to the site's `ogDefaultImage`). */
  ogImage: string;
}

/**
 * Resolve an OpenGraph image reference to an absolute URL.
 *
 * OG consumers (X, Slack, Discord, LinkedIn, iMessage) require an absolute
 * URL; `ogDefaultImage` values are site-relative paths (`/nook/og.png`), so
 * they are joined to the site origin here. Already-absolute references
 * (`https:`, `data:`, protocol-relative `//`) pass through untouched.
 */
function absolutizeOgImage(image: string, domain: string): string {
  if (image.startsWith("//")) return `https:${image}`;
  if (/^[a-z][a-z0-9+.-]*:/i.test(image)) return image;
  return `https://${domain}${image.startsWith("/") ? "" : "/"}${image}`;
}

export function resolvePageHeadMeta(
  props: PageHeadProps,
  site: Site,
  pathname: string
): ResolvedPageHeadMeta {
  const title = `${props.title}${site.titleSuffix}`;
  /**
   * The canonical URL is the *public* browser URL, never any internal route
   * prefix. Subdomain routing is host-aware (root routes dispatch by
   * `useSite()`), so `useLocation()` returns the public path. The strip below
   * is a defensive no-op for the public path and still yields the canonical
   * `https://lineage.freno.me/privacy` if a prefixed form ever appears.
   */
  const publicPath =
    site.baseRoutePrefix &&
    (pathname === site.baseRoutePrefix ||
      pathname.startsWith(site.baseRoutePrefix + "/"))
      ? pathname.slice(site.baseRoutePrefix.length) || "/"
      : pathname;
  const canonical = props.canonical ?? `https://${site.domain}${publicPath}`;
  const ogTitle = props.ogTitle ?? props.title;
  const ogDescription = props.ogDescription ?? props.description;
  const ogImage = absolutizeOgImage(
    props.ogImage ?? site.ogDefaultImage,
    site.domain
  );

  return {
    title,
    description: props.description,
    canonical,
    ogTitle,
    ogDescription,
    ogImage
  };
}