import type { Metadata } from "next";

/**
 * Central SEO configuration — the single source of truth for the canonical
 * origin, brand naming, and shared metadata construction. Every page that needs
 * a canonical URL, an Open Graph card, or JSON-LD should build it from here so
 * the values can never drift between routes.
 */

export const SITE_NAME = "Podcast Distribution AI";

export const SITE_TAGLINE = "From topic idea to published podcast in minutes";

export const SITE_DESCRIPTION =
  "Podcast Distribution AI is an all-in-one AI platform that writes your script, records realistic multi-voice audio, and designs cover art — turning a topic into a finished episode in minutes.";

/** Brand accent (--brand, light theme) as a hex literal for OG image rendering. */
export const BRAND_HEX = "#e65000";

/**
 * The canonical, absolute origin of the deployment (no trailing slash).
 *
 * Canonical tags, sitemap entries and OG URLs are only correct if this is the
 * real public origin, so a production build refuses to silently fall back to
 * localhost: an unset NEXT_PUBLIC_APP_URL would otherwise ship canonicals
 * pointing at http://localhost:3000 and de-index the whole site.
 */
function resolveSiteUrl(): string {
  const raw = process.env.NEXT_PUBLIC_APP_URL?.trim();

  if (raw) {
    try {
      const url = new URL(raw);
      // Strip any trailing slash so `${SITE_URL}${path}` never doubles up.
      return url.origin;
    } catch {
      throw new Error(
        `[seo] NEXT_PUBLIC_APP_URL is not a valid absolute URL: ${JSON.stringify(raw)}`
      );
    }
  }

  if (process.env.NODE_ENV === "production") {
    throw new Error(
      "[seo] NEXT_PUBLIC_APP_URL must be set in production — it is the canonical origin used for canonical tags, the sitemap, robots.txt and Open Graph URLs."
    );
  }

  return "http://localhost:3000";
}

export const SITE_URL = resolveSiteUrl();

/** Resolve a root-relative path to its absolute canonical URL. */
export function absoluteUrl(path = "/"): string {
  return path === "/" ? `${SITE_URL}/` : `${SITE_URL}${path.startsWith("/") ? path : `/${path}`}`;
}

/**
 * The site-wide social card (app/opengraph-image.tsx).
 *
 * It has to be restated on every page: Next merges `metadata` shallowly, so a
 * page that defines its own `openGraph` object replaces the root layout's
 * entirely — including the images the file convention contributed. Leaving this
 * out silently drops og:image from every page but the homepage.
 */
const DEFAULT_OG_IMAGE = {
  url: "/opengraph-image",
  width: 1200,
  height: 630,
  alt: `${SITE_NAME} — from a topic idea to a finished podcast in minutes`,
};

interface PageMetaOptions {
  title: string;
  description: string;
  /** Root-relative path, e.g. "/pricing". Used for the canonical + OG URL. */
  path: string;
  /** Keep the page out of the index (authed surfaces, share links, utilities). */
  noIndex?: boolean;
  /** Override the social card image path (defaults to the site-wide OG card). */
  image?: string;
  type?: "website" | "article";
}

/**
 * Build a complete, canonical-tagged Metadata object for a page. Next.js merges
 * this over the root layout's metadata, so only the differing fields are set.
 */
export function pageMetadata({
  title,
  description,
  path,
  noIndex = false,
  image,
  type = "website",
}: PageMetaOptions): Metadata {
  const url = absoluteUrl(path);
  const images = image ? [{ url: image }] : [DEFAULT_OG_IMAGE];

  return {
    title,
    description,
    alternates: { canonical: url },
    openGraph: {
      title: `${title} · ${SITE_NAME}`,
      description,
      url,
      siteName: SITE_NAME,
      type,
      locale: "en_US",
      images,
    },
    twitter: {
      card: "summary_large_image",
      title: `${title} · ${SITE_NAME}`,
      description,
      images,
    },
    ...(noIndex
      ? { robots: { index: false, follow: false, nocache: true, googleBot: { index: false, follow: false } } }
      : {}),
  };
}

/** Metadata for surfaces that must never be indexed (app, admin, auth). */
export const NO_INDEX: Metadata = {
  robots: {
    index: false,
    follow: false,
    nocache: true,
    googleBot: { index: false, follow: false, noimageindex: true },
  },
};

const MONTHS = [
  "january", "february", "march", "april", "may", "june",
  "july", "august", "september", "october", "november", "december",
];

/**
 * Convert a human "Month D, YYYY" stamp (as rendered on the legal pages) into a
 * calendar-only ISO-8601 date for schema.org `dateModified`.
 *
 * Parsed explicitly rather than via `new Date(...)` so the result can never be
 * shifted a day by the server's timezone. Returns undefined for anything it does
 * not recognise, so callers omit the property instead of emitting a bad date.
 */
export function toIsoDate(display: string): string | undefined {
  const match = /^([A-Za-z]+)\s+(\d{1,2}),\s*(\d{4})$/.exec(display.trim());
  if (!match) return undefined;

  const month = MONTHS.indexOf(match[1].toLowerCase());
  if (month < 0) return undefined;

  const day = Number(match[2]);
  if (day < 1 || day > 31) return undefined;

  return `${match[3]}-${String(month + 1).padStart(2, "0")}-${String(day).padStart(2, "0")}`;
}