import { Metadata } from 'next'

if (!process.env.SITE_URL) {
  throw new Error('SITE_URL environment variable is not set (e.g. SITE_URL=https://example.com)')
}

export const SITE_URL = process.env.SITE_URL.replace(/\/$/, '')
export const SITE_NAME = 'Ephemeris'
export const SITE_DESCRIPTION = 'A blog about me and my interests'
export const AUTHOR = { name: 'Frank Borisjuk', handle: 'hangerthem', url: SITE_URL + '/about' }

// Child segments replace `alternates` wholesale, so every page re-declares the feed link
const feedAlternate = { 'application/atom+xml': [{ url: '/feed.xml', title: SITE_NAME }] }

export const metadata: Metadata = {
  metadataBase: new URL(SITE_URL),
  title: SITE_NAME,
  description: SITE_DESCRIPTION,
  creator: AUTHOR.handle,
  authors: [{ name: AUTHOR.name, url: AUTHOR.url }],
  alternates: { types: feedAlternate },
  openGraph: {
    type: 'website',
    title: SITE_NAME,
    description: SITE_DESCRIPTION,
    url: SITE_URL,
    siteName: SITE_NAME,
  },
  twitter: {
    card: 'summary_large_image',
    title: SITE_NAME,
    description: SITE_DESCRIPTION,
  },
  appleWebApp: {
    title: SITE_NAME,
    statusBarStyle: 'default',
    capable: true,
  },
}

type PageMetadataOptions = {
  title: string
  description: string
  /** Path relative to the site root, starting with a slash. */
  path: string
  /** Open Graph / Twitter image URL. Defaults to the generated site card. */
  image?: string
  openGraph?: Metadata['openGraph']
}

// Generated by app/opengraph-image.tsx. Child segments that set `openGraph` don't inherit
// file-based images, and explicit images win over them, so every page names its image here.
const defaultOgImage = '/opengraph-image'

/** Builds consistent page metadata (title, canonical URL, Open Graph and Twitter card). */
export function pageMetadata({
  title,
  description,
  path,
  image = defaultOgImage,
  openGraph,
}: PageMetadataOptions): Metadata {
  const fullTitle = `${title} | ${SITE_NAME}`
  return {
    title: fullTitle,
    description,
    alternates: { canonical: path, types: feedAlternate },
    openGraph: {
      type: 'website',
      title: fullTitle,
      description,
      url: SITE_URL + path,
      siteName: SITE_NAME,
      images: image,
      ...openGraph,
    },
    twitter: {
      card: 'summary_large_image',
      title: fullTitle,
      description,
      images: image,
    },
  }
}