import type { BasePayload } from 'payload'

import type { I18nConfig } from '../i18n/index.js'

import { buildLocalizedPath } from '../i18n/index.js'

type BuildLlmsTxtArgs = {
  /** Absolute site URL (https://…). */
  baseUrl: string
  config: I18nConfig
  /** Locale for names/descriptions. Defaults to config.defaultLocale. */
  locale?: string
  /** Pages collection slug. Defaults to 'pages'. */
  pagesSlug?: string
  payload: BasePayload
  /** Site settings global slug. Defaults to 'site-settings'. */
  settingsSlug?: string
}

type SettingsShape = {
  siteDescription?: null | string
  siteName?: null | string
}

type PageRow = {
  _status?: string
  id: number | string
  meta?: { description?: unknown; noindex?: boolean } | null
  slug?: unknown
  title?: unknown
}

/**
 * Builds the body of /llms.txt — a Markdown file describing the site for AI
 * agents / LLM crawlers, per the llmstxt.org convention. Mirrors buildRobots /
 * buildSitemapEntries: the plugin already knows the site's name, description,
 * and pages, so it can generate this automatically.
 *
 * Structure (llmstxt.org): H1 site name, a blockquote/summary, then a list of
 * key pages as Markdown links with short descriptions. Agents read this to
 * understand the site quickly without crawling everything.
 *
 * Wire it as a route that returns text/plain:
 *
 *   // app/llms.txt/route.ts
 *   import { buildLlmsTxt } from '@intecion/ipal-kit'
 *   import { getCachedPayload } from '@/lib/content'
 *   import { i18nConfig } from '@/i18n.config'
 *   export const dynamic = 'force-dynamic'
 *   export async function GET() {
 *     const body = await buildLlmsTxt({
 *       payload: await getCachedPayload(),
 *       config: i18nConfig,
 *       baseUrl: process.env.NEXT_PUBLIC_SERVER_URL!,
 *     })
 *     return new Response(body, { headers: { 'Content-Type': 'text/plain; charset=utf-8' } })
 *   }
 *
 * Data comes from the panel (siteName, siteDescription, pages) — nothing
 * hardcoded. Skips drafts and noindex pages (same as the sitemap).
 */
export async function buildLlmsTxt({
  baseUrl,
  config,
  locale,
  pagesSlug = 'pages',
  payload,
  settingsSlug = 'site-settings',
}: BuildLlmsTxtArgs): Promise<string> {
  const loc = locale ?? config.defaultLocale
  const origin = baseUrl.replace(/\/$/, '')

  const settings = (await payload.findGlobal({
    slug: settingsSlug as never,
    depth: 0,
    locale: loc as never,
  })) as SettingsShape

  const name = settings.siteName?.trim() || 'Website'
  const description = settings.siteDescription?.trim()

  // NO where:{_status} filter — collections without drafts enabled don't
  // register the _status field, and querying it throws
  // "path cannot be queried: _status" (a real bug report). Draft filtering
  // happens in memory below, which is safe for every collection. Same as
  // buildSitemapEntries and generateStaticParams.
  const result = await payload.find({
    collection: pagesSlug as never,
    depth: 0,
    limit: 1000,
    locale: loc as never,
  })

  const lines: string[] = [`# ${name}`, '']
  if (description) {
    lines.push(`> ${description}`, '')
  }

  const pageLinks: string[] = []
  for (const raw of result.docs as PageRow[]) {
    if (raw._status && raw._status !== 'published') {continue}
    if (raw.meta?.noindex) {continue}

    const title = typeof raw.title === 'string' ? raw.title : undefined
    const slug = typeof raw.slug === 'string' ? raw.slug : undefined
    if (!title || !slug) {continue}

    const path = buildLocalizedPath({ config, locale: loc, slugs: { [loc]: slug } })
    if (!path) {continue}

    const pageDesc = typeof raw.meta?.description === 'string' ? ` — ${raw.meta.description}` : ''
    pageLinks.push(`- [${title}](${origin}${path})${pageDesc}`)
  }

  if (pageLinks.length > 0) {
    lines.push('## Strony', '', ...pageLinks, '')
  }

  return lines.join('\n')
}