/**
 * The external packages a published browser artifact carries a copy of.
 *
 * Read from the real build configurations rather than declared by hand: each
 * `lib/client.js` plugin bundle is driven through its own `tsdown.config.ts`, and
 * the shell `dist` through `apps/web`'s Vite config. A recording plugin resolves
 * every bare specifier as external and notes it, so the pass walks our own source
 * and stops at the package boundary — which is both fast (about two seconds for
 * the whole repository) and exactly the direct-dependency granularity
 * THIRD_PARTY_NOTICES.md discloses. Erased type imports never appear, because the
 * transform drops them before resolution.
 *
 * Workspace names are followed only on the Vite side, where the shell's aliases
 * map them to source: that is how a browser-only library's own third-party
 * imports — katex and shiki through `ui-primitives`, for one — become visible. A
 * plugin bundle keeps them external, matching the frozen module table it is built
 * against; the wire layers it inlines are host packages that declare their own
 * dependencies, so nothing goes undisclosed.
 *
 * A specifier is recorded only once the host resolves it to a file inside a
 * package. A bundler's own virtual module has no package behind it —
 * `vite/modulepreload-polyfill` is generated by a Vite plugin rather than shipped
 * as a file, so the polyfill in the published `dist` is build glue in the same
 * category as an emitted TypeScript helper, not a redistributed copy of Vite.
 *
 * The pass runs on a clean tree, as a static gate must. The shell's Vite config
 * aliases a few workspace packages to source; every other workspace name would
 * resolve through `node_modules` to a `lib/` entry the real build has emitted but
 * a clean checkout has not, so this module resolves those names to their own
 * source instead. `lib/` is compiled from `src/`, so the third-party edges the
 * pass records are the same either way.
 *
 * rolldown is resolved through tsdown deliberately: the dry run must use the
 * exact bundler the real build uses, which a separate root pin could drift from.
 */

import { existsSync, globSync, readFileSync } from 'node:fs'
import { createRequire } from 'node:module'
import { dirname, join } from 'node:path'

/** The plugin-context member the recorder needs to resolve before recording. */
interface ResolveContext {
  resolve: (
    source: string,
    importer: string,
    options: { skipSelf: boolean },
  ) => Promise<{ id: string } | null>
}

/** A rolldown/Vite plugin shape, narrowed to what the recorder needs. */
interface RecorderPlugin {
  name: string
  enforce?: 'pre'
  resolveId: (
    this: ResolveContext,
    source: string,
    importer: string | undefined,
  ) => Promise<{ id: string; external: true } | null>
}

/**
 * The package a resolved module file belongs to.
 * @param file - absolute path of a resolved module.
 * @returns the package name, or undefined when the file is not inside a package.
 */
function packageOfFile(file: string): string | undefined {
  const marker = file.lastIndexOf('node_modules/')
  if (marker < 0) return undefined
  const rest = file.slice(marker + 'node_modules/'.length)
  const parts = rest.split('/')
  return rest.startsWith('@') ? parts.slice(0, 2).join('/') : parts[0]
}

/**
 * Source aliases for the workspace packages the shell does not already alias.
 *
 * A clean checkout has no `lib/`, so a workspace name would otherwise resolve
 * through `node_modules` to an entry that does not exist yet. Aliases are the
 * right seam rather than a plugin hook, because Vite resolves a stylesheet
 * `@import` through them too — the theme package publishes its stylesheets from
 * `lib/styles/`. `lib/` is compiled from `src/`, so the third-party edges the
 * pass records are the same either way.
 * @param root - repository root.
 * @param existing - the shell's own alias patterns, whose entry choices win.
 * @returns alias entries mapping each remaining workspace name to its source.
 */
function workspaceSourceAliases(root: string, existing: readonly string[]): { find: RegExp | string; replacement: string }[] {
  const aliases: { find: RegExp | string; replacement: string }[] = []
  for (const pattern of ['packages/*/*/package.json', 'vendor/*/package.json']) {
    for (const relative of globSync(pattern, { cwd: root })) {
      const dir = join(root, dirname(relative))
      const manifest = JSON.parse(readFileSync(join(root, relative), 'utf8')) as Manifest & { name?: string }
      const name = manifest.name
      if (name === undefined || !existsSync(join(dir, 'src'))) continue
      if (existing.some(find => find.includes(name))) continue
      const root_ = manifest.exports?.['.']
      const target = typeof root_ === 'string' ? root_ : root_?.default
      const stem = (target ?? './lib/index.js')
        .replace(/^\.\/lib\/types\//, '').replace(/^\.\/lib\//, '').replace(/\.js$/, '')
      const entry = [`${stem}.ts`, `${stem}.tsx`, `${stem}/index.ts`, `${stem}/index.tsx`]
        .map(candidate => join(dir, 'src', candidate))
        .find(candidate => existsSync(candidate))
      // The subpath prefix carries `./client`, `./types`, and `./styles/*` alike:
      // each published subpath mirrors a path under `src/`.
      aliases.push({ find: `${name}/`, replacement: `${join(dir, 'src')}/` })
      if (entry !== undefined) aliases.push({ find: new RegExp(`^${name.replaceAll('/', '\\/')}$`), replacement: entry })
    }
  }
  return aliases
}

/**
 * Build the plugin that records bare specifiers and stops the walk at them.
 * @param seen - set the recorder adds package names to.
 * @returns the recording plugin.
 */
function recorder(seen: Set<string>): RecorderPlugin {
  return {
    name: 'dsh-record-direct-externals',
    enforce: 'pre',
    async resolveId(source, importer) {
      if (importer === undefined) return null // the entry itself
      if (source.startsWith('.') || source.startsWith('/') || source.startsWith('\0')) return null
      if (source.startsWith('virtual:') || source.includes('?')) return null
      // A workspace name that reaches here is one no alias mapped to source, so
      // nothing of ours is left to walk; it is never a third-party disclosure.
      if (source.startsWith('@deepseek-ai/')) return { id: source, external: true }
      if (source.startsWith('node:')) return { id: source, external: true }
      if (!source.startsWith('@deepseek-ai/')) {
        const resolved = await this.resolve(source, importer, { skipSelf: true })
        const name = resolved === null ? undefined : packageOfFile(resolved.id)
        if (name !== undefined) seen.add(name)
      }
      return { id: source, external: true }
    },
  }
}

interface Manifest {
  exports?: Record<string, { default?: string } | string | null>
  files?: string[]
}

/** Read one workspace manifest. */
function manifestOf(dir: string): Manifest {
  return JSON.parse(readFileSync(join(dir, 'package.json'), 'utf8')) as Manifest
}

/** Whether a manifest publishes a tsdown browser bundle at `lib/client.js`. */
function publishesClientBundle(manifest: Manifest): boolean {
  const target = manifest.exports?.['./client']
  return typeof target === 'object' && target !== null && target.default === './lib/client.js'
}

/**
 * Record every external package the plugin client bundles carry.
 * @param root - repository root.
 * @param seen - set the recorder adds package names to.
 */
async function collectFromClientBundles(root: string, seen: Set<string>): Promise<void> {
  const requireFromTsdown = createRequire(createRequire(import.meta.url).resolve('tsdown'))
  const { rolldown } = await import(requireFromTsdown.resolve('rolldown')) as {
    rolldown: (options: Record<string, unknown>) => Promise<{
      generate: (output: Record<string, unknown>) => Promise<unknown>
      close: () => Promise<void>
    }>
  }

  for (const relative of globSync('packages/*/*/tsdown.config.ts', { cwd: root }).sort()) {
    const dir = join(root, dirname(relative))
    if (!publishesClientBundle(manifestOf(dir))) continue
    const loaded = await import(join(root, relative)) as { default: unknown }
    const factory = loaded.default
    const configs = (typeof factory === 'function'
      ? (factory as (inline: { env: Record<string, string> }) => unknown[])({ env: {} })
      : [factory]) as { name?: string; entry?: unknown; plugins?: unknown[] }[]
    // The `/client` config is the browser bundle; its siblings emit the node half.
    const client = configs.find(config => config.name?.endsWith('/client') === true)
    if (client === undefined) continue
    const bundle = await rolldown({
      cwd: dir,
      input: client.entry,
      plugins: [recorder(seen), ...(client.plugins ?? [])],
      platform: 'browser',
    })
    await bundle.generate({ format: 'cjs', minify: false, sourcemap: false })
    await bundle.close()
  }
}

/**
 * Record every external package the prebuilt shell bundle carries.
 * @param root - repository root.
 * @param seen - set the recorder adds package names to.
 */
async function collectFromShellBundle(root: string, seen: Set<string>): Promise<void> {
  for (const relative of globSync('apps/*/vite.config.ts', { cwd: root }).sort()) {
    const dir = join(root, dirname(relative))
    // Vite belongs to the app that builds with it, so it resolves from there.
    const { build, resolveConfig } = await import(createRequire(join(dir, 'package.json')).resolve('vite')) as {
      build: (options: Record<string, unknown>) => Promise<unknown>
      resolveConfig: (options: Record<string, unknown>, command: string) => Promise<{
        resolve: { alias: { find: string | RegExp }[] }
      }>
    }
    // The shell already aliases some workspace names to source, and its entry
    // choices win: a stylesheet `@import` resolves through aliases rather than a
    // plugin hook, so only the names it leaves out get one from here.
    const resolved = await resolveConfig({ root: dir, logLevel: 'error' }, 'build')
    await build({
      root: dir,
      logLevel: 'error',
      plugins: [recorder(seen)],
      resolve: { alias: workspaceSourceAliases(root, resolved.resolve.alias.map(entry => String(entry.find))) },
      build: { write: false, minify: false, sourcemap: false, reportCompressedSize: false },
    })
  }
}

/**
 * The external packages a published browser artifact carries a copy of.
 * @param root - repository root.
 * @returns package names, workspace names excluded.
 */
export async function browserBundledExternals(root: string): Promise<Set<string>> {
  const seen = new Set<string>()
  await collectFromClientBundles(root, seen)
  await collectFromShellBundle(root, seen)
  return seen
}