/**
 * Host single-instance guard. A profile may end up with the same plugin
 * reachable from two sources (an npm install and a `link:` install side by
 * side); without this guard the second instance would re-register the same
 * webserver routes and settings namespaces and fail the boot. mountOnce makes
 * the second host apply a no-op for the lifetime of the first instance.
 *
 * The registry rides a global symbol so two module instances of the same
 * package still share one verdict. `ctx.effect` runs its callback immediately
 * and treats the callback's return value as the fiber disposer, so the
 * unmarker is returned, not run.
 * @module dsh-web-notes/mount-once
 */

const MOUNTED = Symbol.for('dsh-web-notes.mounted-plugins')

interface MountRegistry {
  [MOUNTED]?: Set<string>
}

function mountedSet(): Set<string> {
  const registry = globalThis as MountRegistry
  return (registry[MOUNTED] ??= new Set())
}

/**
 * Wrap a cordis plugin apply so the package runs at most once per process.
 * @param packageName - npm package identity shared by every install source.
 * @param fn - the original plugin apply.
 * @returns an apply of the same shape.
 */
export function mountOnce<T extends (...args: any[]) => unknown>(packageName: string, fn: T): T {
  return ((...args: unknown[]) => {
    const mounted = mountedSet()
    if (mounted.has(packageName)) return
    mounted.add(packageName)
    const ctx = args[0] as { effect?: (effect: () => unknown) => unknown } | undefined
    ctx?.effect?.(() => () => {
      mounted.delete(packageName)
    })
    return fn(...args)
  }) as T
}