// Plugin scripts and stylesheets of admin controllers (D-14, D-16). A
// controller's list or form schema names its files as absolute URLs under
// {base}/assets/; they load when that controller's view opens, never
// earlier. Every script loads once per URL as a module script, and a script
// that fails to load is forgotten, so a later navigation can try again.
// Stylesheet links belong to one controller: the router disables them on
// every navigation to another controller or to a screen that is not a
// controller view, so plugin CSS never styles a view it was not written for.
// Only the router picks the enabled controller; a schema response that
// arrives after its view was left adds its links disabled. Stylesheets of
// plugin field types are global instead (GLOBAL_STYLE_OWNER): a field type's
// element can appear in any controller's form, so its links are never
// disabled on navigation.
// Files load only through script and link elements; nothing here fetches.
import type { ControllerAssets } from '../api/types'
import { runtime } from './runtime'

/** Attribute naming the controller that owns a plugin stylesheet link. */
export const OWNER_ATTRIBUTE = 'data-summer-controller'

/** Owner of stylesheet links that stay enabled on every screen (field types). */
export const GLOBAL_STYLE_OWNER = '*'

const scripts = new Map<string, Promise<void>>()
// Links by controller and URL: two controllers of one plugin may share a
// file, and each keeps its own link so disabling one never hides the other.
const styles = new Map<string, { owner: string; link: HTMLLinkElement }>()
// The controller whose links are enabled; '' enables none.
let active = ''

/** The URL prefix every plugin asset must start with. */
export function assetPrefix(): string {
  return `${runtime.base}/assets/`
}

/**
 * Whether a URL may load as a plugin asset: a same-origin path under
 * {base}/assets/ with no dot segment, backslash, whitespace or control
 * character (browsers strip or rewrite those before resolving). A
 * percent-encoded dot counts as a dot: the URL parser resolves %2e%2e like
 * .., which would climb out of the asset prefix.
 */
export function assetAllowed(url: string): boolean {
  if (!url.startsWith(assetPrefix()) || url.includes('\\')) {
    return false
  }
  for (const char of url) {
    const code = char.codePointAt(0) ?? 0
    if (code <= 0x20 || code === 0x7f) {
      return false
    }
  }
  const path = url.split(/[?#]/, 1)[0] ?? ''
  return !path.split('/').some((segment) => {
    const dots = segment.toLowerCase().replaceAll('%2e', '.')
    return dots === '.' || dots === '..'
  })
}

/** Loads one module script; the same URL always yields the same promise. */
export function loadScript(url: string): Promise<void> {
  if (!assetAllowed(url)) {
    return Promise.reject(new Error(`plugin script outside ${assetPrefix()}: ${url}`))
  }
  const known = scripts.get(url)
  if (known) {
    return known
  }
  const loading = new Promise<void>((resolve, reject) => {
    const script = document.createElement('script')
    script.type = 'module'
    script.addEventListener('load', () => resolve(), { once: true })
    script.addEventListener(
      'error',
      () => {
        scripts.delete(url)
        script.remove()
        reject(new Error(`plugin script failed to load: ${url}`))
      },
      { once: true },
    )
    script.src = url
    document.head.appendChild(script)
  })
  scripts.set(url, loading)
  return loading
}

/** Adds a stylesheet link per new URL, owned by the controller. */
export function loadStyles(controllerId: string, urls: readonly string[]): void {
  for (const url of urls) {
    const key = `${controllerId}\n${url}`
    if (!assetAllowed(url) || styles.has(key)) {
      continue
    }
    const link = document.createElement('link')
    link.rel = 'stylesheet'
    link.setAttribute(OWNER_ATTRIBUTE, controllerId)
    link.disabled = !styleEnabled(controllerId)
    link.href = url
    styles.set(key, { owner: controllerId, link })
    document.head.appendChild(link)
  }
}

/**
 * Enables this controller's stylesheet links, now and as they are added,
 * and disables every other one; '' disables them all. The router calls it
 * on every navigation.
 */
export function activateStyles(controllerId: string): void {
  active = controllerId
  for (const { owner, link } of styles.values()) {
    link.disabled = !styleEnabled(owner)
  }
}

/** Whether links of this owner are enabled now: the active controller's and the global ones. */
function styleEnabled(owner: string): boolean {
  return owner === GLOBAL_STYLE_OWNER || owner === active
}

/**
 * Adds stylesheet links that stay enabled on every screen: the styles of
 * plugin field types, whose elements may render in any controller's form.
 */
export function loadGlobalStyles(urls: readonly string[]): void {
  loadStyles(GLOBAL_STYLE_OWNER, urls)
}

/**
 * Adds the controller's stylesheet links and loads its scripts. The links
 * are enabled only while the router shows that controller, so a response
 * for a view already left never restyles the current one. The promise
 * resolves once every script has loaded or failed, with the URLs that
 * failed; it never rejects. Views start this without awaiting it.
 */
export async function loadControllerAssets(
  controllerId: string,
  assets: ControllerAssets | null | undefined,
): Promise<string[]> {
  loadStyles(controllerId, assets?.styles ?? [])
  const urls = assets?.scripts ?? []
  const results = await Promise.allSettled(urls.map((url) => loadScript(url)))
  return urls.filter((_, index) => results[index]?.status === 'rejected')
}