/**
 * desktop/src/deep-link.ts — B2: terminalapp:// deep-link parsing.
 *
 * Maps the OS custom-protocol URL `terminalapp://join/<id>` onto the existing
 * frontend's `/?join=<id>` route (see DESKTOP_PLAN §4.3). Pure + hand-validated
 * (no URL-parsing surprises): the URL class does the heavy lifting inside a
 * try/catch so a malformed link yields null instead of throwing at the boundary.
 */

import type { DeepLink } from './types.js'

/** Custom protocol registered with the OS (electron app.setAsDefaultProtocolClient). */
export const DEEP_LINK_PROTOCOL = 'terminalapp'

/** The single legal host segment: terminalapp://join/<id>. */
const JOIN_HOST = 'join'

/** URL.protocol includes the trailing colon, so compare against that form. */
const PROTOCOL_WITH_COLON = `${DEEP_LINK_PROTOCOL}:`

/**
 * Parse `terminalapp://join/<id>` into a DeepLink, or null if it is not a
 * well-formed join link. Rejects: wrong scheme, wrong host, missing/empty id,
 * ids with '/' or control chars, and anything the URL parser chokes on.
 */
export function parseDeepLink(url: string): DeepLink | null {
  let parsed: URL
  try {
    parsed = new URL(url)
  } catch {
    return null
  }

  if (parsed.protocol !== PROTOCOL_WITH_COLON) return null
  if (parsed.host !== JOIN_HOST) return null

  // pathname is '/<id>' for a single segment; strip the leading slash and require
  // exactly one non-empty segment (no nested paths like join/a/b).
  const rawPath = parsed.pathname.replace(/^\/+/, '')
  if (rawPath === '' || rawPath.includes('/')) return null

  const id = safeDecode(rawPath)
  if (id === null) return null
  if (!isValidId(id)) return null

  return { join: id }
}

/** Render a DeepLink as the frontend query-route the window navigates to. */
export function deepLinkToPath(link: DeepLink): string {
  return `/?join=${encodeURIComponent(link.join)}`
}

/** decodeURIComponent can throw on malformed percent-encoding — narrow to null. */
function safeDecode(value: string): string | null {
  try {
    return decodeURIComponent(value)
  } catch {
    return null
  }
}

/** An id is valid if it is non-empty, not whitespace-only, and control-char free. */
function isValidId(id: string): boolean {
  if (id.trim() === '') return false
  if (id.includes('/')) return false
  // Reject C0/C1 control characters (they can't be part of a real session id).
  for (const ch of id) {
    const code = ch.charCodeAt(0)
    if (code <= 0x1f || (code >= 0x7f && code <= 0x9f)) return false
  }
  return true
}