/**
 * desktop/src/remote-hosts.ts — D-1: remote-host mode (PLAN_NATIVE_TUNNEL,
 * Track C-Desktop). Pure, Electron-free helpers over the RemoteHost list held in
 * DesktopPrefs, plus the URL validation that guards what the BrowserWindow is
 * allowed to load.
 *
 * A "remote host" is one of the user's own machines exposed through the mTLS
 * reverse tunnel at `https://<name>.terminal.yaojia.wang/`. The desktop app can
 * switch the main window between "This machine (local)" (the embedded loopback
 * server, which keeps running) and any configured remote host; the device client
 * certificate from the OS keychain (see main.ts / D-2) is the only auth gate.
 *
 * Every function is PURE and returns NEW objects (immutability — coding-style
 * CRITICAL rule); none mutate their arguments. No `electron` import, so this file
 * is unit-testable in plain Node.
 */

import { randomUUID } from 'node:crypto'
import type { DesktopPrefs, RemoteHost } from './types.js'

/**
 * The tunnel DNS zone (PLAN_NATIVE_TUNNEL: wildcard `*.terminal.yaojia.wang`).
 * Overridable so a differently-named deployment isn't hard-blocked. A remote host
 * URL must be https (mixed-content + mTLS both require TLS) and, by default, live
 * under this zone — a boundary sanity check, not the security boundary itself
 * (that is mTLS at nginx + the will-navigate origin lock).
 */
export const TERMINAL_ZONE_SUFFIX = process.env.WEBTERM_TUNNEL_ZONE ?? '.terminal.yaojia.wang'

/** Parse an origin, returning null for anything malformed. */
function originOf(url: string): string | null {
  try {
    return new URL(url).origin
  } catch {
    return null
  }
}

/**
 * Validate + normalize a user-entered remote-host URL. Returns the canonical
 * `https://<host>/` form, or null when the input is not a usable https tunnel URL
 * (unparseable, non-https, or — by default — outside the tunnel zone). Validation
 * at the boundary: everything downstream may trust the returned string.
 */
export function normalizeRemoteUrl(raw: string): string | null {
  let parsed: URL
  try {
    parsed = new URL(raw.trim())
  } catch {
    return null
  }
  if (parsed.protocol !== 'https:') return null
  if (parsed.hostname === '') return null
  if (TERMINAL_ZONE_SUFFIX !== '' && !parsed.hostname.endsWith(TERMINAL_ZONE_SUFFIX)) {
    return null
  }
  // Canonical form: origin + trailing slash (path/query/hash stripped — the
  // frontend is served from the root, and the origin is all the lock compares).
  return `${parsed.origin}/`
}

/**
 * Build a RemoteHost from user input, or null if the name is blank or the URL is
 * not a valid https tunnel URL. The id is a fresh uuid (stable across renames).
 */
export function makeRemoteHost(name: string, url: string): RemoteHost | null {
  const trimmedName = name.trim()
  const normalizedUrl = normalizeRemoteUrl(url)
  if (trimmedName === '' || normalizedUrl === null) return null
  return { id: randomUUID(), name: trimmedName, url: normalizedUrl }
}

/** Look up a configured host by id. */
export function findRemoteHost(
  prefs: Readonly<DesktopPrefs>,
  id: string,
): RemoteHost | undefined {
  return prefs.remoteHosts.find((host) => host.id === id)
}

/**
 * Immutably append a host, de-duplicating by URL so re-adding the same machine
 * replaces the old entry (and its name) rather than piling up duplicates.
 */
export function addRemoteHost(
  prefs: Readonly<DesktopPrefs>,
  host: RemoteHost,
): DesktopPrefs {
  const withoutDup = prefs.remoteHosts.filter((existing) => existing.url !== host.url)
  return { ...prefs, remoteHosts: [...withoutDup, host] }
}

/**
 * Immutably remove a host by id. If the removed host was selected, selection
 * falls back to local (selectedHostId → null) so we never point at a gone host.
 */
export function removeRemoteHost(prefs: Readonly<DesktopPrefs>, id: string): DesktopPrefs {
  const remoteHosts = prefs.remoteHosts.filter((host) => host.id !== id)
  const selectedHostId = prefs.selectedHostId === id ? null : prefs.selectedHostId
  return { ...prefs, remoteHosts, selectedHostId }
}

/**
 * Immutably select a host (null → local). Selecting an unknown id is a no-op —
 * the caller stays on whatever was selected, never a dangling reference.
 */
export function selectHost(prefs: Readonly<DesktopPrefs>, id: string | null): DesktopPrefs {
  if (id === null) return { ...prefs, selectedHostId: null }
  if (findRemoteHost(prefs, id) === undefined) return { ...prefs }
  return { ...prefs, selectedHostId: id }
}

/**
 * The currently-selected remote host, or null when local is selected (either
 * selectedHostId is null, or it dangles at a host that no longer exists).
 */
export function selectedRemoteHost(prefs: Readonly<DesktopPrefs>): RemoteHost | null {
  if (prefs.selectedHostId === null) return null
  return findRemoteHost(prefs, prefs.selectedHostId) ?? null
}

/** The origin a remote host's window should be locked to, or null if malformed. */
export function remoteHostOrigin(host: Readonly<RemoteHost>): string | null {
  return originOf(host.url)
}