import { z } from 'zod'

export const PAIRING_OFFER_VERSION = 2

export const PairingOfferSchema = z.object({
  v: z.literal(PAIRING_OFFER_VERSION),
  endpoint: z.string().min(1),
  deviceToken: z.string().min(1),
  // Why: the desktop's Curve25519 public key, base64-encoded. The mobile client
  // uses this to derive a shared secret via ECDH for end-to-end encryption.
  publicKeyB64: z.string().min(1)
})

export type PairingOffer = z.infer<typeof PairingOfferSchema>

export function encodePairingOffer(offer: PairingOffer): string {
  const json = JSON.stringify(offer)
  const base64url = Buffer.from(json, 'utf-8')
    .toString('base64')
    .replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=+$/, '')
  // Why: Android camera intents and Expo Router preserve query params more
  // reliably than URL fragments when launching a custom-scheme app.
  return `orca://pair?code=${base64url}`
}

export function decodePairingOffer(url: string): PairingOffer {
  const code = extractPairingCodeFromUrl(url)
  if (!code) {
    throw new Error('Invalid pairing URL: must start with orca://pair and include a pairing code')
  }
  return decodePairingBase64(code)
}

function extractPairingCodeFromUrl(url: string): string | null {
  let parsed: URL
  try {
    parsed = new URL(url)
  } catch {
    return null
  }
  // Why: prefix checks accepted routes like `orca://pairing?...`; only the
  // pairing deep-link host may carry runtime auth material.
  if (parsed.protocol !== 'orca:' || parsed.hostname !== 'pair') {
    return null
  }
  if (parsed.pathname !== '' && parsed.pathname !== '/') {
    return null
  }
  const code = parsed.searchParams.get('code')
  if (code) {
    return code
  }
  return parsed.hash ? parsed.hash.slice(1) || null : null
}

// Why: accept either an `orca://pair?...` URL or the bare base64
// string so the mobile paste-pair flow can take whichever the user
// actually copied from desktop.
export function parsePairingCode(input: string): PairingOffer | null {
  const trimmed = input.trim()
  if (!trimmed) {
    return null
  }
  try {
    if (trimmed.toLowerCase().startsWith('orca://')) {
      return decodePairingOffer(trimmed)
    }
    return decodePairingBase64(trimmed)
  } catch {
    return null
  }
}

function decodePairingBase64(base64url: string): PairingOffer {
  const base64 = base64url.replace(/-/g, '+').replace(/_/g, '/')
  const json = Buffer.from(base64, 'base64').toString('utf-8')
  return PairingOfferSchema.parse(JSON.parse(json))
}