/**
 * Signed-request helper. Must match backend/app/services/signed_request.py exactly.
 *
 * Message format:
 *   TrumpSignal · {ACTION}
 *   wallet: {wallet_lowercase}
 *   timestamp: {ms}
 *   body: {sha256_hex or "-"}
 */

async function sha256Hex(text: string): Promise<string> {
  const buf = await crypto.subtle.digest('SHA-256', new TextEncoder().encode(text))
  return Array.from(new Uint8Array(buf))
    .map((b) => b.toString(16).padStart(2, '0'))
    .join('')
}

/** Canonical JSON: sorted keys, no whitespace. Must match Python's json.dumps(..., sort_keys, separators). */
function canonicalJson(v: unknown): string {
  if (v === null || typeof v !== 'object') return JSON.stringify(v)
  if (Array.isArray(v)) return '[' + v.map(canonicalJson).join(',') + ']'
  const keys = Object.keys(v as object).sort()
  return '{' + keys.map((k) => JSON.stringify(k) + ':' + canonicalJson((v as Record<string, unknown>)[k])).join(',') + '}'
}

export async function bodyHash(body: unknown | null): Promise<string> {
  if (body === null || body === undefined) return '-'
  return sha256Hex(canonicalJson(body))
}

export async function buildSignMessage(
  action: string,
  wallet: string,
  timestampMs: number,
  body: unknown | null,
): Promise<string> {
  const h = await bodyHash(body)
  return `TrumpSignal · ${action}\nwallet: ${wallet.toLowerCase()}\ntimestamp: ${timestampMs}\nbody: ${h}`
}

export interface SignedEnvelope {
  wallet: string
  timestamp: number
  signature: string
}

/**
 * Produce {timestamp, signature} for a given action + optional body.
 * Caller supplies wagmi's `signMessageAsync`.
 */
/**
 * Get-or-create a cached "view" envelope for a wallet. Reused across page loads
 * within a 4-minute window (server accepts 5-min skew). Backend's replay-guard
 * is disabled for the view action so the same sig can be used multiple times.
 */
const VIEW_TTL_MS = 20 * 60 * 1000   // 20 min — backend's replay-guard is disabled for view actions

/**
 * Read-only: returns a cached, not-yet-expired view envelope if one exists.
 * Never signs — never triggers a wallet popup. Returns null if no fresh cache.
 */
export function getCachedViewEnvelope(action: string, wallet: string): SignedEnvelope | null {
  if (typeof window === 'undefined') return null
  const cacheKey = `ts:view:${action}:${wallet.toLowerCase()}`
  const raw = sessionStorage.getItem(cacheKey)
  if (!raw) return null
  try {
    const env = JSON.parse(raw) as SignedEnvelope
    if (Date.now() - env.timestamp < VIEW_TTL_MS) return env
  } catch (err) {
    console.warn('[signedRequest] corrupt cached envelope, ignoring', err)
    sessionStorage.removeItem(cacheKey)
  }
  return null
}

export async function getOrCreateViewEnvelope(params: {
  action: string
  wallet: string
  signMessageAsync: (args: { message: string }) => Promise<string>
}): Promise<SignedEnvelope> {
  if (typeof window === 'undefined') throw new Error('view envelope requires browser')
  const wallet = params.wallet.toLowerCase()
  const cacheKey = `ts:view:${params.action}:${wallet}`
  const raw = sessionStorage.getItem(cacheKey)
  if (raw) {
    try {
      const env = JSON.parse(raw) as SignedEnvelope
      if (Date.now() - env.timestamp < VIEW_TTL_MS) return env
    } catch (err) {
      console.warn('[signedRequest] corrupt cached envelope, ignoring', err)
      sessionStorage.removeItem(cacheKey)
    }
  }
  const env = await signRequest({
    action: params.action,
    wallet,
    body: null,
    signMessageAsync: params.signMessageAsync,
  })
  sessionStorage.setItem(cacheKey, JSON.stringify(env))
  return env
}

export async function signRequest(params: {
  action: string
  wallet: string
  body: unknown | null
  signMessageAsync: (args: { message: string }) => Promise<string>
}): Promise<SignedEnvelope> {
  const timestamp = Date.now()
  const message = await buildSignMessage(params.action, params.wallet, timestamp, params.body)
  const signature = await params.signMessageAsync({ message })
  return { wallet: params.wallet.toLowerCase(), timestamp, signature }
}