/**
 * T14 · Revocation subscriber (INV12 data-plane teardown owner, FIX 4). Subscribes to the frozen
 * §4.2 `relay:revocations` bus and maps a `KillSignal` onto the EXISTING §4.1 wire (no new frame
 * type) via T11's `drainHost(…, revoked)` — immediate teardown (grace forced to 0) within
 * `REVOCATION_PUSH_BUDGET_MS`. P3/P5 PUBLISH; every P1 node SUBSCRIBES (P1 never imports P5 —
 * the KillSignal shape lives in relay-contracts, keeping the DAG acyclic).
 *
 * Security: scope selection is blast-radius-bounded (host ⊂ account ⊂ global); a host this node
 * doesn't serve is a no-op (no cross-tenant reach, INV1). `signal.reason` is metadata only, never
 * written as terminal payload/log content (INV10). A malformed signal is dropped + counted — a
 * poisoned message can neither kill the bus nor trigger a spurious teardown.
 */
import {
  KillSignalSchema,
  RELAY_REVOCATIONS_CHANNEL,
  type KillSignal,
  type RevocationScope,
} from 'relay-contracts'
import type { AgentTunnel } from './agent-listener.js'
import { DRAIN_REASON } from './drain.js'

export interface Subscription {
  close(): void
}

export interface RevocationSubscriberDeps {
  subscribe(channel: string, onMessage: (raw: string) => void): Subscription
  drainHost(hostId: string, reason: typeof DRAIN_REASON.revoked): Promise<void>
  tunnels(): ReadonlyMap<string, AgentTunnel>
  now: () => number
  onApplied?(signal: KillSignal, hostsAffected: number, elapsedMs: number): void
  onDropped?(): void // malformed-signal counter (metadata only, INV10)
}

/**
 * Pure scope→hosts selector: which of THIS node's live hosts a signal hits. `accountOf` maps a
 * live hostId to its accountId (carried on the tunnel). Testable in isolation.
 */
export function hostsForScope(
  scope: RevocationScope,
  liveHosts: ReadonlyMap<string, AgentTunnel>,
  accountOf: (hostId: string) => string | undefined,
): readonly string[] {
  switch (scope.kind) {
    case 'host':
      return liveHosts.has(scope.hostId) ? [scope.hostId] : []
    case 'account':
      return [...liveHosts.keys()].filter((h) => accountOf(h) === scope.accountId)
    case 'global':
      return [...liveHosts.keys()]
  }
}

function parseKillSignal(raw: string): KillSignal | null {
  let json: unknown
  try {
    json = JSON.parse(raw)
  } catch {
    return null
  }
  const result = KillSignalSchema.safeParse(json)
  return result.success ? result.data : null
}

export function startRevocationSubscriber(deps: RevocationSubscriberDeps): Subscription {
  const accountOf = (hostId: string): string | undefined => deps.tunnels().get(hostId)?.accountId

  const sub = deps.subscribe(RELAY_REVOCATIONS_CHANNEL, (raw) => {
    const startedAt = deps.now()
    const signal = parseKillSignal(raw)
    if (signal === null) {
      deps.onDropped?.() // dropped + counted; bus stays alive, no teardown fired
      return
    }
    const hosts = hostsForScope(signal.scope, deps.tunnels(), accountOf)
    // Fire immediate teardown (reason=revoked ⇒ grace forced to 0 in T11) for each in-scope host.
    void Promise.all(hosts.map((hostId) => deps.drainHost(hostId, DRAIN_REASON.revoked))).then(() => {
      deps.onApplied?.(signal, hosts.length, deps.now() - startedAt)
    })
  })

  return { close: () => sub.close() }
}