export const REMOTE_LIVENESS_TIMEOUT_MS = 10_000
export const REMOTE_LIVENESS_FAILURE_LIMIT = 3
// Even at the capped retry path, consecutive liveness observations are at most
// about 48s apart (ticket mint + socket open + backoff + the next status probe).
// One minute keeps a continuous outage together without carrying old failures.
export const REMOTE_LIVENESS_FAILURE_WINDOW_MS = 60_000

export interface RemoteLivenessFailure {
  failures: number
  shouldReset: boolean
}

interface RemoteConnectionDescriptor {
  baseUrl?: null | string
  mode?: null | string
}

export interface RevalidateRemoteConnectionOptions<TConnection extends RemoteConnectionDescriptor> {
  connectionPromise: Promise<TConnection>
  currentConnectionPromise: () => null | Promise<TConnection>
  log: (message: string) => void
  probe: (url: string, options: { timeoutMs: number }) => Promise<unknown>
  resetConnection: () => void
  tracker: RemoteLivenessTracker
}

export interface RemoteRevalidationResult {
  ok: true
  rebuilt: boolean
}

/**
 * Coalesces revalidation work for one cached connection promise.
 *
 * Every Desktop BrowserWindow owns a renderer gateway loop. When several
 * windows observe the same disconnect they can all ask the Electron main
 * process to revalidate the shared primary connection at once. Those calls
 * must count as one probe, not several consecutive failures.
 */
export class RemoteRevalidationCoordinator {
  readonly #inflightByConnection = new WeakMap<object, Promise<unknown>>()

  run<T>(connection: object, task: () => Promise<T>): Promise<T> {
    const existing = this.#inflightByConnection.get(connection) as Promise<T> | undefined

    if (existing) {
      return existing
    }

    const pending = Promise.resolve().then(task)

    const clear = () => {
      if (this.#inflightByConnection.get(connection) === pending) {
        this.#inflightByConnection.delete(connection)
      }
    }

    this.#inflightByConnection.set(connection, pending)
    // Clean up on both outcomes without creating an unhandled rejected branch.
    void pending.then(clear, clear)

    return pending
  }
}

/**
 * Tracks consecutive remote liveness failures independently per gateway.
 * A successful probe clears the streak, and reaching the limit consumes it so
 * a rebuilt connection starts from a clean state.
 */
export class RemoteLivenessTracker {
  readonly #failureLimit: number
  readonly #failureWindowMs: number
  readonly #failuresByBaseUrl = new Map<string, { failures: number; lastFailureAt: number }>()
  readonly #now: () => number

  constructor(
    failureLimit = REMOTE_LIVENESS_FAILURE_LIMIT,
    failureWindowMs = REMOTE_LIVENESS_FAILURE_WINDOW_MS,
    now: () => number = Date.now
  ) {
    if (!Number.isInteger(failureLimit) || failureLimit < 1) {
      throw new Error('Remote liveness failure limit must be a positive integer.')
    }

    if (!Number.isFinite(failureWindowMs) || failureWindowMs < 1) {
      throw new Error('Remote liveness failure window must be positive.')
    }

    this.#failureLimit = failureLimit
    this.#failureWindowMs = failureWindowMs
    this.#now = now
  }

  recordSuccess(baseUrl: string): void {
    this.#failuresByBaseUrl.delete(baseUrl)
  }

  recordFailure(baseUrl: string): RemoteLivenessFailure {
    const now = this.#now()
    const previous = this.#failuresByBaseUrl.get(baseUrl)
    const withinFailureWindow = previous && now - previous.lastFailureAt <= this.#failureWindowMs
    const failures = (withinFailureWindow ? previous.failures : 0) + 1
    const shouldReset = failures >= this.#failureLimit

    if (shouldReset) {
      this.#failuresByBaseUrl.delete(baseUrl)
    } else {
      this.#failuresByBaseUrl.set(baseUrl, { failures, lastFailureAt: now })
    }

    return { failures, shouldReset }
  }

  clear(): void {
    this.#failuresByBaseUrl.clear()
  }
}

/**
 * Probe the cached primary remote connection and apply the failure policy.
 * The caller owns single-flight coordination; identity checks here ensure an
 * old async result cannot mutate or reset a replacement connection.
 */
export async function revalidateRemoteConnection<TConnection extends RemoteConnectionDescriptor>({
  connectionPromise,
  currentConnectionPromise,
  log,
  probe,
  resetConnection,
  tracker
}: RevalidateRemoteConnectionOptions<TConnection>): Promise<RemoteRevalidationResult> {
  let connection: TConnection

  try {
    connection = await connectionPromise
  } catch {
    // The cached boot already rejected; its own recovery path will clear it.
    return { ok: true, rebuilt: false }
  }

  if (currentConnectionPromise() !== connectionPromise) {
    return { ok: true, rebuilt: false }
  }

  if (connection.mode !== 'remote' || !connection.baseUrl) {
    return { ok: true, rebuilt: false }
  }

  const baseUrl = connection.baseUrl.replace(/\/+$/, '')

  try {
    await probe(`${baseUrl}/api/status`, { timeoutMs: REMOTE_LIVENESS_TIMEOUT_MS })

    if (currentConnectionPromise() !== connectionPromise) {
      return { ok: true, rebuilt: false }
    }

    tracker.recordSuccess(baseUrl)

    return { ok: true, rebuilt: false }
  } catch {
    if (currentConnectionPromise() !== connectionPromise) {
      return { ok: true, rebuilt: false }
    }

    const failure = tracker.recordFailure(baseUrl)

    if (!failure.shouldReset) {
      log(
        `Cached remote Hermes backend failed liveness probe (${failure.failures}/${REMOTE_LIVENESS_FAILURE_LIMIT}); keeping connection for retry.`
      )

      return { ok: true, rebuilt: false }
    }

    log('Cached remote Hermes backend failed liveness probe; dropping stale connection.')
    resetConnection()

    return { ok: true, rebuilt: true }
  }
}