/**
 * Offline UX state machine — TASK-0095 R2 (the S12 gate's named unit test:
 * "the banner count aggregation (the CRDT + outbox sum)" + the R2 states).
 *
 * Pure (no React, no `navigator`, no store) — a hook feeds it live inputs,
 * a component renders its output. The logic (AGENTS rule 23: domain logic
 * independent from the UI):
 *
 *   - the BANNER count = the provider's CRDT-pending edits (`localPendingCount`)
 *     + the outbox pending count — ONE number, the sum (the spec's "one
 *     number, the sum");
 *   - the banner is VISIBLE when `navigator.onLine` is false OR the provider
 *     is `offline` OR the provider has been `reconnecting` for ≥ 5 s (the
 *     blip threshold — a brief blip < 5 s shows NO banner, only the chip
 *     flashing "Reconnecting…");
 *   - the top-bar CHIP: online → green "Live", reconnecting → amber, offline
 *     → gray "Offline" (the TASK-0092/0093 chip, finalized here) + the a11y
 *     `aria-label="Connection: offline, 12 changes pending"`.
 *
 * `crdtPending` is 0 until the Yjs `RealtimeProvider` is wired into the
 * editor (TASK-0136 R6); today the web app uses the legacy JSON client, so
 * the banner count is the outbox count. The input is a plain number so the
 * provider can be slotted in later without touching this logic.
 */

/** The normalized connection phase the UI renders (3 chip states). */
export type ConnectionPhase = "online" | "reconnecting" | "offline";

/** A brief reconnecting blip (< 5 s) → no banner, the chip flashes. */
export const RECONNECT_BANNER_THRESHOLD_MS = 5_000;

export interface OfflineStatusInput {
  /** `navigator.onLine` (false = the browser is offline). */
  readonly navigatorOnline: boolean;
  /** The (normalized) provider connection phase. */
  readonly phase: ConnectionPhase;
  /** The ms clock at which `phase` was entered (the 5 s blip basis). */
  readonly phaseSinceMs: number;
  /** The current ms clock (injected for determinism). */
  readonly nowMs: number;
  /** The provider's CRDT-pending edits (`localPendingCount`; 0 today). */
  readonly crdtPending: number;
  /** The outbox pending count. */
  readonly outboxPending: number;
  /** The outbox failed count (the "Review failed changes" link). */
  readonly outboxFailed: number;
}

export interface OfflineStatus {
  /** True → render the banner. */
  readonly bannerVisible: boolean;
  /** The ONE pending number (CRDT + outbox sum) — the banner count. */
  readonly pendingCount: number;
  /** The outbox failed count (the "Review failed changes" link). */
  readonly failedCount: number;
  /** True when the failed list is non-empty (show the review link). */
  readonly showReviewLink: boolean;
  /** The top-bar chip state. */
  readonly chip: ConnectionPhase;
  /** A brief reconnecting blip (< 5 s) — the chip flashes, no banner. */
  readonly reconnectFlash: boolean;
  /** The a11y label ("Connection: offline, 12 changes pending"). */
  readonly ariaLabel: string;
}

/** The chip's display word (the aria-label + the visible text). */
export const PHASE_LABEL: Record<ConnectionPhase, string> = {
  online: "Live",
  reconnecting: "Reconnecting…",
  offline: "Offline",
};

/**
 * Normalize a raw provider status (the legacy JSON client's `RealtimeStatus`
 * or the Yjs `ConnectionState`) into the 3-phase chip model.
 */
export function normalizePhase(
  status: string | null | undefined,
): ConnectionPhase {
  switch (status) {
    case "connected":
    case "syncing":
      return "online";
    case "reconnecting":
    case "connecting":
      return "reconnecting";
    case "offline":
    case "closed":
    case "disconnected":
      return "offline";
    default:
      // Unknown / absent (not connected yet) → treat as offline (the safe
      // direction: the banner shows until we have a live connection).
      return "offline";
  }
}

export function computeOfflineStatus(input: OfflineStatusInput): OfflineStatus {
  const reconnectingMs =
    input.phase === "reconnecting" ? Math.max(0, input.nowMs - input.phaseSinceMs) : 0;
  const reconnectingTooLong =
    input.phase === "reconnecting" && reconnectingMs >= RECONNECT_BANNER_THRESHOLD_MS;

  // The banner: the browser is offline, OR the provider is offline, OR the
  // provider has been reconnecting past the 5 s blip threshold.
  const bannerVisible =
    !input.navigatorOnline || input.phase === "offline" || reconnectingTooLong;

  // The chip: the provider's status (online = green "Live", reconnecting =
  // amber, offline = gray "Offline") — except a browser-level offline forces
  // the gray "Offline" (the provider cannot be live without a network). A
  // LONG reconnect (> 5 s) keeps the amber chip while the banner also shows.
  const chip: ConnectionPhase = !input.navigatorOnline ? "offline" : input.phase;

  // The blip flash: the chip is amber (a transient reconnecting — a < 5 s
  // blip flashes it with no banner; a longer one keeps it amber + banner).
  const reconnectFlash = chip === "reconnecting";

  // The ONE pending number (the spec's "one number, the sum").
  const pendingCount = input.crdtPending + input.outboxPending;
  const failedCount = input.outboxFailed;
  const showReviewLink = failedCount > 0;

  const ariaLabel = `Connection: ${PHASE_LABEL[chip].replace("…", "")}, ${pendingCount} changes pending`;

  return {
    bannerVisible,
    pendingCount,
    failedCount,
    showReviewLink,
    chip,
    reconnectFlash,
    ariaLabel,
  };
}