import { designToken } from "@ekklesia/design-tokens";
import type { ModuleUiImporter } from "@ekklesia/module-ui-host";
import { type ReactElement, useCallback, useEffect, useRef, useState } from "react";
import {
  bootstrapDisplayHost,
  type DisplayHostBootstrap,
  type EkklesiaHostConfig,
  HostProtocolError,
} from "../host-protocol.js";
import { DisplayUiFrame } from "./DisplayUiFrame.js";
import {
  type DisplayConnectivity,
  type DisplayConnectivitySource,
  watchDisplayConnectivity,
} from "./offline-status.js";
import { PairingScreen } from "./PairingScreen.js";

type DisplayState =
  | { readonly status: "loading"; readonly generation: number }
  | {
      readonly status: "ready";
      readonly bootstrap: DisplayHostBootstrap & { status: "ready" };
      /** Changes only when the mounted display must be replaced, never merely because the network
       * came back. It keys the frame, so it is the one thing that can remount a running display. */
      readonly generation: number;
    }
  /** No identity this display can use yet: show a pairing code rather than a human login form. */
  | { readonly status: "pairing" }
  | { readonly status: "unavailable" }
  | { readonly status: "failed" };

export interface DisplayAppProps {
  readonly config: EkklesiaHostConfig;
  readonly moduleId: string;
  /** Test/composition seam only. Production uses the generic loader's native dynamic import. */
  readonly importModule?: ModuleUiImporter;
  /** Where connectivity and cache-fallback signals come from (ADR 0043). The browser entry point
   * supplies the real ones; omitting it leaves a display that simply never reports being offline. */
  readonly connectivity?: DisplayConnectivitySource;
  /** How long the display must stay offline before the corner indicator appears. Test seam only. */
  readonly offlineIndicatorDelayMs?: number;
  /** The shortest interval between two revalidations prompted by refused module requests. Test seam
   * only. */
  readonly revalidationIntervalMs?: number;
  /** How often a running display re-resolves its descriptor on its own. Test seam only. */
  readonly periodicRevalidationMs?: number;
  /** The first automatic retry delay after a failed start; doubles to a one-minute ceiling. Test seam
   * only. */
  readonly retryBaseMs?: number;
}

/** A Wi-Fi reassociation or a switch reboot lasts seconds and needs no comment on a lobby wall. Only
 * an outage that outlasts this is worth the corner indicator. */
export const DISPLAY_OFFLINE_INDICATOR_DELAY_MS = 10_000;

/** A module whose requests are being refused prompts at most one revalidation in this interval. A
 * display that is merely missing one permission must not turn every refused request into two more. */
export const DISPLAY_REVALIDATION_INTERVAL_MS = 15_000;

/** A running display asks again this often, so a module upgraded on the server is picked up and a
 * revocation is noticed even by a module that makes no requests of its own. */
export const DISPLAY_PERIODIC_REVALIDATION_MS = 5 * 60_000;

/** A display that could not start tries again on its own: from this delay, doubling to a minute. A
 * kiosk that boots before its server — after a power cut, say — must come up without anyone pressing
 * Retry. */
export const DISPLAY_RETRY_BASE_MS = 2_000;
export const DISPLAY_RETRY_MAX_MS = 60_000;

/** Whether a fresh resolution describes exactly the display already mounted. Compared structurally:
 * the descriptor and principal are small, server-produced, and carry nothing volatile, so any
 * difference — a new version, a new contribution, a different principal — is a real one. */
function sameDisplay(left: DisplayHostBootstrap, right: DisplayHostBootstrap): boolean {
  return (
    JSON.stringify([left.descriptor, left.principal]) ===
    JSON.stringify([right.descriptor, right.principal])
  );
}

/** `value`, but only once it has been continuously true for `delayMs`. Becoming false is immediate. */
function useSustained(value: boolean, delayMs: number): boolean {
  const [sustained, setSustained] = useState(value && delayMs <= 0);
  useEffect(() => {
    if (!value) {
      setSustained(false);
      return;
    }
    if (delayMs <= 0) {
      setSustained(true);
      return;
    }
    const timer = setTimeout(() => setSustained(true), delayMs);
    return () => clearTimeout(timer);
  }, [delayMs, value]);
  return sustained;
}

function isDenied(error: unknown): boolean {
  return (
    error instanceof HostProtocolError &&
    (error.code === "DISPLAY_ACCESS_DENIED" || error.code === "HOST_UNAUTHENTICATED")
  );
}

const displayStyles = {
  host: {
    height: "100%",
    minHeight: "100dvh",
    minWidth: 0,
    overflow: "hidden",
    width: "100%",
  },
  message: {
    alignItems: "center",
    color: designToken("text.secondary"),
    display: "flex",
    flexDirection: "column",
    fontFamily: designToken("typography.family-sans"),
    gap: designToken("spacing.md"),
    height: "100%",
    justifyContent: "center",
    margin: 0,
    minHeight: "100dvh",
    padding: "1rem",
    textAlign: "center",
  },
  retry: {
    background: "transparent",
    border: `${designToken("border.width")} solid currentColor`,
    borderRadius: designToken("radius.md"),
    color: "inherit",
    cursor: "pointer",
    font: "inherit",
    padding: `${designToken("spacing.xs")} ${designToken("spacing.md")}`,
  },
  offline: {
    background: designToken("status.warning-background"),
    borderRadius: designToken("radius.pill"),
    color: designToken("text.warning"),
    fontFamily: designToken("typography.family-sans"),
    fontSize: designToken("typography.size-sm"),
    insetBlockStart: designToken("spacing.md"),
    insetInlineEnd: designToken("spacing.md"),
    padding: `${designToken("spacing.2xs")} ${designToken("spacing.md")}`,
    position: "absolute",
  },
} as const;

/**
 * A small, honest indicator: this screen is not currently in touch with Ekklesia, or is running
 * from code it cached earlier.
 *
 * Deliberately unobtrusive and deliberately not an error. An unattended screen showing a full-page
 * failure because a switch rebooted is worse than one quietly saying so in a corner, and the screen
 * recovers on its own the moment connectivity returns.
 */
function OfflineIndicator(props: { readonly connectivity: DisplayConnectivity }): ReactElement {
  // Neutral wording: this is on a wall the congregation reads, and the product name is the
  // installation's to choose, not the platform's (ADR 0046).
  const label = props.connectivity.usingFallback
    ? props.connectivity.fallbackKind === "artifact"
      ? "Offline — showing the last downloaded display code"
      : "Offline — showing the last downloaded display"
    : "Offline — reconnecting";
  return (
    <div data-testid="display-offline" role="status" style={displayStyles.offline}>
      {label}
    </div>
  );
}

function DisplayMessage(props: {
  readonly children: string;
  readonly testId: string;
  readonly onRetry?: () => void;
}): ReactElement {
  return (
    <div aria-live="polite" data-testid={props.testId} style={displayStyles.message}>
      <p style={{ margin: 0 }}>{props.children}</p>
      {props.onRetry ? (
        <button onClick={props.onRetry} style={displayStyles.retry} type="button">
          Retry
        </button>
      ) : undefined}
    </div>
  );
}

/**
 * The host for one display-capable module, with no Dashboard application mounted around it.
 *
 * Bootstrap is principal-first, so an anonymous browser never probes a module descriptor. The
 * descriptor itself is permission-protected server-side; only after it succeeds can an artifact URL
 * reach the generic loader. A changed `moduleId` or retry aborts the old fetch and keys a new frame,
 * so neither a late descriptor nor a late import can replace the current display.
 */
export function DisplayApp(props: DisplayAppProps): ReactElement {
  const [state, setState] = useState<DisplayState>({ generation: 0, status: "loading" });
  const [attempt, setAttempt] = useState(0);
  const [connectivity, setConnectivity] = useState<DisplayConnectivity>({
    online: true,
    usingFallback: false,
  });
  const {
    config,
    connectivity: connectivitySource,
    importModule,
    moduleId,
    offlineIndicatorDelayMs = DISPLAY_OFFLINE_INDICATOR_DELAY_MS,
    periodicRevalidationMs = DISPLAY_PERIODIC_REVALIDATION_MS,
    retryBaseMs = DISPLAY_RETRY_BASE_MS,
    revalidationIntervalMs = DISPLAY_REVALIDATION_INTERVAL_MS,
  } = props;
  /** Consecutive automatic retries since the display last started successfully. */
  const failures = useRef(0);
  const stateRef = useRef(state);
  stateRef.current = state;
  const revalidation = useRef<{ inFlight: AbortController | undefined; lastAt: number }>({
    inFlight: undefined,
    lastAt: 0,
  });

  /**
   * Resolves the descriptor again **without** taking the running display down (ADR 0043).
   *
   * A display that is showing something keeps showing it while the question is asked. Only the
   * answer decides what happens: the same display means nothing changes at all; a new version or a
   * different principal replaces the frame; a refusal is a revoked or expired device and returns the
   * screen to pairing (ADR 0036); and any other failure is the network still settling, so the frame
   * stays. A display that is not showing anything simply starts over.
   */
  const revalidate = useCallback(
    (reason: "online" | "authorization" | "periodic"): void => {
      const current = stateRef.current;
      if (current.status !== "ready") {
        if (reason === "online") {
          setAttempt((value) => value + 1);
        }
        return;
      }
      const tracker = revalidation.current;
      const nowMs = Date.now();
      if (
        tracker.inFlight !== undefined ||
        (reason === "authorization" && nowMs - tracker.lastAt < revalidationIntervalMs)
      ) {
        return;
      }
      tracker.lastAt = nowMs;
      const abort = new AbortController();
      tracker.inFlight = abort;
      void bootstrapDisplayHost(config, moduleId, abort.signal)
        .then((next) => {
          const latest = stateRef.current;
          if (abort.signal.aborted || latest.status !== "ready") {
            return;
          }
          if (!sameDisplay(latest.bootstrap, next)) {
            setState({ bootstrap: next, generation: latest.generation + 1, status: "ready" });
          }
        })
        .catch((error: unknown) => {
          if (!abort.signal.aborted && isDenied(error)) {
            setState({ status: "pairing" });
          }
        })
        .finally(() => {
          if (tracker.inFlight === abort) {
            tracker.inFlight = undefined;
          }
        });
    },
    [config, moduleId, revalidationIntervalMs],
  );

  useEffect(
    () => () => {
      revalidation.current.inFlight?.abort();
      revalidation.current.inFlight = undefined;
    },
    [],
  );

  const onAuthorizationResponse = useCallback(() => revalidate("authorization"), [revalidate]);

  // While running: ask again now and then, without disturbing anything when the answer is the same.
  useEffect(() => {
    if (state.status !== "ready" || periodicRevalidationMs <= 0) {
      return;
    }
    const timer = setInterval(() => revalidate("periodic"), periodicRevalidationMs);
    return () => clearInterval(timer);
  }, [periodicRevalidationMs, revalidate, state.status]);

  // Could not start: try again on its own, backing off. Pairing is not a failure — it has its own
  // polling — and a ready display has nothing to retry.
  useEffect(() => {
    if (state.status === "ready") {
      failures.current = 0;
      return;
    }
    if (state.status !== "failed" && state.status !== "unavailable") {
      return;
    }
    const delay = Math.min(DISPLAY_RETRY_MAX_MS, retryBaseMs * 2 ** Math.min(failures.current, 10));
    failures.current += 1;
    const timer = setTimeout(() => setAttempt((value) => value + 1), delay);
    return () => clearTimeout(timer);
  }, [retryBaseMs, state.status]);

  useEffect(() => {
    if (!connectivitySource) {
      return;
    }
    const monitor = watchDisplayConnectivity(connectivitySource);
    setConnectivity(monitor.current());
    const unsubscribe = monitor.subscribe((next) => {
      setConnectivity(next);
      // Nobody presses Retry on a lobby television. When the browser says the network is back, the
      // display resolves its descriptor again — which is also what stops a screen from sitting on
      // cached code after the server returns, since a fresh descriptor naming a new version replaces
      // the frame and the network-first worker fetches it (ADR 0043). The same answer leaves the
      // running display exactly where it was.
      if (next.online) {
        revalidate("online");
      }
    });
    return () => {
      unsubscribe();
      monitor.close();
    };
  }, [connectivitySource, revalidate]);

  useEffect(() => {
    const abort = new AbortController();
    revalidation.current.inFlight?.abort();
    setState({ generation: attempt, status: "loading" });
    void bootstrapDisplayHost(config, moduleId, abort.signal)
      .then((bootstrap) => {
        if (abort.signal.aborted) {
          return;
        }
        setState({ bootstrap, generation: attempt, status: "ready" });
      })
      .catch((error: unknown) => {
        if (abort.signal.aborted) {
          return;
        }
        // A denied or unauthenticated descriptor is the ordinary state of a screen nobody has
        // paired yet, not an error worth logging on every wall in the building.
        if (isDenied(error)) {
          setState({ status: "pairing" });
          return;
        }
        console.error("[ekklesia] display host bootstrap failed", error);
        setState(
          error instanceof HostProtocolError && error.code === "DISPLAY_NOT_AVAILABLE"
            ? { status: "unavailable" }
            : { status: "failed" },
        );
      });
    return () => abort.abort();
  }, [attempt, config, moduleId]);

  const retry = (): void => setAttempt((current) => current + 1);
  const showOffline = useSustained(
    !connectivity.online || connectivity.usingFallback,
    offlineIndicatorDelayMs,
  );

  return (
    <div data-testid="display-host" style={displayStyles.host}>
      {showOffline ? <OfflineIndicator connectivity={connectivity} /> : undefined}
      {state.status === "loading" ? (
        <DisplayMessage testId="display-host-loading">Loading display…</DisplayMessage>
      ) : undefined}
      {state.status === "pairing" ? (
        <PairingScreen config={config} moduleId={moduleId} onRetry={retry} />
      ) : undefined}
      {state.status === "unavailable" ? (
        <DisplayMessage onRetry={retry} testId="display-host-unavailable">
          This display is unavailable.
        </DisplayMessage>
      ) : undefined}
      {state.status === "failed" ? (
        <DisplayMessage onRetry={retry} testId="display-host-error">
          This display could not be reached.
        </DisplayMessage>
      ) : undefined}
      {state.status === "ready" ? (
        <DisplayUiFrame
          config={config}
          descriptor={state.bootstrap.descriptor}
          {...(importModule ? { importModule } : {})}
          key={`${state.bootstrap.descriptor.id}@${state.bootstrap.descriptor.version}:${state.generation}`}
          onAuthorizationResponse={onAuthorizationResponse}
          principal={state.bootstrap.principal}
        />
      ) : undefined}
    </div>
  );
}