import {
  createContext,
  useCallback,
  useContext,
  useEffect,
  useReducer,
  useRef,
  useState,
  type ReactNode,
} from "react";
import {
  checkLicenseRevocation,
  getEdition,
  readLicense,
  storeLicense,
  type Edition,
  type LicenseInfo,
  type RevocationCheck,
  type RevocationOutcome,
} from "../services/licenseService";
import { logInfo, logWarn } from "../services/logService";

/**
 * Machine-level license context — loaded ONCE at boot, above ProfileProvider.
 *
 * Modeled on ProfileContext (createContext<T | null>, useReducer, consumer hook
 * that throws). Mounting above the profile layer means it survives the
 * `BrowserRouter key={refreshKey}` remount that a profile switch triggers — the
 * license is a property of the machine, not of the active profile.
 *
 * Error recovery (CWE-703): the provider is a SPOF. If the boot invoke throws,
 * we expose a NEUTRAL state (previous edition preserved, `status: "error"`) and
 * retry with capped exponential backoff. Consumers must render a neutral
 * placeholder while `status !== "ready"` — never the upsell — so a transient IPC
 * failure never locks a paying user out.
 *
 * Key validation is orthogonal to that load lifecycle: a rejected `submitKey`
 * leaves the stored license — and therefore `status` — untouched, and surfaces
 * `validationError` instead. The retry loop keys off `status === "error"`, so
 * it can never arm on a bad key and auto-clear the message the user is reading,
 * and `ready` consumers never regress on a typo'd key.
 *
 * Revocation (#365, which replaces D13 of #347): the revoked state lives in Rust,
 * next to the key, and survives the session. It reaches this context as
 * `info.revoked`, and Rust resolves the edition of a revoked key to "free". Nothing
 * here decides it. One request goes out on the app's own initiative: the revocation
 * check, started at boot when a key is stored, and after a key is entered (#373),
 * in the background. Rust runs the checks one at a time and sends at most once per
 * 24 h for a key, and an unreachable server changes nothing.
 */

type LicenseStatus = "idle" | "loading" | "ready" | "error";

interface LicenseState {
  status: LicenseStatus;
  edition: Edition;
  info: LicenseInfo | null;
  /** Load-lifecycle error — target of the CWE-703 retry loop. */
  error: string | null;
  validating: boolean;
  /** Key-submission error — never retried, cleared on the next submit. */
  validationError: string | null;
}

/** Exported for the functions below and their tests — not part of the context API. */
export type LicenseAction =
  | { type: "LOAD_START" }
  | { type: "LOAD_DONE"; edition: Edition; info: LicenseInfo | null }
  | { type: "LOAD_ERROR"; error: string }
  | { type: "VALIDATE_START" }
  | { type: "VALIDATE_DONE"; info: LicenseInfo; edition: Edition }
  | { type: "VALIDATE_ERROR"; error: string };

/** Exported for unit tests only — not part of the context API. */
export const initialLicenseState: LicenseState = {
  status: "idle",
  edition: "free",
  info: null,
  error: null,
  validating: false,
  validationError: null,
};

/**
 * Identity of the stored license, as far as the client can tell (#347): the same email,
 * edition, issue and expiry dates mean the same key, entered again. `null` without a key.
 */
export function licenseIdentity(info: LicenseInfo | null): string | null {
  return info === null
    ? null
    : `${info.email}|${info.edition}|${info.issued_at}|${info.expires_at}`;
}

/** Exported for unit tests only — not part of the context API. */
export function licenseReducer(state: LicenseState, action: LicenseAction): LicenseState {
  switch (action.type) {
    case "LOAD_START":
      return { ...state, status: "loading", error: null };
    case "LOAD_DONE":
      return { ...state, status: "ready", edition: action.edition, info: action.info, error: null };
    case "LOAD_ERROR":
      // Preserve the last-known edition: an error must not downgrade a paying
      // user to the upsell (that is what fail-closed + `ready` guard protect).
      return { ...state, status: "error", error: action.error };
    case "VALIDATE_START":
      return { ...state, validating: true, validationError: null };
    case "VALIDATE_DONE":
      // The edition is the one Rust resolved for the stored key, not the one the
      // key claims: a revoked key entered again stays in the Free edition (#365).
      return {
        status: "ready",
        edition: action.edition,
        info: action.info,
        error: null,
        validating: false,
        validationError: null,
      };
    case "VALIDATE_ERROR":
      // Status untouched: "ready" stays ready (no gating flash on a typo'd
      // key), and a boot-error retry loop keeps running through the failure.
      return { ...state, validating: false, validationError: action.error };
  }
}

type SubmitKeyResult =
  | { ok: true; info: LicenseInfo }
  | { ok: false; error: string };

export interface SubmitKeyDeps {
  storeLicense: (key: string) => Promise<LicenseInfo>;
  getEdition: () => Promise<Edition>;
  dispatch: (action: LicenseAction) => void;
  /**
   * The provider's one launcher of the revocation check (#373): it returns at once and
   * the check runs in the background (see `revocationCheckLauncher`).
   */
  startRevocationCheck: (wasRevoked: boolean) => void;
}

/**
 * Store a key, then take the edition Rust resolves for it: one resolution point, which
 * knows a revoked key (Free) and an active account Premium. If that read fails, the
 * key's own edition stands in, or "free" when the key came back revoked.
 *
 * A stored key is then checked online right away (#373), not at the next start: the
 * check is launched after VALIDATE_DONE and not awaited, so the entry answers without
 * waiting for the license server. A revoked key shows the key's edition until the
 * check answers, then the reload brings Free. A refused key sends nothing.
 */
export async function performSubmitKey(deps: SubmitKeyDeps, key: string): Promise<SubmitKeyResult> {
  deps.dispatch({ type: "VALIDATE_START" });
  let info: LicenseInfo;
  try {
    info = await deps.storeLicense(key);
  } catch (e) {
    const message = e instanceof Error ? e.message : String(e);
    deps.dispatch({ type: "VALIDATE_ERROR", error: message });
    return { ok: false, error: message };
  }
  let edition: Edition;
  try {
    edition = await deps.getEdition();
  } catch {
    edition = info.revoked ? "free" : info.edition;
  }
  deps.dispatch({ type: "VALIDATE_DONE", info, edition });
  deps.startRevocationCheck(info.revoked);
  return { ok: true, info };
}

/**
 * Starter of the revocation check at app start (#365, D1). It is consumed by the FIRST
 * "ready" state, whatever the key state, and runs the check only if a key is stored then;
 * a reload of the context never starts it again. A key entered later is checked by the
 * entry itself (`performSubmitKey`, #373). A key entered before the first ready state gets
 * two checks from here, the entry's and this starter's: Rust runs the checks one at a
 * time, and the second one reads the first one's attempt and sends nothing.
 */
export function createRevocationCheckStarter(run: (wasRevoked: boolean) => void) {
  let consumed = false;
  return (status: LicenseStatus, info: LicenseInfo | null): void => {
    if (consumed || status !== "ready") return;
    consumed = true;
    if (info !== null) run(info.revoked);
  };
}

/** One line of the in-app log per outcome: what was sent, and what it changed. */
export const REVOCATION_LOG: Record<RevocationOutcome, string> = {
  no_license: "License check: no valid key stored, nothing sent",
  not_due: "License check: last attempt less than 24 h ago, nothing sent",
  valid: "License check: the license server confirms the key",
  revoked: "License check: the license server says the key was revoked",
  unreachable: "License check: the license server could not be reached or answered with an error, nothing changed",
  unknown: "License check: the license server gave no usable answer, nothing changed",
  storage: "License check: the attempt or the server's answer could not be recorded, nothing changed",
};

export interface RevocationCheckDeps {
  checkLicenseRevocation: () => Promise<RevocationCheck>;
  refresh: () => Promise<void>;
  logInfo: (...args: unknown[]) => void;
  logWarn: (...args: unknown[]) => void;
}

/**
 * Run the revocation check and write its outcome to the in-app log (Settings →
 * System → Logs): it is a request the user did not ask for, so it must be visible.
 * The context is reloaded only when the revoked state changed. A command that fails
 * is logged and changes nothing.
 */
export async function performRevocationCheck(
  deps: RevocationCheckDeps,
  wasRevoked: boolean,
): Promise<void> {
  let result: RevocationCheck;
  try {
    result = await deps.checkLicenseRevocation();
  } catch (e) {
    deps.logWarn("License check: the check could not run, nothing changed", e);
    return;
  }
  deps.logInfo(REVOCATION_LOG[result.outcome]);
  if (result.revoked !== wasRevoked) await deps.refresh();
}

/**
 * The one launcher of the revocation check, shared by the start (`createRevocationCheckStarter`)
 * and the entry of a key (`performSubmitKey`, #373). It returns at once: the check runs in the
 * background, so nothing that launches it waits for the license server.
 */
export function revocationCheckLauncher(deps: RevocationCheckDeps): (wasRevoked: boolean) => void {
  return (wasRevoked) => {
    void performRevocationCheck(deps, wasRevoked);
  };
}

interface LicenseContextValue {
  status: LicenseStatus;
  edition: Edition;
  features: string[];
  info: LicenseInfo | null;
  error: string | null;
  validating: boolean;
  validationError: string | null;
  /** The license server revoked the stored key (#365). Persisted by Rust. */
  revoked: boolean;
  refresh: () => Promise<void>;
  submitKey: (key: string) => Promise<SubmitKeyResult>;
}

/**
 * What the context exposes of a state. A plain function so the derivation is tested: the
 * provider's own state never loads under renderToStaticMarkup, where effects do not run.
 */
export function licenseContextValue(
  state: LicenseState,
  refresh: () => Promise<void>,
  submitKey: (key: string) => Promise<SubmitKeyResult>,
): LicenseContextValue {
  return {
    status: state.status,
    edition: state.edition,
    features: state.info?.features ?? [],
    info: state.info,
    error: state.error,
    validating: state.validating,
    validationError: state.validationError,
    revoked: state.info?.revoked ?? false,
    refresh,
    submitKey,
  };
}

const LicenseContext = createContext<LicenseContextValue | null>(null);

// Capped exponential backoff for boot-error retries: 1s, 2s, 4s, ... max 30s.
const RETRY_BASE_MS = 1000;
const RETRY_MAX_MS = 30_000;

export function LicenseProvider({ children }: { children: ReactNode }) {
  const [state, dispatch] = useReducer(licenseReducer, initialLicenseState);
  const retryAttempt = useRef(0);

  const refresh = useCallback(async () => {
    dispatch({ type: "LOAD_START" });
    try {
      const [edition, info] = await Promise.all([getEdition(), readLicense()]);
      dispatch({ type: "LOAD_DONE", edition, info });
    } catch (e) {
      dispatch({
        type: "LOAD_ERROR",
        error: e instanceof Error ? e.message : String(e),
      });
    }
  }, []);

  // Revocation check: launched at app start (see createRevocationCheckStarter) and after a
  // key is entered (see performSubmitKey), by the same launcher.
  const [launchRevocationCheck] = useState(() =>
    revocationCheckLauncher({ checkLicenseRevocation, refresh, logInfo, logWarn }),
  );

  const submitKey = useCallback(
    (key: string) =>
      performSubmitKey(
        { storeLicense, getEdition, dispatch, startRevocationCheck: launchRevocationCheck },
        key,
      ),
    [launchRevocationCheck],
  );

  // Load once at boot.
  useEffect(() => {
    void refresh();
  }, [refresh]);

  const [checkAtStart] = useState(() => createRevocationCheckStarter(launchRevocationCheck));
  useEffect(() => {
    checkAtStart(state.status, state.info);
  }, [checkAtStart, state.status, state.info]);

  // Error recovery: retry with capped exponential backoff (CWE-703). Load
  // errors only by construction — validation failures never set status.
  useEffect(() => {
    if (state.status === "ready") {
      retryAttempt.current = 0;
      return;
    }
    if (state.status !== "error") return;
    const attempt = retryAttempt.current;
    retryAttempt.current = attempt + 1;
    const delay = Math.min(RETRY_MAX_MS, RETRY_BASE_MS * 2 ** attempt);
    const timer = window.setTimeout(() => {
      void refresh();
    }, delay);
    return () => window.clearTimeout(timer);
  }, [state.status, refresh]);

  const value = licenseContextValue(state, refresh, submitKey);

  return <LicenseContext.Provider value={value}>{children}</LicenseContext.Provider>;
}

export function useLicenseContext(): LicenseContextValue {
  const ctx = useContext(LicenseContext);
  if (!ctx) throw new Error("useLicenseContext must be used within LicenseProvider");
  return ctx;
}