import { useCallback, useEffect, useMemo, useReducer } from "react";
import {
  getOnboardingCounters,
  hideChecklist,
  showChecklist,
  type OnboardingSnapshot,
} from "../services/onboardingService";
import { logError } from "../services/logService";
import { computeChecklist, type Checklist } from "../utils/onboardingChecklist";
import { useEntitlement } from "./useEntitlement";
import type { OnboardingCounters } from "../shared/types";

// State of the getting-started checklist (#351). The reducer and its initial
// state are exported so the state machine is tested without renderHook (same
// pattern as `licenseReducer`, `feedbackReducer`, `migrationReducer`).

export type OnboardingChecklistStatus = "loading" | "ready" | "error";

export interface OnboardingChecklistState {
  status: OnboardingChecklistStatus;
  /** Null until the first successful load. */
  counters: OnboardingCounters | null;
  /** True when an import folder has been chosen (read with the counters). */
  importFolderSet: boolean;
  /** Dismissed by the user. Untouched by a load error. */
  hidden: boolean;
  /** Message of the last load error, null otherwise. */
  error: string | null;
}

export type OnboardingChecklistAction =
  | { type: "LOAD_START" }
  | { type: "LOAD_DONE"; snapshot: OnboardingSnapshot }
  | { type: "LOAD_ERROR"; error: string }
  | { type: "HIDE" }
  | { type: "SHOW" };

export const initialOnboardingChecklistState: OnboardingChecklistState = {
  status: "loading",
  counters: null,
  importFolderSet: false,
  hidden: false,
  error: null,
};

export function onboardingChecklistReducer(
  state: OnboardingChecklistState,
  action: OnboardingChecklistAction,
): OnboardingChecklistState {
  switch (action.type) {
    case "LOAD_START":
      // The previous counters stay so a refresh does not blank the list.
      return { ...state, status: "loading", error: null };
    case "LOAD_DONE":
      return {
        ...state,
        status: "ready",
        counters: action.snapshot.counters,
        importFolderSet: action.snapshot.importFolderSet,
        hidden: action.snapshot.hidden,
        error: null,
      };
    case "LOAD_ERROR":
      // `hidden` is deliberately kept: a failed read must not resurface a
      // checklist the user dismissed.
      return { ...state, status: "error", error: action.error };
    case "HIDE":
      return { ...state, hidden: true };
    case "SHOW":
      return { ...state, hidden: false };
  }
}

function errorMessage(e: unknown): string {
  return e instanceof Error ? e.message : String(e);
}

/**
 * Getting-started checklist of the dashboard: counters read from the profile
 * database, dismissal preference, and the Budget entitlement that decides
 * whether the sixth row is locked.
 */
export function useOnboardingChecklist() {
  const [state, dispatch] = useReducer(
    onboardingChecklistReducer,
    initialOnboardingChecklistState,
  );
  const { allowed: budgetAllowed, ready: budgetReady } = useEntitlement("budget");

  const refresh = useCallback(async () => {
    dispatch({ type: "LOAD_START" });
    try {
      const snapshot = await getOnboardingCounters();
      dispatch({ type: "LOAD_DONE", snapshot });
    } catch (e) {
      const error = errorMessage(e);
      logError("Onboarding: failed to load checklist counters", error);
      dispatch({ type: "LOAD_ERROR", error });
    }
  }, []);

  // Read-only local SELECTs: a StrictMode double run is harmless.
  useEffect(() => {
    void refresh();
  }, [refresh]);

  const hide = useCallback(async () => {
    try {
      await hideChecklist();
      dispatch({ type: "HIDE" });
    } catch (e) {
      logError("Onboarding: failed to hide checklist", errorMessage(e));
    }
  }, []);

  const show = useCallback(async () => {
    try {
      await showChecklist();
      dispatch({ type: "SHOW" });
    } catch (e) {
      logError("Onboarding: failed to show checklist", errorMessage(e));
    }
  }, []);

  const checklist: Checklist | null = useMemo(
    () =>
      state.counters
        ? computeChecklist(state.counters, {
            importFolderSet: state.importFolderSet,
            budgetAllowed,
          })
        : null,
    [state.counters, state.importFolderSet, budgetAllowed],
  );

  return {
    status: state.status,
    checklist,
    /** Raw counters; the dashboard reads `transactions` to decide on the empty state (#352). */
    counters: state.counters,
    hidden: state.hidden,
    /** Message of the last load error, null otherwise. */
    error: state.error,
    budgetReady,
    refresh,
    hide,
    show,
  };
}