/**
 * @file supplierAutomat.js
 * @description Manages cached supplier list (`GET /api/supplier`) for the active company.
 *
 * Upstream Triggers:
 * - `authAutomat`: Subscribes to auth state changes (`syncWithAuth`) — triggers
 *   `actions.load()` on `'authed'` with a `selectedCompanyId`, and `actions.clear()` on `'anon'`.
 * - `sseAutomat`: Calls `actions.reload()` upon receiving a `'supplier'` SSE event.
 * - UI / Routes: Calls to `actions.load()`, `actions.reload()`, or `actions.setSuppliers()`.
 */

import { Automat } from 'react-automat';
import { supplier as supplierApi } from '../api';
import { requireArray, requireDefined, requireObject } from '../utils/apiShape';
import authAutomat from './authAutomat';

/**
 * @typedef {Object} Supplier
 * @property {string|number} id Supplier identifier.
 * @property {string} name Supplier name.
 */

/**
 * @typedef {Object} SupplierState
 * @property {Array<Supplier>} suppliers Company-scoped suppliers.
 * @property {'idle'|'loading'|'ready'|'failed'} status Load lifecycle state.
 * @property {Error|null} error Last load error.
 */

/** @type {SupplierState} */
const initialState = {
  suppliers: [],
  status: 'idle',
  error: null,
};

let supplierAutomat;

/**
 * Fetches the company-scoped supplier list.
 *
 * @returns {Promise<Array<Supplier>>} Supplier list.
 */
async function fetchSuppliers() {
  const data = await supplierApi.list();
  requireObject(data, 'GET /api/supplier');
  return requireArray(data.suppliers, 'suppliers');
}

/** In-flight `load()` promise so concurrent consumers share one request. */
let inflightLoad = null;

/**
 * Loads the supplier list once, deduplicating concurrent callers.
 *
 * @returns {Promise<Array<Supplier>>} Loaded suppliers.
 */
function loadSuppliers() {
  if (inflightLoad) return inflightLoad;
  inflightLoad = (async () => {
    supplierAutomat.setState({ status: 'loading', error: null });
    try {
      const suppliers = await fetchSuppliers();
      supplierAutomat.setState({ suppliers, status: 'ready', error: null });
      return suppliers;
    } catch (error) {
      supplierAutomat.setState({ status: 'failed', error });
      throw error;
    } finally {
      inflightLoad = null;
    }
  })();
  return inflightLoad;
}

const actions = {
  /**
   * Loads the supplier list, exposing a loading/failed lifecycle.
   *
   * @returns {Promise<Array<Supplier>>} Loaded suppliers.
   */
  load() {
    return loadSuppliers();
  },

  /**
   * Silently re-fetches the supplier list while keeping the current state.
   *
   * @returns {Promise<Array<Supplier>>} Fresh suppliers.
   */
  async reload() {
    try {
      const suppliers = await fetchSuppliers();
      supplierAutomat.setState({ suppliers, status: 'ready', error: null });
      return suppliers;
    } catch (error) {
      supplierAutomat.setState({ error });
      throw error;
    }
  },

  /**
   * Creates a supplier and refreshes the cached list.
   *
   * @param {{name: string}} body Creation payload.
   * @returns {Promise<Supplier>} Created supplier.
   */
  async create(body) {
    const data = await supplierApi.create(body);
    requireObject(data, 'POST /api/supplier');
    requireObject(data.supplier, 'supplier');
    requireDefined(data.supplier.id, 'supplier.id');
    await supplierAutomat.actions.reload();
    return data.supplier;
  },

  /**
   * Renames a supplier and refreshes the cached list.
   *
   * @param {string|number} id Supplier identifier.
   * @param {{name: string}} body Update payload.
   * @returns {Promise<Supplier>} Updated supplier.
   */
  async update(id, body) {
    const data = await supplierApi.update(id, body);
    requireObject(data, 'PATCH /api/supplier/:id');
    requireObject(data.supplier, 'supplier');
    requireDefined(data.supplier.id, 'supplier.id');
    await supplierAutomat.actions.reload();
    return data.supplier;
  },

  /**
   * Deletes a supplier and refreshes the cached list.
   *
   * @param {string|number} id Supplier identifier.
   * @returns {Promise<void>}
   */
  async remove(id) {
    await supplierApi.delete(id);
    await supplierAutomat.actions.reload();
  },

  /**
   * Replaces the cached list without a round-trip.
   *
   * @param {Array<Supplier>} suppliers Suppliers to cache.
   * @returns {void}
   */
  setSuppliers(suppliers) {
    supplierAutomat.setState({
      suppliers: Array.isArray(suppliers) ? suppliers : [],
      status: 'ready',
      error: null,
    });
  },

  /**
   * Forgets the cached list and returns to the initial state.
   *
   * @returns {void}
   */
  clear() {
    supplierAutomat.setState({ ...initialState });
  },
};

/**
 * Company-scoped supplier cache. Loads automatically once an authenticated
 * session with a selected company exists and is cleared when auth is gone.
 *
 * @type {Automat<SupplierState>}
 */
supplierAutomat = new Automat(initialState, actions, { name: 'supplier' });

/**
 * Derives the cache key from the auth state: the selected company while
 * authenticated, otherwise `null`.
 *
 * @param {import('./authAutomat').AuthState} authState Auth automat state.
 * @returns {string|null} Cache key.
 */
function authKey(authState) {
  if (authState?.status !== 'authed' || !authState.user) return null;
  const companyId = authState.user.selectedCompanyId;
  return companyId == null ? null : String(companyId);
}

let lastAuthKey;

/**
 * Loads the supplier list when auth/company becomes available and forgets it
 * when the session ends.
 *
 * @param {import('./authAutomat').AuthState} authState Auth automat state.
 * @returns {void}
 */
function syncWithAuth(authState) {
  const key = authKey(authState);
  if (key === lastAuthKey) return;
  lastAuthKey = key;
  if (key == null) {
    supplierAutomat.actions.clear();
  } else {
    void supplierAutomat.actions.load().catch(() => {});
  }
}

authAutomat.subscribe(syncWithAuth);
syncWithAuth(authAutomat.state);

export default supplierAutomat;