import isEqual from 'lodash/isEqual';
import isNil from 'lodash/isNil';
import { IRequestState, ISkipQueryFn } from './RxRequestStore';

export type PartialKey<Obj, Key extends keyof Obj> = Omit<Obj, Key> &
  { [key in Key]?: Obj[Key] };

export type VarsCondition<Vars> = (vars: Vars) => boolean;

/**
 * Skips the request if the provided condition function returns true.
 * If that happens, sets the store state to the provided value.
 *
 * If you would like for the resulting data to depend on the variables,
 * just provide the generic skipQuery callback and do not use this function.
 *
 * @param condition - function of variables which should return true when the request should be skipped
 * @param value - value to be used when request is skipped
 */
export function skipIf<Vars, Data>(
  condition: VarsCondition<Vars>,
  value: Data
): ISkipQueryFn<Vars, Data> {
  return (vars: Vars) => {
    if (condition(vars)) return value;
    return undefined;
  };
}

/**
 * Skips the request if variables are exactly null.
 * Sets the store state to the provided value
 *
 * @param value - value to hold as the result of the request which never happened
 */
export function skipIfNull<Vars, Data>(
  value: Data | null = null
): ISkipQueryFn<Vars, Data> {
  return (vars: Vars) => {
    if (isNil(vars)) return value;
    return undefined;
  };
}

export interface CheckRequestResult {
  /** Should call loadData to request new data */
  request: boolean;
  /** Should render spinner */
  spinner: boolean;
  /** Should render error */
  error: boolean;
  /** Should render data */
  component: boolean;
}

export type CheckRequestStateFn<Vars, Data> = (
  state: IRequestState<Vars, Data>,
  variables: Vars | undefined
) => CheckRequestResult;

/**
 * Checks request store state in order to determine what to do
 *
 * @param state - request store state
 * @param variables - target variables
 * @returns object with the following boolean fields:
 *  - request - should call loadData to request new data
 *  - spinner - should render spinner
 *  - error - should render error
 *  - component - should render data
 */
export function checkRequestState<Vars, Data>(
  state: IRequestState<Vars, Data>,
  variables: Vars
): CheckRequestResult {
  const result = {
    request: false,
    spinner: false,
    error: false,
    component: false
  };

  if (!state) return result;

  if (!isEqual(state.variables, variables)) {
    result.request = true;
    result.spinner = true;
  } else if (state.loading) {
    result.spinner = true;
  } else if (state.error) {
    result.error = true;
  } else if (state.loaded) {
    result.component = true;
  } else {
    result.spinner = true;
    result.request = true;
  }

  return result;
}