import type { AnalyticsEvent, EventMiddlewareFn, ScreenMiddlewareFn, ScreenEvent } from '../types';

/**
 * Enriches every event with a fixed set of extra properties.
 *
 * ```ts
 * analytics.addEventMiddleware(
 *   createPropertyEnricher({ app_version: '2.1.0', environment: 'production' })
 * );
 * ```
 */
export function createPropertyEnricher(
  properties: Record<string, any>
): EventMiddlewareFn {
  return (event, next) => {
    next({
      ...event,
      properties: { ...properties, ...event.properties },
    });
  };
}

/**
 * Filters out events that don't pass the predicate.
 * If the predicate returns false the event is dropped silently.
 *
 * ```ts
 * analytics.addEventMiddleware(
 *   createEventFilter((event) => event.name !== 'internal_debug_event')
 * );
 * ```
 */
export function createEventFilter(
  predicate: (event: AnalyticsEvent) => boolean
): EventMiddlewareFn {
  return (event, next) => {
    if (predicate(event)) {
      next(event);
    }
  };
}

/**
 * Transforms event names and/or properties before they reach adapters.
 *
 * ```ts
 * analytics.addEventMiddleware(
 *   createEventTransformer((event) => ({
 *     ...event,
 *     name: event.name.toLowerCase().replace(/ /g, '_'),
 *   }))
 * );
 * ```
 */
export function createEventTransformer(
  transform: (event: AnalyticsEvent) => AnalyticsEvent
): EventMiddlewareFn {
  return (event, next) => {
    next(transform(event));
  };
}

/**
 * Adds UTM / attribution properties to every event.
 * Useful when you capture UTM params from a deep link.
 *
 * ```ts
 * analytics.addEventMiddleware(
 *   createAttributionEnricher({ utm_source: 'email', utm_medium: 'newsletter' })
 * );
 * ```
 */
export function createAttributionEnricher(
  attribution: Record<string, string>
): EventMiddlewareFn {
  return (event, next) => {
    next({
      ...event,
      properties: {
        ...event.properties,
        ...attribution,
      },
    });
  };
}

/**
 * Screen middleware: filters out screens that match a blocklist.
 *
 * ```ts
 * analytics.addScreenMiddleware(
 *   createScreenFilter(['Loading', 'Splash'])
 * );
 * ```
 */
export function createScreenFilter(
  blocklist: string[]
): ScreenMiddlewareFn {
  const blocked = new Set(blocklist.map((s) => s.toLowerCase()));
  return (event: ScreenEvent, next: (event: ScreenEvent) => void) => {
    if (!blocked.has(event.name.toLowerCase())) {
      next(event);
    }
  };
}

/**
 * Screen middleware: enriches every screen event with extra properties.
 */
export function createScreenEnricher(
  properties: Record<string, any>
): ScreenMiddlewareFn {
  return (event: ScreenEvent, next: (event: ScreenEvent) => void) => {
    next({
      ...event,
      properties: { ...properties, ...event.properties },
    });
  };
}