import type * as Effect from "effect/Effect";
import type * as Stream from "effect/Stream";
import {
  consumeBusEvents,
  type EventRecord,
  type EventRouteProps,
} from "../EventBridge/EventSource.ts";

/**
 * The `detail` payload ElastiCache delivers to EventBridge. The schema is
 * loosely specified and differs slightly per event kind, so every field is
 * optional (the schema grows over time).
 */
export interface CacheEventDetail {
  /** Human-readable description of what happened. */
  message?: string;
  /** Additional event fields (the schema grows over time). */
  [key: string]: unknown;
}

/** An ElastiCache EventBridge event delivered to the handler. */
export type CacheEvent = EventRecord<CacheEventDetail>;

/**
 * Which ElastiCache notifications to subscribe to. Each kind maps to one of
 * the detail-types ElastiCache publishes to the account's default bus.
 */
export type CacheEventKind =
  | "cache-created"
  | "cache-creation-failed"
  | "cache-updated"
  | "cache-update-failed"
  | "cache-deleted"
  | "cache-limit-approaching"
  | "snapshot-created"
  | "snapshot-creation-failed"
  | "snapshot-copy-failed"
  | "snapshot-export-failed";

const DETAIL_TYPES: Record<CacheEventKind, string> = {
  "cache-created": "Cache Created",
  "cache-creation-failed": "Cache Creation Failed",
  "cache-updated": "Cache Updated",
  "cache-update-failed": "Cache Update Failed",
  "cache-deleted": "Cache Deleted",
  "cache-limit-approaching": "Cache Limit Approaching",
  "snapshot-created": "Snapshot Created",
  "snapshot-creation-failed": "Snapshot Creation Failed",
  "snapshot-copy-failed": "Snapshot Copy Failed",
  "snapshot-export-failed": "Snapshot Export Failed",
};

export interface CacheEventSourceProps extends EventRouteProps {
  /**
   * Logical id for the backing EventBridge rule.
   * @default "ElastiCacheEvents"
   */
  id?: string;
  /**
   * Which notifications to subscribe to.
   * @default all ElastiCache detail-types
   */
  kinds?: readonly CacheEventKind[];
  /**
   * Restrict to events about specific caches or snapshots (matched against
   * the event's top-level `resources`, which carries the resource ARNs).
   */
  resourceArns?: readonly string[];
}

/**
 * Event source connecting ElastiCache notifications to the hosting compute.
 * ElastiCache publishes cache and snapshot lifecycle events — creations,
 * updates, deletions, failures, approaching usage limits — to the account's
 * default EventBridge bus (source `aws.elasticache`); this subscribes the
 * host Function to those events so it can alert on failed snapshots or a
 * cache nearing its usage limits.
 *
 * ElastiCache publishes to EventBridge automatically — no additional
 * resource is created besides the EventBridge rule targeting the host.
 * Provide the host-specific implementation layer (e.g.
 * `AWS.Lambda.EventSource`) on the Function effect.
 *
 * ### Consuming Cache Events
 * **Example:** Alert When a Cache Approaches Its Usage Limit
 * ```typescript
 * import * as AWS from "alchemy/AWS";
 *
 * export default AlertFunction.make(
 *   { main: import.meta.url },
 *   Effect.gen(function* () {
 *     yield* AWS.ElastiCache.consumeCacheEvents(
 *       { kinds: ["cache-limit-approaching", "snapshot-creation-failed"] },
 *       (events) =>
 *         Stream.runForEach(events, (event) =>
 *           Effect.logError(
 *             `${event["detail-type"]}: ${event.resources.join(", ")}`,
 *           ),
 *         ),
 *     );
 *     return {};
 *   }).pipe(Effect.provide(AWS.Lambda.EventSource)),
 * );
 * ```
 */
export const consumeCacheEvents = <StreamReq = never, Req = never>(
  props: CacheEventSourceProps,
  process: (
    events: Stream.Stream<CacheEvent, never, StreamReq>,
  ) => Effect.Effect<void, never, Req>,
) =>
  consumeBusEvents(
    props.id ?? "ElastiCacheEvents",
    {
      source: ["aws.elasticache"],
      ...(props.kinds !== undefined
        ? { "detail-type": props.kinds.map((kind) => DETAIL_TYPES[kind]) }
        : {}),
      ...(props.resourceArns !== undefined
        ? { resources: [...props.resourceArns] }
        : {}),
    },
    { description: props.description, state: props.state },
    process,
  );