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 DMS delivers to EventBridge when a replication
 * instance or replication task changes state (source `aws.dms`). Fields not
 * shared by every event kind are optional (the schema grows over time).
 */
export interface DmsReplicationEventDetail {
  /** The DMS event categories, e.g. `["failure"]`, `["state change"]`. */
  category?: string;
  /** The DMS event id, e.g. `DMS-EVENT-0079`. */
  eventId?: string;
  /** The event message, e.g. `Replication task has stopped.`. */
  eventMessage?: string;
  /** Human-readable event type, e.g. `REPLICATION_TASK_STOPPED`. */
  eventType?: string;
  /** The source identifier (instance or task identifier). */
  sourceId?: string;
  /** Additional event fields (the schema grows over time). */
  [key: string]: unknown;
}

/** A DMS EventBridge event delivered to the handler. */
export type DmsReplicationEvent = EventRecord<DmsReplicationEventDetail>;

/** Which DMS state-change events to subscribe to. */
export type DmsReplicationEventKind = "instance-state" | "task-state";

const DETAIL_TYPES: Record<DmsReplicationEventKind, string> = {
  "instance-state": "DMS Replication Instance State Change",
  "task-state": "DMS Replication Task State Change",
};

export interface ReplicationEventSourceProps extends EventRouteProps {
  /**
   * Logical id for the backing EventBridge rule.
   * @default "DmsReplicationEvents"
   */
  id?: string;
  /**
   * Which state-change events to subscribe to.
   * @default all kinds
   */
  kinds?: readonly DmsReplicationEventKind[];
}

/**
 * Event source connecting DMS replication state changes to the hosting
 * compute. DMS publishes replication instance and replication task state
 * changes (creation, failover, failure, task stop/start) to the account's
 * default EventBridge bus (source `aws.dms`); this subscribes the host
 * Function to those events so it can alert on failures or chain
 * post-migration automation.
 *
 * DMS 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 Replication Events
 * **Example:** Alert On Task Failures
 * ```typescript
 * import * as AWS from "alchemy/AWS";
 *
 * export default AlertFunction.make(
 *   { main: import.meta.url },
 *   Effect.gen(function* () {
 *     yield* AWS.DMS.consumeReplicationEvents(
 *       { kinds: ["task-state"] },
 *       (events) =>
 *         Stream.runForEach(events, (event) =>
 *           event.detail.category === "failure"
 *             ? Effect.log(`DMS task ${event.detail.sourceId} failed`)
 *             : Effect.void,
 *         ),
 *     );
 *     return {};
 *   }).pipe(Effect.provide(AWS.Lambda.EventSource)),
 * );
 * ```
 */
export const consumeReplicationEvents = <StreamReq = never, Req = never>(
  props: ReplicationEventSourceProps,
  process: (
    events: Stream.Stream<DmsReplicationEvent, never, StreamReq>,
  ) => Effect.Effect<void, never, Req>,
) =>
  consumeBusEvents(
    props.id ?? "DmsReplicationEvents",
    {
      source: ["aws.dms"],
      "detail-type": (
        props.kinds ?? (Object.keys(DETAIL_TYPES) as DmsReplicationEventKind[])
      ).map((kind) => DETAIL_TYPES[kind]),
    },
    { description: props.description, state: props.state },
    process,
  );