import type { Actor, CommittedEvent, Message, Messages, Patch, State } from "./messages";
import type { ProjectionMap, ProjectionPatch } from "./projection";
/**
 * State reducers apply partial state patches to a state, and returns the new state
 * - `state` the original state
 * - `patch` the patches to apply, considering rules like:
 *    - using `undefined` values to delete fields from the original state
 *    - recursively merging vs copying objects (like arrays)
 */
export type StateReducer<S extends State> = (state: Readonly<S>, patch: Readonly<Patch<S>> | undefined) => Readonly<S>;
/**
 * Event reducers apply events to a reduced state, and returns the new patch
 * - `state` the current reduced state
 * - `event` the event to be applied
 */
export type EventReducer<S extends State, E extends Messages, K extends keyof E> = (state: Readonly<S>, event: CommittedEvent<Pick<E, K>>) => Readonly<Patch<S>>;
/**
 * Projector reducers apply events as "state patches" to the resulting projection map
 * - `event` the committed event being projected
 * - `map` a reference to the resulting projection map
 */
export type ProjectorReducer<S extends State, E extends Messages, K extends keyof E> = (event: CommittedEvent<Pick<E, K>>, map: ProjectionMap<S>) => Promise<ProjectionPatch<S>[]>;
/**
 * Command handlers handle commands and emit events
 * - `data` the command's payload
 * - `state` the state of the artifact handling this command - Empty for systems
 * - `actor?` the actor invoking the command
 */
export type CommandHandler<S extends State, C extends Messages, E extends Messages, K extends keyof C> = (data: Readonly<C[K]>, state: Readonly<S>, actor?: Actor) => Promise<Message<E>[]>;
/**
 * Invariants validate aggregate preconditions before processing commands,
 * allowing state and authorization checks in a declarative way
 */
export type Invariant<S extends State> = {
    description: string;
    valid: (state: Readonly<S>, actor?: Actor) => boolean;
};
/**
 * Actor handlers extract process manager actor ids from input events
 * - `event` the committed event being handled
 */
export type ActorHandler<E extends Messages, K extends keyof E> = (event: CommittedEvent<Pick<E, K>>) => string;
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