/**
 * Type-level utility: extract a specific variant from a discriminated union.
 */
export type ExtractMetadata<TMetadata, TField extends keyof TMetadata, TValue extends TMetadata[TField]> = Extract<TMetadata, Record<TField, TValue>>;
/**
 * A type guard function for a specific variant of event metadata.
 */
export type MetadataGuard<TMetadata, TVariant extends TMetadata> = (metadata: TMetadata) => metadata is TVariant;
/**
 * Map of discriminant values to their corresponding type guard functions.
 *
 * Keyed by `TValues` — the actual list of values passed to `defineEventMetadata` —
 * not by the full `TMetadata[TField]` union. That way, accessing a guard for
 * an omitted variant is a type error instead of an `undefined` at runtime.
 */
export type MetadataGuards<TMetadata, TField extends keyof TMetadata, TValues extends TMetadata[TField] & (string | number)> = {
    [V in TValues]: MetadataGuard<TMetadata, ExtractMetadata<TMetadata, TField, V>>;
};
/**
 * Create type-safe guard functions for a discriminated union metadata type.
 *
 * Returns an object mapping each discriminant value to a type guard function.
 * When a guard returns true, TypeScript narrows the metadata to the specific
 * variant, giving access to variant-specific fields.
 *
 * The double-invocation `defineEventMetadata<Type>()(field, values)` is needed
 * because TypeScript doesn't support partial type inference.
 *
 * @template TMetadata - The full discriminated union type
 *
 * @example
 * ```typescript
 * type EventMetadata =
 *   | { scope: 'project'; projectId: string }
 *   | { scope: 'team'; teamId: string }
 *   | { scope: 'global' }
 *
 * const metadata = defineEventMetadata<EventMetadata>()('scope', [
 *   'project',
 *   'team',
 *   'global',
 * ])
 *
 * if (metadata.project(event.metadata)) {
 *   // TypeScript narrows: event.metadata is { scope: 'project'; projectId: string }
 *   event.metadata.projectId // string
 * }
 * ```
 */
export declare function defineEventMetadata<TMetadata extends Record<string, unknown>>(): <TField extends keyof TMetadata & string, const TValues extends ReadonlyArray<TMetadata[TField] & (string | number)>>(field: TField, values: TValues) => MetadataGuards<TMetadata, TField, TValues[number]>;