import { StandardSchemaDictionary } from "../../@types/standard.js";
import { Extension, MergedExtensionDefine } from "../../@types/extension.js";
import { Format, Partial } from "ts-vista";
/** The complete options for an extension. */
type CompleteExtensionOptions<Define extends StandardSchemaDictionary, Ext extends readonly Extension<StandardSchemaDictionary>[]> = {
  /** Inner extensions to merge. */extends: Ext; /** The env variable definitions. */
  define: Define;
};
/** Extension options with `extends`. */
type ExtensionOptions<Define extends StandardSchemaDictionary, Ext extends readonly Extension<StandardSchemaDictionary>[]> = Format<Partial<CompleteExtensionOptions<Define, Ext>, "extends">>;
/**
* Structural return type of `createExtension`.
*
* Identical in shape to `Extension<MergedExtensionDefine<Define, Ext>>` but
* declared inline so that TypeScript does not re-check the
* `StandardSchemaDictionary` constraint on the computed `MergedExtensionDefine`
* at the generic declaration site.
*/
type FlattenedExtension<Define extends StandardSchemaDictionary, Ext extends readonly Extension<StandardSchemaDictionary>[] = readonly never[]> = {
  define: MergedExtensionDefine<Define, Ext>;
};
/**
* Create an extension that can be passed to `createEnv` via the `extends`
* option.
*
* Nested `define`s are flattened in array order.
* The outer `define` wins on key collision.
*
* ### Example
*
* ```ts
* const base = createExtension({
*     define: {
*         NODE_ENV: z.enum(["development", "production"]),
*     },
* });
*
* const withPort = createExtension({
*     extends: [base],
*     define: {
*         PORT: z.number(),
*     },
* });
*
* const env = createEnv({
*     target: "server",
*     runtimeEnv: process.env,
*     extends: [
*          withPort,
*     ],
*     define: {
*         API_URL: z.string().url(),
*     },
* });
* ```
*/
declare function createExtension<const Define extends StandardSchemaDictionary, const Ext extends readonly Extension<StandardSchemaDictionary>[] = readonly never[]>(extension: ExtensionOptions<Define, Ext>): FlattenedExtension<Define, Ext>;
export { createExtension };
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