type EnvValue = string | number | boolean;
interface EnvFieldConfig<T extends EnvValue> {
    type: 'string' | 'number' | 'boolean' | 'enum';
    required: boolean;
    defaultValue?: T;
    validators: Array<(value: T) => string | null>;
    transformer: (raw: string) => T;
    enumValues?: readonly string[];
}
type InferEnvType<T> = T extends EnvField<infer U> ? U : never;
type EnvSchema = Record<string, EnvField<EnvValue>>;
type InferEnv<T extends EnvSchema> = {
    [K in keyof T]: InferEnvType<T[K]>;
};
/**
 * A builder for defining environment variable validation rules.
 */
export declare class EnvField<T extends EnvValue> {
    /** @internal */
    _config: EnvFieldConfig<T>;
    constructor(config: EnvFieldConfig<T>);
    /** Mark the field as required (default). */
    required(): EnvField<T>;
    /** Mark the field as optional with a default value. */
    default(value: T): EnvField<T>;
    /** Add a custom validation rule. */
    validate(fn: (value: T) => string | null): EnvField<T>;
}
/**
 * Define a string environment variable.
 *
 * @example
 * ```ts
 * const env = createEnv({
 *   DATABASE_URL: envString().url().required(),
 * });
 * ```
 */
export declare function envString(): StringEnvField;
declare class StringEnvField extends EnvField<string> {
    /** Validate that the string is a valid URL. */
    url(): StringEnvField;
    /** Validate minimum length. */
    minLength(min: number): StringEnvField;
    /** Validate that the string matches a pattern. */
    matches(pattern: RegExp): StringEnvField;
    /** Set a default value. */
    default(value: string): StringEnvField;
    /** Mark as required. */
    required(): StringEnvField;
}
/**
 * Define a numeric environment variable.
 * Automatically coerces the string value to a number.
 *
 * @example
 * ```ts
 * const env = createEnv({
 *   PORT: envNumber().port().default(3000),
 * });
 * ```
 */
export declare function envNumber(): NumberEnvField;
declare class NumberEnvField extends EnvField<number> {
    /** Validate that the number is a valid port (1-65535). */
    port(): NumberEnvField;
    /** Validate minimum value. */
    min(min: number): NumberEnvField;
    /** Validate maximum value. */
    max(max: number): NumberEnvField;
    /** Set a default value. */
    default(value: number): NumberEnvField;
    /** Mark as required. */
    required(): NumberEnvField;
}
/**
 * Define a boolean environment variable.
 * Recognizes: "true", "1", "yes", "on" as true.
 *
 * @example
 * ```ts
 * const env = createEnv({
 *   DEBUG: envBoolean().default(false),
 * });
 * ```
 */
export declare function envBoolean(): BooleanEnvField;
declare class BooleanEnvField extends EnvField<boolean> {
    /** Set a default value. */
    default(value: boolean): BooleanEnvField;
    /** Mark as required. */
    required(): BooleanEnvField;
}
/**
 * Define an enum environment variable.
 * Value must be one of the specified options.
 *
 * @example
 * ```ts
 * const env = createEnv({
 *   NODE_ENV: envEnum(['development', 'production', 'test'] as const),
 * });
 * // env.NODE_ENV is 'development' | 'production' | 'test'
 * ```
 */
export declare function envEnum<T extends readonly string[]>(values: T): EnvField<T[number]>;
/**
 * Validate and type-safe environment variables.
 * Throws `EnvConfigError` at startup if validation fails.
 *
 * @example
 * ```ts
 * import { createEnv, envString, envNumber, envBoolean, envEnum } from 'guarden/env';
 *
 * export const env = createEnv({
 *   DATABASE_URL: envString().url().required(),
 *   PORT: envNumber().port().default(3000),
 *   DEBUG: envBoolean().default(false),
 *   NODE_ENV: envEnum(['development', 'production', 'test']),
 * });
 *
 * // Fully typed!
 * env.DATABASE_URL // string
 * env.PORT         // number
 * env.DEBUG        // boolean
 * env.NODE_ENV     // 'development' | 'production' | 'test'
 * ```
 */
export declare function createEnv<T extends EnvSchema>(schema: T, source?: Record<string, string | undefined>): InferEnv<T>;
export {};
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