/**
 * Minimal writable surface needed by {@link Output}.
 *
 * Both `process.stdout` and an in-memory buffer satisfy this,
 * which is what makes output testable.
 */
export interface OutputStream {
    write: (chunk: string) => unknown;
}
/**
 * `json` is machine readable: only {@link Output.data} produces output.
 * `text` is human readable: data is pretty printed and may be colorized.
 */
export type OutputFormat = 'json' | 'text';
export interface Output {
    readonly format: OutputFormat;
    /**
     * The result of a command, e.g., an API response.
     *
     * This is the only thing ever written to stdout,
     * so it is safe to pipe into another program.
     */
    data: (value: unknown) => void;
    /**
     * A plain text command result, e.g., the version or the help guide.
     *
     * Written to stdout verbatim in every format: these results are already
     * a single value, so encoding them as JSON would only make them harder
     * to consume from a pipe.
     */
    text: (value: string) => void;
    /**
     * Human facing progress, context, and confirmations.
     *
     * Written to stderr and suppressed entirely in the json format.
     */
    info: (message?: string) => void;
    /** Human facing warning. Written to stderr in every format. */
    warn: (message: string) => void;
    /** Human facing error. Written to stderr in every format. */
    error: (message: string) => void;
}
export interface CreateOutputOptions {
    format?: OutputFormat;
    stdout?: OutputStream;
    stderr?: OutputStream;
    /** Colorize pretty printed data. Never applied to the json format. */
    colors?: boolean;
}
/**
 * The one {@link Output} implementation: writes to a pair of streams. The
 * process streams make it the real output; in-memory streams make it the
 * test capture (see `create-memory-output.ts`).
 */
export declare class StreamOutput implements Output {
    readonly format: OutputFormat;
    private readonly stdout;
    private readonly stderr;
    private readonly colors;
    constructor({ format, stdout, stderr, colors, }?: CreateOutputOptions);
    data: (value: unknown) => void;
    text: (value: string) => void;
    info: (message?: string) => void;
    warn: (message: string) => void;
    error: (message: string) => void;
}
export declare const createOutput: (options?: CreateOutputOptions) => Output;