import { Writable } from 'stream';
/** A $LESSOPEN replacement: its lines, byte size and alt file name. */
interface AltFile {
    lines: string[];
    size: number;
    /** `-` for pipe preprocessors, the temp file name otherwise. */
    alt: string;
    /** The preprocessor's output as it arrived, for the byte copy a
     *  non-terminal session makes (less's cat_file reads the altpipe
     *  through ch_forw_get, doing no line processing at all). */
    raw: string;
    /** The pipe preprocessor's failure message, reported when the
     *  file is LEFT (less's close_altfile, edit.c:288), not at open. */
    preprocError?: string;
}
/** What a cat session gets back: the alt name for $LESSCLOSE, plus a
 *  file to copy when the replacement is one. Nothing to copy means
 *  the bytes already went out (or the "||" form found it empty). */
interface AltStream {
    alt: string;
    path?: string;
    empty?: boolean;
    preprocError?: string;
}
export declare function openAltFile(filename: string, input?: string): AltFile | null;
/**
 * The $LESSOPEN pipe forms for a session that CATS its input.
 *
 * less keeps the popen stream open and reads through it as it copies
 * (open_altfile's returnfd branch hands edit_ifile the live FILE),
 * so the preprocessor is still running while its output is written -
 * which is why its own stderr lands interleaved rather than all in
 * front. Collecting the output first, as the display path must, gets
 * the bytes right and the order wrong, so this streams instead.
 *
 * The one-byte peek is less's: an empty pipe means no replacement, and
 * only then does the exit status decide between an EMPTY file (the
 * "||" form) and no alt file at all.
 *
 * @param filename - The file being opened.
 * @param out - Where the preprocessor's bytes go, verbatim.
 * @returns The replacement, or null to open the file itself.
 */
export declare function streamAltFile(filename: string, out: Writable): Promise<AltStream | null>;
/**
 * Runs $LESSCLOSE when a preprocessed file is left, like filename.c's
 * close_altfile: the first %s is the original name, the second the
 * replacement.
 *
 * @param altName - The replacement name (`-` for pipes).
 * @param filename - The original file name.
 */
export declare function closeAltFile(altName: string, filename: string, preprocError?: string): void;
export {};