/**
 * Migration engine — file discovery and migration orchestration.
 *
 * The engine walks a directory tree, filters files by extension, and runs
 * migration units in detect-only or detect+apply mode. All file I/O uses
 * Node built-in modules (no external dependencies).
 *
 * Security:
 * - Writes files only when `apply: true` is explicitly set
 * - Skips unreadable files and directories silently
 * - Normalises all output paths to forward slashes
 *
 * @module migrate/engine
 */
import type { MigrationResult, MigrationUnit } from './types.js';
/** Directories that are always skipped during file discovery. */
export declare const DEFAULT_SKIP_DIRS: Set<string>;
/**
 * Discover all files under `basePath` whose extension is in `extensions`.
 *
 * @param basePath   - Root directory to scan
 * @param extensions - Set of extensions to include (e.g. `new Set(['.ts', '.html'])`)
 * @param skipDirs   - Directory names to skip (defaults to {@link DEFAULT_SKIP_DIRS})
 * @returns Sorted array of absolute file paths
 */
export declare function discoverFiles(basePath: string, extensions: Set<string>, skipDirs?: Set<string>): Promise<string[]>;
/** Options for {@link runMigrations}. */
export interface RunOptions {
    /** Root directory to scan for files */
    basePath: string;
    /** Migration units to execute */
    units: MigrationUnit[];
    /** When true, apply transformations and write files. Default: false (detect only). */
    apply?: boolean;
    /** Additional directory names to skip during file discovery */
    skipDirs?: string[];
}
/**
 * Run one or more migration units against a directory tree.
 *
 * In detect-only mode (default), files are scanned but never modified.
 * In apply mode (`apply: true`), each unit's `apply()` function is called
 * and the result is written back to disk.
 *
 * @param options - Configuration for the migration run
 * @returns One {@link MigrationResult} per unit, in the same order as `options.units`
 */
export declare function runMigrations(options: RunOptions): Promise<MigrationResult[]>;