import { RandomSymbolProvider } from './RandomSymbolProvider.js';
import { ColumnTarget } from './ColumnTarget.js';
/** Context passed through the middleware pipeline. */
export interface FrameContext {
    /** Reel column index. */
    readonly reelIndex: number;
    /** Total visible cells. */
    readonly visibleCells: number;
    /** Buffer symbols above visible area. */
    readonly bufferStart: number;
    /** Buffer symbols below visible area. */
    readonly bufferEnd: number;
    /** The symbol array being built (buffer + visible + buffer). Mutable by middleware. */
    symbols: string[];
    /**
     * This reel's target column from `setResult()` / `initialFrame()`, if
     * available. Read it with `getTargetSlot(target, cell)` (cell `0` is the
     * first visible cell; negative cells are buffer-above).
     */
    readonly target?: ColumnTarget;
    /** Whether the reel is currently spinning. */
    readonly isSpinning: boolean;
    /** Arbitrary metadata middleware can use to communicate. */
    metadata: Record<string, unknown>;
}
/** Middleware that participates in frame building. */
export interface FrameMiddleware {
    readonly name: string;
    /** Lower priority runs first. */
    readonly priority: number;
    process(context: FrameContext, next: () => void): void;
}
/**
 * Builds symbol frames using a middleware pipeline.
 *
 * Built-in middleware handles random fill and target placement.
 * Users can inject custom middleware for features like multiplier encoding
 * or triple-prevention.
 */
export declare class FrameBuilder {
    private _randomProvider;
    private _middlewares;
    private _sorted;
    constructor(_randomProvider: RandomSymbolProvider);
    /** Add a middleware to the pipeline. */
    use(middleware: FrameMiddleware): this;
    /** Remove a middleware by name. */
    remove(name: string): this;
    /** Build a frame for a single reel. */
    build(reelIndex: number, visibleCells: number, bufferStart: number, bufferEnd: number, target?: ColumnTarget, isSpinning?: boolean): string[];
    /** Build frames for all reels. */
    buildAll(reelCount: number, visibleCells: number, bufferStart: number, bufferEnd: number, targets?: ColumnTarget[], isSpinning?: boolean): string[][];
    get middleware(): ReadonlyArray<FrameMiddleware>;
}
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