import { Direction } from '../core/ReelAxis.js';
/** A cell coordinate on the reel set. `reel` is column, `cell` is visible cell. */
export interface Cell {
    reel: number;
    cell: number;
}
export interface DropOffset {
    /** Visible cell in the new grid (start-to-end, 0-indexed). */
    cell: number;
    /**
     * Where this symbol "came from" expressed as a virtual cell index.
     * Off-grid values name the cell the symbol enters from: under
     * `gravity: 'forward'` new symbols come from negative indices (before
     * cell 0); under `'reverse'` they come from `visibleCells` and up. An
     * index inside `[0, visibleCells)` is a survivor's OLD cell.
     *
     * Read {@link DropOffset.isNew} rather than testing the sign - the sign
     * only discriminates under forward gravity.
     */
    originalCell: number;
    /**
     * Signed cell distance this symbol travels: `cell - originalCell`.
     * Positive moves toward the end edge (forward gravity), negative toward
     * the start edge (reverse gravity). Zero means the symbol stays put and
     * must NOT be animated.
     */
    offsetCells: number;
    /**
     * True when this is a fresh symbol entering from off-grid, false for a
     * survivor that was already on the reel. The discriminator every caller
     * should branch on; `originalCell < 0` is only equivalent under forward
     * gravity.
     */
    isNew: boolean;
}
/**
 * Compute per-cell drop offsets for one reel given its winner set.
 *
 * Returns one entry per visible cell, top-to-bottom. Cells with
 * `offsetCells === 0` should NOT be animated. they're survivors that
 * didn't move.
 *
 * **Convention** (Moment B): the new grid must place new symbols at the
 * top `winnerCells.length` cells and survivors at the bottom cells in their
 * original top-to-bottom order. This matches how server-side gravity
 * simulations emit cascade results.
 *
 * @param options.initial - When `true` (Moment A. the player's first
 *   spin click), every cell is treated as new regardless of `winnerCells`
 *   (which is normally empty for initial spins). When `false` (Moment B
 *  . cascade refill), an empty `winnerCells` means *no movement on this
 *   reel*; survivor reels in a refill correctly return all-zero offsets.
 *   Default `false` so callers can't accidentally trigger a full re-drop
 *   on a reel that had no winners.
 */
export declare function computeDropOffsets(visibleCells: number, winnerCells: readonly number[], options?: {
    initial?: boolean;
    gravity?: Direction;
}): DropOffset[];
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