/**
 * Overlap aggregation for {@link AreaMembership} lists: when several area sources cover the same
 * receiver, a policy decides which memberships actually apply. Genre-agnostic and pure — policies
 * are `(memberships) => memberships` reducers over one receiver's memberships, so the caller stays
 * in control of magnitude and meaning. Pair with `createAreaEffectField().membershipsOf(receiverId)`.
 */
import type { AreaMembership } from "./areaEffectField.js";
/** Reduce one receiver's overlapping memberships to the subset that applies under a stacking rule. */
export type AreaStackPolicy<P> = (memberships: readonly AreaMembership<P>[]) => AreaMembership<P>[];
/** Read a comparable magnitude from a membership (e.g. buff strength, damage per tick). */
export type MagnitudeOf<P> = (membership: AreaMembership<P>) => number;
/**
 * Every overlapping membership applies independently (no deduplication) — the default for hazards,
 * fields, and lights where two sources genuinely stack.
 *
 * @capability area-stack-independent apply every overlapping area membership independently
 */
export declare function independentStacks<P>(): AreaStackPolicy<P>;
/**
 * Keep at most one membership per `stackKey`. With `magnitudeOf` the strongest per key wins (ties
 * broken by `sourceId` for determinism); without it the first-seen per key wins. Use for
 * unique-by-key buffs where reapplying the same aura should not stack.
 *
 * @capability area-stack-unique keep one area membership per stack key, strongest wins
 */
export declare function uniqueByStackKey<P>(magnitudeOf?: MagnitudeOf<P>): AreaStackPolicy<P>;
/**
 * Keep at most `limit` memberships per `stackKey` (the highest-magnitude ones when `magnitudeOf` is
 * given, else the first-seen). Models capped stacks — e.g. a poison that stacks up to 5 times.
 *
 * @capability area-stack-capped cap area memberships per stack key at a maximum count
 */
export declare function cappedStacks<P>(limit: number, magnitudeOf?: MagnitudeOf<P>): AreaStackPolicy<P>;
/**
 * Reduce to the single strongest membership overall (`weakest = false` picks the weakest); ties broken
 * by `sourceId`. Use when only the best or worst overlapping source should apply.
 *
 * @capability area-stack-extremum keep only the strongest or weakest overlapping area membership
 */
export declare function extremumStack<P>(magnitudeOf: MagnitudeOf<P>, weakest?: boolean): AreaStackPolicy<P>;
/**
 * Sum a numeric magnitude across memberships — additive aggregation for a total field strength
 * (total damage per tick, total slow). A terminal reducer, not a filter, so it returns the number.
 *
 * @capability area-stack-additive sum a magnitude across overlapping area memberships
 */
export declare function sumMagnitude<P>(memberships: readonly AreaMembership<P>[], magnitudeOf: MagnitudeOf<P>): number;