import type { PositionAnchor } from './types';
/**
 * Anchor state in the fusion engine's hybrid anchor behavior model.
 *
 * - `'none'`: No anchor active; GPS measurements accepted, PDR ignored
 * - `'anchor-only'`: Anchor active and in exclusive period; GPS rejected, PDR accepted
 * - `'transition'`: Anchor active but past exclusive period; GPS accepted with increasing weight
 */
export type AnchorState = 'none' | 'anchor-only' | 'transition';
/**
 * Configuration for anchor state computation.
 */
export interface AnchorStateConfig {
    /** Duration in ms where anchor is exclusive (GPS rejected). Default: 5000 */
    anchorOnlyPeriodMs: number;
}
/**
 * Default anchor state configuration.
 */
export declare const DEFAULT_ANCHOR_STATE_CONFIG: AnchorStateConfig;
/**
 * Compute anchor state from current time and config.
 *
 * Pure function with no side effects or Date.now() calls.
 * All time values are passed explicitly for deterministic testing.
 *
 * @param anchor - Current position anchor, or undefined if none set
 * @param anchorSetTimeMs - Timestamp (ms) when anchor was set, or undefined
 * @param nowMs - Current timestamp in milliseconds
 * @param config - Anchor state configuration
 * @returns The current anchor state
 *
 * @example
 * ```ts
 * // No anchor
 * getAnchorState(undefined, undefined, Date.now(), config); // 'none'
 *
 * // Anchor just set (within anchor-only period)
 * getAnchorState(anchor, 1000, 3000, { anchorOnlyPeriodMs: 5000 }); // 'anchor-only'
 *
 * // Anchor set 6s ago (past anchor-only period, within TTL)
 * getAnchorState(anchor, 1000, 7000, { anchorOnlyPeriodMs: 5000 }); // 'transition'
 *
 * // Anchor expired (past TTL)
 * getAnchorState(anchor, 1000, 40000, { anchorOnlyPeriodMs: 5000 }); // 'none'
 * ```
 */
export declare function getAnchorState(anchor: PositionAnchor | undefined, anchorSetTimeMs: number | undefined, nowMs: number, config: AnchorStateConfig): AnchorState;
/**
 * Calculate the decay factor for anchor confidence during transition.
 *
 * Uses exponential decay so anchor confidence smoothly decreases,
 * allowing GPS to gradually take over.
 *
 * @param anchorSetTimeMs - When anchor was set
 * @param nowMs - Current time
 * @param config - Anchor state config (for transition start time)
 * @param halfLifeMs - Half-life of anchor confidence decay in ms
 * @returns Decay factor from 0 to 1 (1 = full confidence, 0 = no confidence)
 *
 * @example
 * ```ts
 * // At start of transition (elapsed = anchorOnlyPeriodMs)
 * getAnchorConfidenceDecay(0, 5000, config, 10000); // ~1.0
 *
 * // One half-life into transition
 * getAnchorConfidenceDecay(0, 15000, config, 10000); // ~0.5
 * ```
 */
export declare function getAnchorConfidenceDecay(anchorSetTimeMs: number, nowMs: number, config: AnchorStateConfig, halfLifeMs: number): number;