/**
 * The _PropertyValues_ mechanism provides a means for passing configuration type values between different components running in the server process such as plugins and input connections.
 *
 * A plugin can both *emit* values and *listen* for values emitted by others.
 *
 * The difference between the _PropertyValues_ mechanism and _Event Emitters_ in NodeJs is that when  `onPropertyValues` is called, the `callback()` function will be invoked and passed an array containing all of the previous values for that _property name_, starting with the initial value of `undefined`. If no values have been emitted for that _property name_ the callback will be invoked with a value of `undefined`.
 * *
 * **PropertyValue** has the following structure:
 * ```typescript
 * interface PropertyValue {
 *   timestamp: number // millis
 *   setter: string // plugin id, server, provider id
 *   name: string
 *   value: any
 * }
 * ```
 *
 * _Note that the value can be also a function._
 *
 * This mechanism allows plugins to _offer_ extensions via _"Well Known Properties"_, for example
 * - additional [NMEA0183 sentence parsers for custom sentences](https://github.com/SignalK/nmea0183-signalk/pull/193) via `nmea0183sentenceParser`
 * - additional PGN definitions for propietary or custom PGNs
 *
 * Code handling incoming _PropertyValues_ should be fully reactive due to:
 * - Plugins being able to emit _PropertyValues_ when they activated and / or started
 * - There being no defined load / startup order for plugins / connections.
 *
 * So even if all plugins / connections emit during their startup, you cannot depend on a specific _PropertyValue_ being available. It may be present when your code starts or it may arrive after your code has started.
 *
 *
 * **Note: The _PropertyValues_ mechanism is not intended to be used for data passing on a regular basis, as the total history makes it a potential memory leak.**
 *
 * To safeguard against a component accidentally emitting regularly, via a fixed upper bound is enforced for the value array per _property name_. New values will be ignored if the upper bound is reached and are logged as errors.
 * @category Server API
 */
export interface PropertyValuesEmitter {
    /**
     * Emit a property value that can be received by listeners.
     * @param name - The property name identifier
     * @param value - The value to emit (can be any type including functions)
     * @category Property Values
     */
    emitPropertyValue(name: string, value: unknown): void;
    /**
     * @category Property Values
     */
    onPropertyValues(name: string, cb: PropertyValuesCallback): Unsubscribe;
}
/** @category Server API */
export interface PropertyValue {
    /** Timestamp in milliseconds */
    timestamp: number;
    /** Source identifier (plugin id, server, provider id) */
    setter: string;
    /** Property name */
    name: string;
    /** The property value (can be any type including functions) */
    value: unknown;
}
/**
 * Callback function for property value subscriptions.
 * The history array starts with `undefined` as the initial value.
 * @category Server API
 */
export type PropertyValuesCallback = (propValuesHistory: (PropertyValue | undefined)[]) => void;
/** @category Server API */
export declare class PropertyValues {
    private streams;
    private count;
    static readonly MAX_VALUES_COUNT = 1000;
    onPropertyValues(propName: string, cb: PropertyValuesCallback): () => void;
    emitPropertyValue(pv: PropertyValue): void;
    private getStreamTuple;
}
/**
 * @inline
 * @category Server API
 */
type Unsubscribe = () => void;
export {};
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