steelbreeze/state

import { Consumer, Supplier } from '@steelbreeze/types';

/**
 * Logging integration for state; provides callbacks for logging events thereby allowing integration of third party logging tools.
 */
export namespace log {
    /** The registered logging consumers. */
    const consumers: Array<{ consumer: Consumer<string>, category: number }> = [];

    /** Logging category used when new state machine elements are created. */
    export const Create = 1;

    /** Logging category used when states are entered during state machine instance initialisation or state transitions. */
    export const Entry = 2;

    /** Logging category used when states are exited during state machine instance initialisation or state transitions. */
    export const Exit = 4;

    /** Logging category used when trigger events are evaluated during state transitions. */
    export const Evaluate = 8;

    /** Logging category used when state transitions are traversed. */
    export const Transition = 16;

    /** Logging category used for user generated log events. */
    export const User = 128;

    /**
     * Adds a new log event consumer that will be called when log events of a particular category or categories are raised.
     * @param consumer The callback that will be invoked with the log message.
     * @param categories The categorory or categories for which the consumer callback will be invoked.
     * @returns Returns an id for the consumer so that it can be removed if desired.
     */
    export function add(consumer: Consumer<string>, ...categories: number[]): number {
        return consumers.push({ consumer, category: categories.reduce((p, c) => p | c) });
    }

    /**
     * Removes a log event consumer.
     * @param index The id of the consumer previously returned by the add function.
     */
    export function remove(index: number): void {
        delete consumers[index];
    }

    /**
     * Raises a log event
     * @param producer A callback used to generate the log message.
     * @param category The category of message.
     * @remarks The producer callback will only be called if there is a registered consumer for the category of message.
     */
    export function write(producer: Supplier<string>, category: number): void {
        let message: string | undefined;

        consumers.forEach(consumer => {
            if (consumer && category & consumer.category) {
                consumer.consumer(message || (message = producer()));
            }
        });
    }
}