import { Option } from "scats";
import { ScheduledTask } from "./tasks-model.js";
/**
 * Class responsible for polling and processing tasks from a queue.
 * Tasks are processed concurrently, with a limit on the maximum number of concurrently running tasks.
 */
export declare class TasksPipeline {
    private readonly maxConcurrentTasks;
    private readonly pollNextTask;
    private readonly peekNextStartAfter;
    private readonly processTask;
    private readonly loopInterval;
    private tasksInProcess;
    private loopRunning;
    private nextLoopTime;
    private periodicTaskFetcher;
    private stopRequested;
    private tasksCountListener;
    private readonly loopTimer;
    /**
     * Creates an instance of TasksPipeline.
     *
     * @param maxConcurrentTasks Maximum number of tasks to be processed concurrently.
     * @param pollNextTask A function to fetch the next task to process.
     * @param peekNextStartAfter a function to fetch next start_after value to reduce sleep time
     * @param processTask A function that processes a fetched task.
     * @param loopInterval Interval in milliseconds between polling attempts if no tasks are found.
     */
    constructor(maxConcurrentTasks: number, pollNextTask: () => Promise<Option<ScheduledTask>>, peekNextStartAfter: () => Promise<Option<Date>>, processTask: (t: ScheduledTask) => Promise<void>, loopInterval?: number);
    /**
     * Starts the periodic task polling loop.
     */
    start(): void;
    /**
     * Stops the task polling loop and waits for all running tasks to complete.
     */
    stop(): Promise<void>;
    /**
     * Triggers the polling loop immediately if it is not already running.
     */
    triggerLoop(): void;
    /**
     * Internal method that performs a single polling loop.
     * It attempts to fetch and start processing tasks until the maximum number of concurrent tasks is reached.
     */
    private loop;
    /**
     * Fetches the next pending task using the poll function and schedules it for processing.
     *
     * @returns The next operation to perform in the loop.
     */
    private fetchNextTask;
    /**
     * Starts processing a task and handles any errors that might occur.
     * Once processing is finished, triggers the next polling loop.
     *
     * @param t The task to be processed.
     */
    private processTaskInLoop;
    /**
     * Marks a task as completed, decreases the number of active tasks and notifies the listener if needed.
     */
    private taskIsDone;
}