/**
 * Session-scoped outbound message queue for reliable widget delivery.
 */
import type { ChatMessage } from "../../../utils/globals";
/** Requeue `sending` rows stuck longer than this (crash / abort mid-flight). */
export declare const STALE_SENDING_MS = 30000;
/** Reuse a recently created channel for `newChannel` drain instead of POSTing again. */
export declare const LAST_CREATED_CHANNEL_TTL_MS: number;
export type OutboxEntryState = "pending" | "sending" | "failed";
export interface OutboxEntry {
    messageId: string;
    channelId: string;
    distinctId: string;
    body: string;
    content_type: ChatMessage["content_type"];
    metadata: Record<string, unknown>;
    created_at: string;
    state: OutboxEntryState;
    attempts: number;
    /** Epoch ms — do not drain before this instant (exponential backoff). */
    nextRetryAt: number;
    /** Epoch ms — when the row entered `sending` (stale recovery). */
    sendingSince?: number;
    /** When set, drain creates a channel before POSTing the message. */
    newChannel?: {
        skipGreeting: boolean;
    };
}
export interface LastCreatedChannelHint {
    channelId: string;
    at: number;
}
export declare function outboxStorageKey(projectToken: string, distinctId: string): string;
export declare function lastCreatedChannelStorageKey(storageKey: string): string;
export declare function readLastCreatedChannelHint(storageKey: string, now?: number): LastCreatedChannelHint | null;
export declare function writeLastCreatedChannelHint(storageKey: string, channelId: string): void;
export declare class MessageOutbox {
    private readonly _storageKey;
    /** Fallback when sessionStorage is unavailable or writes fail. */
    private _memory;
    constructor(_storageKey: string);
    list(): OutboxEntry[];
    get(messageId: string): OutboxEntry | undefined;
    upsert(entry: OutboxEntry): void;
    patch(messageId: string, partial: Partial<OutboxEntry>): void;
    remove(messageId: string): void;
    /** Entries eligible for drain (not in backoff, not actively sending). */
    dueEntries(now?: number): OutboxEntry[];
    /**
     * Recover rows left in `sending` after a crash, tab kill, or aborted fetch.
     */
    requeueStaleSending(maxAgeMs?: number, now?: number): void;
    private _readStorage;
    private _write;
}
/** Backoff: 1s, 2s, 4s, … capped at 60s. */
export declare function nextOutboxRetryAt(attempts: number, now?: number): number;