import type { ContextAccessor } from "#context/key.js";
import type { StepInput } from "#harness/types.js";
import type { HandleMessageStreamEvent } from "#protocol/message.js";
import type { SessionHandle } from "#channel/session.js";
import type { DeliverPayload } from "#channel/types.js";
import type { FetchFileResult, FetchFileFunction } from "#shared/channel-definition.js";
/**
 * Context available to every adapter handler (`deliver` and event handlers).
 *
 * `state` is a mutable reference to the adapter's durable state. The runtime
 * auto-snapshots it at step boundaries — no manual `serialize()` needed.
 *
 * `ctx` provides read/write access to durable context keys (the same
 * {@link ContextAccessor} that tools and providers use).
 *
 * `session` is a live handle to the current session — id, auth,
 * continuation token, plus an imperative {@link SessionHandle.setContinuationToken}
 * for channels that need to re-key the session mid-turn (e.g. Slack's
 * auto-anchor on first post).
 */
export interface ChannelAdapterContext<TState = Record<string, unknown>> {
    /**
     * Mutable adapter state. Auto-serialized at step boundaries via
     * JSON snapshot. The adapter reads and writes this directly.
     */
    state: TState;
    /**
     * Read/write access to durable context keys. Seed keys here for tools
     * to read during the turn.
     */
    readonly ctx: ContextAccessor;
    /**
     * Live handle to the current session.
     */
    readonly session: SessionHandle;
}
/**
 * Extracts the state type from a {@link ChannelAdapterContext} generic.
 * Used internally so adapter-level types can declare their state shape
 * once (via `TCtx`) and have helpers narrow consistently.
 */
type StateOf<TCtx> = TCtx extends ChannelAdapterContext<infer S> ? S : Record<string, unknown>;
/**
 * Extracts the `data` field type from a stream event by its `type` discriminant.
 * Events that carry no `data` field (e.g. `session.completed`) resolve to `undefined`.
 */
type EventData<T extends HandleMessageStreamEvent["type"]> = Extract<HandleMessageStreamEvent, {
    type: T;
}> extends {
    data: infer D;
} ? D : undefined;
/**
 * A single outbound event handler. Receives the event's `data` (not the full
 * envelope) and the adapter context. Void return — side effects only.
 */
type EventHandler<T extends HandleMessageStreamEvent["type"], TCtx extends ChannelAdapterContext<any> = ChannelAdapterContext> = (data: EventData<T>, ctx: TCtx) => void | Promise<void>;
/**
 * Map of outbound event handlers keyed by event type. The adapter declares
 * handlers for the event types it cares about. For undeclared types, the
 * framework's default handlers run.
 */
export type ChannelEventHandlers<TCtx extends ChannelAdapterContext<any> = ChannelAdapterContext> = {
    [K in HandleMessageStreamEvent["type"]]?: EventHandler<K, TCtx>;
};
/**
 * Enriched return shape from a channel's {@link ChannelAdapter.fetchFile}
 * function. Return a bare {@link Buffer} when only bytes are known, or
 * this record when the fetch discovers a more accurate `mediaType` or
 * `filename` (e.g. from an HTTP `Content-Type` header).
 *
 * When fields are provided, staging prefers them over the values the
 * channel populated at ingestion time.
 */
export type { FetchFileResult };
export type ChannelInstrumentationMetadata = Readonly<Record<string, unknown>>;
export type ChannelInstrumentationMetadataProjector = (state: Record<string, unknown> | undefined) => ChannelInstrumentationMetadata;
/**
 * Plain-object channel adapter with durable state, an optional inbound
 * delivery hook, event handlers, and optional attachment resolution.
 */
export type ChannelAdapter<TCtx extends ChannelAdapterContext<any> = ChannelAdapterContext> = {
    /**
     * Stable durable identifier for serialization across step boundaries.
     * Must be unique across all adapters visible to one runtime bundle.
     *
     * Defaults to {@link HTTP_ADAPTER_KIND} (`"http"`) for the canonical
     * session channel and every behaviorless authored channel, or is derived
     * from the route file path as `channel:<name>` once
     * `runtime/resolve-channel.ts` rewrites authored adapters that carry
     * behavior.
     */
    readonly kind: string;
    /**
     * Initial state shape. Auto-serialized at step boundaries via JSON
     * snapshot. On rehydration, the runtime restores the serialized state
     * and re-attaches the adapter's behavior functions from the registry.
     */
    readonly state?: Record<string, unknown>;
    /**
     * Inbound hook: fires once per delivery before the harness starts.
     *
     * Return a {@link StepInput} to override the input the harness sees, or
     * return void to use the default payload projection.
     */
    deliver?(payload: DeliverPayload, ctx: TCtx): StepInput | void | Promise<StepInput | void>;
    /**
     * Optional factory that builds the adapter context for this adapter.
     *
     * @internal
     */
    createAdapterContext?(base: ChannelAdapterContext<StateOf<TCtx>>): TCtx;
    /**
     * Fetches bytes for a URL encountered in `FilePart.data`.
     *
     * Called by the staging pipeline when it encounters a `URL` object
     * on a `FilePart`. Return `null` to let the URL pass through to the
     * model provider (e.g. public images). Return bytes or
     * {@link FetchFileResult} to stage the file to the sandbox.
     *
     * Credentials should be captured in the closure at channel
     * construction time.
     */
    readonly fetchFile?: FetchFileFunction;
    /**
     * Framework-owned observability projection for the active channel.
     *
     * Channel implementations decide which state fields are safe and
     * meaningful to expose to instrumentation callbacks. The harness reads
     * the resulting projection through a seed context key rather than
     * inspecting adapter state directly.
     */
    readonly instrumentation?: {
        readonly metadata?: ChannelInstrumentationMetadataProjector;
    };
} & ChannelEventHandlers<TCtx>;
/**
 * Produces the default {@link StepInput} when no custom adapter `deliver`
 * hook is defined.
 *
 * Passes through both `message` and `inputResponses` from the delivery
 * payload so tool-approval responses (and other HITL replies) reach the
 * harness even when the channel has no bespoke deliver logic.
 */
export declare function defaultDeliverResult(payload: DeliverPayload): StepInput | undefined;
/**
 * Returns the durable kind for an adapter.
 */
export declare function getAdapterKind(adapter: ChannelAdapter): string;
/**
 * Calls an adapter's event handler for a given event. Adapters perform side
 * effects rather than transforming events; after the handler runs, the
 * runtime refreshes `session.waiting` with the live continuation token so a
 * handler that re-keyed the session publishes the new resume handle.
 *
 * Throwing handlers are logged and swallowed so a downstream delivery
 * failure does not corrupt the event stream write path.
 */
export declare function callAdapterEventHandler(adapter: ChannelAdapter, event: HandleMessageStreamEvent, ctx: ChannelAdapterContext): Promise<HandleMessageStreamEvent>;