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/**
* Pure state logic of the chat: a reducer folding server messages and
* connection changes into the UI state. Keeping it a plain function makes the
* whole conversation flow testable without React or a WebSocket.
*/
import type {
AcpAvailableCommand,
AcpContentBlock,
AcpPlanEntry,
AcpPermissionOption,
AcpToolCallContent,
AcpToolCallLocation,
ServerMessage,
} from "./protocol";
/** The UI's view of one tool call, folded from tool_call / tool_call_update. */
export interface ToolCall {
toolCallId: string;
title: string;
toolKind: string;
status: string;
contents: AcpToolCallContent[];
locations: AcpToolCallLocation[];
}
/** One entry of the conversation thread. */
export type ThreadItem =
| { kind: "user"; text: string }
| { kind: "agent"; text: string; closed: boolean }
| { kind: "thought"; text: string; closed: boolean }
| { kind: "tool"; call: ToolCall }
| { kind: "error"; text: string };
/** A permission request awaiting the user's decision. */
export interface PermissionRequestState {
requestId: string;
title: string;
options: AcpPermissionOption[];
}
export type ConnectionStatus = "connecting" | "online" | "offline";
/** The whole state the UI renders from. */
export interface ChatState {
connection: ConnectionStatus;
sessionId: string | null;
turnActive: boolean;
thread: ThreadItem[];
plan: AcpPlanEntry[];
permissions: PermissionRequestState[];
/** Slash commands the agent announced (available_commands_update). */
commands: AcpAvailableCommand[];
}
export const initialState: ChatState = {
connection: "connecting",
sessionId: null,
turnActive: false,
thread: [],
plan: [],
permissions: [],
commands: [],
};
/** Everything that can change the state. */
export type ChatEvent =
| { type: "server"; message: ServerMessage }
| { type: "connection"; status: ConnectionStatus };
/**
* reduce returns the next state for an event. It never mutates its input.
*
* @example
* let state = initialState;
* state = reduce(state, { type: "server", message: { type: "hello", sessionId: "s1" } });
* state.sessionId; // "s1"
*/
export function reduce(state: ChatState, event: ChatEvent): ChatState {
if (event.type === "connection") {
return { ...state, connection: event.status };
}
// Unknown or not-yet-handled message types must never break the UI.
const handler = serverHandlers[event.message.type];
return handler ? handler(state, event.message) : state;
}
type MessageHandler = (state: ChatState, msg: ServerMessage) => ChatState;
/** One handler per server message type; unknown types fall through in reduce. */
const serverHandlers: Record<string, MessageHandler> = {
// A hello opens every (re)connection, right before the full history
// replay: resetting everything here makes reconnects idempotent.
hello: (state, msg) => ({
...state,
connection: "online",
sessionId: msg.sessionId ?? null,
turnActive: msg.turnActive ?? false,
thread: [],
plan: [],
permissions: [],
commands: [],
}),
user_message: (state, msg) =>
withItem(state, { kind: "user", text: msg.text ?? "" }),
turn_started: (state) => ({ ...state, turnActive: true }),
turn_ended: (state) => ({
...state,
turnActive: false,
thread: closeStreamItems(state.thread),
}),
session_update: reduceUpdate,
permission_request: addPermission,
permission_resolved: (state, msg) => ({
...state,
permissions: state.permissions.filter((p) => p.requestId !== msg.requestId),
}),
error: (state, msg) =>
withItem(state, { kind: "error", text: msg.message ?? "unknown error" }),
};
/**
* One handler per ACP update kind; the rest (current_mode_update, ...) are
* not rendered yet, and ignoring them keeps the UI forward-compatible.
*/
const updateHandlers: Record<string, MessageHandler> = {
agent_message_chunk: (state, msg) =>
appendStreamText(state, "agent", blockText(msg.update?.content)),
agent_thought_chunk: (state, msg) =>
appendStreamText(state, "thought", blockText(msg.update?.content)),
tool_call: upsertToolCall,
tool_call_update: upsertToolCall,
plan: (state, msg) => ({ ...state, plan: msg.update?.entries ?? [] }),
available_commands_update: (state, msg) => ({
...state,
commands: msg.update?.availableCommands ?? [],
}),
};
function reduceUpdate(state: ChatState, msg: ServerMessage): ChatState {
const handler = msg.update
? updateHandlers[msg.update.sessionUpdate]
: undefined;
return handler ? handler(state, msg) : state;
}
/** blockText extracts the text of a single content block, if any. */
function blockText(
content: AcpContentBlock | AcpToolCallContent[] | undefined,
): string {
if (!content || Array.isArray(content)) {
return "";
}
return content.text ?? "";
}
function withItem(state: ChatState, item: ThreadItem): ChatState {
return { ...state, thread: [...state.thread, item] };
}
/** Streamed chunks accumulate into the last open item of the same kind. */
function appendStreamText(
state: ChatState,
kind: "agent" | "thought",
text: string,
): ChatState {
const thread = [...state.thread];
const last = thread[thread.length - 1];
if (last && last.kind === kind && !last.closed) {
thread[thread.length - 1] = { ...last, text: last.text + text };
return { ...state, thread };
}
thread.push({ kind, text, closed: false });
return { ...state, thread };
}
/**
* upsertToolCall folds a tool_call or tool_call_update into the thread:
* updates merge only the fields they carry, and an update for an unknown id
* creates the entry (the adapter may resume a call after a reconnect).
*/
function upsertToolCall(state: ChatState, msg: ServerMessage): ChatState {
const update = msg.update;
if (!update || !update.toolCallId) {
return state;
}
const contents = Array.isArray(update.content) ? update.content : undefined;
const thread = [...state.thread];
const index = thread.findIndex(
(item) =>
item.kind === "tool" && item.call.toolCallId === update.toolCallId,
);
if (index >= 0) {
const existing = thread[index] as Extract<ThreadItem, { kind: "tool" }>;
thread[index] = {
kind: "tool",
call: {
...existing.call,
title: update.title ?? existing.call.title,
toolKind: update.kind ?? existing.call.toolKind,
status: update.status ?? existing.call.status,
contents: contents ?? existing.call.contents,
locations: update.locations ?? existing.call.locations,
},
};
return { ...state, thread };
}
thread.push({
kind: "tool",
call: {
toolCallId: update.toolCallId,
title: update.title ?? "Tool call",
toolKind: update.kind ?? "other",
status: update.status ?? "pending",
contents: contents ?? [],
locations: update.locations ?? [],
},
});
return { ...state, thread };
}
function addPermission(state: ChatState, msg: ServerMessage): ChatState {
if (
!msg.requestId ||
state.permissions.some((p) => p.requestId === msg.requestId)
) {
return state;
}
return {
...state,
permissions: [
...state.permissions,
{
requestId: msg.requestId,
title: msg.request?.toolCall?.title ?? "The agent asks for permission",
options: msg.request?.options ?? [],
},
],
};
}
/** turn_ended closes every streaming item so the next turn starts fresh. */
function closeStreamItems(thread: ThreadItem[]): ThreadItem[] {
return thread.map((item) =>
item.kind === "agent" || item.kind === "thought"
? { ...item, closed: true }
: item,
);
}
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