/**
 * pi ExtensionAPI event subscriptions.
 *
 * Bridges pi's lifecycle events into the sidecar's state model.
 * Emits structured state updates that the WebSocket broadcaster (T-1.5)
 * can forward as IC-1 `{ type: "state"; value: ... }` frames.
 *
 * Subscribes to:
 *   - agent_start / agent_end  → "thinking" / "idle"
 *   - tool_start / tool_end    → "tool" (with tool name)
 *   - awaiting_input           → "awaiting-input"
 *
 * Owner: T-1.4
 */

import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";

/** IC-1 state values */
export type AgentState = "thinking" | "tool" | "idle" | "awaiting-input";

export interface StateEvent {
  value: AgentState;
  tool?: string;
  ts: number;
}

export type StateCallback = (event: StateEvent) => void;

/**
 * Subscribe to pi agent lifecycle events.
 *
 * Note: `pi.on()` returns void and has no unsubscribe mechanism — event
 * handlers are scoped to the extension lifetime, not to individual calls.
 * The returned function is a no-op kept for API compatibility.
 */
export function subscribeAgentEvents(
  pi: ExtensionAPI,
  onState: StateCallback,
): () => void {
  // agent_start → thinking
  pi.on("agent_start", () => {
    onState({ value: "thinking", ts: Date.now() });
  });

  // agent_end → idle
  pi.on("agent_end", () => {
    onState({ value: "idle", ts: Date.now() });
  });

  // tool_execution_start → tool (carries toolName directly on the event)
  pi.on("tool_execution_start", (event) => {
    onState({ value: "tool", tool: event.toolName, ts: Date.now() });
  });

  // tool_execution_end → thinking (agent loop continues after tool completes)
  pi.on("tool_execution_end", () => {
    onState({ value: "thinking", ts: Date.now() });
  });

  // input → awaiting-input (fired when pi pauses to wait for user input)
  pi.on("input", () => {
    onState({ value: "awaiting-input", ts: Date.now() });
  });

  return () => {
    // No-op: pi event subscriptions cannot be cancelled.
  };
}