import type { BaseEvent } from "../types.js";

const TRACE_EVENTS = new Set([
  "agent.spawn.proposed", "agent.spawned", "agent.completed", "agent.failed", "agent.cancelled",
  "handoff.sent", "handoff.received", "blackboard.event", "workflow.started", "workflow.node.started",
  "workflow.node.completed", "workflow.completed", "verification.completed", "result.completed",
]);

function text(event: BaseEvent, key: string): string | undefined {
  return typeof event[key] === "string" ? event[key] as string : undefined;
}

function number(event: BaseEvent, key: string): number | undefined {
  return typeof event[key] === "number" ? event[key] as number : undefined;
}

export function isTraceEvent(event: BaseEvent): boolean { return TRACE_EVENTS.has(event.eventType); }

export function traceLine(event: BaseEvent): string | undefined {
  if (!isTraceEvent(event)) return undefined;
  const at = event.timestamp.slice(11, 19);
  const node = text(event, "nodeId") ?? text(event, "fromNodeId") ?? "root";
  const peer = text(event, "toNodeId");
  const size = number(event, "payloadChars") ?? number(event, "taskChars");
  if (event.eventType === "handoff.sent" || event.eventType === "handoff.received") return `${at} ${event.eventType.replace("handoff.", "handoff ")} ${node}${peer ? ` → ${peer}` : ""}${size === undefined ? "" : ` (${size} chars)`}`;
  if (event.eventType === "result.completed") return `${at} result ${text(event, "terminalState") ?? "unknown"}`;
  if (event.eventType === "agent.failed") return `${at} failed ${node}: ${text(event, "errorClass") ?? "unknown"}`;
  return `${at} ${event.eventType.replaceAll(".", " ")} ${node}`;
}

export function formatTrace(events: readonly BaseEvent[]): string {
  const lines = events.map(traceLine).filter((line): line is string => line !== undefined);
  return lines.length ? lines.join("\n") : "No UltraPi trace events for this run.";
}