import type { UIMessageChunk } from "ai";

export type BackendSseEvent = {
  event: string;
  data: Record<string, unknown>;
};

export function backendEventToUiChunk(
  item: BackendSseEvent,
  textId: string,
): UIMessageChunk | null {
  if (item.event === "text_delta") {
    return { type: "text-delta", id: textId, delta: String(item.data.text || "") };
  }
  if (item.event === "progress") {
    return {
      type: "data-cad-progress",
      id: `progress_${String(item.data.step || Date.now())}`,
      data: item.data,
    };
  }
  if (["requirements_document", "completion_checklist", "completion_audit", "agent_thinking", "tool_call", "candidate_result", "candidate_review", "geometry_diagnostic", "geometry_conclusion", "step_review", "checkpoint", "rollback", "final_review", "task_terminal"].includes(item.event)) {
    const review = item.data.review && typeof item.data.review === "object"
      ? item.data.review as Record<string, unknown>
      : null;
    const status = item.event === "task_terminal"
      ? (String(item.data.lifecycle || "") === "failed" ? "error" : "success")
      : (item.event === "candidate_review" && String(review?.verdict || "") === "reject")
        || (item.event === "final_review" && String(review?.verdict || "") === "repair" && Number(review?.confidence || 0) >= 0.85)
        ? "error"
      : String(item.data.status || "running");
    return {
      type: "data-cad-progress",
      id: `${item.event}_${String(item.data.taskId || Date.now())}_${String(item.data.nodeId || "")}`,
      data: { step: item.event, label: ({
        requirements_document: "冻结需求", completion_checklist: "完成清单", completion_audit: "完成审计", agent_thinking: "建模判断", tool_call: "建模工具", candidate_result: "候选构建", candidate_review: "候选独立复核", geometry_diagnostic: "几何诊断", geometry_conclusion: "几何结论", step_review: "步骤审查", checkpoint: "构建检查点", rollback: "回滚检查点", final_review: "最终视觉复核", task_terminal: "生成任务",
      } as Record<string, string>)[item.event], status, message: String(
        item.data.message || item.data.reason || (review?.evidence instanceof Array ? review.evidence.join("；") : ""),
      ),
      ...(item.data.taskId ? { taskId: String(item.data.taskId) } : {}),
      ...(item.data.nodeId ? { nodeId: String(item.data.nodeId) } : {}),
      ...(item.data.lifecycle ? { lifecycle: String(item.data.lifecycle) } : {}),
      },
    };
  }
  if (item.event === "cad_result") {
    const taskId = String(item.data.taskId || "");
    const revisionId = String(item.data.revisionId || Date.now());
    return {
      type: "data-cad-result",
      // Each revision is a distinct progressive result. Reusing only the task
      // id makes the AI SDK reconcile intermediate revisions into one part.
      id: `result_${taskId}_${revisionId}`,
      data: item.data,
    };
  }
  if (item.event === "cad_error") {
    return {
      type: "data-cad-error",
      id: `error_${Date.now()}`,
      data: item.data,
    };
  }
  return null;
}