/* =============================================================================
 * A00_Common/design/design_follow_server.ts
 * 계산 자리 follow 「서버」(PLAN 511-B B-5) — 끌기 도구 꼴: 조작 중 = 화면 셈(미리보기) · 잠잠 뒤 서버 Node
 * route · follow 두 단계(`stage.follow` · until follow · 저장 정본 맥락은 창구가 프로젝트 id 로 붙임)를 묻고
 * 답이 오면 묶음을 노선부터 다시 돌림 → 같은 노선 초안이면 서버 값(곁 자료 다시 붙임)으로 바꿈.
 * 판이 both 면 null(화면 셈 그대로). 열쇠 = 노선 초안 + 저장 노선 계획고 편집(follow 는 노선에만 기댐).
 * ========================================================================== */

import { readState } from "../b_page_state";
import {
  withFollowSides,
  type FollowSides,
} from "../../B05_Profile/logic/B05_Profile_Pipeline_Grade";
import { calcOnServerNow } from "./design_calc_sites";
import { afterQuiet, serverCalc } from "./design_calc_server";
import type { FollowPatch, PipelineInputs } from "./logic/design_pipeline_types";

const ID = "stage.follow";
let held: { key: string; patch: FollowPatch } | null = null;
let asked: string | null = null;

/** 서버 follow 값 — 같은 열쇠 답이 있으면 그 값 · 없으면 null(화면 셈) + 잠잠 뒤 묻고 `redraw`. */
export function followFromServer(
  projectId: string,
  inputs: Readonly<PipelineInputs>,
  before: unknown,
  savedEdits: unknown,
  redraw: () => void,
): FollowPatch | null {
  if (!calcOnServerNow("follow") || !inputs.route) return null;
  const key = JSON.stringify([inputs.route, savedEdits]);
  if (held?.key === key) return held.patch;
  if (asked === key) return null;
  asked = key;
  const { route, alignment, pipes, structures, plusStations } = inputs;
  const stages = {
    until: "follow",
    input: { route, alignment, pipes, structures, plusStations },
    before_draft: before,
    pipe_ids: readState("pipe-ids", projectId),
    saved_edits: savedEdits,
  };
  const body = JSON.stringify({ run: [ID], inputs: { stages } });
  void afterQuiet(ID, (signal) => serverCalc("follow", [ID], body, signal)).then((results) => {
    if (asked === key) asked = null;
    const got = results?.[ID] as ({ patch: FollowPatch } & FollowSides) | undefined;
    if (!got) return;
    held = { key, patch: withFollowSides(got.patch, got) };
    redraw();
  });
  return null;
}