/* =============================================================================
 * M02_DF_Diagram.ts
 * 단가산출 다이어그램 — 자유 배치(정함 점검 8 · 9 · 12 · 「상자 · 선 약속」)
 * 상자(입력 · 함수 · 출력)를 끌어 아무 자리에 놓음(on.move) · 판 끌기 · 확대 / 축소 · 「한눈에」 · 「줄 맞추기」 ·
 * 상자 = 종류 · 이름 · 오른쪽 위 단위 · 색 · 왼쪽 받는 알약 · 오른쪽 내보내는 알약(알약에 지금 값) ·
 * 선 = 굽은 선 · 내보내는 알약을 끌어 받는 알약에 놓으면 on.link(막히면 까닭 한 줄) · 고른 상자와 이어진 선만 진하게.
 * SheetLogic 다이어그램(M01_SL_Diagram)을 옮겨 고쳐 씀 — 그 파일에 기대지 않음. 그리기만(바꾸는 것은 부른 쪽이 Model 로).
 * ========================================================================== */

import { currentLanguageIndex } from "@ui/ui_template_locale";
import { createButton, el, showConfirmDialog } from "@ui/ui_template_elements";
import {
  portsIn,
  portsOut,
  type CfBox,
  type CfKind,
  type CfLogic,
  type CfPill,
  type CfPort,
} from "./M02_DF_Model";
import "./M02_DF_Diagram.css";

const TEXT = {
  Title: ["다이어그램", "Diagram"],
  K_input: ["입력", "Input"],
  K_function: ["함수", "Function"],
  K_output: ["출력", "Output"],
  AddInput: ["+ 입력", "+ Input"],
  AddFunc: ["+ 함수", "+ Function"],
  AddOutput: ["+ 출력", "+ Output"],
  ZoomIn: ["확대", "Zoom in"],
  ZoomOut: ["축소", "Zoom out"],
  Fit: ["한눈에", "Fit all"],
  Arrange: ["줄 맞추기", "Line up"],
  Cancel: ["취소", "Cancel"],
  Connect: ["잇기", "Connect"],
  Disconnect: ["끊기", "Disconnect"],
  Remove: ["상자 지우기", "Remove box"],
  AskRemove: [
    "「{v}」 상자를 지울까요? 이어진 선도 함께 끊어짐",
    "Remove box “{v}”? Its lines go too",
  ],
  PickTarget: ["「{v}」 을 받을 알약을 누르세요", "Tap the pill that receives “{v}”"],
  Empty: ["상자가 없음 — 「+ 입력」 으로 시작", "No boxes — start with “+ Input”"],
  NoIn: ["받는 알약이 없는 상자", "This box has no receiving pill"],
  SameBox: ["같은 상자 안에서는 이을 수 없음", "Can't connect inside the same box"],
  NotIn: ["받는 알약에 놓아야 이어짐", "Drop it on a receiving pill"],
  NoMatch: [
    "같은 이름 받는 알약 없음 — 알약에 바로 놓으세요",
    "No pill with that name — drop on a pill",
  ],
  Taken: ["이미 이어진 알약 — 먼저 그 선을 끊으세요", "Pill already linked — disconnect first"],
  From: ["어디서", "From"],
  To: ["어디로", "To"],
  Value: ["지금 값", "Now"],
  PlusIn: [
    "받는 자리 — 내보내는 알약을 여기에 놓으면 받는 알약이 생김",
    "Drop an output pill here to add an input",
  ],
  LineOf: ["선 · {a} → {b}", "Line · {a} → {b}"],
  Hint: [
    "상자 머리를 끌어 옮김 · 빈 곳 끌어 판 옮김 · 휠로 확대",
    "Drag head to move · drag space to pan",
  ],
} as const;

const tt = (key: keyof typeof TEXT, fill: Record<string, string> = {}): string =>
  TEXT[key][currentLanguageIndex as 0 | 1].replace(/\{(\w)\}/g, (_m, k: string) => fill[k] ?? "");

/** 종류별 기본 색(상자마다 바꾼 색이 먼저) */
export const KIND_COLOR: Record<CfKind, string> = {
  input: "#2a6fb0",
  function: "#7a4fb5",
  output: "#c2610c",
};

export interface DiagramOn {
  select(id: string | null): void;
  move(boxId: string, x: number, y: number): void;
  /** 잇기 — 막히면 까닭(쉬운 말) */
  link(from: CfPort, to: CfPort): string | null | void;
  unlink(linkId: string): void;
  add(kind: CfKind, x: number, y: number): void;
  remove(boxId: string): void;
}

export interface DiagramOpts {
  /** 상자 id → 알약 이름 → 지금 값 */
  values?: Record<string, Record<string, unknown>>;
  /** 고른 상자 id · 선 id */
  selected?: string | null;
}

/* ── 알약 · 자리(DOM 없음) ─────────────────────────────────────────── */

/** 알약 — Model 의 받는 · 내보내는 알약 */
export function pillsOf(box: CfBox): { ins: CfPill[]; outs: CfPill[] } {
  return { ins: portsIn(box), outs: portsOut(box) };
}

/** 떨군 자리 → 받을 끝 · 상자에 떨구면 같은 이름 알약(받는 알약이 하나면 그것) · 못 정하면 까닭 */
export function resolveDrop(
  lg: CfLogic,
  from: CfPort,
  target: { box: string; name: string | null; dir: "in" | "out" | null } | null,
): { to: CfPort } | { why: string } {
  if (!target) return { why: tt("NotIn") };
  if (target.box === from.box) return { why: tt("SameBox") };
  if (target.dir === "out") return { why: tt("NotIn") };
  const box = lg.boxes.find((b) => b.id === target.box);
  // 함수 상자 몸통 · 「+」 받는 자리 — 보낸 알약 이름으로 받는 알약을 새로(Model 이 만들고 이름이 겹치면 「이름 (2)」)
  if (box?.kind === "function" && target.name === null)
    return { to: { box: box.id, name: from.name } };
  const ins = box ? pillsOf(box).ins : [];
  if (!box || !ins.length) return { why: tt("NoIn") };
  const name =
    target.name ??
    ins.find((p) => p.name === from.name)?.name ??
    (ins.length === 1 ? ins[0].name : null);
  if (!name) return { why: tt("NoMatch") };
  if (lg.links.some((l) => l.to.box === box.id && l.to.name === name)) return { why: tt("Taken") };
  return { to: { box: box.id, name } };
}

/** 「줄 맞추기」 — 선을 따라 왼→오 차례(가장 긴 길) · 같은 차례는 위→아래 · 돌면 그대로 */
export function arrange(
  lg: CfLogic,
  gap = { x: 260, y: 130 },
): Record<string, { x: number; y: number }> {
  const depth = new Map<string, number>(lg.boxes.map((b) => [b.id, 0]));
  for (let round = 0; round < lg.boxes.length; round++) {
    let moved = false;
    for (const l of lg.links) {
      const d = (depth.get(l.from.box) ?? 0) + 1;
      if (depth.has(l.to.box) && d > (depth.get(l.to.box) ?? 0)) {
        depth.set(l.to.box, d);
        moved = true;
      }
    }
    if (!moved) break;
  }
  const rows = new Map<number, number>();
  const out: Record<string, { x: number; y: number }> = {};
  for (const b of [...lg.boxes].sort((a, c) => a.y - c.y)) {
    const d = depth.get(b.id) ?? 0;
    const r = rows.get(d) ?? 0;
    rows.set(d, r + 1);
    out[b.id] = { x: 40 + d * gap.x, y: 40 + r * gap.y };
  }
  return out;
}

/** 저절로 맞출 때 가장 작은 확대 — 알약 글이 너무 작아지지 않게(더 줄이기는 축소 단추로) */
export const FIT_MIN = 0.9;

/** 모두 보이게 맞춤 — 상자 둘레 → 확대 · 판 자리 · FIT_MIN 아래로 안 내림(넘치면 왼쪽 위부터 보임) */
export function fitView(
  rects: { x: number; y: number; w: number; h: number }[],
  view: { w: number; h: number },
  pad = 40,
): { zoom: number; panX: number; panY: number } {
  if (!rects.length) return { zoom: 1, panX: 0, panY: 0 };
  const x0 = Math.min(...rects.map((r) => r.x)) - pad;
  const y0 = Math.min(...rects.map((r) => r.y)) - pad;
  const x1 = Math.max(...rects.map((r) => r.x + r.w)) + pad;
  const y1 = Math.max(...rects.map((r) => r.y + r.h)) + pad;
  const zoom = clampZoom(Math.max(FIT_MIN, Math.min(view.w / (x1 - x0), view.h / (y1 - y0), 1.5)));
  /** 남으면 가운데 · 넘치면 왼쪽(위) 끝부터 */
  const place = (size: number, from: number, to: number): number =>
    Math.max(0, (size - (to - from) * zoom) / 2) - from * zoom;
  return { zoom, panX: place(view.w, x0, x1), panY: place(view.h, y0, y1) };
}

const clampZoom = (z: number): number => Math.min(2, Math.max(0.25, +z.toFixed(3)));

/* ── 그리기 ─────────────────────────────────────────────────────── */

interface HostState {
  selected: string | null;
  linking: CfPort | null;
  pill: { box: string; name: string; dir: "in" | "out" } | null;
  note: string;
  zoom: number;
  panX: number;
  panY: number;
  fitted: boolean;
  watch?: ResizeObserver;
}

const states = new WeakMap<HTMLElement, HostState>();
const SVG = "http://www.w3.org/2000/svg";

/** 알약 값 글 — 수는 천 단위 쉼표 · 소수 셋째 자리까지(끝 0 지움) · 표는 「· ○줄」 · 글은 그대로 */
export const showValue = (v: unknown): string => {
  if (v === null || v === undefined || v === "") return "";
  if (typeof v === "number")
    return Number.isFinite(v) ? v.toLocaleString("ko-KR", { maximumFractionDigits: 3 }) : "";
  if (Array.isArray(v)) {
    const head = Array.isArray(v[0]) && v[0].every((c) => typeof c === "string") ? 1 : 0;
    return `· ${Math.max(0, v.length - head).toLocaleString("ko-KR")}줄`;
  }
  return String(v).slice(0, 12);
};

export function renderDiagram(
  host: HTMLElement,
  lg: CfLogic,
  on: DiagramOn,
  opts: DiagramOpts = {},
): void {
  const st: HostState = states.get(host) ?? {
    selected: null,
    linking: null,
    pill: null,
    note: "",
    zoom: 1,
    panX: 0,
    panY: 0,
    fitted: false,
  };
  if (opts.selected !== undefined) st.selected = opts.selected;
  states.set(host, st);
  const values = opts.values ?? {};
  const boxName = (id: string): string => lg.boxes.find((b) => b.id === id)?.name ?? "";
  const redraw = (): void => renderDiagram(host, lg, on, { ...opts, selected: st.selected });
  const select = (id: string | null): void => {
    st.selected = id;
    st.pill = null;
    st.note = "";
    on.select(id);
    redraw();
  };
  const tryLink = (from: CfPort, target: Parameters<typeof resolveDrop>[2]): void => {
    const got = resolveDrop(lg, from, target);
    st.linking = null;
    st.note = "why" in got ? got.why : on.link(from, got.to) || "";
    redraw();
  };

  /* 판 · 세상(확대 · 옮김을 한 번에) */
  const world = el("div", { className: "m02-dfdg__world" });
  const svg = document.createElementNS(SVG, "svg");
  svg.classList.add("m02-dfdg__lines");
  world.append(svg);
  const view = el("div", {
    className: "m02-dfdg__view",
    attrs: { "aria-label": tt("Title") },
    children: [world],
  });
  const applyView = (): void => {
    world.style.transform = `translate(${st.panX}px, ${st.panY}px) scale(${st.zoom})`;
    zoomLabel.textContent = `${Math.round(st.zoom * 100)}%`;
  };
  /** 화면 점 → 세상 자리 */
  const toWorld = (cx: number, cy: number): { x: number; y: number } => {
    const r = view.getBoundingClientRect();
    return { x: (cx - r.left - st.panX) / st.zoom, y: (cy - r.top - st.panY) / st.zoom };
  };

  /* 상자 */
  const pillEl = (b: CfBox, p: CfPill, dir: "in" | "out"): HTMLElement => {
    const wired = dir === "out" || lg.links.some((l) => l.to.box === b.id && l.to.name === p.name);
    const chosen = st.pill?.box === b.id && st.pill.name === p.name && st.pill.dir === dir;
    const btn = el("button", {
      className: [
        "m02-dfdg__pill",
        `is-${dir}`,
        wired ? "" : "is-empty",
        chosen ? "is-chosen" : "",
        st.linking && dir === "in" && b.id !== st.linking.box ? "is-target" : "",
      ].join(" "),
      attrs: {
        type: "button",
        "data-box": b.id,
        "data-name": p.name,
        "data-dir": dir,
        title: `${p.name} (${p.unit || "-"})`,
      },
      children: [
        el("span", { className: "m02-dfdg__pill-name", text: wired ? p.name : `? ${p.name}` }),
        el("span", { className: "m02-dfdg__pill-value", text: showValue(values[b.id]?.[p.name]) }),
      ],
    });
    btn.addEventListener("click", (ev) => {
      ev.stopPropagation();
      if (st.linking && dir === "in") return tryLink(st.linking, { box: b.id, name: p.name, dir });
      st.pill = chosen ? null : { box: b.id, name: p.name, dir };
      st.linking = null;
      st.note = "";
      redraw();
    });
    if (dir === "out")
      btn.addEventListener("pointerdown", (ev) => dragLink(ev, { box: b.id, name: p.name }));
    return btn;
  };

  /** 함수 상자 왼쪽 흐린 「+」 — 여기(또는 몸통)에 놓으면 받는 알약이 새로 생김 */
  const plusSlot = (b: CfBox): HTMLElement => {
    const slot = el("button", {
      className: `m02-dfdg__pill is-in is-plus${st.linking && st.linking.box !== b.id ? " is-target" : ""}`,
      text: "+",
      attrs: {
        type: "button",
        "data-box": b.id,
        "data-dir": "in",
        "data-plus": "1",
        title: tt("PlusIn"),
      },
    });
    slot.addEventListener("click", (ev) => {
      ev.stopPropagation();
      if (st.linking) return tryLink(st.linking, { box: b.id, name: null, dir: "in" });
      st.note = tt("PlusIn");
      redraw();
    });
    return slot;
  };

  const boxEl = (b: CfBox): HTMLElement => {
    const { ins, outs } = pillsOf(b);
    const head = el("div", {
      className: "m02-dfdg__head",
      children: [
        el("span", { className: "m02-dfdg__kind", text: tt(`K_${b.kind}` as keyof typeof TEXT) }),
        el("strong", { className: "m02-dfdg__name", text: b.name }),
        el("span", { className: "m02-dfdg__unit", text: b.unit || "-" }),
      ],
    });
    const node = el("div", {
      className: `m02-dfdg__box is-${b.kind}${st.selected === b.id ? " is-selected" : ""}`,
      attrs: {
        "data-box": b.id,
        tabindex: "0",
        role: "button",
        "aria-label": `${tt(`K_${b.kind}` as keyof typeof TEXT)} · ${b.name}`,
      },
      children: [
        head,
        el("div", {
          className: "m02-dfdg__pills",
          children: [
            el("div", {
              className: "m02-dfdg__ins",
              children: [
                ...ins.map((p) => pillEl(b, p, "in")),
                ...(b.kind === "function" ? [plusSlot(b)] : []),
              ],
            }),
            el("div", {
              className: "m02-dfdg__outs",
              children: outs.map((p) => pillEl(b, p, "out")),
            }),
          ],
        }),
      ],
    });
    node.style.left = `${b.x}px`;
    node.style.top = `${b.y}px`;
    node.style.setProperty("--cf-color", b.color || KIND_COLOR[b.kind]);
    node.addEventListener("click", (ev) => {
      ev.stopPropagation();
      if (st.linking) return tryLink(st.linking, { box: b.id, name: null, dir: null });
      select(st.selected === b.id ? null : b.id);
    });
    node.addEventListener("keydown", (ev) => {
      if (ev.target !== node) return;
      if (ev.key === "Enter" || ev.key === " ") {
        ev.preventDefault();
        node.click();
      }
      const step = ev.shiftKey ? 50 : 10;
      const d = {
        ArrowLeft: [-step, 0],
        ArrowRight: [step, 0],
        ArrowUp: [0, -step],
        ArrowDown: [0, step],
      }[ev.key];
      if (d && st.selected === b.id) {
        ev.preventDefault();
        on.move(b.id, Math.round(b.x + d[0]), Math.round(b.y + d[1]));
      }
    });
    head.addEventListener("pointerdown", (ev) => dragBox(ev, b, node));
    return node;
  };

  world.append(...lg.boxes.map(boxEl));

  /* 위 줄 — 이름 · 더하기 · 확대 · 고른 것 */
  const zoomLabel = el("span", { className: "m02-dfdg__zoom" });
  const setZoom = (z: number, cx?: number, cy?: number): void => {
    const r = view.getBoundingClientRect();
    const px = cx ?? r.left + r.width / 2;
    const py = cy ?? r.top + r.height / 2;
    const at = toWorld(px, py);
    st.zoom = clampZoom(z);
    st.panX = px - r.left - at.x * st.zoom;
    st.panY = py - r.top - at.y * st.zoom;
    applyView();
    drawLines();
  };
  const fit = (): void => {
    const rects = lg.boxes.map((b) => {
      const n = world.querySelector<HTMLElement>(`.m02-dfdg__box[data-box="${CSS.escape(b.id)}"]`);
      return { x: b.x, y: b.y, w: n?.offsetWidth ?? 180, h: n?.offsetHeight ?? 80 };
    });
    const r = view.getBoundingClientRect();
    Object.assign(st, fitView(rects, { w: r.width, h: r.height }));
    applyView();
    drawLines();
  };
  const freeSpot = (): { x: number; y: number } => {
    const r = view.getBoundingClientRect();
    const c = toWorld(r.left + r.width / 3, r.top + r.height / 3);
    let y = c.y;
    while (lg.boxes.some((b) => Math.abs(b.x - c.x) < 160 && Math.abs(b.y - y) < 90)) y += 100;
    return { x: Math.round(c.x), y: Math.round(y) };
  };
  /** 작은 단추 */
  const sm = (
    label: keyof typeof TEXT,
    onClick: () => void,
    variant: "ghost" | "filled" | "danger" = "ghost",
  ) => createButton({ label: tt(label), size: "sm", variant, onClick });
  const addBtn = (kind: CfKind, label: keyof typeof TEXT): HTMLButtonElement =>
    sm(label, () => {
      const at = freeSpot();
      on.add(kind, at.x, at.y);
    });
  const endName = (e: CfPort): string => `${boxName(e.box)} · ${e.name}`;

  const selLink = lg.links.find((l) => l.id === st.selected) ?? null;
  const selBox = lg.boxes.find((b) => b.id === st.selected) ?? null;
  const askRemove = async (b: CfBox): Promise<void> => {
    if (await showConfirmDialog(tt("AskRemove", { v: b.name }), tt("Remove"))) on.remove(b.id);
  };
  const tools: HTMLElement[] = [];
  if (st.linking) {
    tools.push(
      el("span", { text: tt("PickTarget", { v: st.linking.name }) }),
      sm("Cancel", () => ((st.linking = null), redraw())),
    );
  } else if (st.pill) {
    const p = st.pill;
    const mine = (e: CfPort): boolean => e.box === p.box && e.name === p.name;
    const where = lg.links
      .filter((l) => mine(p.dir === "in" ? l.to : l.from))
      .map((l) => endName(p.dir === "in" ? l.from : l.to))
      .join(", ");
    const now = `${tt("Value")} ${showValue(values[p.box]?.[p.name]) || "—"}`;
    const dir = where ? `${tt(p.dir === "in" ? "From" : "To")} ${where}` : "";
    tools.push(el("span", { text: [p.name, now, dir].filter(Boolean).join(" · ") }));
    if (p.dir === "out")
      tools.push(
        sm(
          "Connect",
          () => ((st.linking = { box: p.box, name: p.name }), (st.pill = null), redraw()),
          "filled",
        ),
      );
  } else if (selLink) {
    const line = tt("LineOf", { a: endName(selLink.from), b: endName(selLink.to) });
    tools.push(
      el("span", { text: line }),
      sm("Disconnect", () => on.unlink(selLink.id), "danger"),
    );
  } else if (selBox) {
    tools.push(sm("Remove", () => void askRemove(selBox), "danger"));
  }

  const bar = el("div", {
    className: "m02-dfdg__bar",
    children: [
      el("strong", { className: "m02-dfdg__title", text: tt("Title") }),
      addBtn("input", "AddInput"),
      addBtn("function", "AddFunc"),
      addBtn("output", "AddOutput"),
      el("span", { className: "m02-dfdg__gap" }),
      sm("ZoomOut", () => setZoom(st.zoom / 1.2)),
      zoomLabel,
      sm("ZoomIn", () => setZoom(st.zoom * 1.2)),
      sm("Fit", fit),
      sm("Arrange", () => {
        for (const [id, p] of Object.entries(arrange(lg))) on.move(id, p.x, p.y);
      }),
    ],
  });
  const root = el("div", {
    className: `m02-dfdg${st.linking ? " is-linking" : ""}`,
    children: [
      bar,
      el("div", {
        className: "m02-dfdg__tools",
        children: [
          ...tools,
          el("span", { className: "m02-dfdg__note", text: st.note }),
          el("span", { className: "m02-dfdg__hint", text: tools.length ? "" : tt("Hint") }),
        ],
      }),
      lg.boxes.length ? view : el("p", { className: "m02-dfdg__hint", text: tt("Empty") }),
    ],
  });
  root.addEventListener("keydown", (ev) => {
    if (ev.key === "Escape" && (st.linking || st.pill)) {
      st.linking = null;
      st.pill = null;
      redraw();
    }
    if (ev.key !== "Delete" || (ev.target as HTMLElement).closest("input, textarea")) return;
    if (selLink) on.unlink(selLink.id);
    else if (selBox) void askRemove(selBox);
  });
  view.addEventListener("click", (ev) => {
    if (ev.target === view || ev.target === world) select(null);
  });
  view.addEventListener(
    "wheel",
    (ev) => {
      ev.preventDefault();
      setZoom(st.zoom * (ev.deltaY < 0 ? 1.1 : 1 / 1.1), ev.clientX, ev.clientY);
    },
    { passive: false },
  );
  view.addEventListener("pointerdown", (ev) => {
    if (ev.target !== view && ev.target !== world && ev.target !== svg) return;
    dragPan(ev);
  });
  host.replaceChildren(root);
  applyView();

  /* 선 — 알약 자리를 재서 세상 좌표로 */
  function drawLines(): void {
    svg.replaceChildren();
    const at = (end: CfPort, dir: "in" | "out"): { x: number; y: number } | null => {
      const pill = world.querySelector<HTMLElement>(
        `.m02-dfdg__pill[data-box="${CSS.escape(end.box)}"][data-name="${CSS.escape(end.name)}"][data-dir="${dir}"]`,
      );
      if (!pill) return null;
      const r = pill.getBoundingClientRect();
      return toWorld(dir === "out" ? r.right : r.left, r.top + r.height / 2);
    };
    for (const l of lg.links) {
      const a = at(l.from, "out");
      const b = at(l.to, "in");
      if (!a || !b) continue;
      const dx = Math.max(40, Math.abs(b.x - a.x) / 2);
      const d = `M${a.x},${a.y} C${a.x + dx},${a.y} ${b.x - dx},${b.y} ${b.x},${b.y}`;
      const strong =
        st.selected === l.id ||
        (selBox !== null && (l.from.box === selBox.id || l.to.box === selBox.id));
      const g = document.createElementNS(SVG, "g");
      g.setAttribute(
        "class",
        `m02-dfdg__link${strong ? " is-strong" : ""}${st.selected !== null && !strong ? " is-dim" : ""}`,
      );
      g.setAttribute("data-link", l.id);
      g.setAttribute("data-ends", [a.x, a.y, b.x, b.y].map((n) => n.toFixed(1)).join(","));
      for (const cls of ["m02-dfdg__hit", "m02-dfdg__wire"]) {
        const p = document.createElementNS(SVG, "path");
        p.setAttribute("d", d);
        p.setAttribute("class", cls);
        g.append(p);
      }
      g.addEventListener("click", (ev) => {
        ev.stopPropagation();
        select(st.selected === l.id ? null : l.id);
      });
      svg.append(g);
    }
  }
  const firstFit = (): void => {
    if (st.fitted || !lg.boxes.length || !view.clientWidth) return drawLines();
    st.fitted = true;
    fit();
  };
  st.watch?.disconnect();
  st.watch = typeof ResizeObserver === "undefined" ? undefined : new ResizeObserver(firstFit);
  st.watch?.observe(view);
  if (view.isConnected) firstFit();

  /* 끌기 셋 — 상자 · 판 · 선 */
  function follow(
    ev: PointerEvent,
    move: (m: PointerEvent) => void,
    end: (u: PointerEvent, moved: boolean) => void,
  ): void {
    if (ev.button !== 0) return;
    const x0 = ev.clientX;
    const y0 = ev.clientY;
    let moved = false;
    const mv = (m: PointerEvent): void => {
      if (!moved && Math.hypot(m.clientX - x0, m.clientY - y0) < 5) return;
      moved = true;
      move(m);
    };
    const up = (u: PointerEvent): void => {
      window.removeEventListener("pointermove", mv);
      window.removeEventListener("pointerup", up);
      if (moved) {
        // 끈 뒤 바로 따라오는 click 만 삼킴 — 안 오면 곧 풀어 다음 누름은 그대로
        const swallow = (c: MouseEvent): void => c.stopPropagation();
        window.addEventListener("click", swallow, { capture: true, once: true });
        setTimeout(() => window.removeEventListener("click", swallow, { capture: true }), 0);
      }
      end(u, moved);
    };
    window.addEventListener("pointermove", mv);
    window.addEventListener("pointerup", up);
  }

  function dragBox(ev: PointerEvent, b: CfBox, node: HTMLElement): void {
    const start = toWorld(ev.clientX, ev.clientY);
    let x = b.x;
    let y = b.y;
    follow(
      ev,
      (m) => {
        const now = toWorld(m.clientX, m.clientY);
        x = Math.round(b.x + now.x - start.x);
        y = Math.round(b.y + now.y - start.y);
        node.style.left = `${x}px`;
        node.style.top = `${y}px`;
        drawLines();
      },
      (_u, moved) => {
        if (moved) on.move(b.id, x, y);
      },
    );
  }

  function dragPan(ev: PointerEvent): void {
    const p0 = { x: st.panX, y: st.panY };
    follow(
      ev,
      (m) => {
        st.panX = p0.x + m.clientX - ev.clientX;
        st.panY = p0.y + m.clientY - ev.clientY;
        applyView();
      },
      () => undefined,
    );
  }

  function dragLink(ev: PointerEvent, from: CfPort): void {
    ev.stopPropagation();
    const pill = ev.currentTarget as HTMLElement;
    const r = pill.getBoundingClientRect();
    const a = toWorld(r.right, r.top + r.height / 2);
    let line: SVGPathElement | null = null;
    follow(
      ev,
      (m) => {
        const b = toWorld(m.clientX, m.clientY);
        if (!line) {
          line = document.createElementNS(SVG, "path");
          line.setAttribute("class", "m02-dfdg__drag");
          svg.append(line);
        }
        line.setAttribute("d", `M${a.x},${a.y} L${b.x},${b.y}`);
      },
      (u, moved) => {
        if (!moved) return;
        line?.remove();
        const hit = document.elementFromPoint(u.clientX, u.clientY) as HTMLElement | null;
        const p = hit?.closest<HTMLElement>(".m02-dfdg__pill");
        const bx = hit?.closest<HTMLElement>(".m02-dfdg__box");
        tryLink(
          from,
          p
            ? {
                box: p.dataset.box ?? "",
                name: p.dataset.name ?? null,
                dir: (p.dataset.dir as "in" | "out") ?? null,
              }
            : bx
              ? { box: bx.dataset.box ?? "", name: null, dir: null }
              : null,
        );
      },
    );
  }
}