/* =============================================================================
 * B09_Estimation_UI_Tabs_Bill_Drag.ts
 * B09 설계내역서 줄 끌기(PLAN 204-1) — 줄을 잡아 위아래 = 자리 · 좌우 = 레벨(한 칸 = 1em) · 공용 표 위 덧그림.
 *
 *   놓을 자리 = 줄 사이 틈(포인터가 줄 가운데 위 = 그 줄 앞) · 끄는 줄 자손 = 함께 감 · 자기 자손 안 = 못 놓음
 *   레벨 = 위 줄 + 1(위 줄 아래로 · 항목이면 저절로 묶음) ~ 아래 줄 레벨 · 맨 위(1) = 맨 위 줄만
 *   놓기 = 표 drop(`…_Bill_Edit` dropMove — 메뉴와 같은 지킬 것) · 미리 보기 선(못 놓음 = is-bad · 커서 not-allowed)
 *   잡기 = 글 칸 · 단추 밖 아무 칸 · 6px 넘게 움직여야 끌기(그냥 누름 = 줄 고름)
 * ========================================================================== */

import type { DataRow } from "@ui/ui_template_data_table";
import type { BillTable } from "./B09_Estimation_UI_Tabs_Bill_Edit";

export interface DropAt {
  parent: string | null;
  before: string | null;
  level: number;
}

const holds = (row: DataRow): boolean => row.key !== "fee" && !String(row.key).startsWith("mat:");

/** 틈 gap(0 ~ 줄 수 · 그 줄 앞) · 바라는 레벨 → 놓을 자리 · 같은 자리 · 못 놓음 = null */
export function dropAt(rows: DataRow[], from: number, gap: number, want: number): DropAt | null {
  const row = rows[from];
  if (!row) return null;
  const lv = (r: DataRow | undefined): number => Number(r?.level ?? 1);
  let end = from + 1;
  while (end < rows.length && lv(rows[end]) > lv(row)) end += 1;
  if (gap > from && gap < end) return null; // 자기 자손 안
  const rest = [...rows.slice(0, from), ...rows.slice(end)];
  const g = gap <= from ? gap : gap - (end - from);
  const up = rest[g - 1];
  const down = rest[g];
  const max = up ? lv(up) + (holds(up) ? 1 : 0) : 1;
  const min = Math.max(down ? lv(down) : 1, lv(row) === 1 ? 1 : 2);
  if (min > max) return null;
  const level = Math.min(max, Math.max(min, want));
  if (level === lv(row) && (gap === from || gap === end)) return null; // 제자리
  let parent: DataRow | undefined = up;
  const byKey = new Map(rest.map((r) => [String(r.key), r]));
  while (parent && lv(parent) >= level) parent = byKey.get(String(parent.parent ?? ""));
  return {
    parent: parent ? String(parent.key) : null,
    before: down && lv(down) === level ? String(down.key) : null,
    level,
  };
}

/** 표 root 에 줄 끌기를 붙임 — 놓으면 done(끈 줄 키) 뒤 drop 실행 */
export function attachDrag(root: HTMLElement, table: BillTable, done: (key: string) => void): void {
  let endAt = 0;
  // 끌고 난 누름 = 줄 고름 아님
  root.addEventListener(
    "click",
    (event) => {
      if (Date.now() - endAt < 300) event.stopPropagation();
    },
    true,
  );
  root.addEventListener("pointerdown", (down) => {
    const target = down.target as Element;
    if (down.button !== 0 || !table.drop || target.closest("input,textarea,select,button,a"))
      return;
    const tr = target.closest<HTMLElement>("tr[data-i]");
    if (!tr || !root.contains(tr)) return;
    const from = Number(tr.dataset.i);
    const step = parseFloat(getComputedStyle(tr).fontSize) || 14;
    const line = document.createElement("div");
    line.className = "b09-estimation__drop";
    let on = false;
    let run: (() => void) | null = null;
    let seen = "";
    const move = (event: PointerEvent): void => {
      const dx = event.clientX - down.clientX;
      if (!on && Math.abs(dx) + Math.abs(event.clientY - down.clientY) < 6) return;
      if (!on) {
        on = true;
        document.body.append(line);
        document.body.style.userSelect = "none";
        window.getSelection()?.removeAllRanges();
      }
      const trs = table.rows.map((_r, i) => root.querySelector<HTMLElement>(`tr[data-i="${i}"]`));
      let gap = trs.length;
      let y = trs.at(-1)?.getBoundingClientRect().bottom ?? 0;
      for (const [i, el] of trs.entries()) {
        const box = el?.getBoundingClientRect();
        if (box && event.clientY < box.top + box.height / 2) {
          [gap, y] = [i, box.top];
          break;
        }
      }
      const want = Number(table.rows[from]?.level ?? 1) + Math.round(dx / step);
      const at = dropAt(table.rows, from, gap, want);
      const key = `${gap}|${at?.level}`;
      if (key !== seen) {
        seen = key;
        run = at ? table.drop!(from, at.parent, at.before) : null;
      }
      const box = root.getBoundingClientRect();
      const left = box.left + ((at?.level ?? want) - 1) * step + 8;
      Object.assign(line.style, {
        top: `${y - 1}px`,
        left: `${left}px`,
        width: `${Math.max(box.right - left, 40)}px`,
      });
      line.classList.toggle("is-bad", !run);
      document.body.style.cursor = run ? "grabbing" : "not-allowed";
    };
    const stop = (event: PointerEvent): void => {
      window.removeEventListener("pointermove", move);
      window.removeEventListener("pointerup", stop);
      window.removeEventListener("pointercancel", stop);
      line.remove();
      document.body.style.userSelect = "";
      document.body.style.cursor = "";
      if (!on) return;
      endAt = Date.now();
      if (event.type === "pointerup" && run) {
        done(String(table.rows[from].key));
        run();
      }
    };
    window.addEventListener("pointermove", move);
    window.addEventListener("pointerup", stop);
    window.addEventListener("pointercancel", stop);
  });
}