/* =============================================================================
 * B05_Profile_UI_Structures_Fields.ts
 * 「구조물 배치」 폼 입력 조각 — 라벨 필드·숫자칸·셀렉트·측점번호+잔여거리 두 칸.
 *
 * 패널 본체(B05_Profile_UI_Structures_Panel)가 700줄 한계에 닿아 분리했다.
 * 측점 두 칸은 구 비정규 측점 UI와 같은 입력 방식이다(2026-08-17 사용자 확정) —
 * 저장은 누가거리(m), 화면 입출력만 측점번호+잔여거리.
 * ========================================================================== */

import { chainageToStation } from "./B05_Profile_Util_Station";

export function field(labelText: string, input: HTMLElement): HTMLLabelElement {
  const wrapper = document.createElement("label");
  wrapper.className = "b05-route__field";
  const caption = document.createElement("span");
  caption.textContent = labelText;
  wrapper.append(caption, input);
  return wrapper;
}

export function numberInput(step = "0.1", min = "0"): HTMLInputElement {
  const input = document.createElement("input");
  input.type = "number";
  input.step = step;
  input.min = min;
  return input;
}

export function select(options: ReadonlyArray<[string, string]>): HTMLSelectElement {
  const element = document.createElement("select");
  element.replaceChildren(...options.map(([value, label]) => new Option(label, value)));
  return element;
}

/** 측점번호 + 잔여거리 두 칸 묶음. */
export interface StationFields {
  wrap: HTMLElement;
  station: HTMLInputElement;
  remainder: HTMLInputElement;
  /** 두 칸을 누가거리로 읽는다. 비었으면 null, 형식 오류면 붉히고 null. */
  read: (intervalM: number, required: boolean) => number | null;
  /** 누가거리를 두 칸에 나눠 싣는다. null이면 비운다. */
  write: (chainageM: number | null, intervalM: number) => void;
  clearInvalid: () => void;
}

export function stationFields(labelText: string): StationFields {
  const station = numberInput("1", "0");
  station.placeholder = "측점";
  const remainder = numberInput("0.1", "0");
  remainder.placeholder = "+m";
  const pair = document.createElement("div");
  pair.className = "b05-structure__station-pair";
  pair.append(station, remainder);
  const wrap = field(labelText, pair);
  const markInvalid = (bad: boolean): void => {
    station.classList.toggle("is-invalid", bad);
    remainder.classList.toggle("is-invalid", bad);
  };
  return {
    wrap,
    station,
    remainder,
    read(intervalM, required) {
      const stationText = station.value.trim();
      const remainderText = remainder.value.trim();
      if (!stationText && !remainderText) {
        markInvalid(required);
        return null;
      }
      const stationNo = stationText ? Number(stationText) : 0;
      const rest = remainderText ? Number(remainderText) : 0;
      const valid =
        Number.isFinite(stationNo) && stationNo >= 0 && Number.isFinite(rest) && rest >= 0;
      markInvalid(!valid);
      return valid ? stationNo * intervalM + rest : null;
    },
    write(chainageM, intervalM) {
      if (chainageM === null) {
        station.value = "";
        remainder.value = "";
        return;
      }
      const parts = chainageToStation(chainageM, intervalM);
      station.value = String(parts.station);
      remainder.value = parts.remainder.toFixed(1);
    },
    clearInvalid: () => markInvalid(false),
  };
}