/* =============================================================================
 * common_util/common_util_structure_underdrain.ts
 * 맹암거(cross_underdrain · A군 점형) 제원을 횡단 측점에 얹는다(288-1).
 *
 * 기준 측점(0.02 m 안) 횡단 dict 에 `underdrain` = 높이 · 경사 — 횡단도가 돌 무늬 형상을 그리고,
 * 설계 계산은 그 측점을 측구 없이 지대 낮은 쪽 한 경사로 기울임(`tilted`).
 * 파이썬 짝 = `B06_Section/B06_Section_Engine_Tilt.py`(`load_underdrains` · `attach_underdrains`).
 * ========================================================================== */

export const UNDERDRAIN_TYPE_ID = "cross_underdrain";
const EDGE_TOLERANCE_M = 0.02;

/** 맹암거 제원 — 높이 · 경사가 비면 null(높이 없으면 형상 없음 · 경사 없으면 표준 횡단경사). */
export interface UnderdrainSpec {
  structure_id: string | null;
  chainage_m: number;
  height_m: number | null;
  slope_pct: number | null;
}

export interface UnderdrainInput {
  structure_id?: string | null;
  type_id: string;
  chainage_m?: number | null;
  start_m?: number | null;
  options?: Record<string, unknown> | null;
}

const positive = (value: unknown): number | null => {
  const parsed = value === "" || value === null || value === undefined ? NaN : Number(value);
  return Number.isFinite(parsed) && parsed > 0 ? parsed : null;
};

/** 구조물 목록의 맹암거 제원(파이썬 `load_underdrains` 짝). */
export function underdrainSpecsFrom(structures: readonly UnderdrainInput[]): UnderdrainSpec[] {
  return structures.flatMap((structure) => {
    const at = structure.chainage_m ?? structure.start_m;
    if (structure.type_id !== UNDERDRAIN_TYPE_ID || typeof at !== "number") return [];
    const options = structure.options ?? {};
    return [
      {
        structure_id: structure.structure_id ?? null,
        chainage_m: at,
        height_m: positive(options.culvert_height_m),
        slope_pct: positive(options.culvert_slope_pct),
      },
    ];
  });
}

/** 기준 측점 횡단 dict 에 `underdrain` 을 얹는다(옛 값은 걷음) — 얹은 개수(파이썬 `attach_underdrains` 짝). */
export function attachUnderdrainSpecs(
  sections: Array<Record<string, unknown>>,
  specs: readonly UnderdrainSpec[],
): number {
  let attached = 0;
  for (const section of sections) {
    delete section.underdrain;
    const chainage = Number(section.chainage_m);
    const hit = specs.find((spec) => Math.abs(spec.chainage_m - chainage) <= EDGE_TOLERANCE_M);
    if (!hit) continue;
    section.underdrain = { ...hit };
    attached += 1;
  }
  return attached;
}