/* =============================================================================
 * B06_Section_UI_Cross_Underdrain.ts
 * 맹암거 횡단 형상(288-1 · 요구 183-3).
 *
 *   · 노면 = 설계 노면 — 서버 · TS 짝이 암거 경사로 지대 낮은 쪽 한 경사로 기울여 냄 · 측구 없음.
 *   · 옵셋선 = 노면을 암거 높이만큼 아래로 같은 각도.
 *   · 성토 쪽 = 옵셋선을 성토 사면과 만날 때까지 · 절토 쪽 = 절토 사면을 아래로 늘여 옵셋선과 만남.
 *   · 노면 · 양쪽 선 · 옵셋선이 둘러싼 안 = 돌 무늬(흙막이 돌 그리기 `drawStones`).
 * 높이가 비면 그리지 않음(수치를 지어내지 않음).
 * ========================================================================== */

import type { CrossDesign } from "./B06_Section_Api_Fetch";
import type { OffsetPoint } from "./B06_Section_UI_Cross_Culvert_Types";
import { drawStones } from "./B06_Section_UI_Cross_Wall_Hatch";
import type { UnderdrainSpec } from "@util/common_util_structure_underdrain";

const SVG_NS = "http://www.w3.org/2000/svg";
let clipSeq = 0;

type Edge = { offset_m: number; elevation_m: number };

/** 한쪽 둘레(노면 끝 → 옵셋선과 만나는 자리) — `outward` = 바깥 부호(+1 좌 · −1 우). */
function sidePath(
  edge: Edge,
  outward: 1 | -1,
  line: readonly Edge[],
  roadGrade: number,
  heightM: number,
): OffsetPoint[] {
  const start = { offset: edge.offset_m, elevation: edge.elevation_m };
  const offZ = (o: number) => edge.elevation_m + roadGrade * (o - edge.offset_m) - heightM;
  const outside = line
    .filter((p) => (p.offset_m - edge.offset_m) * outward > 1e-6)
    .sort((a, b) => (a.offset_m - b.offset_m) * outward);
  const first = outside[0];
  if (!first) return [start, { offset: start.offset, elevation: offZ(start.offset) }];
  if (first.elevation_m >= edge.elevation_m) {
    // 절토 — 사면을 안쪽 아래로 늘여 옵셋선과 만남
    const k = (first.elevation_m - edge.elevation_m) / (first.offset_m - edge.offset_m);
    const d = Math.abs(k - roadGrade) < 1e-9 ? 0 : -heightM / (k - roadGrade);
    const offset = edge.offset_m + d;
    return [start, { offset, elevation: offZ(offset) }];
  }
  // 성토 — 사면을 따라 내려가다 옵셋선을 만나는 자리
  const path: OffsetPoint[] = [start];
  let prev = edge;
  for (const point of outside) {
    const fa = prev.elevation_m - offZ(prev.offset_m);
    const fb = point.elevation_m - offZ(point.offset_m);
    if (fb <= 0) {
      const t = fa / (fa - fb);
      const offset = prev.offset_m + (point.offset_m - prev.offset_m) * t;
      path.push({ offset, elevation: offZ(offset) });
      return path;
    }
    path.push({ offset: point.offset_m, elevation: point.elevation_m });
    prev = point;
  }
  path.push({ offset: prev.offset_m, elevation: offZ(prev.offset_m) });
  return path;
}

/** 맹암거 형상 둘레 — 좌 노면 끝 → 우 노면 끝 → 우 둘레 → 옵셋선 → 좌 둘레(위로). 높이 없으면 null. */
export function underdrainOutline(
  design: CrossDesign,
  heightM: number | null,
): OffsetPoint[] | null {
  const edges = design.road_edges;
  if (!edges || !(heightM && heightM > 0)) return null;
  const { left, right } = edges;
  const span = left.offset_m - right.offset_m;
  if (!(Math.abs(span) > 1e-9)) return null;
  const grade = (left.elevation_m - right.elevation_m) / span;
  const line = design.design_line ?? [];
  const leftPath = sidePath(left, 1, line, grade, heightM);
  const rightPath = sidePath(right, -1, line, grade, heightM);
  return [
    { offset: left.offset_m, elevation: left.elevation_m },
    ...rightPath,
    ...leftPath.slice(1).reverse(),
  ];
}

/** 맹암거 형상을 그린다(돌 무늬 · 둘레 클립). 그렸으면 그 무리 — 둘레에 고름 표식(`data-structure-id` · 288-2). */
export function appendUnderdrainOverlay(
  svg: SVGElement,
  spec: UnderdrainSpec | undefined,
  design: CrossDesign,
  x: (offset: number) => number,
  y: (elevation: number) => number,
): SVGGElement | null {
  const outline = spec ? underdrainOutline(design, spec.height_m) : null;
  if (!spec || !outline) return null;
  const px = (p: OffsetPoint): [number, number] => [x(p.offset), y(p.elevation)];
  const points = outline.map((p) => px(p).join(",")).join(" ");
  const group = document.createElementNS(SVG_NS, "g") as SVGGElement;
  group.setAttribute("class", "b06-chart__underdrain");
  const body = document.createElementNS(SVG_NS, "polygon");
  body.setAttribute("points", points);
  body.setAttribute("class", "b06-chart__underdrain-body");
  if (spec.structure_id) body.setAttribute("data-structure-id", spec.structure_id);
  clipSeq += 1;
  const clipId = `b06-underdrain-clip-${clipSeq}`;
  const clip = document.createElementNS(SVG_NS, "clipPath");
  clip.setAttribute("id", clipId);
  const clipShape = document.createElementNS(SVG_NS, "polygon");
  clipShape.setAttribute("points", points);
  clip.append(clipShape);
  const stones = document.createElementNS(SVG_NS, "g");
  stones.setAttribute("clip-path", `url(#${clipId})`);
  const height = spec.height_m!;
  const offsets = outline.map((p) => p.offset);
  const [lo, hi] = [Math.min(...offsets), Math.max(...offsets)];
  const { left, right } = design.road_edges;
  const grade = (left.elevation_m - right.elevation_m) / (left.offset_m - right.offset_m);
  const roadZ = (o: number) => left.elevation_m + grade * (o - left.offset_m);
  const at = (u: number, v: number): OffsetPoint => {
    const offset = lo + (hi - lo) * u;
    return { offset, elevation: roadZ(offset) - height * (v + 0.5) };
  };
  const [ax, ay] = px(at(0, 0));
  const [bx, by] = px(at(1, 0));
  drawStones(
    stones,
    {
      spanM: Math.hypot(hi - lo, grade * (hi - lo)),
      pixelsPerMeter: Math.abs(x(1) - x(0)) || 1,
      point: (u, v) => px(at(u, v)),
      leanDegrees: (Math.atan2(bx - ax, -(by - ay)) * 180) / Math.PI,
    },
    false,
    height,
  );
  group.append(body, clip, stones);
  svg.append(group);
  return group;
}