/* =============================================================================
 * B06_Section_Cross_Design_Surface_Geom.ts
 * 암선 · 포장층 **기하**(m 좌표) — 그리기는 `../B06_Section_UI_Cross_Design_Surface`(472-3).
 * ========================================================================== */

import type { PavementEntry } from "@util/common_util_structure_pavement";
import type { CrossDesign } from "../B06_Section_Api_Fetch";

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

/** 암선 — 유효 지반 샘플을 `offsetM` 만큼 올린 꺾은선들(빈 · 무효 샘플에서 끊음 · 두 점 이상만). */
export function rockBoundarySegments(
  samples: Array<{ offset_m?: number; elevation_m?: number | null; valid: boolean }>,
  offsetM: number,
): Edge[][] {
  const segments: Edge[][] = [];
  let current: Edge[] = [];
  for (const sample of samples) {
    const elevation = sample.elevation_m;
    if (sample.valid === false || elevation === null || !Number.isFinite(elevation ?? NaN)) {
      if (current.length > 1) segments.push(current);
      current = [];
      continue;
    }
    current.push({ offset_m: sample.offset_m ?? 0, elevation_m: (elevation as number) + offsetM });
  }
  if (current.length > 1) segments.push(current);
  return segments;
}

/** 확폭 끈 구간 — 규격 폭 끝(좌 = left − 확폭좌 · 우 = right + 확폭우 · 표고는 두 끝 사이 직선). */
function standardEdges(edges: { left: Edge; right: Edge }, design: CrossDesign) {
  const { left, right } = edges;
  const span = right.offset_m - left.offset_m || 1;
  const at = (offset: number): Edge => ({
    offset_m: offset,
    elevation_m:
      left.elevation_m + ((right.elevation_m - left.elevation_m) * (offset - left.offset_m)) / span,
  });
  return {
    left: at(left.offset_m - (design.widening_left_m ?? 0)),
    right: at(right.offset_m + (design.widening_right_m ?? 0)),
  };
}

/**
 * 포장층 — 노면선(= 포장 윗면) 아래로 두께만큼. 노면공 범위(`section.pavement`)면 그 두께 ·
 * 확폭 켬/끔(여러 건은 아래로 차례로 쌓음) · 없으면 카드 포장 켬일 때 표준 두께.
 * 층마다 네 꼭짓점(좌상 · 우상 · 우하 · 좌하).
 */
export function pavementLayers(
  design: CrossDesign,
  pavement?: readonly PavementEntry[] | null,
): Array<{ entry: PavementEntry | null; corners: Edge[] }> {
  const edges = design.carriageway_edges ?? design.road_edges;
  if (!edges) return [];
  const layers = pavement?.length ? pavement : design.paved ? [null] : [];
  let depth = 0;
  return layers.map((entry) => {
    const thickness = entry?.thickness_m ?? design.pavement_thickness_m ?? 0.2;
    const { left, right } = entry && !entry.widening_on ? standardEdges(edges, design) : edges;
    const corners = [
      { offset_m: left.offset_m, elevation_m: left.elevation_m - depth },
      { offset_m: right.offset_m, elevation_m: right.elevation_m - depth },
      { offset_m: right.offset_m, elevation_m: right.elevation_m - depth - thickness },
      { offset_m: left.offset_m, elevation_m: left.elevation_m - depth - thickness },
    ];
    depth += thickness;
    return { entry, corners };
  });
}