/* =============================================================================
 * B05_Profile/logic/B05_Profile_Grade_Ground.ts
 * 첫 계획선(계획고 = 지반고) 꼭짓점 — 종단 지반 표본 · 측점 → base_pvi (344-2).
 *
 * 짝 = 파이썬 `B05_Profile_Engine_Grade_Profile.design_ground_following_profile` 의 base_pvi 몫
 * (1순위만 · 관 정착 · 직선 분할 폴백은 짝 없음). 그 위 선형은 이미 짝인 `buildAlignment`
 * (`B05_Profile_UI_Profile_Alignment.ts`). 거울 시험 = resources/tester/test_344_2_route_pairs.py.
 * 1순위가 못 서는 땅(유효 지반 둘 미만 · 연장 0)이면 null — 부르는 쪽이 「서버로 다시 셈」 표시만.
 * ========================================================================== */

import {
  buildCurves,
  evaluateAt,
  type AlignmentNode,
  type AlignmentPolicy,
} from "./B05_Profile_UI_Profile_Alignment";

/** 종단 지반 표본 한 점 — 저장 종단 `samples[]` 꼴. */
export interface GroundSample {
  chainage_m: number;
  elevation_m?: number | null;
  valid?: boolean;
}

export interface GroundFollowingInput {
  samples: ReadonlyArray<GroundSample>;
  /** 측점 누가거리 — 모든 측점이 꼭짓점. */
  stations: ReadonlyArray<number>;
  policy: AlignmentPolicy;
  startOffsetM?: number;
  endOffsetM?: number;
}

/** 파이썬 `round(value, digits)` 와 같은 값(이진 값 그대로 십진 반올림). */
const roundTo = (value: number, digits: number): number => Number(value.toFixed(digits));

/** `np.interp` — 오름차순 xs · 범위 밖은 양 끝값. */
function interp(xs: number[], ys: number[], value: number): number {
  if (value <= xs[0]) return ys[0];
  if (value >= xs[xs.length - 1]) return ys[ys.length - 1];
  let low = 0;
  let high = xs.length - 1;
  while (high - low > 1) {
    const mid = (low + high) >> 1;
    if (xs[mid] <= value) low = mid;
    else high = mid;
  }
  const span = xs[high] - xs[low];
  return span <= 0 ? ys[high] : ys[low] + ((ys[high] - ys[low]) * (value - xs[low])) / span;
}

/** 파이썬 `ground_profile` 짝 — 누가거리 순 · 빈 지반은 선형 보간. 유효 둘 미만이면 null. */
export function groundProfile(
  samples: ReadonlyArray<GroundSample>,
): { chainage: number[]; ground: number[] } | null {
  const rows = samples
    .map((sample) => ({
      s: Number(sample.chainage_m ?? 0),
      z: (sample.valid ?? true) && sample.elevation_m != null ? Number(sample.elevation_m) : NaN,
    }))
    .sort((a, b) => a.s - b.s);
  const finite = rows.filter((row) => Number.isFinite(row.z));
  if (finite.length < 2 || rows.length < 2) return null;
  const fs = finite.map((row) => row.s);
  const fz = finite.map((row) => row.z);
  return { chainage: rows.map((row) => row.s), ground: rows.map((row) => interp(fs, fz, row.s)) };
}

/** 종단곡선을 넣어도 측점마다 `target` 을 지나게 하는 꼭짓점 표고 — 파이썬 `pass_through` 짝. */
export function passThrough(baseS: number[], target: number[], policy: AlignmentPolicy): number[] {
  let baseZ = [...target];
  for (let round = 0; round < 12; round += 1) {
    const pvi = baseS.map((s, index) => ({ chainage_m: s, elevation_m: baseZ[index] }));
    const curves = buildCurves(pvi, policy, {}, []);
    const error = baseS.map((s, index) => target[index] - evaluateAt(baseS, baseZ, curves, s));
    error[0] = 0;
    error[error.length - 1] = 0;
    if (Math.max(...error.map(Math.abs)) < 1e-4) break;
    baseZ = baseZ.map((z, index) => z + error[index]);
  }
  return baseZ;
}

/** 첫 계획선 꼭짓점(base_pvi · 0.000001 m) — 못 서는 땅이면 null(서버로 다시 셈). */
export function groundFollowingBasePvi(input: GroundFollowingInput): AlignmentNode[] | null {
  const profile = groundProfile(input.samples);
  if (!profile) return null;
  const { chainage, ground } = profile;
  const total = chainage[chainage.length - 1];
  if (!(total > 0)) return null;

  let nodeS = [
    ...new Set(
      input.stations
        .filter((value) => Number.isFinite(value) && value >= 0 && value <= total)
        .map((value) => roundTo(value, 3)),
    ),
  ].sort((a, b) => a - b);
  if (nodeS.length < 2) nodeS = chainage.map((value) => roundTo(value, 3));
  if (nodeS[0] > 0) nodeS.unshift(0);
  if (nodeS[nodeS.length - 1] < total) nodeS.push(roundTo(total, 3));

  const target = nodeS.map((s) => interp(chainage, ground, s));
  target[0] += input.startOffsetM ?? 0;
  target[target.length - 1] += input.endOffsetM ?? 0;
  const baseZ = passThrough(nodeS, target, input.policy);
  return nodeS.map((s, index) => ({
    chainage_m: roundTo(s, 6),
    elevation_m: roundTo(baseZ[index], 6),
  }));
}