import type { CrossSection, SectionSample } from "./B06_Section_Api_Fetch";
import { CROSS_HEIGHT, CROSS_PAD, validElevation } from "./B06_Section_UI_Section_Common";

const AREA_OVERLAY_HEADROOM_PX = 58;

interface CrossPlotMetrics {
  sourceSamples: SectionSample[];
  minOffset: number;
  maxOffset: number;
  elevationMid: number;
  displaySpan: number;
  displayMax: number;
  pixelsPerMeter: number;
  heightPx: number;
}

export function crossPlotMetrics(
  section: CrossSection,
  verticalExaggeration: number,
  widthPx: number,
  crossHalfWidth?: number,
  designElevation?: number,
  forcedHeightPx?: number,
): CrossPlotMetrics | null {
  const sourceSamples = section.samples.filter(
    (sample) =>
      crossHalfWidth === undefined || Math.abs(sample.offset_m ?? 0) <= crossHalfWidth + 1e-6,
  );
  const valid = sourceSamples.filter(validElevation);
  if (!valid.length) return null;
  const offsets = sourceSamples.map((sample) => sample.offset_m ?? 0);
  const minOffset = Math.min(...offsets, -1);
  const maxOffset = Math.max(...offsets, 1);
  const elevations = valid.map((sample) => sample.elevation_m);
  if (designElevation !== undefined && Number.isFinite(designElevation))
    elevations.push(designElevation);
  const rawMin = Math.min(...elevations);
  const rawMax = Math.max(...elevations);
  const elevationMid = (rawMin + rawMax) / 2;
  const padding = rawMax > rawMin ? (rawMax - rawMin) * 0.08 : 0.5;
  const pixelsPerMeter =
    (widthPx - CROSS_PAD.left - CROSS_PAD.right) / Math.max(maxOffset - minOffset, 1e-6);
  const rawSpan = Math.max(
    (rawMax - rawMin + padding * 2) * Math.max(verticalExaggeration, 0.1),
    1e-6,
  );
  const naturalHeight =
    rawSpan * pixelsPerMeter + CROSS_PAD.top + CROSS_PAD.bottom + AREA_OVERLAY_HEADROOM_PX;
  const heightPx = forcedHeightPx ?? Math.max(naturalHeight, CROSS_HEIGHT);
  const displaySpan = Math.max(heightPx - CROSS_PAD.top - CROSS_PAD.bottom, 1e-6) / pixelsPerMeter;
  const displayMax = elevationMid + displaySpan / 2 + AREA_OVERLAY_HEADROOM_PX / pixelsPerMeter / 2;
  return {
    sourceSamples,
    minOffset,
    maxOffset,
    elevationMid,
    displaySpan,
    displayMax,
    pixelsPerMeter,
    heightPx,
  };
}

export function crossCardNaturalHeight(
  section: CrossSection,
  verticalExaggeration: number,
  widthPx: number,
  crossHalfWidth?: number,
  designElevation?: number,
): number {
  return (
    crossPlotMetrics(section, verticalExaggeration, widthPx, crossHalfWidth, designElevation)
      ?.heightPx ?? CROSS_HEIGHT
  );
}