import { useEffect, useRef } from 'react';
import { useMap } from '@vis.gl/react-maplibre';
import type { HydrDataStep } from '@tabs/prediction/services/predictionApi';

interface HydrParticleOverlayProps {
  hydrStep: HydrDataStep | null;
}

const PARTICLE_COUNT = 3000;
const MAX_AGE = 300;
const SPEED_SCALE = 0.15;
const DT = 600;
const DEG_TO_RAD = Math.PI / 180;
const PI_4 = Math.PI / 4;
const FADE_ALPHA = 0.02; // 프레임당 페이드량 (낮을수록 긴 꼬리)

export default function HydrParticleOverlay({ hydrStep }: HydrParticleOverlayProps) {
  const { current: map } = useMap();
  const animRef = useRef<number>();

  useEffect(() => {
    if (!map || !hydrStep) return;

    const container = map.getContainer();
    const canvas = document.createElement('canvas');
    canvas.style.cssText = 'position:absolute;top:0;left:0;pointer-events:none;z-index:5;';
    canvas.width = container.clientWidth;
    canvas.height = container.clientHeight;
    container.appendChild(canvas);
    const ctx = canvas.getContext('2d')!;

    const {
      value: [u2d, v2d],
      grid,
    } = hydrStep;
    const { boundLonLat, lonInterval, latInterval } = grid;

    const lons: number[] = [boundLonLat.left];
    for (const d of lonInterval) lons.push(lons[lons.length - 1] + d);
    const lats: number[] = [boundLonLat.bottom];
    for (const d of latInterval) lats.push(lats[lats.length - 1] + d);

    function bisect(arr: number[], val: number): number {
      let lo = 0,
        hi = arr.length - 2;
      while (lo <= hi) {
        const mid = (lo + hi) >> 1;
        if (val < arr[mid]) hi = mid - 1;
        else if (val >= arr[mid + 1]) lo = mid + 1;
        else return mid;
      }
      return -1;
    }

    function getUV(lon: number, lat: number): [number, number] {
      const col = bisect(lons, lon);
      const row = bisect(lats, lat);
      if (col < 0 || row < 0) return [0, 0];
      const fx = (lon - lons[col]) / (lons[col + 1] - lons[col]);
      const fy = (lat - lats[row]) / (lats[row + 1] - lats[row]);
      const u00 = u2d[row]?.[col] ?? 0,
        u01 = u2d[row]?.[col + 1] ?? u00;
      const u10 = u2d[row + 1]?.[col] ?? u00,
        u11 = u2d[row + 1]?.[col + 1] ?? u00;
      const v00 = v2d[row]?.[col] ?? 0,
        v01 = v2d[row]?.[col + 1] ?? v00;
      const v10 = v2d[row + 1]?.[col] ?? v00,
        v11 = v2d[row + 1]?.[col + 1] ?? v00;
      const _1fx = 1 - fx,
        _1fy = 1 - fy;
      return [
        u00 * _1fx * _1fy + u01 * fx * _1fy + u10 * _1fx * fy + u11 * fx * fy,
        v00 * _1fx * _1fy + v01 * fx * _1fy + v10 * _1fx * fy + v11 * fx * fy,
      ];
    }

    const bbox = boundLonLat;
    const bboxW = bbox.right - bbox.left;
    const bboxH = bbox.top - bbox.bottom;

    // 파티클: 위치 + 이전 화면좌표 (선분 1개만 그리면 됨)
    const pLon = new Float64Array(PARTICLE_COUNT);
    const pLat = new Float64Array(PARTICLE_COUNT);
    const pAge = new Int32Array(PARTICLE_COUNT);
    const pPrevX = new Float32Array(PARTICLE_COUNT); // 이전 프레임 화면 X
    const pPrevY = new Float32Array(PARTICLE_COUNT); // 이전 프레임 화면 Y
    const pHasPrev = new Uint8Array(PARTICLE_COUNT); // 이전 좌표 유효 여부

    for (let i = 0; i < PARTICLE_COUNT; i++) {
      pLon[i] = bbox.left + Math.random() * bboxW;
      pLat[i] = bbox.bottom + Math.random() * bboxH;
      pAge[i] = Math.floor(Math.random() * MAX_AGE);
      pHasPrev[i] = 0;
    }

    function resetParticle(i: number) {
      pLon[i] = bbox.left + Math.random() * bboxW;
      pLat[i] = bbox.bottom + Math.random() * bboxH;
      pAge[i] = 0;
      pHasPrev[i] = 0;
    }

    // Mercator 수동 투영
    function lngToMercX(lng: number, worldSize: number): number {
      return ((lng + 180) / 360) * worldSize;
    }
    function latToMercY(lat: number, worldSize: number): number {
      return ((1 - Math.log(Math.tan(PI_4 + (lat * DEG_TO_RAD) / 2)) / Math.PI) / 2) * worldSize;
    }

    // 지도 이동 시 캔버스 초기화 + 이전 좌표 무효화
    const onMove = () => {
      ctx.clearRect(0, 0, canvas.width, canvas.height);
      for (let i = 0; i < PARTICLE_COUNT; i++) pHasPrev[i] = 0;
    };
    map.on('move', onMove);

    function animate() {
      const w = canvas.width;
      const h = canvas.height;

      // ── 페이드: 기존 내용을 서서히 지움 (destination-out) ──
      ctx.globalCompositeOperation = 'destination-out';
      ctx.fillStyle = `rgba(0, 0, 0, ${FADE_ALPHA})`;
      ctx.fillRect(0, 0, w, h);
      ctx.globalCompositeOperation = 'source-over';

      // 뷰포트 transform (프레임당 1회)
      const zoom = map.getZoom();
      const center = map.getCenter();
      const bearing = map.getBearing();
      const worldSize = 512 * Math.pow(2, zoom);
      const cx = lngToMercX(center.lng, worldSize);
      const cy = latToMercY(center.lat, worldSize);
      const halfW = w / 2;
      const halfH = h / 2;
      const bearingRad = -bearing * DEG_TO_RAD;
      const cosB = Math.cos(bearingRad);
      const sinB = Math.sin(bearingRad);
      const hasBearing = Math.abs(bearing) > 0.01;

      // ── 파티클당 선분 1개만 그리기 (3000 선분) ──
      ctx.strokeStyle = 'rgba(255, 255, 255, 0.8)';
      ctx.lineWidth = 1.5;
      ctx.beginPath();

      for (let i = 0; i < PARTICLE_COUNT; i++) {
        const lon = pLon[i],
          lat = pLat[i];
        const [u, v] = getUV(lon, lat);
        const speed2 = u * u + v * v;
        if (speed2 < 0.000001) {
          resetParticle(i);
          continue;
        }

        const cosLat = Math.cos(lat * DEG_TO_RAD);
        pLon[i] = lon + (u * SPEED_SCALE * DT) / (cosLat * 111320);
        pLat[i] = lat + (v * SPEED_SCALE * DT) / 111320;
        pAge[i]++;

        if (
          pLon[i] < bbox.left ||
          pLon[i] > bbox.right ||
          pLat[i] < bbox.bottom ||
          pLat[i] > bbox.top ||
          pAge[i] > MAX_AGE
        ) {
          resetParticle(i);
          continue;
        }

        // 수동 Mercator 투영
        let dx = lngToMercX(pLon[i], worldSize) - cx;
        let dy = latToMercY(pLat[i], worldSize) - cy;
        if (hasBearing) {
          const rx = dx * cosB - dy * sinB;
          const ry = dx * sinB + dy * cosB;
          dx = rx;
          dy = ry;
        }
        const sx = dx + halfW;
        const sy = dy + halfH;

        // 이전 좌표가 있으면 선분 1개 추가
        if (pHasPrev[i]) {
          ctx.moveTo(pPrevX[i], pPrevY[i]);
          ctx.lineTo(sx, sy);
        }

        pPrevX[i] = sx;
        pPrevY[i] = sy;
        pHasPrev[i] = 1;
      }

      ctx.stroke();

      animRef.current = requestAnimationFrame(animate);
    }

    animRef.current = requestAnimationFrame(animate);

    const onResize = () => {
      canvas.width = container.clientWidth;
      canvas.height = container.clientHeight;
    };
    map.on('resize', onResize);

    return () => {
      cancelAnimationFrame(animRef.current!);
      map.off('resize', onResize);
      map.off('move', onMove);
      canvas.remove();
    };
  }, [map, hydrStep]);

  return null;
}
