import * as THREE from "three";
import * as Astronomy from "astronomy-engine";

import { CELESTIAL_CONFIG, EARTH_CONFIG } from "./constants.js";
import { latLonToVector3 } from "./utils.js";

const textureLoader = new THREE.TextureLoader();
const defaultSunDirection = new THREE.Vector3(1, 0.2, 0.4).normalize();
const defaultMoonDirection = new THREE.Vector3(-0.6, 0.45, -0.2).normalize();

let celestialRoot = null;
let skySphere = null;
let brightStarsGroup = null;
let sunSprite = null;
let moonSprite = null;
let sunHaloSprite = null;
let moonHaloSprite = null;
let brightStarTexture = null;
let sunDirection = defaultSunDirection.clone();
let moonDirection = defaultMoonDirection.clone();
let lastUpdatedAt = 0;
let linkedSunLight = null;
let linkedBackLight = null;
let linkedEarth = null;
let brightStarSprites = [];
let celestialRotationQuaternion = new THREE.Quaternion();
let celestialViewQuaternion = new THREE.Quaternion();
let runtimeOrientationEuler = {
  ...CELESTIAL_CONFIG.orientationEulerRad,
};
let runtimeFollowConfig = {
  ...CELESTIAL_CONFIG.followEarthRotation,
};
const scratchEuler = new THREE.Euler(0, 0, 0, "YXZ");

function normalizeDegrees180(value) {
  let normalized = value;
  while (normalized <= -180) normalized += 360;
  while (normalized > 180) normalized -= 360;
  return normalized;
}

function computeGreenwichMeanSiderealDegrees(date) {
  const jd = date.getTime() / 86400000 + 2440587.5;
  const t = (jd - 2451545.0) / 36525.0;
  const gmst =
    280.46061837 +
    360.98564736629 * (jd - 2451545.0) +
    0.000387933 * t * t -
    (t * t * t) / 38710000;
  return THREE.MathUtils.euclideanModulo(gmst, 360);
}

function computeSubsolarLocalDirection(date) {
  const vector = Astronomy.GeoVector(Astronomy.Body.Sun, date, false);
  const radius = Math.sqrt(
    vector.x * vector.x +
    vector.y * vector.y +
    vector.z * vector.z,
  );
  if (!Number.isFinite(radius) || radius === 0) {
    return defaultSunDirection.clone();
  }

  const rightAscensionDeg = THREE.MathUtils.radToDeg(
    Math.atan2(vector.y, vector.x),
  );
  const declinationDeg = THREE.MathUtils.radToDeg(
    Math.asin(THREE.MathUtils.clamp(vector.z / radius, -1, 1)),
  );
  const gmstDeg = computeGreenwichMeanSiderealDegrees(date);
  const subsolarLonDeg = normalizeDegrees180(rightAscensionDeg - gmstDeg);

  return latLonToVector3(declinationDeg, subsolarLonDeg, 1).normalize();
}

function getPhysicalSunDirection(date = new Date()) {
  const localSunDirection = computeSubsolarLocalDirection(date);
  if (!linkedEarth) {
    return localSunDirection;
  }

  return localSunDirection
    .clone()
    .applyQuaternion(linkedEarth.quaternion)
    .normalize();
}

function getCelestialEuler() {
  const { x, y, z } = runtimeOrientationEuler;
  return new THREE.Euler(x, y, z, "YXZ");
}

function refreshCelestialOrientation() {
  celestialRotationQuaternion.setFromEuler(getCelestialEuler());
  refreshCelestialView();
}

function refreshCelestialView() {
  if (linkedEarth && runtimeFollowConfig.enabled) {
    const followX = runtimeFollowConfig.x
      ? (linkedEarth.rotation.x - EARTH_CONFIG.tiltRad) * (runtimeFollowConfig.invertX ? -1 : 1)
      : 0;
    const followY = runtimeFollowConfig.y
      ? linkedEarth.rotation.y * (runtimeFollowConfig.invertY ? -1 : 1)
      : 0;
    const followZ = runtimeFollowConfig.z
      ? linkedEarth.rotation.z * (runtimeFollowConfig.invertZ ? -1 : 1)
      : 0;

    scratchEuler.set(
      followX,
      followY,
      followZ,
      "YXZ",
    );
    celestialViewQuaternion.setFromEuler(scratchEuler);
  } else {
    celestialViewQuaternion.identity();
  }

  if (celestialRoot) {
    celestialRoot.quaternion
      .copy(celestialRotationQuaternion)
      .multiply(celestialViewQuaternion);
  }
}

function applyCelestialOrientation(direction) {
  return direction
    .clone()
    .applyQuaternion(celestialRotationQuaternion)
    .applyQuaternion(celestialViewQuaternion)
    .normalize();
}

function configureTextureEncoding(texture) {
  if (!texture) return;
  if ("colorSpace" in texture && THREE.SRGBColorSpace) {
    texture.colorSpace = THREE.SRGBColorSpace;
  } else if ("encoding" in texture && THREE.sRGBEncoding) {
    texture.encoding = THREE.sRGBEncoding;
  }
}

function createDiscTexture(stops, size = 256) {
  const canvas = document.createElement("canvas");
  canvas.width = size;
  canvas.height = size;
  const ctx = canvas.getContext("2d");
  const gradient = ctx.createRadialGradient(
    size / 2,
    size / 2,
    0,
    size / 2,
    size / 2,
    size / 2,
  );

  stops.forEach(([offset, color]) => gradient.addColorStop(offset, color));
  ctx.fillStyle = gradient;
  ctx.fillRect(0, 0, size, size);

  const texture = new THREE.CanvasTexture(canvas);
  configureTextureEncoding(texture);
  texture.needsUpdate = true;
  return texture;
}

function createSprite({ texture, scale, opacity = 1, name, color = 0xffffff }) {
  const material = new THREE.SpriteMaterial({
    map: texture,
    transparent: true,
    opacity,
    depthWrite: false,
    depthTest: true,
    toneMapped: false,
    color,
  });
  const sprite = new THREE.Sprite(material);
  sprite.name = name;
  sprite.scale.setScalar(scale);
  sprite.renderOrder = 100;
  return sprite;
}

function createSkySphere() {
  const geometry = new THREE.SphereGeometry(
    CELESTIAL_CONFIG.skyRadius,
    64,
    64,
  );
  const material = new THREE.MeshBasicMaterial({
    color: 0xffffff,
    side: THREE.BackSide,
    transparent: CELESTIAL_CONFIG.skyOpacity < 1,
    opacity: CELESTIAL_CONFIG.skyOpacity,
    depthWrite: false,
    depthTest: false,
    fog: false,
  });

  const mesh = new THREE.Mesh(geometry, material);
  mesh.name = "celestial-sky-sphere";
  mesh.renderOrder = -1000;
  mesh.raycast = () => {};

  textureLoader.load(
    CELESTIAL_CONFIG.starMapUrl,
    (texture) => {
      configureTextureEncoding(texture);
      material.map = texture;
      material.needsUpdate = true;
    },
    undefined,
    () => {
      console.warn("Failed to load celestial star map texture");
    },
  );

  return mesh;
}

function geoVectorToWorldDirection(vector) {
  return new THREE.Vector3(vector.x, vector.z, vector.y).normalize();
}

function raDecToWorldDirection(raDeg, decDeg) {
  const raRad = THREE.MathUtils.degToRad(raDeg);
  const decRad = THREE.MathUtils.degToRad(decDeg);

  const x = Math.cos(decRad) * Math.cos(raRad);
  const y = Math.sin(decRad);
  const z = Math.cos(decRad) * Math.sin(raRad);

  return new THREE.Vector3(x, z, y).normalize();
}

function colorFromBvIndex(colorIndex) {
  if (colorIndex <= -0.2) return 0xa8c9ff;
  if (colorIndex <= 0.0) return 0xc8dcff;
  if (colorIndex <= 0.3) return 0xf4f7ff;
  if (colorIndex <= 0.7) return 0xfff4dc;
  if (colorIndex <= 1.1) return 0xffdfb0;
  if (colorIndex <= 1.5) return 0xffc47f;
  return 0xffa35e;
}

function scaleFromMagnitude(mag) {
  const brightness = THREE.MathUtils.clamp(
    1 - (mag - (-1.5)) / (CELESTIAL_CONFIG.brightStarMinMag - (-1.5)),
    0,
    1,
  );
  return THREE.MathUtils.lerp(
    CELESTIAL_CONFIG.brightStarMinScale,
    CELESTIAL_CONFIG.brightStarMaxScale,
    Math.pow(brightness, 0.72),
  );
}

function createBrightStarTexture() {
  return createDiscTexture([
    [0, "rgba(255,255,255,1)"],
    [0.18, "rgba(255,255,255,0.98)"],
    [0.46, "rgba(215,230,255,0.42)"],
    [1, "rgba(128,168,255,0)"],
  ], 128);
}

function createBrightStarsGroup() {
  const group = new THREE.Group();
  group.name = "bright-stars-group";
  group.visible = true;
  return group;
}

async function loadBrightStars() {
  try {
    const response = await fetch(CELESTIAL_CONFIG.brightStarsUrl);
    if (!response.ok) {
      throw new Error(`HTTP ${response.status}`);
    }

    const stars = await response.json();
    const filteredStars = stars
      .filter((star) => Number.isFinite(star?.raDeg) && Number.isFinite(star?.decDeg))
      .filter((star) => star.mag <= CELESTIAL_CONFIG.brightStarMinMag)
      .sort((a, b) => a.mag - b.mag)
      .slice(0, CELESTIAL_CONFIG.brightStarMaxCount);

    brightStarTexture = createBrightStarTexture();
    brightStarSprites = filteredStars.map((star) => {
      const sprite = createSprite({
        texture: brightStarTexture,
        scale: scaleFromMagnitude(star.mag),
        opacity: CELESTIAL_CONFIG.brightStarOpacity,
        name: `bright-star-${star.name}`,
        color: colorFromBvIndex(star.colorIndex ?? 0.4),
      });
      sprite.position
        .copy(raDecToWorldDirection(star.raDeg, star.decDeg))
        .multiplyScalar(CELESTIAL_CONFIG.brightStarDistance);
      sprite.userData.star = star;
      return sprite;
    });

    brightStarSprites.forEach((sprite) => brightStarsGroup?.add(sprite));
  } catch (error) {
    console.warn("Failed to load bright star layer", error);
  }
}

function computeBodyDirection(body, date) {
  const vector = Astronomy.GeoVector(body, date, false);
  return geoVectorToWorldDirection(vector);
}

function updateSpritePositions() {
  if (sunSprite) {
    sunSprite.position.copy(sunDirection).multiplyScalar(CELESTIAL_CONFIG.sunDistance);
  }
  if (sunHaloSprite) {
    sunHaloSprite.position.copy(sunDirection).multiplyScalar(CELESTIAL_CONFIG.sunDistance);
  }

  if (moonSprite) {
    moonSprite.position.copy(moonDirection).multiplyScalar(CELESTIAL_CONFIG.moonDistance);
  }
  if (moonHaloSprite) {
    moonHaloSprite.position.copy(moonDirection).multiplyScalar(CELESTIAL_CONFIG.moonDistance);
  }
}

function updateLighting() {
  const physicalSunDirection = getPhysicalSunDirection(
    new Date(lastUpdatedAt || Date.now()),
  );

  if (linkedSunLight) {
    linkedSunLight.color.setHex(CELESTIAL_CONFIG.sunLightColor);
    linkedSunLight.intensity = CELESTIAL_CONFIG.sunLightIntensity;
    linkedSunLight.position
      .copy(physicalSunDirection)
      .multiplyScalar(CELESTIAL_CONFIG.sunLightDistance);
  }

  if (linkedBackLight) {
    linkedBackLight.color.setHex(CELESTIAL_CONFIG.backLightColor);
    linkedBackLight.intensity = CELESTIAL_CONFIG.backLightIntensity;
    linkedBackLight.position
      .copy(physicalSunDirection)
      .multiplyScalar(-CELESTIAL_CONFIG.sunLightDistance * 0.7);
  }
}

function computeCelestialState(date = new Date()) {
  sunDirection = computeBodyDirection(Astronomy.Body.Sun, date);
  moonDirection = computeBodyDirection(Astronomy.Body.Moon, date);
  updateSpritePositions();
  updateLighting();
  lastUpdatedAt = date.getTime();
}

export function initCelestialLayer(
  scene,
  { camera = null, sunLight = null, backLight = null, earth = null } = {},
) {
  if (!scene || !CELESTIAL_CONFIG.enabled) return null;

  disposeCelestialLayer();

  linkedSunLight = sunLight;
  linkedBackLight = backLight;
  linkedEarth = earth;

  celestialRoot = new THREE.Group();
  celestialRoot.name = "celestial-root";
  celestialRoot.position.set(0, 0, 0);

  refreshCelestialOrientation();

  skySphere = createSkySphere();
  brightStarsGroup = createBrightStarsGroup();

  const sunTexture = createDiscTexture([
    [0, "rgba(255,255,255,1)"],
    [0.08, "rgba(255,251,242,1)"],
    [0.22, "rgba(255,242,205,0.98)"],
    [0.52, "rgba(255,211,117,0.9)"],
    [0.82, "rgba(255,162,54,0.18)"],
    [1, "rgba(255,120,32,0)"],
  ]);
  const sunHaloTexture = createDiscTexture([
    [0, "rgba(255,245,214,0.9)"],
    [0.2, "rgba(255,220,154,0.54)"],
    [0.52, "rgba(255,160,72,0.16)"],
    [1, "rgba(255,120,32,0)"],
  ], 512);
  const moonTexture = createDiscTexture([
    [0, "rgba(255,255,255,0.98)"],
    [0.42, "rgba(229,236,248,0.92)"],
    [0.76, "rgba(164,178,202,0.34)"],
    [1, "rgba(80,92,118,0)"],
  ]);
  const moonHaloTexture = createDiscTexture([
    [0, "rgba(226,235,250,0.42)"],
    [0.38, "rgba(188,203,230,0.16)"],
    [1, "rgba(120,136,170,0)"],
  ], 384);

  sunSprite = createSprite({
    texture: sunTexture,
    scale: CELESTIAL_CONFIG.sunScale,
    name: "sun-sprite",
  });
  sunHaloSprite = createSprite({
    texture: sunHaloTexture,
    scale: CELESTIAL_CONFIG.sunHaloScale,
    opacity: 0.78,
    name: "sun-halo-sprite",
  });
  moonSprite = createSprite({
    texture: moonTexture,
    scale: CELESTIAL_CONFIG.moonScale,
    opacity: 0.98,
    name: "moon-sprite",
  });
  moonHaloSprite = createSprite({
    texture: moonHaloTexture,
    scale: CELESTIAL_CONFIG.moonHaloScale,
    opacity: 0.52,
    name: "moon-halo-sprite",
  });

  sunHaloSprite.renderOrder = 98;
  moonHaloSprite.renderOrder = 98;

  celestialRoot.add(skySphere);
  celestialRoot.add(brightStarsGroup);
  celestialRoot.add(sunHaloSprite);
  celestialRoot.add(moonHaloSprite);
  celestialRoot.add(sunSprite);
  celestialRoot.add(moonSprite);
  scene.add(celestialRoot);

  computeCelestialState(new Date());
  loadBrightStars();

  return {
    root: celestialRoot,
    getSunDirection: () => sunDirection.clone(),
    getMoonDirection: () => moonDirection.clone(),
  };
}

export function updateCelestialLayer(date = new Date(), camera = null) {
  if (!celestialRoot) return;

  refreshCelestialView();

  const now = date.getTime();
  if (!lastUpdatedAt || now - lastUpdatedAt >= CELESTIAL_CONFIG.updateIntervalMs) {
    computeCelestialState(date);
  } else {
    updateLighting();
    updateSpritePositions();
  }
}

export function getSunDirection() {
  return getPhysicalSunDirection(new Date(lastUpdatedAt || Date.now()));
}

export function getMoonDirection() {
  return applyCelestialOrientation(moonDirection);
}

export function getCelestialDebugState() {
  return {
    orientationEulerRad: { ...runtimeOrientationEuler },
    followEarthRotation: { ...runtimeFollowConfig },
  };
}

export function setCelestialOrientation(nextEuler = {}) {
  runtimeOrientationEuler = {
    ...runtimeOrientationEuler,
    ...nextEuler,
  };
  refreshCelestialOrientation();
  updateLighting();
  return getCelestialDebugState();
}

export function setCelestialFollow(nextFollow = {}) {
  runtimeFollowConfig = {
    ...runtimeFollowConfig,
    ...nextFollow,
  };
  refreshCelestialView();
  updateLighting();
  return getCelestialDebugState();
}

export function disposeCelestialLayer() {
  if (celestialRoot?.parent) {
    celestialRoot.parent.remove(celestialRoot);
  }

  [skySphere, sunSprite, moonSprite, sunHaloSprite, moonHaloSprite, ...brightStarSprites].forEach((object) => {
    if (!object) return;
    if (object.geometry) object.geometry.dispose();
    if (object.material) {
      if (object.material.map) object.material.map.dispose?.();
      object.material.dispose();
    }
  });

  skySphere = null;
  brightStarsGroup = null;
  sunSprite = null;
  moonSprite = null;
  sunHaloSprite = null;
  moonHaloSprite = null;
  celestialRoot = null;
  brightStarSprites = [];
  brightStarTexture?.dispose?.();
  brightStarTexture = null;

  lastUpdatedAt = 0;
  linkedSunLight = null;
  linkedBackLight = null;
  linkedEarth = null;
  sunDirection.copy(defaultSunDirection);
  moonDirection.copy(defaultMoonDirection);
  runtimeOrientationEuler = {
    ...CELESTIAL_CONFIG.orientationEulerRad,
  };
  runtimeFollowConfig = {
    ...CELESTIAL_CONFIG.followEarthRotation,
  };
}