import * as Cesium from 'cesium'

//片元着色器，直接从源码复制
const SkyBoxFS = `uniform samplerCube u_cubeMap;
    in vec3 v_texCoord;
    out vec4 fragColor;
    void main(){
        vec4 color = texture(u_cubeMap, normalize(v_texCoord));
        fragColor = vec4(czm_gammaCorrect(color).rgb, czm_morphTime);
    }
`;

//顶点着色器有修改，主要是乘了一个旋转矩阵
const SkyBoxVS = `
    in vec3 position;
    out vec3 v_texCoord;
    uniform mat3 u_rotateMatrix;
    void main(){
        vec3 p = czm_viewRotation * u_rotateMatrix * (czm_temeToPseudoFixed * (czm_entireFrustum.y * position));
        gl_Position = czm_projection * vec4(p, 1.0);
        v_texCoord = position.xyz;
    }
`;

const BoxGeometry = Cesium.BoxGeometry;
const Cartesian3 = Cesium.Cartesian3;
const defaultValue = Cesium.defaultValue;
const defined = Cesium.defined;
const destroyObject = Cesium.destroyObject;
const DeveloperError = Cesium.DeveloperError;
const GeometryPipeline = Cesium.GeometryPipeline;
const Matrix3 = Cesium.Matrix3;
const Matrix4 = Cesium.Matrix4;
const Transforms = Cesium.Transforms;
const VertexFormat = Cesium.VertexFormat;
const BufferUsage = Cesium.BufferUsage;
const CubeMap = Cesium.CubeMap;
const DrawCommand = Cesium.DrawCommand;
const loadCubeMap = Cesium.loadCubeMap;
const RenderState = Cesium.RenderState;
const VertexArray = Cesium.VertexArray;
const BlendingState = Cesium.BlendingState;
const SceneMode = Cesium.SceneMode;
const ShaderProgram = Cesium.ShaderProgram;
const ShaderSource = Cesium.ShaderSource;

const skyboxMatrix3 = new Matrix3();

// 存储默认天空盒
let defaultSkybox = null
// 存储当前天空盒
let currentSkybox = null

const checkSkyBoxEventHandler = (scene) => {
  let position = scene.camera.position;
  let cameraHeight = Cesium.Cartographic.fromCartesian(position).height;
  if (cameraHeight < 240000) {
    scene.skyBox = currentSkybox;
    scene.skyAtmosphere.show = false;
  } else {
    scene.skyBox = defaultSkybox;
    scene.skyAtmosphere.show = true;
  }
}


/**
* 为了兼容高版本的Cesium，因为新版cesium中getRotation被移除
*/
if (!Cesium.defined(Cesium.Matrix4.getRotation)) {
  Cesium.Matrix4.getRotation = Cesium.Matrix4.getMatrix3
}

/**
* 近景天空盒
* @type Object
* @default undefined
*/
export default class SkyBoxOnGround {
  constructor(options) {
    this.sources = options.sources;
    this._sources = undefined;
    /**
     * Determines if the sky box will be shown.
     *
     * @type {Boolean}
     * @default true
     */
    this.show = defaultValue(options.show, true);

    this._command = new DrawCommand({
      modelMatrix: Matrix4.clone(Matrix4.IDENTITY),
      owner: this
    });
    this._cubeMap = undefined;

    this._attributeLocations = undefined;
    this._useHdr = undefined;

    // 将生成的天空盒传出保存
    currentSkybox = this;
  }

  update(frameState, useHdr) {
    const that = this;

    if (!this.show) {
      return undefined;
    }

    if ((frameState.mode !== SceneMode.SCENE3D) && (frameState.mode !== SceneMode.MORPHING)) {
      return undefined;
    }

    if (!frameState.passes.render) {
      return undefined;
    }

    const context = frameState.context;

    if (this._sources !== this.sources) {
      this._sources = this.sources;
      const sources = this.sources;

      if ((!defined(sources.positiveX)) || (!defined(sources.negativeX)) || (!defined(sources.positiveY)) || (!defined(sources.negativeY)) || (!defined(sources.positiveZ)) || (!defined(sources.negativeZ))) {
        throw new DeveloperError('this.sources is required and must have positiveX, negativeX, positiveY, negativeY, positiveZ, and negativeZ properties.');
      }

      if ((typeof sources.positiveX !== typeof sources.negativeX) || (typeof sources.positiveX !== typeof sources.positiveY) || (typeof sources.positiveX !== typeof sources.negativeY) || (typeof sources.positiveX !== typeof sources.positiveZ) || (typeof sources.positiveX !== typeof sources.negativeZ)) {
        throw new DeveloperError('this.sources properties must all be the same type.');
      }

      if (typeof sources.positiveX === 'string') {
        loadCubeMap(context, this._sources).then(function (cubeMap) {
          that._cubeMap = that._cubeMap && that._cubeMap.destroy();
          that._cubeMap = cubeMap;
        });
      } else {
        this._cubeMap = this._cubeMap && this._cubeMap.destroy();
        this._cubeMap = new CubeMap({
          context: context,
          source: sources
        });
      }
    }

    const command = this._command;

    command.modelMatrix = Transforms.eastNorthUpToFixedFrame(frameState.camera._positionWC);

    if (!defined(command.vertexArray)) {
      command.uniformMap = {
        u_cubeMap: function () {
          return that._cubeMap;
        },
        u_rotateMatrix: function () {
          return Matrix4.getRotation(command.modelMatrix, skyboxMatrix3);
        },
      };

      const geometry = BoxGeometry.createGeometry(BoxGeometry.fromDimensions({
        dimensions: new Cartesian3(2.0, 2.0, 2.0),
        vertexFormat: VertexFormat.POSITION_ONLY
      }));
      const attributeLocations = this._attributeLocations = GeometryPipeline.createAttributeLocations(geometry);

      command.vertexArray = VertexArray.fromGeometry({
        context: context,
        geometry: geometry,
        attributeLocations: attributeLocations,
        bufferUsage: BufferUsage._DRAW
      });

      command.renderState = RenderState.fromCache({
        blending: BlendingState.ALPHA_BLEND
      });
    }

    if (!defined(command.shaderProgram) || this._useHdr !== useHdr) {
      const fs = new ShaderSource({
        defines: [useHdr ? 'HDR' : ''],
        sources: [SkyBoxFS]
      });
      command.shaderProgram = ShaderProgram.fromCache({
        context: context,
        vertexShaderSource: SkyBoxVS,
        fragmentShaderSource: fs,
        attributeLocations: this._attributeLocations
      });
      this._useHdr = useHdr;
    }

    if (!defined(this._cubeMap)) {
      return undefined;
    }
    return command;
  }

  setSkyBox(viewer) {

    // 自带的默认天空盒
    defaultSkybox = viewer.scene.skyBox;

    // 渲染前监听并判断相机位置
    viewer.scene.preUpdate.addEventListener(checkSkyBoxEventHandler);
  }

  removeSkyBox(viewer) {
    if(!viewer || !defaultSkybox) return;

    viewer.scene.preUpdate.removeEventListener(checkSkyBoxEventHandler);
    viewer.scene.skyBox = defaultSkybox;
    viewer.scene.skyAtmosphere.show = true;
    defaultSkybox = null;
  }

  isDestroyed() {
    return false
  }

  destroy() {
    defaultSkybox = null;
    currentSkybox = null;
    const command = this._command;
    command.vertexArray = command.vertexArray && command.vertexArray.destroy();
    command.shaderProgram = command.shaderProgram && command.shaderProgram.destroy();
    this._cubeMap = this._cubeMap && this._cubeMap.destroy();
    return destroyObject(this);
  }
}