/* 引入Cesium */
// import * as Cesium from 'Cesium';

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;

//片元着色器，直接从源码复制
const SkyBoxFS =
	"uniform samplerCube u_cubeMap;\n\
  varying vec3 v_texCoord;\n\
  void main()\n\
  {\n\
  vec4 color = textureCube(u_cubeMap, normalize(v_texCoord));\n\
  gl_FragColor = vec4(czm_gammaCorrect(color).rgb, czm_morphTime);\n\
  }\n\
  ";

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

/**
 * 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
 * @ignore 忽略注释，注释不生成Doc
 */
class SkyBoxOnGround {

	/**
	 * 近景天空盒 初始化
	 * @ignore
	 */
	constructor(options) {

		/**
		 * 近景天空盒
		 * @type Object
		 * @default undefined
		 */
		this.sources = options.sources;
		this._sources = undefined;

		/**
		 * Determines if the sky box will be shown.
		 * @ignore 忽略注释，注释不生成Doc
		 * @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;
	}
}

const skyboxMatrix3 = new Matrix3();
SkyBoxOnGround.prototype.update = function(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") {
			// Given urls for cube-map images.  Load them.
			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;
};
SkyBoxOnGround.prototype.isDestroyed = function() {
	return false;
};
SkyBoxOnGround.prototype.destroy = function() {
	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);
};

export default SkyBoxOnGround;