import { ShaderChunk, UniformsUtils, MeshDepthMaterial, RGBADepthPacking, MeshDistanceMaterial, ShaderLib, Matrix4, Vector3, Mesh, CylinderGeometry, Vector2, MeshStandardMaterial, DoubleSide } from 'three';

/**
 * Regular expression for matching the `void main() {` opener line in GLSL.
 * @type {RegExp}
 */
const voidMainRegExp = /\bvoid\s+main\s*\(\s*\)\s*{/g;

/**
 * Recursively expands all `#include <xyz>` statements within string of shader code.
 * Copied from three's WebGLProgram#parseIncludes for external use.
 *
 * @param {string} source - The GLSL source code to evaluate
 * @return {string} The GLSL code with all includes expanded
 */
function expandShaderIncludes( source ) {
  const pattern = /^[ \t]*#include +<([\w\d./]+)>/gm;
  function replace(match, include) {
    let chunk = ShaderChunk[include];
    return chunk ? expandShaderIncludes(chunk) : match
  }
  return source.replace( pattern, replace )
}

/*
 * This is a direct copy of MathUtils.generateUUID from Three.js, to preserve compatibility with three
 * versions before 0.113.0 as it was changed from Math to MathUtils in that version.
 * https://github.com/mrdoob/three.js/blob/dd8b5aa3b270c17096b90945cd2d6d1b13aaec53/src/math/MathUtils.js#L16
 */

const _lut = [];

for (let i = 0; i < 256; i++) {
  _lut[i] = (i < 16 ? '0' : '') + (i).toString(16);
}

function generateUUID() {

  // http://stackoverflow.com/questions/105034/how-to-create-a-guid-uuid-in-javascript/21963136#21963136

  const d0 = Math.random() * 0xffffffff | 0;
  const d1 = Math.random() * 0xffffffff | 0;
  const d2 = Math.random() * 0xffffffff | 0;
  const d3 = Math.random() * 0xffffffff | 0;
  const uuid = _lut[d0 & 0xff] + _lut[d0 >> 8 & 0xff] + _lut[d0 >> 16 & 0xff] + _lut[d0 >> 24 & 0xff] + '-' +
    _lut[d1 & 0xff] + _lut[d1 >> 8 & 0xff] + '-' + _lut[d1 >> 16 & 0x0f | 0x40] + _lut[d1 >> 24 & 0xff] + '-' +
    _lut[d2 & 0x3f | 0x80] + _lut[d2 >> 8 & 0xff] + '-' + _lut[d2 >> 16 & 0xff] + _lut[d2 >> 24 & 0xff] +
    _lut[d3 & 0xff] + _lut[d3 >> 8 & 0xff] + _lut[d3 >> 16 & 0xff] + _lut[d3 >> 24 & 0xff];

  // .toUpperCase() here flattens concatenated strings to save heap memory space.
  return uuid.toUpperCase()

}

// Local assign polyfill to avoid importing troika-core
const assign = Object.assign || function(/*target, ...sources*/) {
  let target = arguments[0];
  for (let i = 1, len = arguments.length; i < len; i++) {
    let source = arguments[i];
    if (source) {
      for (let prop in source) {
        if (Object.prototype.hasOwnProperty.call(source, prop)) {
          target[prop] = source[prop];
        }
      }
    }
  }
  return target
};


const epoch = Date.now();
const CONSTRUCTOR_CACHE = new WeakMap();
const SHADER_UPGRADE_CACHE = new Map();

// Material ids must be integers, but we can't access the increment from Three's `Material` module,
// so let's choose a sufficiently large starting value that should theoretically never collide.
let materialInstanceId = 1e10;

/**
 * A utility for creating a custom shader material derived from another material's
 * shaders. This allows you to inject custom shader logic and transforms into the
 * builtin ThreeJS materials without having to recreate them from scratch.
 *
 * @param {THREE.Material} baseMaterial - the original material to derive from
 *
 * @param {Object} options - How the base material should be modified.
 * @param {Object=} options.defines - Custom `defines` for the material
 * @param {Object=} options.extensions - Custom `extensions` for the material, e.g. `{derivatives: true}`
 * @param {Object=} options.uniforms - Custom `uniforms` for use in the modified shader. These can
 *        be accessed and manipulated via the resulting material's `uniforms` property, just like
 *        in a ShaderMaterial. You do not need to repeat the base material's own uniforms here.
 * @param {String=} options.timeUniform - If specified, a uniform of this name will be injected into
 *        both shaders, and it will automatically be updated on each render frame with a number of
 *        elapsed milliseconds. The "zero" epoch time is not significant so don't rely on this as a
 *        true calendar time.
 * @param {String=} options.vertexDefs - Custom GLSL code to inject into the vertex shader's top-level
 *        definitions, above the `void main()` function.
 * @param {String=} options.vertexMainIntro - Custom GLSL code to inject at the top of the vertex
 *        shader's `void main` function.
 * @param {String=} options.vertexMainOutro - Custom GLSL code to inject at the end of the vertex
 *        shader's `void main` function.
 * @param {String=} options.vertexTransform - Custom GLSL code to manipulate the `position`, `normal`,
 *        and/or `uv` vertex attributes. This code will be wrapped within a standalone function with
 *        those attributes exposed by their normal names as read/write values.
 * @param {String=} options.fragmentDefs - Custom GLSL code to inject into the fragment shader's top-level
 *        definitions, above the `void main()` function.
 * @param {String=} options.fragmentMainIntro - Custom GLSL code to inject at the top of the fragment
 *        shader's `void main` function.
 * @param {String=} options.fragmentMainOutro - Custom GLSL code to inject at the end of the fragment
 *        shader's `void main` function. You can manipulate `gl_FragColor` here but keep in mind it goes
 *        after any of ThreeJS's color postprocessing shader chunks (tonemapping, fog, etc.), so if you
 *        want those to apply to your changes use `fragmentColorTransform` instead.
 * @param {String=} options.fragmentColorTransform - Custom GLSL code to manipulate the `gl_FragColor`
 *        output value. Will be injected near the end of the `void main` function, but before any
 *        of ThreeJS's color postprocessing shader chunks (tonemapping, fog, etc.), and before the
 *        `fragmentMainOutro`.
 * @param {function({fragmentShader: string, vertexShader:string}):
 *        {fragmentShader: string, vertexShader:string}} options.customRewriter - A function
 *        for performing custom rewrites of the full shader code. Useful if you need to do something
 *        special that's not covered by the other builtin options. This function will be executed before
 *        any other transforms are applied.
 * @param {boolean=} options.chained - Set to `true` to prototype-chain the derived material to the base
 *        material, rather than the default behavior of copying it. This allows the derived material to
 *        automatically pick up changes made to the base material and its properties. This can be useful
 *        where the derived material is hidden from the user as an implementation detail, allowing them
 *        to work with the original material like normal. But it can result in unexpected behavior if not
 *        handled carefully.
 *
 * @return {THREE.Material}
 *
 * The returned material will also have two new methods, `getDepthMaterial()` and `getDistanceMaterial()`,
 * which can be called to get a variant of the derived material for use in shadow casting. If the
 * target mesh is expected to cast shadows, then you can assign these to the mesh's `customDepthMaterial`
 * (for directional and spot lights) and/or `customDistanceMaterial` (for point lights) properties to
 * allow the cast shadow to honor your derived shader's vertex transforms and discarded fragments. These
 * will also set a custom `#define IS_DEPTH_MATERIAL` or `#define IS_DISTANCE_MATERIAL` that you can look
 * for in your derived shaders with `#ifdef` to customize their behavior for the depth or distance
 * scenarios, e.g. skipping antialiasing or expensive shader logic.
 */
function createDerivedMaterial(baseMaterial, options) {
  // Generate a key that is unique to the content of these `options`. We'll use this
  // throughout for caching and for generating the upgraded shader code. This increases
  // the likelihood that the resulting shaders will line up across multiple calls so
  // their GL programs can be shared and cached.
  const optionsKey = getKeyForOptions(options);

  // First check to see if we've already derived from this baseMaterial using this
  // unique set of options, and if so reuse the constructor to avoid some allocations.
  let ctorsByDerivation = CONSTRUCTOR_CACHE.get(baseMaterial);
  if (!ctorsByDerivation) {
    CONSTRUCTOR_CACHE.set(baseMaterial, (ctorsByDerivation = Object.create(null)));
  }
  if (ctorsByDerivation[optionsKey]) {
    return new ctorsByDerivation[optionsKey]()
  }

  const privateBeforeCompileProp = `_onBeforeCompile${optionsKey}`;

  // Private onBeforeCompile handler that injects the modified shaders and uniforms when
  // the renderer switches to this material's program
  const onBeforeCompile = function (shaderInfo, renderer) {
    baseMaterial.onBeforeCompile.call(this, shaderInfo, renderer);

    // Upgrade the shaders, caching the result by incoming source code
    const cacheKey = this.customProgramCacheKey() + '|' + shaderInfo.vertexShader + '|' + shaderInfo.fragmentShader;
    let upgradedShaders = SHADER_UPGRADE_CACHE[cacheKey];
    if (!upgradedShaders) {
      const upgraded = upgradeShaders(this, shaderInfo, options, optionsKey);
      upgradedShaders = SHADER_UPGRADE_CACHE[cacheKey] = upgraded;
    }

    // Inject upgraded shaders and uniforms into the program
    shaderInfo.vertexShader = upgradedShaders.vertexShader;
    shaderInfo.fragmentShader = upgradedShaders.fragmentShader;
    assign(shaderInfo.uniforms, this.uniforms);

    // Inject auto-updating time uniform if requested
    if (options.timeUniform) {
      shaderInfo.uniforms[options.timeUniform] = {
        get value() {return Date.now() - epoch}
      };
    }

    // Users can still add their own handlers on top of ours
    if (this[privateBeforeCompileProp]) {
      this[privateBeforeCompileProp](shaderInfo);
    }
  };

  const DerivedMaterial = function DerivedMaterial() {
    return derive(options.chained ? baseMaterial : baseMaterial.clone())
  };

  const derive = function(base) {
    // Prototype chain to the base material
    const derived = Object.create(base, descriptor);

    // Store the baseMaterial for reference; this is always the original even when cloning
    Object.defineProperty(derived, 'baseMaterial', { value: baseMaterial });

    // Needs its own ids
    Object.defineProperty(derived, 'id', { value: materialInstanceId++ });
    derived.uuid = generateUUID();

    // Merge uniforms, defines, and extensions
    derived.uniforms = assign({}, base.uniforms, options.uniforms);
    derived.defines = assign({}, base.defines, options.defines);
    derived.defines[`TROIKA_DERIVED_MATERIAL_${optionsKey}`] = ''; //force a program change from the base material
    derived.extensions = assign({}, base.extensions, options.extensions);

    // Don't inherit EventDispatcher listeners
    derived._listeners = undefined;

    return derived
  };

  const descriptor = {
    constructor: {value: DerivedMaterial},
    isDerivedMaterial: {value: true},

    type: {
      get: () => baseMaterial.type,
      set: (value) => {baseMaterial.type = value;}
    },

    isDerivedFrom: {
      writable: true,
      configurable: true,
      value: function (testMaterial) {
        const base = this.baseMaterial;
        return testMaterial === base || (base.isDerivedMaterial && base.isDerivedFrom(testMaterial)) || false
      }
    },

    customProgramCacheKey: {
      writable: true,
      configurable: true,
      value: function () {
        return baseMaterial.customProgramCacheKey() + '|' + optionsKey
      }
    },

    onBeforeCompile: {
      get() {
        return onBeforeCompile
      },
      set(fn) {
        this[privateBeforeCompileProp] = fn;
      }
    },

    copy: {
      writable: true,
      configurable: true,
      value: function (source) {
        baseMaterial.copy.call(this, source);
        if (!baseMaterial.isShaderMaterial && !baseMaterial.isDerivedMaterial) {
          assign(this.extensions, source.extensions);
          assign(this.defines, source.defines);
          assign(this.uniforms, UniformsUtils.clone(source.uniforms));
        }
        return this
      }
    },

    clone: {
      writable: true,
      configurable: true,
      value: function () {
        const newBase = new baseMaterial.constructor();
        return derive(newBase).copy(this)
      }
    },

    /**
     * Utility to get a MeshDepthMaterial that will honor this derived material's vertex
     * transformations and discarded fragments.
     */
    getDepthMaterial: {
      writable: true,
      configurable: true,
      value: function() {
        let depthMaterial = this._depthMaterial;
        if (!depthMaterial) {
          depthMaterial = this._depthMaterial = createDerivedMaterial(
            baseMaterial.isDerivedMaterial
              ? baseMaterial.getDepthMaterial()
              : new MeshDepthMaterial({ depthPacking: RGBADepthPacking }),
            options
          );
          depthMaterial.defines.IS_DEPTH_MATERIAL = '';
          depthMaterial.uniforms = this.uniforms; //automatically recieve same uniform values
        }
        return depthMaterial
      }
    },

    /**
     * Utility to get a MeshDistanceMaterial that will honor this derived material's vertex
     * transformations and discarded fragments.
     */
    getDistanceMaterial: {
      writable: true,
      configurable: true,
      value: function() {
        let distanceMaterial = this._distanceMaterial;
        if (!distanceMaterial) {
          distanceMaterial = this._distanceMaterial = createDerivedMaterial(
            baseMaterial.isDerivedMaterial
              ? baseMaterial.getDistanceMaterial()
              : new MeshDistanceMaterial(),
            options
          );
          distanceMaterial.defines.IS_DISTANCE_MATERIAL = '';
          distanceMaterial.uniforms = this.uniforms; //automatically recieve same uniform values
        }
        return distanceMaterial
      }
    },

    dispose: {
      writable: true,
      configurable: true,
      value() {
        const {_depthMaterial, _distanceMaterial} = this;
        if (_depthMaterial) _depthMaterial.dispose();
        if (_distanceMaterial) _distanceMaterial.dispose();
        baseMaterial.dispose.call(this);
      }
    }
  };

  ctorsByDerivation[optionsKey] = DerivedMaterial;
  return new DerivedMaterial()
}


function upgradeShaders(material, {vertexShader, fragmentShader}, options, key) {
  let {
    vertexDefs,
    vertexMainIntro,
    vertexMainOutro,
    vertexTransform,
    fragmentDefs,
    fragmentMainIntro,
    fragmentMainOutro,
    fragmentColorTransform,
    customRewriter,
    timeUniform
  } = options;

  vertexDefs = vertexDefs || '';
  vertexMainIntro = vertexMainIntro || '';
  vertexMainOutro = vertexMainOutro || '';
  fragmentDefs = fragmentDefs || '';
  fragmentMainIntro = fragmentMainIntro || '';
  fragmentMainOutro = fragmentMainOutro || '';

  // Expand includes if needed
  if (vertexTransform || customRewriter) {
    vertexShader = expandShaderIncludes(vertexShader);
  }
  if (fragmentColorTransform || customRewriter) {
    // We need to be able to find postprocessing chunks after include expansion in order to
    // put them after the fragmentColorTransform, so mark them with comments first. Even if
    // this particular derivation doesn't have a fragmentColorTransform, other derivations may,
    // so we still mark them.
    fragmentShader = fragmentShader.replace(
      /^[ \t]*#include <((?:tonemapping|encodings|colorspace|fog|premultiplied_alpha|dithering)_fragment)>/gm,
      '\n//!BEGIN_POST_CHUNK $1\n$&\n//!END_POST_CHUNK\n'
    );
    fragmentShader = expandShaderIncludes(fragmentShader);
  }

  // Apply custom rewriter function
  if (customRewriter) {
    let res = customRewriter({vertexShader, fragmentShader});
    vertexShader = res.vertexShader;
    fragmentShader = res.fragmentShader;
  }

  // The fragmentColorTransform needs to go before any postprocessing chunks, so extract
  // those and re-insert them into the outro in the correct place:
  if (fragmentColorTransform) {
    let postChunks = [];
    fragmentShader = fragmentShader.replace(
      /^\/\/!BEGIN_POST_CHUNK[^]+?^\/\/!END_POST_CHUNK/gm, // [^]+? = non-greedy match of any chars including newlines
      match => {
        postChunks.push(match);
        return ''
      }
    );
    fragmentMainOutro = `${fragmentColorTransform}\n${postChunks.join('\n')}\n${fragmentMainOutro}`;
  }

  // Inject auto-updating time uniform if requested
  if (timeUniform) {
    const code = `\nuniform float ${timeUniform};\n`;
    vertexDefs = code + vertexDefs;
    fragmentDefs = code + fragmentDefs;
  }

  // Inject a function for the vertexTransform and rename all usages of position/normal/uv
  if (vertexTransform) {
    // Hoist these defs to the very top so they work in other function defs
    vertexShader = `vec3 troika_position_${key};
vec3 troika_normal_${key};
vec2 troika_uv_${key};
${vertexShader}
`;
    vertexDefs = `${vertexDefs}
void troikaVertexTransform${key}(inout vec3 position, inout vec3 normal, inout vec2 uv) {
  ${vertexTransform}
}
`;
    vertexMainIntro = `
troika_position_${key} = vec3(position);
troika_normal_${key} = vec3(normal);
troika_uv_${key} = vec2(uv);
troikaVertexTransform${key}(troika_position_${key}, troika_normal_${key}, troika_uv_${key});
${vertexMainIntro}
`;
    vertexShader = vertexShader.replace(/\b(position|normal|uv)\b/g, (match, match1, index, fullStr) => {
      return /\battribute\s+vec[23]\s+$/.test(fullStr.substr(0, index)) ? match1 : `troika_${match1}_${key}`
    });

    // Three r152 introduced the MAP_UV token, replace it too if it's pointing to the main 'uv'
    // Perhaps the other textures too going forward?
    if (!(material.map && material.map.channel > 0)) {
      vertexShader = vertexShader.replace(/\bMAP_UV\b/g, `troika_uv_${key}`);
    }
  }

  // Inject defs and intro/outro snippets
  vertexShader = injectIntoShaderCode(vertexShader, key, vertexDefs, vertexMainIntro, vertexMainOutro);
  fragmentShader = injectIntoShaderCode(fragmentShader, key, fragmentDefs, fragmentMainIntro, fragmentMainOutro);

  return {
    vertexShader,
    fragmentShader
  }
}

function injectIntoShaderCode(shaderCode, id, defs, intro, outro) {
  if (intro || outro || defs) {
    shaderCode = shaderCode.replace(voidMainRegExp, `
${defs}
void troikaOrigMain${id}() {`
    );
    shaderCode += `
void main() {
  ${intro}
  troikaOrigMain${id}();
  ${outro}
}`;
  }
  return shaderCode
}


function optionsJsonReplacer(key, value) {
  return key === 'uniforms' ? undefined : typeof value === 'function' ? value.toString() : value
}

let _idCtr = 0;
const optionsHashesToIds = new Map();
function getKeyForOptions(options) {
  const optionsHash = JSON.stringify(options, optionsJsonReplacer);
  let id = optionsHashesToIds.get(optionsHash);
  if (id == null) {
    optionsHashesToIds.set(optionsHash, (id = ++_idCtr));
  }
  return id
}

// Copied from threejs WebGLPrograms.js so we can resolve builtin materials to their shaders
// TODO how can we keep this from getting stale?
const MATERIAL_TYPES_TO_SHADERS = {
  MeshDepthMaterial: 'depth',
  MeshDistanceMaterial: 'distanceRGBA',
  MeshNormalMaterial: 'normal',
  MeshBasicMaterial: 'basic',
  MeshLambertMaterial: 'lambert',
  MeshPhongMaterial: 'phong',
  MeshToonMaterial: 'toon',
  MeshStandardMaterial: 'physical',
  MeshPhysicalMaterial: 'physical',
  MeshMatcapMaterial: 'matcap',
  LineBasicMaterial: 'basic',
  LineDashedMaterial: 'dashed',
  PointsMaterial: 'points',
  ShadowMaterial: 'shadow',
  SpriteMaterial: 'sprite'
};

/**
 * Given a Three.js `Material` instance, find the shaders/uniforms that will be
 * used to render that material.
 *
 * @param material - the Material instance
 * @return {object} - the material's shader info: `{uniforms:{}, fragmentShader:'', vertexShader:''}`
 */
function getShadersForMaterial(material) {
  let builtinType = MATERIAL_TYPES_TO_SHADERS[material.type];
  return builtinType ? ShaderLib[builtinType] : material //TODO fallback for unknown type?
}

/**
 * Find all uniforms and their types within a shader code string.
 *
 * @param {string} shader - The shader code to parse
 * @return {object} mapping of uniform names to their glsl type
 */
function getShaderUniformTypes(shader) {
  let uniformRE = /\buniform\s+(int|float|vec[234]|mat[34])\s+([A-Za-z_][\w]*)/g;
  let uniforms = Object.create(null);
  let match;
  while ((match = uniformRE.exec(shader)) !== null) {
    uniforms[match[2]] = match[1];
  }
  return uniforms
}

/**
 * Helper for smoothing out the `m.getInverse(x)` --> `m.copy(x).invert()` conversion
 * that happened in ThreeJS r123.
 * @param {Matrix4} srcMatrix
 * @param {Matrix4} [tgtMatrix]
 */
function invertMatrix4(srcMatrix, tgtMatrix = new Matrix4()) {
  if (typeof tgtMatrix.invert === 'function') {
    tgtMatrix.copy(srcMatrix).invert();
  } else {
    tgtMatrix.getInverse(srcMatrix);
  }
  return tgtMatrix
}

/*
Input geometry is a cylinder with r=1, height in y dimension from 0 to 1,
divided into a reasonable number of height segments.
*/

const vertexDefs = `
uniform vec3 pointA;
uniform vec3 controlA;
uniform vec3 controlB;
uniform vec3 pointB;
uniform float radius;
varying float bezierT;

vec3 cubicBezier(vec3 p1, vec3 c1, vec3 c2, vec3 p2, float t) {
  float t2 = 1.0 - t;
  float b0 = t2 * t2 * t2;
  float b1 = 3.0 * t * t2 * t2;
  float b2 = 3.0 * t * t * t2;
  float b3 = t * t * t;
  return b0 * p1 + b1 * c1 + b2 * c2 + b3 * p2;
}

vec3 cubicBezierDerivative(vec3 p1, vec3 c1, vec3 c2, vec3 p2, float t) {
  float t2 = 1.0 - t;
  return -3.0 * p1 * t2 * t2 +
    c1 * (3.0 * t2 * t2 - 6.0 * t2 * t) +
    c2 * (6.0 * t2 * t - 3.0 * t * t) +
    3.0 * p2 * t * t;
}
`;

const vertexTransform = `
float t = position.y;
bezierT = t;
vec3 bezierCenterPos = cubicBezier(pointA, controlA, controlB, pointB, t);
vec3 bezierDir = normalize(cubicBezierDerivative(pointA, controlA, controlB, pointB, t));

// Make "sideways" always perpendicular to the camera ray; this ensures that any twists
// in the cylinder occur where you won't see them: 
vec3 viewDirection = normalMatrix * vec3(0.0, 0.0, 1.0);
if (bezierDir == viewDirection) {
  bezierDir = normalize(cubicBezierDerivative(pointA, controlA, controlB, pointB, t == 1.0 ? t - 0.0001 : t + 0.0001));
}
vec3 sideways = normalize(cross(bezierDir, viewDirection));
vec3 upish = normalize(cross(sideways, bezierDir));

// Build a matrix for transforming this disc in the cylinder:
mat4 discTx;
discTx[0].xyz = sideways * radius;
discTx[1].xyz = bezierDir * radius;
discTx[2].xyz = upish * radius;
discTx[3].xyz = bezierCenterPos;
discTx[3][3] = 1.0;

// Apply transform, ignoring original y
position = (discTx * vec4(position.x, 0.0, position.z, 1.0)).xyz;
normal = normalize(mat3(discTx) * normal);
`;

const fragmentDefs = `
uniform vec3 dashing;
varying float bezierT;
`;

const fragmentMainIntro = `
if (dashing.x + dashing.y > 0.0) {
  float dashFrac = mod(bezierT - dashing.z, dashing.x + dashing.y);
  if (dashFrac > dashing.x) {
    discard;
  }
}
`;

// Debugging: separate color for each of the 6 sides:
// const fragmentColorTransform = `
// float sideNum = floor(vUV.x * 6.0);
// vec3 mixColor = sideNum < 1.0 ? vec3(1.0, 0.0, 0.0) :
//   sideNum < 2.0 ? vec3(0.0, 1.0, 1.0) :
//   sideNum < 3.0 ? vec3(1.0, 1.0, 0.0) :
//   sideNum < 4.0 ? vec3(0.0, 0.0, 1.0) :
//   sideNum < 5.0 ? vec3(0.0, 1.0, 0.0) :
//   vec3(1.0, 0.0, 1.0);
// gl_FragColor.xyz = mix(gl_FragColor.xyz, mixColor, 0.5);
// `



function createBezierMeshMaterial(baseMaterial) {
  return createDerivedMaterial(
    baseMaterial,
    {
      chained: true,
      uniforms: {
        pointA: {value: new Vector3()},
        controlA: {value: new Vector3()},
        controlB: {value: new Vector3()},
        pointB: {value: new Vector3()},
        radius: {value: 0.01},
        dashing: {value: new Vector3()} //on, off, offset
      },
      vertexDefs,
      vertexTransform,
      fragmentDefs,
      fragmentMainIntro
    }
  )
}

let geometry = null;

const defaultBaseMaterial = /*#__PURE__*/new MeshStandardMaterial({color: 0xffffff, side: DoubleSide});


/**
 * A ThreeJS `Mesh` that bends a tube shape along a 3D cubic bezier path. The bending is done
 * by deforming a straight cylindrical geometry in the vertex shader based on a set of four
 * control point uniforms. It patches the necessary GLSL into the mesh's assigned `material`
 * automatically.
 *
 * The cubiz bezier path is determined by its four `Vector3` properties:
 * - `pointA`
 * - `controlA`
 * - `controlB`
 * - `pointB`
 *
 * The tube's radius is controlled by its `radius` property, which defaults to `0.01`.
 *
 * You can also give the tube a dashed appearance with two properties:
 *
 * - `dashArray` - an array of two numbers, defining the length of "on" and "off" parts of
 *   the dash. Each is a 0-1 ratio of the entire path's length. (Actually this is the `t` length
 *   used as input to the cubic bezier function, not its visible length.)
 * - `dashOffset` - offset of where the dash starts. You can animate this to make the dashes move.
 *
 * Note that the dashes will appear like a hollow tube, not solid. This will be more apparent on
 * thicker tubes.
 *
 * TODO: proper geometry bounding sphere and raycasting
 * TODO: allow control of the geometry's segment counts
 */
class BezierMesh extends Mesh {
  static getGeometry() {
    return geometry || (geometry =
      new CylinderGeometry(1, 1, 1, 6, 64).translate(0, 0.5, 0)
    )
  }

  constructor() {
    super(
      BezierMesh.getGeometry(),
      defaultBaseMaterial
    );

    this.pointA = new Vector3();
    this.controlA = new Vector3();
    this.controlB = new Vector3();
    this.pointB = new Vector3();
    this.radius = 0.01;
    this.dashArray = new Vector2();
    this.dashOffset = 0;

    // TODO - disabling frustum culling until I figure out how to customize the
    //  geometry's bounding sphere that gets used
    this.frustumCulled = false;
  }

  // Handler for automatically wrapping the base material with our upgrades. We do the wrapping
  // lazily on _read_ rather than write to avoid unnecessary wrapping on transient values.
  get material() {
    let derivedMaterial = this._derivedMaterial;
    const baseMaterial = this._baseMaterial || this._defaultMaterial || (this._defaultMaterial = defaultBaseMaterial.clone());
    if (!derivedMaterial || derivedMaterial.baseMaterial !== baseMaterial) {
      derivedMaterial = this._derivedMaterial = createBezierMeshMaterial(baseMaterial);
      // dispose the derived material when its base material is disposed:
      baseMaterial.addEventListener('dispose', function onDispose() {
        baseMaterial.removeEventListener('dispose', onDispose);
        derivedMaterial.dispose();
      });
    }
    return derivedMaterial
  }
  set material(baseMaterial) {
    this._baseMaterial = baseMaterial;
  }

  // Create and update material for shadows upon request:
  get customDepthMaterial() {
    return this.material.getDepthMaterial()
  }
  set customDepthMaterial(m) {
    // future: let the user override with their own?
  }
  get customDistanceMaterial() {
    return this.material.getDistanceMaterial()
  }
  set customDistanceMaterial(m) {
    // future: let the user override with their own?
  }

  onBeforeRender() {
    const {uniforms} = this.material;
    const {pointA, controlA, controlB, pointB, radius, dashArray, dashOffset} = this;
    uniforms.pointA.value.copy(pointA);
    uniforms.controlA.value.copy(controlA);
    uniforms.controlB.value.copy(controlB);
    uniforms.pointB.value.copy(pointB);
    uniforms.radius.value = radius;
    uniforms.dashing.value.set(dashArray.x, dashArray.y, dashOffset || 0);
  }

  raycast(/*raycaster, intersects*/) {
    // TODO - just fail for now
  }
}

export { BezierMesh, createDerivedMaterial, expandShaderIncludes, getShaderUniformTypes, getShadersForMaterial, invertMatrix4, voidMainRegExp };