text: import * as util from'./util';
  import define from './define';
  import Collection from './collection';
  import Core from './core';
  import incExts from './extensions';
  import * as is from './is';
  import Emitter from './emitter';
  
  // registered extensions to cytoscape, indexed by name
  let extensions = {};
  
  // registered modules for extensions, indexed by name
  let modules = {};
  
  function setExtension( type, name, registrant ){
  
    let ext = registrant;
  
    let overrideErr = function( field ){
      util.warn( 'Can not register `' + name + '` for `' + type + '` since `' + field + '` already exists in the prototype and can not be overridden' );
    };
  
    if( type === 'core' ){
      if( Core.prototype[ name ] ){
        return overrideErr( name );
      } else {
        Core.prototype[ name ] = registrant;
      }
  
    } else if( type === 'collection' ){
      if( Collection.prototype[ name ] ){
        return overrideErr( name );
      } else {
        Collection.prototype[ name ] = registrant;
      }
  
    } else if( type === 'layout' ){
      // fill in missing layout functions in the prototype
  
      let Layout = function( options ){
        this.options = options;
  
        registrant.call( this, options );
  
        // make sure layout has _private for use w/ std apis like .on()
        if( !is.plainObject( this._private ) ){
          this._private = {};
        }
  
        this._private.cy = options.cy;
        this._private.listeners = [];
  
        this.createEmitter();
      };
  
      let layoutProto = Layout.prototype = Object.create( registrant.prototype );
  
      let optLayoutFns = [];
  
      for( let i = 0; i < optLayoutFns.length; i++ ){
        let fnName = optLayoutFns[ i ];
  
        layoutProto[ fnName ] = layoutProto[ fnName ] || function(){ return this; };
      }
  
      // either .start() or .run() is defined, so autogen the other
      if( layoutProto.start && !layoutProto.run ){
        layoutProto.run = function(){ this.start(); return this; };
      } else if( !layoutProto.start && layoutProto.run ){
        layoutProto.start = function(){ this.run(); return this; };
      }
  
      let regStop = registrant.prototype.stop;
      layoutProto.stop = function(){
        let opts = this.options;
  
        if( opts && opts.animate ){
          let anis = this.animations;
  
          if( anis ){
            for( let i = 0; i < anis.length; i++ ){
              anis[ i ].stop();
            }
          }
        }
  
        if( regStop ){
          regStop.call( this );
        } else {
          this.emit( 'layoutstop' );
        }
  
        return this;
      };
  
      if( !layoutProto.destroy ){
        layoutProto.destroy = function(){
          return this;
        };
      }
  
      layoutProto.cy = function(){
        return this._private.cy;
      };
  
      let getCy = layout => layout._private.cy;
  
      let emitterOpts = {
        addEventFields: function( layout, evt ){
          evt.layout = layout;
          evt.cy = getCy(layout);
          evt.target = layout;
        },
        bubble: function(){ return true; },
        parent: function( layout ){ return getCy(layout); }
      };
  
      util.assign( layoutProto, {
        createEmitter: function(){
          this._private.emitter = new Emitter( emitterOpts, this );
  
          return this;
        },
        emitter: function(){ return this._private.emitter; },
        on: function( evt, cb ){ this.emitter().on( evt, cb ); return this; },
        one: function( evt, cb ){ this.emitter().one( evt, cb ); return this; },
        once: function( evt, cb ){ this.emitter().one( evt, cb ); return this; },
        removeListener: function( evt, cb ){ this.emitter().removeListener( evt, cb ); return this; },
        removeAllListeners: function(){ this.emitter().removeAllListeners(); return this; },
        emit: function( evt, params ){ this.emitter().emit( evt, params ); return this; }
      } );
  
      define.eventAliasesOn( layoutProto );
  
      ext = Layout; // replace with our wrapped layout
  
    } else if( type === 'renderer' && name !== 'null' && name !== 'base' ){
      // user registered renderers inherit from base
  
      let BaseRenderer = getExtension( 'renderer', 'base' );
      let bProto = BaseRenderer.prototype;
      let RegistrantRenderer = registrant;
      let rProto = registrant.prototype;
  
      let Renderer = function(){
        BaseRenderer.apply( this, arguments );
        RegistrantRenderer.apply( this, arguments );
      };
  
      let proto = Renderer.prototype;
  
      for( let pName in bProto ){
        let pVal = bProto[ pName ];
        let existsInR = rProto[ pName ] != null;
  
        if( existsInR ){
          return overrideErr( pName );
        }
  
        proto[ pName ] = pVal; // take impl from base
      }
  
      for( let pName in rProto ){
        proto[ pName ] = rProto[ pName ]; // take impl from registrant
      }
  
      bProto.clientFunctions.forEach( function( name ){
        proto[ name ] = proto[ name ] || function(){
          util.error( 'Renderer does not implement `renderer.' + name + '()` on its prototype' );
        };
      } );
  
      ext = Renderer;
  
    } else if (type === '__proto__' || type === 'constructor' || type === 'prototype'){
      // to avoid potential prototype pollution
      return util.error( type + ' is an illegal type to be registered, possibly lead to prototype pollutions' );
    }
  
    return util.setMap( {
      map: extensions,
      keys: [ type, name ],
      value: ext
    } );
  }
  
  function getExtension( type, name ){
    return util.getMap( {
      map: extensions,
      keys: [ type, name ]
    } );
  }
  
  function setModule( type, name, moduleType, moduleName, registrant ){
    return util.setMap( {
      map: modules,
      keys: [ type, name, moduleType, moduleName ],
      value: registrant
    } );
  }
  
  function getModule( type, name, moduleType, moduleName ){
    return util.getMap( {
      map: modules,
      keys: [ type, name, moduleType, moduleName ]
    } );
  }
  
  let extension = function(){
    // e.g. extension('renderer', 'svg')
    if( arguments.length === 2 ){
      return getExtension.apply( null, arguments );
    }
  
    // e.g. extension('renderer', 'svg', { ... })
    else if( arguments.length === 3 ){
      return setExtension.apply( null, arguments );
    }
  
    // e.g. extension('renderer', 'svg', 'nodeShape', 'ellipse')
    else if( arguments.length === 4 ){
      return getModule.apply( null, arguments );
    }
  
    // e.g. extension('renderer', 'svg', 'nodeShape', 'ellipse', { ... })
    else if( arguments.length === 5 ){
      return setModule.apply( null, arguments );
    }
  
    else {
      util.error( 'Invalid extension access syntax' );
    }
  
  };
  
  // allows a core instance to access extensions internally
  Core.prototype.extension = extension;
  
  // included extensions
  incExts.forEach( function( group ){
    group.extensions.forEach( function( ext ){
      setExtension( group.type, ext.name, ext.impl );
    } );
  } );
  
  export default extension;
  