Mixins

/**
 * Element class mixin that provides the core API for Polymer's meta-programming
 * features including template stamping, data-binding, attribute deserialization,
 * and property change observation.
 */
function ElementMixin<T extends Constructor<HTMLElement>>(base: T): T & ElementMixinConstructor;

interface ElementMixinConstructor {
  new(): ElementMixin;
  
  /** Polymer version */
  polymerElementVersion: string;
  
  /** Template for the element */
  template: HTMLTemplateElement;
  
  /** Import path for resolving URLs */
  importPath: string;
  
  /** Create property effects from property config */
  createProperties(props: PropertyDeclarations): void;
  
  /** Create observers from observer array */
  createObservers(observers: string[], dynamicFns: object): void;
  
  /** Finalize element class metadata */
  finalize(): void;
}

interface ElementMixin {
  /** Root element of stamped template */
  root: ShadowRoot | HTMLElement;
  
  /** Map of id->element for template elements */
  $: {[id: string]: Element};
  
  /** Element's import path */
  importPath: string;
  
  /** Application root path */
  rootPath: string;
  
  /** Update ShadyCSS styles */
  updateStyles(properties?: StyleProperties): void;
  
  /** Resolve URL relative to import path */
  resolveUrl(url: string, base?: string): string;
}

import { ElementMixin } from '@polymer/polymer/lib/mixins/element-mixin.js';

// Creating a custom base class
class MyElementBase extends ElementMixin(HTMLElement) {
  constructor() {
    super();
    console.log('Custom base element created');
  }
  
  // Add shared functionality
  commonMethod() {
    return 'shared behavior';
  }
}

// Using the custom base
class MyElement extends MyElementBase {
  static get is() { return 'my-element'; }
  
  static get template() {
    return html`<div>[[message]]</div>`;
  }
  
  ready() {
    super.ready();
    console.log(this.commonMethod()); // "shared behavior"
  }
}

/**
 * Mixin that provides property effects including computed properties,
 * observers, and template binding
 */
function PropertyEffects<T extends Constructor<HTMLElement>>(base: T): T & PropertyEffectsConstructor;

interface PropertyEffectsConstructor {
  /** Create computed property */
  createComputedProperty(property: string, expression: string, dynamicFns: object): void;
  
  /** Create property observer */
  createPropertyObserver(property: string, method: string, dynamicFn: boolean): void;
  
  /** Create read-only property */
  createReadOnlyProperty(property: string, protectedSetter: boolean): void;
  
  /** Create reflected property */
  createReflectedProperty(property: string): void;
  
  /** Create notifying property */
  createNotifyingProperty(property: string): void;
}

interface PropertyEffects {
  /** Set property value and notify */
  _setProperty(property: string, value: any): void;
  
  /** Get property value */
  _getProperty(property: string): any;
  
  /** Notify property change */
  _notifyPropertyChange(property: string, value: any, oldValue: any): void;
  
  /** Create method observer */
  _createMethodObserver(expression: string, dynamicFns: object): void;
}

/**
 * Mixin that provides property configuration and flattening
 */
function PropertiesMixin<T extends Constructor<HTMLElement>>(base: T): T & PropertiesMixinConstructor;

interface PropertiesMixinConstructor {
  /** Flattened properties from class hierarchy */
  _properties: PropertyDeclarations;
  
  /** Finalize property configuration */
  finalize(): void;
  
  /** Create properties from configuration */
  createProperties(props: PropertyDeclarations): void;
}

interface PropertiesMixin {
  /** Initialize properties with defaults */
  _initializeProperties(): void;
  
  /** Check if property can have default applied */
  _canApplyPropertyDefault(property: string): boolean;
}

/**
 * Mixin that provides template stamping capabilities
 */
function TemplateStamp<T extends Constructor<HTMLElement>>(base: T): T & TemplateStampConstructor;

interface TemplateStampConstructor {
  /** Parse template for binding information */
  _parseTemplate(template: HTMLTemplateElement): TemplateInfo;
}

interface TemplateStamp {
  /** Stamp template into DocumentFragment */
  _stampTemplate(template: HTMLTemplateElement): DocumentFragment;
  
  /** Bind template with data */
  _bindTemplate(template: HTMLTemplateElement): void;
}

/**
 * Mixin that provides property accessors and attribute sync
 */
function PropertyAccessors<T extends Constructor<HTMLElement>>(base: T): T & PropertyAccessorsConstructor;

interface PropertyAccessorsConstructor {
  /** Observed attributes for this element */
  observedAttributes: string[];
  
  /** Create property accessor */
  createPropertyAccessor(property: string, readOnly?: boolean): void;
}

interface PropertyAccessors {
  /** Handle attribute changes */
  attributeChangedCallback(name: string, old: string, value: string): void;
  
  /** Deserialize attribute to property */
  _deserializeValue(value: string, type: PropertyType): any;
  
  /** Serialize property to attribute */
  _serializeValue(value: any): string;
  
  /** Check if element has property accessor */
  _hasAccessor(property: string): boolean;
}

/**
 * Mixin that provides gesture event listening capabilities
 */
function GestureEventListeners<T extends Constructor<HTMLElement>>(base: T): T & GestureEventListenersConstructor;

interface GestureEventListeners {
  /** Add gesture event listener */
  _addEventListenerToNode(node: Node, eventName: string, handler: (e: Event) => void): void;
  
  /** Remove gesture event listener */
  _removeEventListenerFromNode(node: Node, eventName: string, handler: (e: Event) => void): void;
}

import { GestureEventListeners } from '@polymer/polymer/lib/mixins/gesture-event-listeners.js';

class GestureElement extends GestureEventListeners(PolymerElement) {
  ready() {
    super.ready();
    
    // Add gesture listeners
    this._addEventListenerToNode(this, 'tap', this._onTap.bind(this));
    this._addEventListenerToNode(this, 'track', this._onTrack.bind(this));
  }
  
  _onTap(e) {
    console.log('Tap gesture detected');
  }
  
  _onTrack(e) {
    console.log('Track gesture:', e.detail.state, e.detail.dx, e.detail.dy);
  }
}

/**
 * Mixin that provides mutable data handling
 */
function MutableData<T extends Constructor<HTMLElement>>(base: T): T & MutableDataConstructor;

/**
 * Optional mutable data mixin
 */
function OptionalMutableData<T extends Constructor<HTMLElement>>(base: T): T & OptionalMutableDataConstructor;

interface MutableDataMixin {
  /** Force data system to reevaluate paths */
  _mutablePropertyChange(path: string, value: any, mutable: boolean): void;
}

/**
 * Mixin that provides directional layout support
 */
function DirMixin<T extends Constructor<HTMLElement>>(base: T): T & DirMixinConstructor;

interface DirMixin {
  /** Current text direction */
  dir: string;
}

/**
 * Mixin that allows controlling element upgrade timing
 */
function DisableUpgradeMixin<T extends Constructor<HTMLElement>>(base: T): T & DisableUpgradeMixinConstructor;

interface DisableUpgradeMixin {
  /** Disable element upgrade */
  _disableUpgrade: boolean;
}

/**
 * Find observed attributes getter in constructor chain
 */
function findObservedAttributesGetter(constructor: Constructor): () => string[];

/**
 * Mixin that provides strict binding parsing
 */
function StrictBindingParser<T extends Constructor<HTMLElement>>(base: T): T & StrictBindingParserConstructor;

/**
 * Wraps a mixin function to ensure it's only applied once per class hierarchy
 */
function dedupingMixin<T extends Constructor, U>(mixinFunction: (base: T) => U): (base: T) => U;

import { dedupingMixin } from '@polymer/polymer/lib/utils/mixin.js';

// Create a deduplicating mixin
const MyMixin = dedupingMixin((base) => {
  class MyMixinImpl extends base {
    myMixinMethod() {
      return 'mixin functionality';
    }
  }
  return MyMixinImpl;
});

// Safe to apply multiple times - only applied once
class ElementA extends MyMixin(PolymerElement) {}
class ElementB extends MyMixin(MyMixin(PolymerElement)) {} // MyMixin only applied once

type Constructor<T = {}> = new (...args: any[]) => T;

interface PropertyDeclarations {
  [property: string]: PropertyType | PropertyDeclaration;
}

interface TemplateInfo {
  dynamicFns?: {[property: string]: boolean};
}

interface StyleProperties {
  [property: string]: string;
}