Aurelia Observer Test + evaluate + connectable-binding change

app.html

<template>
  <require from="./example"></require>
  <binding-intercept-example if.bind="show"></binding-intercept-example>
</template>

app.js

export class App {
  show = true;
  
  // constructor() {
  //   setInterval(() => this.show = !this.show, 2000);
  // }
}

binding-intercept.js

export function bindingIntercept(interceptor) {
  return function interception(definition, propertyName, descriptor) {
    let viewModelValue = descriptor.initializer && descriptor.initializer();
    
    let observers = new Map();
    let observerId = 0;
    
    
    const observableGetter = function() { return viewModelValue; }

    observableGetter.getObserver = function(targetClass) {
      const thisObserverId = observerId++;
      return {
        // doNotCache: true,
        expressionHook: function(expression, binding) {
          if (!expression.__intercepted__) {
            expression.assign = (scope, value) => {
              // assignement coming from View
              if (this.interceptorInstance.next)
                this.interceptorInstance.next(value);
            }
            expression.evaluate = (scope, lookupFunctions) => {
              return this.lastValue;
            }
            expression.__intercepted__ = true;
          }
          // workaround: 
          // updates value the first time after the expression is hooked
          // -- unfortunately the target is first evaluated and then connected
          // this is called during connect and therefore the initial value sneaks in.
          binding.updateTarget(binding.sourceExpression.evaluate(binding.source, binding.lookupFunctions));
        },
        bindings: new Set(),
        subscribe: function(context, binding) {
          if (this.bindings.size === 0) {
            this.lastValue = undefined;
            this.interceptorInstance = getInterceptor(interceptor, viewModelValue, this);
          }
          
          this.bindings.add(binding);
          observers.set(thisObserverId, this);
        },
        unsubscribe: function(context, binding) {
          this.bindings.delete(binding);
          
          if (this.bindings.size === 0) {
            observers.delete(thisObserverId);
            
            if (this.interceptorInstance.dispose) {
              this.interceptorInstance.dispose();
              this.interceptorInstance = undefined;
            }
          }
        }
      }
    }
    
    delete descriptor.writable;
    delete descriptor.initializer;
    
    Object.defineProperty(descriptor, 'set', {
      value: function (newViewModelValue) {
        // assignement coming from ViewModel:
        viewModelValue = newViewModelValue;
        updateObservers(interceptor, viewModelValue, observers);
      }
    });
    Object.defineProperty(descriptor, 'get', {
      value: observableGetter
    });
  }
}

function getBindingValueSetter(observer) {
  return function (value) {
    if (observer.lastValue !== value) {
      observer.lastValue = value;
      if (observer.interceptorInstance) {
        for (let binding of observer.bindings) {
          binding.call('Binding:source');
        }
      }
    }
  }
}

function updateObservers(interceptor, viewModelValue, observers) {
  for (let observer of observers.values()) {
    if (observer.interceptorInstance.dispose) {
      observer.interceptorInstance.dispose();
    }
    
    observer.interceptorInstance = getInterceptor(interceptor, viewModelValue, observer);
    
    for (let binding of observer.bindings) {
      binding.call('Binding:source');
    }
  }
}

function getInterceptor(interceptor, viewModelValue, observer) {
  return interceptor(viewModelValue, getBindingValueSetter(observer)) || {};
}

connectable-binding.js

import * as aureliaBinding from 'aurelia-binding';

export const sourceContext = 'Binding:source';
const slotNames = [];
const versionSlotNames = [];

for (let i = 0; i < 100; i++) {
  slotNames.push(`_observer${i}`);
  versionSlotNames.push(`_observerVersion${i}`);
}

function addObserver(observer, expression) {
  // find the observer.
  let observerSlots = this._observerSlots === undefined ? 0 : this._observerSlots;
  let i = observerSlots;
  while (i-- && this[slotNames[i]] !== observer) {
    // Do nothing
  }
  
  // if we are not already observing, put the observer in an open slot and subscribe.
  if (i === -1) {
    i = 0;
    while (this[slotNames[i]]) {
      i++;
    }
    this[slotNames[i]] = observer;
    observer.subscribe(sourceContext, this);
    // increment the slot count.
    if (i === observerSlots) {
      this._observerSlots = i + 1;
    }
  }
  
  // monkey patching /start
  if (observer && observer.expressionHook) {
    observer.expressionHook(expression, this);
  }
  // monkey patching /end
  
  // set the "version" when the observer was used.
  if (this._version === undefined) {
    this._version = 0;
  }
  this[versionSlotNames[i]] = this._version;
}

function observeProperty(obj, propertyName, expression) {
  let observer = this.observerLocator.getObserver(obj, propertyName);
  addObserver.call(this, observer, expression);
}

aureliaBinding.AccessScope.prototype.connect = function connect(binding, scope) {
  let context = aureliaBinding.getContextFor(this.name, scope, this.ancestor);
    // monkey patching observeProperty
  binding.observeProperty = observeProperty;
  binding.observeProperty(context, this.name, this);
}

aureliaBinding.AccessMember.prototype.connect = function connect(binding, scope) {
  this.object.connect(binding, scope);
  let obj = this.object.evaluate(scope);
  if (obj) {
    // monkey patching observeProperty
    binding.observeProperty = observeProperty;
    binding.observeProperty(obj, this.name, this);
  }
}

aureliaBinding.AccessMember.prototype.connect = function connect(binding, scope) {
  this.object.connect(binding, scope);
  let obj = this.object.evaluate(scope);
  if (obj) {
    // monkey patching observeProperty
    binding.observeProperty = observeProperty;
    binding.observeProperty(obj, this.name, this);
  }
}

aureliaBinding.AccessKeyed.prototype.connect = function connect(binding, scope) {
  this.object.connect(binding, scope);
  let obj = this.object.evaluate(scope);
  if (obj instanceof Object) {
    this.key.connect(binding, scope);
    let key = this.key.evaluate(scope);
    // observe the property represented by the key as long as it's not an array
    // being accessed by an integer key which would require dirty-checking.
    if (key !== null && key !== undefined
      && !(Array.isArray(obj) && typeof(key) === 'number')) {
      // monkey patching observeProperty
      binding.observeProperty = observeProperty;
      binding.observeProperty(obj, key, this);
    }
  }
}

example.html

<template>
  <p>Promise Binding: ${somePromise ? somePromise : 'loading... (TENARY)'}</p>
  <p>Promise Binding: ${somePromise + ' post-concat'}</p>
  <p>Promise Binding: ${'pre-concat ' + somePromise + ' post-concat'}</p>
  <p>Promise Binding: ${somePromise || 'loading (OR ||)...'}</p>
  <button click.delegate="changePromise()">New Promise</button>
  <br/><br/>
  <p>Obj Promise Binding: ${someObjPromise.value || 'loading...'}</p>
  
  <br/><br/>
  <p>Timer Binding: ${someTimer}</p>
  
  <br/><br/>
  Two Way Binding (see console):<br/>
  <input value.bind="firstName">
  <button click.delegate="changeFirstName()">Change Name to Bazyli</button>
</template>

example.js

import {bindingIntercept} from './binding-intercept';

export class BindingInterceptExample {
  @bindingIntercept(promiseBinding)
  somePromise = new Promise(resolve => setTimeout(() => resolve('Hello!'), 2000));
  
  changePromise() {
    this.somePromise = new Promise(resolve => setTimeout(() => resolve('Awesome!'), 2000));
  }
  
  @bindingIntercept(promiseBinding)
  someObjPromise = new Promise(resolve => setTimeout(() => resolve({value: 'accessed promise.value!'}), 2000));
  
  @bindingIntercept(timer) someTimer;
  
  @bindingIntercept(twoWayIntercept) firstName = 'Rob';
  
  changeFirstName() {
    this.firstName = 'Bazyli';
  }
}

function promiseBinding(promise, bindingValueSetter) {
  bindingValueSetter(undefined); // initial value;
  promise.then(value => bindingValueSetter(value));
}

function timer(any, bindingValueSetter) {
  let i = 0;
  let timer = setInterval(() => bindingValueSetter(i++), 1000);
  return {
    dispose: () => clearInterval(timer)
  }
}

function twoWayIntercept(value, bindingValueSetter) {
  console.log('ViewModel changed value to:', value);
  bindingValueSetter(value); // initial value;
  
  return {
    next: (value) => {
      console.log('View changed value to:', value)
    }
  }
}

index.html

<!doctype html>
<html>
  <head>
    <title>Aurelia</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
  </head>
  <body aurelia-app>
    <h1>Loading...</h1>
    
    <script src="https://jdanyow.github.io/rjs-bundle/node_modules/requirejs/require.js"></script>
    <script src="https://jdanyow.github.io/rjs-bundle/config.js"></script>
    <script src="https://jdanyow.github.io/rjs-bundle/bundles/aurelia.js"></script>
    <script src="https://jdanyow.github.io/rjs-bundle/bundles/babel.js"></script>
    <script>
      require(['./connectable-binding', 'aurelia-bootstrapper']);
    </script>
  </body>
</html>