experiments with value relationships

value.js

function ValueReference(src, dest, forward) {
  if (!forward) {
    this.src = src;
    this.dest = dest;
  } else {
    this.src = dest;
    this.dest = src;
  }
  
  this.operations = []; 
}

ValueReference.prototype = {
  value : null,
  operations : null,
  addOperation : function(apply, revert) {
    this.operations.push({
      apply: apply,
      revert: revert
    });
  },
  change : function(value) {
    var val = this.src.value();
    var dest = this.dest;
    this.operations.forEach(function(operation) {
      dest.apply(operation.apply(val));
    });
  }
};

function Value(primitive) {
  this._refs = [];
  this._value = primitive;
  this._history = [];
}

Value.prototype = {
  _refs : null,
  _value : null,
  _history : null,
  
  refs : function(value, forward) {
    if (forward) {
      this._refs.push(new ValueReference(this, value));
      return this;
    } else {
      return value.refs(this, true);
    }
  },
  
  unrefs : function(value) {
    this._refs = _refs.filter(function(i) {
      return value !== i;
    });
    
    return this;
  },
  
  value : function() {
    return this._value;
  },
    
  apply: function(primitive) {
    // todo: handle functions?

    this._history.push(this._value);
    this._value = primitive;
    
    this.notify();
    
    return this;
  },
    
  revert : function() {
    this._value = this._history.pop();
    this.notify();

    return this;
  },
  
  notify : function() {
    console.log('notify', this._value);
    var that = this;
    this._refs.forEach(function(ref) {
      ref.change(that);
    });
  },
    
  add : function(value) {
    // todo handle another Value or function
    
    var ref = this._refs[this._refs.length-1];
    
    ref.addOperation(function(a) {
      return a + value;
    }, function(a) {
      return a - value;
    });
    
    return this;
  },
  
  multiply : function(value) {
    var ref = this._refs[this._refs.length-1];
    ref.addOperation(function(a) {
      return a * value;
    }, function(b) {
      return a / value;
    });
  }
};

var v = function(initial) {
  return new Value(initial);
};

var a = v(0);
var b = v(0);
var c = v(0);
b.refs(a).add(1);
c.refs(b).multiply(10);
a.apply(1);

console.log('a', a.value(), 'b', b.value(), 'c', c.value());
console.log(b.value() === 2);
a.apply(2);
console.log('a', a.value(), 'b', b.value(), 'c', c.value());

console.log(b.value() === 3, c.value() === 30);

a.revert();
console.log(b.value() === 2, c.value() === 20);

a.revert();
console.log(b.value() === 2, c.value() === 10);


// todo: unref
// todo: track history for undo state