class Observer {
  constructor(data) {
    this._data = data;
    this.walk(this._data);
  }

  walk(data) {
    Object.keys(data).forEach((key) => { this.defineRective(data, key, data[key]) })
  };
  defineRective(vm, key, value) {
    var self = this;
    if (value && typeof value === "object") {
      this.walk(value);
    }
    Object.defineProperty(vm, key, {
      get: function() {
        return value;
      },
      set: function(newVal) {
        if (value != newVal) {
          if (newVal && typeof newVal === "object") {
            self.walk(newVal);
          }
          value = newVal;
        }
      }
    })
  }
}

module.exports = Observer;

defineRective(vm, key, value) {
  // 将这个属性的依赖表达式存储在闭包中。
  var dep = new Dep();
  var self = this;
  if (value && typeof value === "object") {
    this.walk(value);
  }
  Object.defineProperty(vm, key, {
    get: function() {
      return value;
    },
    set: function(newVal) {
      if (value != newVal) {
        if (newVal && typeof newVal === "object") {
          self.walk(newVal);
        }
        value = newVal;
        // 通知所有的 viewModel 更新
        dep.notify();
      }
    }
  })
}

class Dep {
  constructor() {
    // 依赖列表
    this.dependences = [];
  }
  // 添加依赖
  addDep(watcher) {
    if (watcher) {
      this.dependences.push(watcher);
    }
  }
  // 通知所有依赖更新
  notify() {
    this.dependences.forEach((watcher) => {
      watcher.update();
    })
  }
}

module.exports = Dep;

var uid = 0;
class Watcher {
  constructor(viewModel, exp, callback) {
    this.viewModel = viewModel;
    this.id = uid++;
    this.exp = exp;
    this.callback = callback;
    this.oldValue = "";
    this.update();
  }

  get() {
    Dep.target = this;
    var res = this.compute(this.viewModel, this.exp);
    Dep.target = null;
    return res;
  }

  update() {
    var newValue = this.get();
    if (this.oldValue === newValue) {
      return;
    }
    // callback 里进行Dom 的更新操作
    this.callback(newValue, this.oldValue);
    this.oldValue = newValue;
  }

  compute(viewModel, exp) {
    var res = replaceWith(viewModel, exp);
    return res;
  }
}

module.exports = Watcher;

Object.defineProperty(vm, key, {
  get: function() {
    var watcher = Dep.target;
    if (watcher && !dep.dependences[watcher.id]) {
      dep.addDep(watcher);
    }
    return value;
  },
  set: function(newVal) {
    if (value != newVal) {
      if (newVal && typeof newVal === "object") {
        self.walk(newVal);
      }
      value = newVal;
      dep.notify();
    }
  }
})

const Observer = require('./Observer.js');
const Watcher = require('./watcher.js');
var data = {
  a: 10,
  b: {
    c: 5,
    d: {
      e: 20,
    }
  }
}

var observe = new Observer(data);

var watcher = new Watcher(data, "a+b.c", function(newValue, oldValue) {
  console.log("new value is " + newValue);
  console.log("oldValue is " + oldValue);
});
console.log("\r\n");
console.log("a has changed to 50,then the expr should has value 55");
data.a = 50;

console.log("\r\n");
console.log("b.c has changed to 50,then the expr should has value 122");
data.b.c = 72;;

console.log("\r\n");
console.log("b.c has reseted an object,then the expr should has value 80");
data.b = { c: 30 }