import {
	assign,
	blankObject,
	differs,
	dispatchObservers,
	get,
	observe
} from './shared.js';

function Store(state) {
	this._state = state ? assign({}, state) : {};
	this._observers = { pre: blankObject(), post: blankObject() };
	this._changeHandlers = [];
	this._dependents = [];
}

assign(Store.prototype, {
	get,
	observe
}, {
	_add: function(component, props) {
		this._dependents.push({
			component: component,
			props: props
		});
	},

	_init: function(props) {
		var state = {};
		for (let i = 0; i < props.length; i += 1) {
			var prop = props[i];
			state['$' + prop] = this._state[prop];
		}
		return state;
	},

	_remove: function(component) {
		let i = this._dependents.length;
		while (i--) {
			if (this._dependents[i].component === component) {
				this._dependents.splice(i, 1);
				return;
			}
		}
	},

	onchange: function(callback) {
		this._changeHandlers.push(callback);
		return {
			cancel: function() {
				var index = this._changeHandlers.indexOf(callback);
				if (~index) this._changeHandlers.splice(index, 1);
			}
		};
	},

	set: function(newState) {
		var oldState = this._state,
			changed = {},
			dirty = false;

		for (var key in newState) {
			if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
		}
		if (!dirty) return;

		this._state = assign({}, oldState, newState);

		for (var i = 0; i < this._changeHandlers.length; i += 1) {
			this._changeHandlers[i](this._state, changed);
		}

		dispatchObservers(this, this._observers.pre, changed, this._state, oldState);

		var dependents = this._dependents.slice(); // guard against mutations
		for (var i = 0; i < dependents.length; i += 1) {
			var dependent = dependents[i];
			var componentState = {};
			dirty = false;

			for (var j = 0; j < dependent.props.length; j += 1) {
				var prop = dependent.props[j];
				if (prop in changed) {
					componentState['$' + prop] = this._state[prop];
					dirty = true;
				}
			}

			if (dirty) dependent.component.set(componentState);
		}

		dispatchObservers(this, this._observers.post, changed, this._state, oldState);
	}
});

export default Store;