function noop() {}

function assign(target) {
	var k,
		source,
		i = 1,
		len = arguments.length;
	for (; i < len; i++) {
		source = arguments[i];
		for (k in source) target[k] = source[k];
	}

	return target;
}

function destroy(detach) {
	if (!this._destroyed) {
		this.fire('destroy');

		if (detach !== false) this._fragment.unmount();
		this._fragment.destroy();
		this._fragment = null;

		this._state = {};
		this._destroyed = true;
	}
}

function differs(a, b) {
	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
}

function dispatchObservers(component, group, newState, oldState) {
	for (var key in group) {
		if (!(key in newState)) continue;

		var newValue = newState[key];
		var oldValue = oldState[key];

		if (differs(newValue, oldValue)) {
			var callbacks = group[key];
			if (!callbacks) continue;

			for (var i = 0; i < callbacks.length; i += 1) {
				var callback = callbacks[i];
				if (callback.__calling) continue;

				callback.__calling = true;
				callback.call(component, newValue, oldValue);
				callback.__calling = false;
			}
		}
	}
}

function get(key) {
	return key ? this._state[key] : this._state;
}

function fire(eventName, data) {
	var handlers =
		eventName in this._handlers && this._handlers[eventName].slice();
	if (!handlers) return;

	for (var i = 0; i < handlers.length; i += 1) {
		handlers[i].call(this, data);
	}
}

function observe(key, callback, options) {
	var group = options && options.defer
		? this._observers.post
		: this._observers.pre;

	(group[key] || (group[key] = [])).push(callback);

	if (!options || options.init !== false) {
		callback.__calling = true;
		callback.call(this, this._state[key]);
		callback.__calling = false;
	}

	return {
		cancel: function() {
			var index = group[key].indexOf(callback);
			if (~index) group[key].splice(index, 1);
		}
	};
}

function on(eventName, handler) {
	if (eventName === 'teardown') return this.on('destroy', handler);

	var handlers = this._handlers[eventName] || (this._handlers[eventName] = []);
	handlers.push(handler);

	return {
		cancel: function() {
			var index = handlers.indexOf(handler);
			if (~index) handlers.splice(index, 1);
		}
	};
}

function set(newState) {
	if (this._destroyed) return;
	this._set(assign({}, newState));
	if (this._root._lock) return;
	this._root._lock = true;
	callAll(this._root._beforecreate);
	callAll(this._root._oncreate);
	callAll(this._root._aftercreate);
	this._root._lock = false;
}

function callAll(fns) {
	while (fns && fns.length) fns.pop()();
}

var proto = {
	destroy: destroy,
	get: get,
	fire: fire,
	observe: observe,
	on: on,
	set: set,
	teardown: destroy
};

function recompute ( state, newState, oldState, isInitial ) {
	if ( isInitial || ( 'x' in newState && differs( state.x, oldState.x ) ) ) {
		state.a = newState.a = template.computed.a( state.x );
		state.b = newState.b = template.computed.b( state.x );
	}
}

var template = (function () {
	return {
		computed: {
			a: x => x * 2,
			b: x => x * 3
		}
	};
}());

function create_main_fragment ( state, component ) {

	return {
		create: noop,

		mount: noop,

		unmount: noop,

		destroy: noop
	};
}

function SvelteComponent ( options ) {
	options = options || {};
	this._state = options.data || {};
	recompute( this._state, this._state, {}, true );

	this._observers = {
		pre: Object.create( null ),
		post: Object.create( null )
	};

	this._handlers = Object.create( null );

	this._root = options._root || this;
	this._yield = options._yield;

	this._destroyed = false;

	this._fragment = create_main_fragment( this._state, this );

	if ( options.target ) {
		this._fragment.create();
		this._fragment.mount( options.target, null );
	}
}

assign( SvelteComponent.prototype, proto );

SvelteComponent.prototype._set = function _set ( newState ) {
	var oldState = this._state;
	this._state = assign( {}, oldState, newState );
	recompute( this._state, newState, oldState, false );
	dispatchObservers( this, this._observers.pre, newState, oldState );
	dispatchObservers( this, this._observers.post, newState, oldState );
};

export default SvelteComponent;