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 appendNode ( node, target ) {
	target.appendChild( node );
}

function insertNode ( node, target, anchor ) {
	target.insertBefore( node, anchor );
}

function detachNode ( node ) {
	node.parentNode.removeChild( node );
}

function createElement ( name ) {
	return document.createElement( name );
}

function createText ( data ) {
	return document.createTextNode( data );
}

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 ) {
	this._set( assign( {}, newState ) );
	this._root._flush();
}

function _flush () {
	if ( !this._renderHooks ) return;

	while ( this._renderHooks.length ) {
		this._renderHooks.pop()();
	}
}

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

var template = (function () {
	return {
		methods: {
			foo ( bar ) {
				console.log( bar );
			}
		},
		events: {
			foo ( node, callback ) {
				// code goes here
			}
		}
	};
}());

function create_main_fragment ( state, component ) {
	var button = createElement( 'button' );

	var foo_handler = template.events.foo.call( component, button, function ( event ) {
		var state = component.get();
		component.foo( state.bar );
	});

	appendNode( createText( "foo" ), button );

	return {
		mount: function ( target, anchor ) {
			insertNode( button, target, anchor );
		},

		unmount: function () {
			detachNode( button );
		},

		destroy: function () {
			foo_handler.teardown();
		}
	};
}

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

	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._torndown = false;

	this._fragment = create_main_fragment( this._state, this );
	if ( options.target ) this._fragment.mount( options.target, null );
}

assign( SvelteComponent.prototype, template.methods, proto );

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

SvelteComponent.prototype.teardown = SvelteComponent.prototype.destroy = function destroy ( detach ) {
	this.fire( 'destroy' );

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

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

export default SvelteComponent;