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

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

	this._computed = blankObject();
	this._sortedComputedProperties = [];

	this._state = assign({}, state);
}

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

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

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

	_sortComputedProperties: function() {
		var computed = this._computed;
		var sorted = this._sortedComputedProperties = [];
		var visited = blankObject();

		function visit(key) {
			if (visited[key]) return;
			var c = computed[key];

			if (c) {
				c.deps.forEach(visit);
				sorted.push(c);
			}
		}

		for (var key in this._computed) visit(key);
	},

	compute: function(key, deps, fn) {
		var store = this;
		var value;

		var c = {
			deps: deps,
			update: function(state, changed, dirty) {
				var values = deps.map(function(dep) {
					if (dep in changed) dirty = true;
					return state[dep];
				});

				if (dirty) {
					var newValue = fn.apply(null, values);
					if (differs(newValue, value)) {
						value = newValue;
						changed[key] = true;
						state[key] = value;
					}
				}
			}
		};

		c.update(this._state, {}, true);

		this._computed[key] = c;
		this._sortComputedProperties();
	},

	get: get,

	observe: observe,

	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 = this._changed = {},
			dirty = false;

		for (var key in newState) {
			if (this._computed[key]) throw new Error("'" + key + "' is a read-only property");
			if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
		}
		if (!dirty) return;

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

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

		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);
	}
});

function combineStores(children, store) {
	if (!store) store = new Store();
	var updates = {};

	for (var key in children) {
		var child = children[key];
		updates[key] = child.get();

		child.onchange(function(state) {
			var update = {};
			update[key] = state;
			store.set(update);
		});
	}

	store.set(updates);
	return store;
}

export { Store, combineStores };