/*---------------------------------------------------------------------------*/
/* Unification */

var __ = new Object(); /* wildcard marker */
__.__ = "__";

function unificationFailed() {
    throw {unificationFailed: true};
}

function unify1(a, b) {
    var i;

    if (a === __) return b;
    if (b === __) return a;

    if (a === b) return a;

    if (Array.isArray(a) && Array.isArray(b)) {
	if (a.length !== b.length) unificationFailed();
	var result = new Array(a.length);
	for (i = 0; i < a.length; i++) {
	    result[i] = unify1(a[i], b[i]);
	}
	return result;
    }

    if (typeof a === "object" && typeof b === "object") {
	/* TODO: consider other kinds of matching. I've chosen to
	   require any field mentioned by either side to be present in
	   both. Does that make sense? */
	var result = ({});
	for (i in a) { if (a.hasOwnProperty(i)) result[i] = true; }
	for (i in b) { if (b.hasOwnProperty(i)) result[i] = true; }
	for (i in result) {
	    if (result.hasOwnProperty(i)) {
		result[i] = unify1(a[i], b[i]);
	    }
	}
	return result;
    }

    unificationFailed();
}

function unify(a, b) {
    try {
	return {result: unify1(a, b)};
    } catch (e) {
	if (e.unificationFailed) return undefined;
	throw e;
    }
}

function anyUnify(aa, bb) {
    for (var i = 0; i < aa.length; i++) {
	for (var j = 0; j < bb.length; j++) {
	    if (unify(aa[i], bb[j])) return true;
	}
    }
    return false;
}

/*---------------------------------------------------------------------------*/
/* Events and Actions */

function Route(isSubscription, pattern, metaLevel, level) {
    this.isSubscription = isSubscription;
    this.pattern = pattern;
    this.metaLevel = (metaLevel === undefined) ? 0 : metaLevel;
    this.level = (level === undefined) ? 0 : level;
}

Route.prototype.drop = function () {
    if (this.metaLevel === 0) { return null; }
    return new Route(this.isSubscription, this.pattern, this.metaLevel - 1, this.level);
};

Route.prototype.lift = function () {
    return new Route(this.isSubscription, this.pattern, this.metaLevel + 1, this.level);
};

function sub(pattern, metaLevel, level) {
    return new Route(true, pattern, metaLevel, level);
}

function pub(pattern, metaLevel, level) {
    return new Route(false, pattern, metaLevel, level);
}

function spawn(behavior, initialRoutes) {
    return { type: "spawn",
	     behavior: behavior,
	     initialRoutes: (initialRoutes === undefined) ? [] : initialRoutes };
}

function updateRoutes(routes) {
    return { type: "routes", routes: routes };
}

function sendMessage(m, metaLevel, isFeedback) {
    return { type: "send",
	     metaLevel: (metaLevel === undefined) ? 0 : metaLevel,
	     message: m,
	     isFeedback: (isFeedback === undefined) ? false : isFeedback };
}

/*---------------------------------------------------------------------------*/
/* Metafunctions */

function dropRoutes(routes) {
    var result = [];
    for (var i = 0; i < routes.length; i++) {
	var r = routes[i].drop();
	if (r) { result.push(r); }
    }
    return result;
}

function liftRoutes(routes) {
    var result = [];
    for (var i = 0; i < routes.length; i++) {
	result.push(routes[i].lift());
    }
    return result;
}

function filterEvent(e, routes) {
    switch (e.type) {
    case "routes":
	var result = [];
	for (var i = 0; i < e.routes.length; i++) {
	    for (var j = 0; j < routes.length; j++) {
		var ri = e.routes[i];
		var rj = routes[j];
		if (ri.isSubscription === !rj.isSubscription
		    && ri.metaLevel === rj.metaLevel
		    && ri.level < rj.level)
		{
		    var u = unify(ri.pattern, rj.pattern);
		    if (u) {
			var rk = new Route(ri.isSubscription, u.result, ri.metaLevel, ri.level);
			result.push(rk);
		    }
		}
	    }
	}
	return result.length ? result : null;
    case "send":
	for (var i = 0; i < routes.length; i++) {
	    var r = routes[i];
	    if (e.metaLevel === r.metaLevel
		&& e.isFeedback === !r.isSubscription
		&& unify(e.message, r.pattern))
	    {
		return e;
	    }
	}
	return null;
    default:
	throw { message: "Event type " + e.type + " not filterable",
		event: e };
    }
}

/*---------------------------------------------------------------------------*/
/* Configurations */

function World(bootActions) {
    this.nextPid = 0;
    this.eventQueue = [];
    this.processTable = {};
    this.downwardRoutes = [];
    this.processActions = [];
    this.activePid = null;
    this.enqueueActions(-1, bootActions);
}

/* Class state / methods */

World.current = null; // parameter

World.send = function (m, metaLevel, isFeedback) {
    World.current.enqueueAction(sendMessage(m, metaLevel, isFeedback));
};

World.updateRoutes = function (routes) {
    World.current.enqueueAction(updateRoutes(routes));
};

World.spawn = function (behavior, initialRoutes) {
    World.current.enqueueAction(spawn(behavior, initialRoutes));
};

/* Instance methods */

World.prototype.enqueueAction = function (action) {
    this.processActions.push([this.activePid, action]);
};

World.prototype.enqueueActions = function (pid, actions) {
    for (var i = 0; i < actions.length; i++) {
	this.processActions.push([pid, actions[i]]);
    }
};

World.prototype.isQuiescent = function () {
    return this.eventQueue.length === 0 && this.processActions.length === 0;
};

World.prototype.step = function () {
    this.dispatchEvents();
    this.performActions();
    return this.stepChildren() || !this.isQuiescent();
};

World.prototype.asChild = function (pid, f) {
    var oldWorld = World.current;
    var result = null;
    World.current = this;
    this.activePid = pid;
    try {
	result = f();
    } catch (e) {
	this.kill(pid, e);
    }
    this.activePid = null;
    World.current = oldWorld;
    return result;
};

World.prototype.kill = function (pid, exn) {
    console.log("Killed process " + pid + (exn ? " with reason " + exn.message : ""));
    delete this.processTable[pid];
    this.issueRoutingUpdate();
};

World.prototype.stepChildren = function () {
    var someChildBusy = false;
    for (var pid in this.processTable) {
	var p = this.processTable[pid];
	if (p.behavior.step /* exists, haven't called it yet */) {
	    var childBusy = this.asChild(pid, function () { p.behavior.step() });
	    someChildBusy = someChildBusy || childBusy;
	}
    }
    return someChildBusy;
};

World.prototype.performActions = function () {
    var queue = this.processActions;
    this.processActions = [];
    var item;
    while ((item = queue.shift())) {
	this.performAction(item[0], item[1]);
    }
};

World.prototype.dispatchEvents = function () {
    var queue = this.eventQueue;
    this.eventQueue = [];
    var item;
    while ((item = queue.shift())) {
	this.dispatchEvent(item);
    }
};

World.prototype.performAction = function (pid, action) {
    switch (action.type) {
    case "spawn":
	var pid = this.nextPid++;
	this.processTable[pid] = { routes: action.initialRoutes, behavior: action.behavior };
	if (behavior.boot) { this.asChild(pid, function () { behavior.boot() }); }
	this.issueRoutingUpdate();
	break;
    case "routes":
	this.processTable[pid].routes = action.routes;
	this.issueRoutingUpdate();
	break;
    case "send":
	if (action.metaLevel === 0) {
	    this.eventQueue.push(action);
	} else {
	    World.send(action.message, action.metaLevel - 1, action.isFeedback);
	}
	break;
    default:
	throw { message: "Action type " + action.type + " not understood",
		action: action };
    }
};

World.prototype.aggregateRoutes = function (base) {
    var acc = base.slice();
    for (var pid in this.processTable) {
	var p = this.processTable[pid];
	for (var i = 0; i < p.routes.length; i++) {
	    acc.push(p.routes[i]);
	}
    }
};

World.prototype.issueRoutingUpdate = function () {
    this.eventQueue.push(updateRoutes(this.aggregateRoutes(this.downwardRoutes)));
    World.updateRoutes(dropRoutes(this.aggregateRoutes([])));
};

World.prototype.dispatchEvent = function (e) {
    for (var pid in this.processTable) {
	var p = this.processTable[pid];
	var e1 = filterEvent(e, p.routes);
	if (e1) { this.asChild(pid, function () { p.behavior.handleEvent(e1) }); }
    }
};

World.prototype.handleEvent = function (e) {
    switch (e.type) {
    case "routes":
	this.downwardRoutes = liftRoutes(e.routes);
	this.issueRoutingUpdate();
	break;
    case "send":
	this.eventQueue.push(sendMessage(e.message, e.metaLevel + 1, e.isFeedback));
	break;
    default:
	throw { message: "Event type " + e.type + " not understood",
		event: e };
    }
};