var async = require("async");
var _     = require("highland");

function joinable(bus) {
  return mesh.fallback(
   mesh.accept(
     sift({ join: { $exists: true }}),
     mesh.map(bus, function(operation, data, writable) {
       async.each(Object.keys(operation.join), function(collection, next) {
         bus(mesh.op("load", {
           multi: true,
           collection: collection,
           query: operation.join[collection](operation)
         }))
          .pipe(_.pipeline(_.collect))
          .on("data", function(items) {
            data[collection] = items;
          })
          .on("end", next);
       }, function() {
         writable.end(data);
       });
     })
   ),
   bus
 )
}

var bus = mesh.top(joinable(api()));

bus("load", {
  collection: "messages",
  join: {
    tags: function(message) {
      return {
        messageId: message.uid
      };
    }
  }
});