red-rings-couchdb/util/build-backend.js

// Generated by CoffeeScript 2.3.1
(function() {
  var Immutable, Key, NOTIFY, SUBSCRIBE, UNSUBSCRIBE, UPDATE, build_backend, changes_semantic, has_key, is_object, is_string, most, not_null, operation;

  build_backend = function({changes, view_changes, semantic, get_key, view_key, fromJS}) {
    // The backend return a function that can be provided to `backend_join`.
    return function(sources) {
      var route, subscriptions_keys, values, view_values;
      // For `update` events it will update the document.
      route = sources.filter(operation(UPDATE)).thru(changes_semantic);
      route.create.forEach(semantic.create);
      route.update.forEach(semantic.update);
      route.delete.forEach(semantic.delete);
      // For `subscribe` events it will GET the document and then notify on that current value
      // and on any future changes. (This is equivalent to a `@most/hold` on the entire database
      // viewed as a stream, basically, but uses little ressources.)
      subscriptions_keys = sources.filter(operation(SUBSCRIBE)).map(Key).multicast();
      // No action is needed for `unsubscribe` events.

      // Fetch current value, return a message similar to a row from `_all_docs`.
      values = subscriptions_keys.filter(is_string).map(get_key).chain(most.fromPromise).filter(not_null); // Can only retrieve string keys from a database
      // Compute values for wandering-country-view/all by querying the server-side view.
      view_values = subscriptions_keys.chain(view_key);
      // The output is the combination of:
      return most.mergeArray([
        // - subscriptions to document changes in the database
        changes.map(function(msg) {
          return Immutable.fromJS(msg).merge({
            op: NOTIFY,
            value: {
              rev: msg.doc._rev // or msg.changes[0].rev
            },
            doc: fromJS(msg.doc),
            key: msg.id
          });
        }),
        // - requested documents in the database
        values.map(function(doc) {
          return Immutable.Map({
            op: NOTIFY,
            id: doc._id,
            key: doc._id,
            value: {
              rev: doc._rev
            },
            doc: fromJS(doc)
          });
        }),
        // - subscriptions to changes in the view
        view_changes.map(function(msg) {
          return Immutable.fromJS(msg).set('op',
        NOTIFY);
        }),
        // - requested entries in the view
        view_values.map(function(msg) {
          return Immutable.fromJS(msg).set('op',
        NOTIFY);
        })
      ]);
    };
  };

  module.exports = build_backend;

  changes_semantic = require('red-rings-semantic');

  ({operation, Key, is_string, is_object, not_null, has_key} = require('abrasive-ducks-transducers'));

  Immutable = require('immutable');

  most = require('most');

  ({UPDATE, SUBSCRIBE, UNSUBSCRIBE, NOTIFY} = require('red-rings/operations'));

}).call(this);