1 files changed, 51 insertions, 0 deletions
diff --git a/backend/reduce.js b/backend/reduce.js
new file mode 100644
index 0000000..3ac9da2
--- /dev/null
+++ b/backend/reduce.js
@@ -0,0 +1,51 @@
+#!/usr/bin/node
+
+const R = require('ramda'),
+  utils = require('./utils');
+
+function aggregatePayloads(config) {
+  // Ramda group() only groups neighbors, so sort beforehand
+  const sorter  = R.props(config.group);
+  const grouper = utils.eqPropses(config.group);
+
+  // sum & count
+  const aggregator = R.pipe(
+    R.sortBy(sorter),
+    R.groupWith(grouper),
+    R.map(
+      R.converge(utils.mergeAllArgs, [
+        R.pipe(
+          R.project(config.group),
+          R.prop(0),
+        ),
+        R.pipe(
+          R.project(R.concat(config.sum, R.of('Count'))),
+          utils.mergeAllWith(R.add),
+          utils.unlist,
+        ),
+      ]),
+    ),
+  );
+
+  return aggregator;
+}
+
+function deriveStatistics(config) {
+  const sorter = R.compose(R.defaultTo(0), R.prop('Winner'));
+
+  // divide sums by counts = averages
+  const transformer = R.map(
+    R.converge(utils.mergeAllArgs, [
+      utils.projectProps(config.group),
+      utils.divPropsByProp('Count', config.sum),
+      utils.projectProps(['Count']),
+    ])
+  );
+
+  return R.compose(transformer, R.sortBy(sorter));
+}
+
+module.exports = {
+  aggregatePayloads,
+  deriveStatistics,
+};