1 files changed, 23 insertions, 0 deletions
diff --git a/lib/unitsToRanges.js b/lib/unitsToRanges.js
new file mode 100644
index 0000000..8ffd7b0
--- /dev/null
+++ b/lib/unitsToRanges.js
@@ -0,0 +1,23 @@
+/**
+ * Convert a list of unit numbers into an addr:flats list. eg. converts 1,2,3,5 into 1-3;5
+ *
+ * @param {Array} units
+ *
+ * @returns {string} addr:flats list
+ */
+module.exports = (units) => {
+  // adapted from https://stackoverflow.com/a/54973116/6702659
+  const unitRanges = units
+    .slice()
+    .sort((a, b) => a - b)
+    .reduce((acc, cur, idx, src) => {
+      if ((idx > 0) && ((cur - src[idx - 1]) === 1)) {
+        acc[acc.length - 1][1] = cur
+      } else {
+        acc.push([cur])
+      }
+      return acc
+    }, [])
+    .map(range => range.join('-'))
+  return unitRanges.length ? unitRanges.join(';') : null
+}