Add comments and rename things for clarity

lib/cycle.js

@@ -89,6 +89,8 @@ export default function config(opts) {
     if (noBleedingDayWithinThresholdBefore(cycleDay)) return true
     return false
 
+    // checks that there are no relevant bleeding days before
+    // the input cycleDay (returns boolean)
     function noBleedingDayWithinThresholdBefore(cycleDay) {
       const localDate = LocalDate.parse(cycleDay.date)
       const threshold = localDate.minusDays(maxBreakInBleeding + 1).toString()
@@ -101,6 +103,9 @@ export default function config(opts) {
     }
   }
 
+  // returns all bleeding days that belong to one menses directly following
+  // the cycle day. used to set or clear new cycle starts when the target day
+  // changes
   function getMensesDaysRightAfter(cycleDay) {
     const bleedingDays = bleedingDaysSortedByDate
       .filter(d => !d.bleeding.exclude)
@@ -110,6 +115,9 @@ export default function config(opts) {
     })
     return recurse(cycleDay, firstFollowingBleedingDayIndex, [])
 
+    // we look at the current bleeding day as well as the next, and decide
+    // whether they belong to one menses. if they do, we collect them, once
+    // they don't, we're done
     function recurse(day, nextIndex, mensesDays) {
       const next = bleedingDays[nextIndex]
       if (!next) return mensesDays
@@ -118,10 +126,11 @@ export default function config(opts) {
       return recurse(next, nextIndex + 1, mensesDays)
     }
 
-    function isWithinThreshold(cycleDay, nextCycleDay) {
-      const localDate = LocalDate.parse(cycleDay.date)
+    // checks whether the two days belong to one menses episode
+    function isWithinThreshold(bleedingDay, nextBleedingDay) {
+      const localDate = LocalDate.parse(bleedingDay.date)
       const threshold = localDate.plusDays(maxBreakInBleeding + 1).toString()
-      return nextCycleDay.date <= threshold
+      return nextBleedingDay.date <= threshold
     }
   }