Extract maybeSetNewCycleStart into own module

lib/set-new-cycle-start.js

@@ -0,0 +1,37 @@
+export default function ({
+  val, cycleDay, mensesDaysAfter, checkIsMensesStart
+}) {
+  // if a bleeding value is deleted or excluded, we need to check if
+  // there are any following bleeding days and if the
+  // next one of them is now a cycle start
+  if (bleedingValueDeletedOrExluded(val)) {
+    cycleDay.bleeding = val
+    cycleDay.isCycleStart = false
+    if (!mensesDaysAfter.length) return
+    const nextOne = mensesDaysAfter[mensesDaysAfter.length - 1]
+    if (checkIsMensesStart(nextOne)) {
+      nextOne.isCycleStart = true
+    }
+  } else if (bleedingValueAddedOrChanged(val)) {
+    cycleDay.bleeding = val
+    cycleDay.isCycleStart = checkIsMensesStart(cycleDay)
+    maybeClearOldCycleStarts(cycleDay)
+  }
+
+  function bleedingValueDeletedOrExluded(val) {
+    const bleedingDeleted = !val
+    const bleedingExcluded = val && val.exclude
+    return bleedingDeleted || bleedingExcluded
+  }
+
+  function bleedingValueAddedOrChanged(symptom, val) {
+    return symptom === 'bleeding' && val
+  }
+
+  function maybeClearOldCycleStarts() {
+  // if we have a new bleeding day, we need to clear the
+  // menses start marker from all following days of this
+  // menses that may have been marked as start before
+    mensesDaysAfter.forEach(day => day.isCycleStart = false)
+  }
+}