Implement minus 8 day rule

lib/sympto/minus-8-day-rule.js

@@ -0,0 +1,26 @@
+import { LocalDate } from 'js-joda'
+import getNfpStatus from './index'
+
+export default function (previousCycles) {
+  const fhms = previousCycles
+    .map(cycle => {
+      const status = getNfpStatus({ cycle })
+      if (status.temperatureShift) {
+        const day = status.temperatureShift.firstHighMeasurementDay
+        const firstCycleDayDate = LocalDate.parse(cycle[0].date)
+        const fhmDate = LocalDate.parse(day.date)
+        return fhmDate.compareTo(firstCycleDayDate) + 1
+      }
+      return null
+    })
+    .filter(val => typeof val === 'number')
+
+  const preOvuLength = Math.min(...fhms) - 8
+
+  // pre ovu length may only be lengthened if we have more than 12 previous fhms
+  // if pre ovu length is less than 5, it shortened even with fewer prev fhms
+  if (preOvuLength < 5) return preOvuLength
+  if (fhms.length >= 12) return preOvuLength
+
+  return null
+}

lib/sympto/pre-ovulatory.js

@@ -1,20 +1,21 @@
 import { LocalDate } from "js-joda"
+import apply8DayRule from './minus-8-day-rule'
 
 export default function(cycle, previousCycles) {
-  // TODO handle no previous cycles
   let preOvuPhaseLength = 5
 
-  //TODO make sure it handles weird cases like fhm < 9
   const minus8DayRuleResult = apply8DayRule(previousCycles)
   if (minus8DayRuleResult) preOvuPhaseLength = minus8DayRuleResult
 
   const startDate = LocalDate.parse(cycle[0].date)
-  const preOvuPhaseEndDate = startDate.plusDays(preOvuPhaseLength - 1).toString()
-  const maybePreOvuDays = cycle.slice(0, 5).filter(d => d.date <= preOvuPhaseEndDate)
+  const preOvuEndDate = startDate.plusDays(preOvuPhaseLength - 1).toString()
+  const maybePreOvuDays = cycle.slice(0, preOvuPhaseLength).filter(d => {
+    return d.date <= preOvuEndDate
+  })
   const preOvulatoryDays = getDaysUntilFertileMucus(maybePreOvuDays)
   let endDate
   if (preOvulatoryDays.length === maybePreOvuDays.length) {
-    endDate = preOvuPhaseEndDate
+    endDate = preOvuEndDate
   } else {
     endDate = preOvulatoryDays[preOvulatoryDays.length - 1].date
   }
@@ -31,11 +32,12 @@ export default function(cycle, previousCycles) {
 }
 
 function getDaysUntilFertileMucus(days) {
-  const firstFertileMucusDayIndex = days.findIndex(day => day.mucus && day.mucus.value > 1)
+  const firstFertileMucusDayIndex = days.findIndex(day => {
+    return day.mucus && day.mucus.value > 1
+  })
+
   if (firstFertileMucusDayIndex > -1) {
     return days.slice(0, firstFertileMucusDayIndex)
   }
   return days
-}
-
-function apply8DayRule(previousCycles) {}
+}