From 326d16a6591f501be0d9eb7a365a05bc99b68903 Mon Sep 17 00:00:00 2001
From: Eddy de Vink <github@eddydev.ink>
Date: Sat, 27 Jun 2026 23:03:53 +0200
Subject: [PATCH] feat: auto-calculate fatMass and muscleMass from weight +
 percentages

---
 src/components/MeasurementForm.tsx | 79 +++++++++++++++++++++---------
 1 file changed, 57 insertions(+), 22 deletions(-)

diff --git a/src/components/MeasurementForm.tsx b/src/components/MeasurementForm.tsx
index f6a11d2..7305670 100644
--- a/src/components/MeasurementForm.tsx
+++ b/src/components/MeasurementForm.tsx
@@ -1,4 +1,4 @@
-import React, { useState } from 'react'
+import React, { useState, useMemo } from 'react'
 import { View, Text, TextInput, TouchableOpacity, StyleSheet, KeyboardAvoidingView, Platform, ScrollView } from 'react-native'
 import DateTimePicker, { DateTimePickerEvent } from '@react-native-community/datetimepicker'
 import { Measurement } from '../types'
@@ -9,17 +9,27 @@ type Props = {
   initialValues?: Partial<Measurement>
 }
 
-const fields: { key: keyof Measurement; label: string; placeholder: string; keyboardType: 'decimal-pad' | 'number-pad' }[] = [
+type FieldDef = {
+  key: keyof Measurement
+  label: string
+  placeholder: string
+  keyboardType: 'decimal-pad' | 'number-pad'
+  computed?: boolean
+}
+
+const fields: FieldDef[] = [
   { key: 'weight', label: 'Gewicht (kg)', placeholder: '75.5', keyboardType: 'decimal-pad' },
   { key: 'bmi', label: 'BMI', placeholder: '22.3', keyboardType: 'decimal-pad' },
   { key: 'bodyFatPercentage', label: 'Vetpercentage (%)', placeholder: '15.2', keyboardType: 'decimal-pad' },
-  { key: 'fatMass', label: 'Vetmassa (kg)', placeholder: '11.5', keyboardType: 'decimal-pad' },
+  { key: 'fatMass', label: 'Vetmassa (kg)', placeholder: '11.5', keyboardType: 'decimal-pad', computed: true },
   { key: 'musclePercentage', label: 'Spierpercentage (%)', placeholder: '40.1', keyboardType: 'decimal-pad' },
-  { key: 'muscleMass', label: 'Spiermassa (kg)', placeholder: '30.3', keyboardType: 'decimal-pad' },
+  { key: 'muscleMass', label: 'Spiermassa (kg)', placeholder: '30.3', keyboardType: 'decimal-pad', computed: true },
   { key: 'visceralFat', label: 'Buikvet (index)', placeholder: '8', keyboardType: 'number-pad' },
   { key: 'bmr', label: 'Stofwisseling (kcal)', placeholder: '1650', keyboardType: 'number-pad' },
 ]
 
+const computedKeys = new Set<keyof Measurement>(['fatMass', 'muscleMass'])
+
 export default function MeasurementForm({ onSubmit, initialValues }: Props) {
   const [pickerOpen, setPickerOpen] = useState(false)
   const [measurementDate, setMeasurementDate] = useState<Date>(() => {
@@ -29,21 +39,31 @@ export default function MeasurementForm({ onSubmit, initialValues }: Props) {
   const [values, setValues] = useState<Record<string, string>>(() => {
     const init: Record<string, string> = {}
     for (const f of fields) {
+      if (f.computed) continue
       init[f.key] = initialValues?.[f.key]?.toString() ?? ''
     }
     return init
   })
 
+  const weight = parseFloat(values.weight) || 0
+  const bodyFatPct = parseFloat(values.bodyFatPercentage) || 0
+  const musclePct = parseFloat(values.musclePercentage) || 0
+
+  const computed = useMemo(() => ({
+    fatMass: weight > 0 && bodyFatPct > 0 ? ((weight * bodyFatPct) / 100).toFixed(1) : '',
+    muscleMass: weight > 0 && musclePct > 0 ? ((weight * musclePct) / 100).toFixed(1) : '',
+  }), [weight, bodyFatPct, musclePct])
+
   const handleSubmit = () => {
     const now = new Date().toISOString()
     const m: Measurement = {
       id: generateId(),
-      weight: parseFloat(values.weight) || 0,
+      weight,
       bmi: parseFloat(values.bmi) || 0,
-      bodyFatPercentage: parseFloat(values.bodyFatPercentage) || 0,
-      fatMass: parseFloat(values.fatMass) || 0,
-      musclePercentage: parseFloat(values.musclePercentage) || 0,
-      muscleMass: parseFloat(values.muscleMass) || 0,
+      bodyFatPercentage: bodyFatPct,
+      fatMass: parseFloat(computed.fatMass) || 0,
+      musclePercentage: musclePct,
+      muscleMass: parseFloat(computed.muscleMass) || 0,
       visceralFat: parseInt(values.visceralFat, 10) || 0,
       bmr: parseFloat(values.bmr) || 0,
       measuredAt: measurementDate.toISOString(),
@@ -91,19 +111,32 @@ export default function MeasurementForm({ onSubmit, initialValues }: Props) {
           />
         )}
 
-        {fields.map(f => (
-          <View key={f.key} style={styles.field}>
-            <Text style={styles.label}>{f.label}</Text>
-            <TextInput
-              style={styles.input}
-              keyboardType={f.keyboardType}
-              placeholder={f.placeholder}
-              value={values[f.key]}
-              onChangeText={v => setField(f.key, v)}
-              placeholderTextColor="#999"
-            />
-          </View>
-        ))}
+        {fields.map(f => {
+          if (f.computed) {
+            const calcValue = f.key === 'fatMass' ? computed.fatMass : computed.muscleMass
+            return (
+              <View key={f.key} style={styles.field}>
+                <Text style={styles.label}>{f.label}</Text>
+                <View style={[styles.input, styles.computedInput]}>
+                  <Text style={styles.computedText}>{calcValue || '—'}</Text>
+                </View>
+              </View>
+            )
+          }
+          return (
+            <View key={f.key} style={styles.field}>
+              <Text style={styles.label}>{f.label}</Text>
+              <TextInput
+                style={styles.input}
+                keyboardType={f.keyboardType}
+                placeholder={f.placeholder}
+                value={values[f.key] ?? ''}
+                onChangeText={v => setField(f.key, v)}
+                placeholderTextColor="#999"
+              />
+            </View>
+          )
+        })}
         <TouchableOpacity style={styles.button} onPress={handleSubmit}>
           <Text style={styles.buttonText}>Opslaan</Text>
         </TouchableOpacity>
@@ -118,6 +151,8 @@ const styles = StyleSheet.create({
   field: { marginBottom: 12 },
   label: { fontSize: 14, fontWeight: '600', color: '#333', marginBottom: 4 },
   input: { backgroundColor: '#fff', borderRadius: 8, padding: 12, fontSize: 16, borderWidth: 1, borderColor: '#ddd' },
+  computedInput: { backgroundColor: '#f0f0f0' },
+  computedText: { fontSize: 16, color: '#666' },
   dateButton: { backgroundColor: '#fff', borderRadius: 8, padding: 12, borderWidth: 1, borderColor: '#ddd' },
   dateButtonText: { fontSize: 16, color: '#333' },
   button: { backgroundColor: '#4CAF50', padding: 16, borderRadius: 8, alignItems: 'center', marginTop: 8 },