feat(csv-import): Enhance source unit handling and custom conversion options

- Updated the source_unit_choices_for_field function to include a custom option for user-defined conversion factors, improving flexibility in unit conversions.
- Modified the AdminCsvTemplateEditorPage to support custom conversion factors, allowing users to input specific scaling factors for their data.
- Added tests to ensure the custom option is correctly included in the source unit choices and functions as expected in the template editor.

backend/csv_parser/field_units.py

@@ -68,7 +68,7 @@ def source_unit_choices_for_field(module: str, db_field: str) -> list[dict[str,
     choices = _UNIT_FAMILY.get(cu)
     if not choices:
         return []
-    return [
+    out: list[dict[str, Any]] = [
         {
             "id": c["id"],
             "label": c["label"],
@@ -77,6 +77,15 @@ def source_unit_choices_for_field(module: str, db_field: str) -> list[dict[str,
         }
         for c in choices
     ]
+    out.append(
+        {
+            "id": "custom",
+            "label": "Benutzerdefiniert (Konvertierungsfaktor, z. B. ml→g je nach Dichte)",
+            "canonical_unit": cu,
+            "is_canonical": False,
+        }
+    )
+    return out
 
 
 def factor_source_to_canonical(module: str, db_field: str, source_unit: str | None) -> float:

backend/tests/test_csv_parser_core.py

@@ -12,6 +12,7 @@ from csv_parser.core import (
     get_csv_import_limits,
     iter_csv_dict_rows,
 )
+from csv_parser.field_units import source_unit_choices_for_field
 from csv_parser.mapping_suggest import build_type_conversions_for_mapping
 from csv_parser.type_converter import convert_value, build_row_after_mapping
 
@@ -213,3 +214,9 @@ def test_datetime_flexible():
     spec = {"type": "datetime", "format": "yyyy-mm-dd HH:MM:SS", "flexible": True}
     dtv = convert_value("15.01.2024 14:30:00", "t", spec)
     assert dtv.month == 1 and dtv.day == 15 and dtv.hour == 14
+
+
+def test_source_unit_choices_include_custom_at_end():
+    opts = source_unit_choices_for_field("nutrition", "protein_g")
+    assert opts[-1]["id"] == "custom"
+    assert any(o["id"] == "mg" for o in opts)

frontend/src/pages/AdminCsvTemplateEditorPage.jsx

@@ -187,6 +187,10 @@ export default function AdminCsvTemplateEditorPage() {
       const hit = opts.find((o) => o.id === sid)
       if (hit) return hit.id
     }
+    if (tc[fieldKey]?.conversion_factor != null && tc[fieldKey]?.conversion_factor !== '') {
+      const hasCustomOpt = opts.some((o) => o.id === 'custom')
+      if (hasCustomOpt) return 'custom'
+    }
     return canonical || ''
   }
 
@@ -204,13 +208,59 @@ export default function AdminCsvTemplateEditorPage() {
       tc[fieldKey] && typeof tc[fieldKey] === 'object'
         ? { ...tc[fieldKey] }
         : { type: 'float', decimal_separator: 'auto', flexible: true }
+    delete base.target_unit
     if (sourceUnitId === canonical || sourceUnitId === '' || sourceUnitId == null) {
       delete base.source_unit
+      delete base.conversion_factor
+    } else if (sourceUnitId === 'custom') {
+      base.source_unit = 'custom'
+      // conversion_factor nur per Eingabefeld setzen/löschen
     } else {
       base.source_unit = sourceUnitId
+      delete base.conversion_factor
+    }
+    tc[fieldKey] = base
+    setTypeConversionsText(JSON.stringify(tc, null, 2))
+    setError(null)
+  }
+
+  const getCustomConversionFactorInputValue = (fieldKey) => {
+    let tc
+    try {
+      tc = JSON.parse(typeConversionsText || '{}')
+    } catch {
+      return ''
+    }
+    const v = tc[fieldKey]?.conversion_factor
+    if (v == null || v === '') return ''
+    return String(v)
+  }
+
+  const updateCustomConversionFactor = (fieldKey, raw) => {
+    let tc
+    try {
+      tc = JSON.parse(typeConversionsText || '{}')
+    } catch {
+      setError('type_conversions: ungültiges JSON (Faktor kann nicht gesetzt werden).')
+      return
+    }
+    const base =
+      tc[fieldKey] && typeof tc[fieldKey] === 'object'
+        ? { ...tc[fieldKey] }
+        : { type: 'float', decimal_separator: 'auto', flexible: true }
+    const t = String(raw).trim().replace(',', '.')
+    if (t === '') {
+      delete base.conversion_factor
+    } else {
+      const n = Number(t)
+      if (Number.isNaN(n)) {
+        setError('Konvertierungsfaktor: bitte eine gültige Zahl eingeben.')
+        return
+      }
+      base.conversion_factor = n
+      base.source_unit = 'custom'
     }
     delete base.target_unit
-    delete base.conversion_factor
     tc[fieldKey] = base
     setTypeConversionsText(JSON.stringify(tc, null, 2))
     setError(null)
@@ -591,36 +641,60 @@ export default function AdminCsvTemplateEditorPage() {
         <div className="card" style={{ padding: 16, marginBottom: 16 }}>
           <div className="form-label">3b. Quelleinheit (optional)</div>
           <p style={{ fontSize: 13, color: 'var(--text2)', marginTop: 8, lineHeight: 1.55 }}>
-            Ziel-Einheit kommt aus dem Datenmodell (z. B. kcal, g, kg, km). Hier nur angeben, falls die CSV
-            abweicht (z. B. FDDB kJ → kcal, Makros in kg → g, Gewicht in lb → kg). Beim Ändern hier werden
-            pro Feld <code>conversion_factor</code> und <code>target_unit</code> entfernt (verhindert
-            Doppel-Umrechnung); bei Bedarf wieder in Abschnitt 4 ergänzen.
+            Ziel-Einheit kommt aus dem Datenmodell (z. B. kcal, g, kg, km). Standard-Umrechnungen wählen; für
+            abweichende Skalen (z. B. Volumen→Masse mit variabler Dichte) &quot;Benutzerdefiniert&quot; und den
+            Faktor eintragen (CSV-Wert × Faktor → Speicher-Einheit). Bei Registry-Optionen werden{' '}
+            <code>target_unit</code> und ein alter <code>conversion_factor</code> entfernt; bei
+            Benutzerdefiniert bleibt der Faktor erhalten, bis du ihn leerst.
           </p>
-          <div style={{ marginTop: 14, display: 'flex', flexDirection: 'column', gap: 12 }}>
+          <div style={{ marginTop: 14, display: 'flex', flexDirection: 'column', gap: 16 }}>
             {unitTargets.map(({ field: fkey, options }) => (
-              <label key={fkey} style={{ display: 'block' }}>
-                <span className="form-label" style={{ display: 'block', marginBottom: 6 }}>
-                  {fkey}
-                </span>
-                <select
-                  className="form-input"
-                  value={getSourceUnitSelectValue(fkey) || ''}
-                  onChange={(e) => updateSourceUnit(fkey, e.target.value)}
-                  style={{
-                    width: '100%',
-                    minHeight: 46,
-                    textAlign: 'left',
-                    padding: '11px 14px',
-                    fontSize: 15,
-                  }}
-                >
-                  {options.map((o) => (
-                    <option key={o.id} value={o.id}>
-                      {o.label}
-                    </option>
-                  ))}
-                </select>
-              </label>
+              <div key={fkey}>
+                <label style={{ display: 'block' }}>
+                  <span className="form-label" style={{ display: 'block', marginBottom: 6 }}>
+                    {fkey}
+                  </span>
+                  <select
+                    className="form-input"
+                    value={getSourceUnitSelectValue(fkey) || ''}
+                    onChange={(e) => updateSourceUnit(fkey, e.target.value)}
+                    style={{
+                      width: '100%',
+                      minHeight: 46,
+                      textAlign: 'left',
+                      padding: '11px 14px',
+                      fontSize: 15,
+                    }}
+                  >
+                    {options.map((o) => (
+                      <option key={o.id} value={o.id}>
+                        {o.label}
+                      </option>
+                    ))}
+                  </select>
+                </label>
+                {getSourceUnitSelectValue(fkey) === 'custom' && (
+                  <div style={{ marginTop: 10 }}>
+                    <span className="form-label" style={{ display: 'block', marginBottom: 6 }}>
+                      Konvertierungsfaktor (× CSV-Wert → Wert in Speicher-Einheit)
+                    </span>
+                    <input
+                      type="text"
+                      inputMode="decimal"
+                      className="form-input"
+                      placeholder="z. B. 1.03 bei ml→g (Dichte ≈ 1,03 g/ml)"
+                      value={getCustomConversionFactorInputValue(fkey)}
+                      onChange={(e) => updateCustomConversionFactor(fkey, e.target.value)}
+                      style={{ width: '100%', textAlign: 'left' }}
+                    />
+                    {getCustomConversionFactorInputValue(fkey) === '' && (
+                      <p style={{ fontSize: 12, color: 'var(--text3)', marginTop: 6 }}>
+                        Ohne Faktor gilt keine zusätzliche Skalierung (wie 1:1 nach dem Parsen).
+                      </p>
+                    )}
+                  </div>
+                )}
+              </div>
             ))}
           </div>
         </div>