M8-R03: hand off channel binding during meter swap

frontend/src/energy/MeterManager.tsx

@@ -83,11 +83,12 @@ function toLocalDateInputString(d: Date): string {
 // ---------------------------------------------------------------------------
 
 interface DeclareMeterFormProps {
+  meters: MeterResponse[]
   onClose: () => void
   onSaved: () => void
 }
 
-function DeclareMeterForm({ onClose, onSaved }: DeclareMeterFormProps) {
+function DeclareMeterForm({ meters, onClose, onSaved }: DeclareMeterFormProps) {
   const [label, setLabel] = useState('')
   const [dateStr, setDateStr] = useState('')
   const [reason, setReason] = useState<string | null>(null)
@@ -100,8 +101,43 @@ function DeclareMeterForm({ onClose, onSaved }: DeclareMeterFormProps) {
   const channels = useSourceChannels(sourceUuid)
 
   const declareMutation = useDeclareMeter()
-  const compatible = (channel: { unit: string; binding_count: number; bound_meter_ids: number[] }) =>
-    ({ electricity: 'kWh', heating: 'GJ', hot_water: 'm³' } as Record<string, string>)[commodity ?? 'electricity'] === channel.unit && channel.binding_count === 0 && channel.bound_meter_ids.length === 0
+  const expectedUnit = ({ electricity: 'kWh', heating: 'GJ', hot_water: 'm³' } as Record<string, string>)[commodity ?? 'electricity']
+  const oldMeter = meters.find((meter) => meter.commodity === commodity && meter.ended_at === null)
+  const isChannelEligible = (uuid: string, startedAt: string) => {
+    const channel = channels.data?.items.find((item) => item.uuid === uuid)
+    if (!channel || channel.unit !== expectedUnit) return false
+
+    // Channel aggregates include closed binding history.  For a meter swap, only
+    // currently open bindings determine whether this channel can be handed off.
+    const openBindings = meters.flatMap((meter) =>
+      (meter.bindings ?? [])
+        .filter((binding) => binding.source_channel_uuid === channel.uuid && binding.ended_at === null)
+        .map((binding) => ({ meter, binding })),
+    )
+    const isUnbound = channel.binding_count === 0 &&
+      channel.bound_meter_ids.length === 0 && openBindings.length === 0
+    const oldBinding = openBindings[0]
+    const canHandoff = reason === 'meter_swap' && oldMeter !== undefined &&
+      openBindings.length === 1 && oldBinding !== undefined &&
+      oldBinding.meter.id === oldMeter.id && oldBinding.meter.commodity === commodity &&
+      startedAt > toLocalDateInputString(parseBackendTimestamp(oldBinding.binding.started_at))
+    return isUnbound || canHandoff
+  }
+  const channelOptions = channels.data?.items
+    .filter((channel) => channel.unit === expectedUnit)
+    .map((channel) => {
+      const canHandoff = !(
+        channel.binding_count === 0 && channel.bound_meter_ids.length === 0
+      ) && isChannelEligible(channel.uuid, dateStr)
+      return {
+        value: channel.uuid,
+        label: `${channel.label} (${channel.unit})${canHandoff ? ' — hand off from current meter' : ''}`,
+        disabled: !isChannelEligible(channel.uuid, dateStr),
+      }
+    }) ?? []
+  const selectedChannelUuid = channelUuid && isChannelEligible(channelUuid, dateStr)
+    ? channelUuid
+    : null
 
   async function handleSubmit(e: React.FormEvent) {
     e.preventDefault()
@@ -127,7 +163,7 @@ function DeclareMeterForm({ onClose, onSaved }: DeclareMeterFormProps) {
         reason: reason as MeterReason,
         note: note.trim() || undefined,
         commodity: commodity ?? 'electricity',
-        ...(channelUuid ? { source_channel_uuid: channelUuid } : {}),
+        ...(selectedChannelUuid ? { source_channel_uuid: selectedChannelUuid } : {}),
       })
       onSaved()
       onClose()
@@ -166,7 +202,11 @@ function DeclareMeterForm({ onClose, onSaved }: DeclareMeterFormProps) {
             type="date"
             required
             value={dateStr}
-            onChange={(e) => setDateStr(e.currentTarget.value)}
+            onChange={(e) => {
+              const nextDateStr = e.currentTarget.value
+              setDateStr(nextDateStr)
+              setChannelUuid((uuid) => uuid && !isChannelEligible(uuid, nextDateStr) ? null : uuid)
+            }}
             data-testid="meter-started-at"
           />
 
@@ -175,17 +215,17 @@ function DeclareMeterForm({ onClose, onSaved }: DeclareMeterFormProps) {
             required
             data={REASON_OPTIONS}
             value={reason}
-            onChange={setReason}
+            onChange={(value) => { setReason(value); setChannelUuid(null) }}
             data-testid="meter-reason"
           />
 
-          <Select label="Commodity" value={commodity} onChange={setCommodity} data={[
+          <Select label="Commodity" value={commodity} onChange={(value) => { setCommodity(value); setChannelUuid(null) }} data={[
             { value: 'electricity', label: 'Electricity' },
             { value: 'heating', label: 'Heating' },
             { value: 'hot_water', label: 'Hot water' },
           ]} />
           <Select label="Bind source (optional)" value={sourceUuid} onChange={(value) => { setSourceUuid(value); setChannelUuid(null) }} data={sources.data?.items.filter((source) => typeof source.uuid === 'string').map((source) => ({ value: source.uuid, label: source.name })) ?? []} />
-          {sourceUuid && <Select label="Compatible source channel (optional)" value={channelUuid} onChange={setChannelUuid} description="Only unbound channels with the required unit are eligible. Suggestions are informational only." data={channels.data?.items.filter(compatible).map((channel) => ({ value: channel.uuid, label: `${channel.label} (${channel.unit})${channel.suggested_commodity ? ` — suggestion: ${channel.suggested_commodity}` : ''}` })) ?? []} />}
+          {sourceUuid && <Select label="Compatible source channel (optional)" value={selectedChannelUuid} onChange={setChannelUuid} description={reason === 'meter_swap' ? 'An unbound channel, or the current same-commodity meter’s single binding, can be selected. Other occupied channels stay unavailable.' : 'Only unbound channels with the required unit are eligible.'} data={channelOptions} />}
 
           <Textarea
             label="Note (optional)"
@@ -534,6 +574,7 @@ export function MeterManager() {
       {/* Declare new meter */}
       {showDeclareForm && (
         <DeclareMeterForm
+          meters={meters}
           onClose={() => setShowDeclareForm(false)}
           onSaved={() => setShowDeclareForm(false)}
         />