Fix in getting a unique deviceinstance

Some services can't cope with a changing DeviceInstance, so instead
of changing it, first check which ones are already used and claim
the first one that isn't used.
Note that checking is done by looking at what has been claimed in
com.victronenergy.settings, not by actually looking at what the
services use.

src/nodes/config-client.js

@@ -31,6 +31,69 @@ module.exports = function (RED) {
     return res.send(serialized)
   })
 
+  // Track last assigned instance numbers
+  const lastAssignedInstances = new Map()
+
+  function findNextAvailableInstance (jsonStr, deviceType) {
+    const data = JSON.parse(jsonStr)
+    const victronSettings = data['com.victronenergy.settings']
+
+    if (!victronSettings) {
+      return null
+    }
+
+    // Get all used instance numbers for the specified device type
+    const usedInstances = new Set()
+
+    function collectInstances (obj) {
+      for (const [key, value] of Object.entries(obj)) {
+        if (typeof value === 'object' && value !== null) {
+          collectInstances(value)
+        } else if (
+          key.endsWith('ClassAndVrmInstance') &&
+            typeof value === 'string' &&
+            value.startsWith(deviceType + ':')
+        ) {
+          const instance = parseInt(value.split(':')[1])
+          if (!isNaN(instance)) {
+            usedInstances.add(instance)
+          }
+        }
+      }
+    }
+
+    collectInstances(victronSettings)
+
+    // Get the last assigned number for this device type, or start at 99
+    let nextInstance = (lastAssignedInstances.get(deviceType) || 99) + 1
+
+    // Keep incrementing until we find an unused number
+    while (usedInstances.has(nextInstance)) {
+      nextInstance++
+    }
+
+    // Store this assignment for future requests
+    lastAssignedInstances.set(deviceType, nextInstance)
+
+    return nextInstance
+  }
+
+  RED.httpNode.get('/victron/deviceinstance/:type', RED.auth.needsPermission('victron-client.read'), (req, res) => {
+    try {
+      const serialized = JSON.stringify(globalClient.system.cache)
+      const nextInstance = findNextAvailableInstance(serialized, req.params.type)
+
+      if (nextInstance === null) {
+        return res.status(404).json({ error: 'No settings found' })
+      }
+
+      res.setHeader('Content-Type', 'application/json')
+      return res.json({ instance: nextInstance })
+    } catch (error) {
+      console.error('Error finding next instance:', error)
+      return res.status(500).json({ error: 'Internal server error' })
+    }
+  })
   /**
      * Victron Energy Configuration Node.
      *

src/nodes/victron-virtual.html

@@ -20,6 +20,21 @@
         const selected = $('select#node-input-device').val()
         $('.input-'+selected).show()
 
+        if (selected) {
+            $.getJSON('victron/deviceinstance/' + selected)
+                .done(function(response) {
+                    if (response && typeof response.instance !== 'undefined') {
+                        // Ensure instance is converted to string
+                        const instanceStr = String(response.instance);
+                        $('#node-input-instance').val(instanceStr);
+                    }
+                })
+                .fail(function(jqXHR, textStatus, errorThrown) {
+                    console.error('Failed to fetch instance:', textStatus, errorThrown);
+                    RED.notify("Error fetching instance number: " + textStatus, "error");
+                });
+        }
+
         if (selected === 'temperature') {
         // Show/hide battery voltage input based on checkbox
         $('#node-input-include-battery').off('change').on('change', function() {
@@ -35,14 +50,14 @@
     }
     }
 
-
     RED.nodes.registerType('victron-virtual',{
         category: 'Victron Energy',
         color: '#f7ab3e',
         paletteLabel: "Virtual Device",
         defaults: {
             name: {value:""},
             device: {value:"", required: true},
+            instance: {value:"", required: true},
             // grid
             grid_nrofphases: {value: 1, required: false},
             // tank
@@ -76,6 +91,7 @@
         <label for="node-input-name"><i class="fa fa-tag"></i> Name</label>
         <input type="text" id="node-input-name" placeholder="Name">
     </div>
+    <input type="hidden" id="node-input-instance">
     <div class="form-row">
         <label for="node-input-device"><i class="fa fa-microchip"></i> Device</label>
         <select id="node-input-device" required onchange="checkSelectedVirtualDevice()">

src/nodes/victron-virtual.js

@@ -259,7 +259,7 @@ module.exports = function (RED) {
       const iface = getIface(device)
 
       // Initially set the DeviceInstance to 100, this may be updated later if it has already been taken
-      iface.DeviceInstance = 100
+      iface.DeviceInstance = Number(config.instance) || 199
       iface.CustomName = config.name || `Virtual ${config.device}`
       iface.Status = 0
       iface.Serial = id || '-'