Apply changes when creating invoices for projects.

app/Models/Project.php

@@ -36,6 +36,7 @@ class Project extends Model
         'end',
         'customer_email',
         'customer_name',
+        'next_invoice_count',
     ];
 
 
@@ -56,6 +57,14 @@ class Project extends Model
         return (is_null($this->start_date)) ? '' : Carbon::createFromFormat('Y-m-d', $this->start_date)->format('d.m.Y');
     }
 
+    /**
+     * Get the next invoice number for this project.
+     */
+    public function getNextInvoiceCountAttribute(): int
+    {
+        return $this->invoices()->max('project_count') + 1 ?? 1;
+    }
+
     /**
      * Get the end_date attribute in local format.
      */
@@ -72,6 +81,9 @@ class Project extends Model
         return $this->belongsTo(Customer::class)->withTrashed();
     }
 
+    /**
+     * Get the invoices for this project.
+     */
     public function invoices(): HasMany
     {
         return $this->hasMany(Invoice::class);