feat: premium ID changes

PluralKit.Core/Database/Repository/ModelRepository.PremiumAllowance.cs

@@ -0,0 +1,49 @@
+using SqlKata;
+using Npgsql;
+
+namespace PluralKit.Core;
+
+public partial class ModelRepository
+{
+    public Task<PremiumAllowance?> GetPremiumAllowance(SystemId system, IPKConnection conn = null)
+        => _db.QueryFirst<PremiumAllowance?>(conn, new Query("premium_allowances").Where("system", system));
+
+    public Task CreatePremiumAllowance(SystemId system, IPKConnection conn = null)
+    {
+        var query = new Query("premium_allowances").AsInsert(new
+        {
+            system = system,
+        });
+
+        return _db.ExecuteQuery(query, "on conflict do nothing");
+    }
+
+    public async Task<PremiumAllowance> UpdatePremiumAllowance(SystemId system, PremiumAllowancePatch patch, IPKConnection conn = null)
+    {
+        var query = patch.Apply(new Query("premium_allowances").Where("system", system));
+        return await _db.QueryFirst<PremiumAllowance>(conn, query, "returning *");
+    }
+
+    public async Task<bool> UpdatePremiumAllowanceForIdChange(SystemId system, IPKConnection conn = null)
+    {
+        var query = new Query("premium_allowances")
+        .AsUpdate(new
+        {
+            id_changes_remaining = new UnsafeLiteral("id_changes_remaining - 1")
+        })
+        .Where("system", system);
+
+        try
+        {
+            await _db.ExecuteQuery(conn, query);
+        }
+        catch (PostgresException pe)
+        {
+            if (!pe.Message.Contains("violates check constraint"))
+                throw;
+            return false;
+        }
+
+        return true;
+    }
+}