feat: add vmid allocator schema

migrations/0006_vmid_allocator.up.sql

@@ -0,0 +1,71 @@
+CREATE TYPE public.vmid_reservation_status AS ENUM ('reserved', 'released');
+
+CREATE TABLE public.cluster_vmid_allocators (
+	cluster_id uuid PRIMARY KEY REFERENCES public.clusters(id) ON DELETE CASCADE,
+	next_vmid integer NOT NULL DEFAULT 100,
+	created_at timestamptz NOT NULL DEFAULT now(),
+	updated_at timestamptz NOT NULL DEFAULT now(),
+	CONSTRAINT cluster_vmid_allocators_next_vmid_check CHECK (next_vmid > 0)
+);
+
+CREATE TABLE public.vmid_reservations (
+	id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+	cluster_id uuid NOT NULL REFERENCES public.clusters(id) ON DELETE CASCADE,
+	proxmox_vmid integer NOT NULL,
+	status public.vmid_reservation_status NOT NULL DEFAULT 'reserved',
+	created_at timestamptz NOT NULL DEFAULT now(),
+	updated_at timestamptz NOT NULL DEFAULT now(),
+	CONSTRAINT vmid_reservations_proxmox_vmid_check CHECK (proxmox_vmid > 0)
+);
+
+CREATE UNIQUE INDEX vmid_reservations_reserved_key
+	ON public.vmid_reservations (cluster_id, proxmox_vmid)
+	WHERE status = 'reserved';
+
+CREATE INDEX vmid_reservations_cluster_id_idx ON public.vmid_reservations (cluster_id);
+
+CREATE OR REPLACE FUNCTION public.reserve_next_vmid(p_cluster_id uuid)
+RETURNS integer
+LANGUAGE plpgsql
+AS $$
+DECLARE
+	candidate integer;
+BEGIN
+	INSERT INTO public.cluster_vmid_allocators (cluster_id)
+	VALUES (p_cluster_id)
+	ON CONFLICT (cluster_id) DO NOTHING;
+
+	SELECT next_vmid
+	INTO candidate
+	FROM public.cluster_vmid_allocators
+	WHERE cluster_id = p_cluster_id
+	FOR UPDATE;
+
+	LOOP
+		EXIT WHEN NOT EXISTS (
+			SELECT 1
+			FROM public.vms
+			WHERE cluster_id = p_cluster_id
+				AND proxmox_vmid = candidate
+		) AND NOT EXISTS (
+			SELECT 1
+			FROM public.vmid_reservations
+			WHERE cluster_id = p_cluster_id
+				AND proxmox_vmid = candidate
+				AND status = 'reserved'
+		);
+
+		candidate := candidate + 1;
+	END LOOP;
+
+	INSERT INTO public.vmid_reservations (cluster_id, proxmox_vmid)
+	VALUES (p_cluster_id, candidate);
+
+	UPDATE public.cluster_vmid_allocators
+	SET next_vmid = candidate + 1,
+		updated_at = now()
+	WHERE cluster_id = p_cluster_id;
+
+	RETURN candidate;
+END;
+$$;