refactor: separate workload class from placement driver

internal/taskassignment/placement.go

@@ -0,0 +1,76 @@
+package taskassignment
+
+import (
+	"errors"
+	"fmt"
+	"slices"
+)
+
+type WorkloadClass string
+
+const (
+	WorkloadContainer WorkloadClass = "container"
+	WorkloadVM        WorkloadClass = "vm"
+)
+
+type Driver string
+
+const (
+	DriverKubernetes  Driver = "kubernetes"
+	DriverOpenSandbox Driver = "opensandbox"
+)
+
+type Placement struct {
+	Class  WorkloadClass `json:"workload_class"`
+	Driver Driver        `json:"driver"`
+}
+
+var (
+	KubernetesContainer = Placement{Class: WorkloadContainer, Driver: DriverKubernetes}
+	OpenSandboxVM       = Placement{Class: WorkloadVM, Driver: DriverOpenSandbox}
+)
+
+func (p Placement) Validate() error {
+	switch p {
+	case KubernetesContainer, OpenSandboxVM:
+		return nil
+	default:
+		return fmt.Errorf("unsupported workload placement %s/%s", p.Class, p.Driver)
+	}
+}
+
+func (p Placement) Key() string { return string(p.Class) + "." + string(p.Driver) }
+
+func PlacementFromLabels(labels []string) (Placement, error) {
+	if !slices.Contains(labels, "self-hosted") {
+		return Placement{}, fmt.Errorf("task runs-on labels must include self-hosted: %v", labels)
+	}
+	legacyPod := slices.Contains(labels, "pod")
+	container := slices.Contains(labels, string(WorkloadContainer))
+	vm := slices.Contains(labels, string(WorkloadVM)) || slices.Contains(labels, "vm-dev")
+	kubernetes := slices.Contains(labels, string(DriverKubernetes))
+	opensandbox := slices.Contains(labels, string(DriverOpenSandbox))
+
+	if legacyPod {
+		if container || vm || kubernetes || opensandbox {
+			return Placement{}, errors.New("legacy pod label cannot be combined with workload or VM driver labels")
+		}
+		return KubernetesContainer, nil
+	}
+	if container == vm {
+		return Placement{}, fmt.Errorf("task runs-on labels must select exactly one workload class: %v", labels)
+	}
+	if kubernetes && opensandbox {
+		return Placement{}, fmt.Errorf("task runs-on labels select multiple drivers: %v", labels)
+	}
+	if container {
+		if opensandbox {
+			return Placement{}, fmt.Errorf("opensandbox does not support container workloads")
+		}
+		return KubernetesContainer, nil
+	}
+	if kubernetes {
+		return Placement{}, fmt.Errorf("kubernetes does not support VM workloads")
+	}
+	return OpenSandboxVM, nil
+}