feat: support x-machines placement constraints in compose files (#90)

pkg/client/compose/machines.go

@@ -0,0 +1,83 @@
+package compose
+
+import (
+	"fmt"
+	"strings"
+)
+
+const MachinesExtensionKey = "x-machines"
+
+// MachinesSource represents the parsed x-machines extension data as slice of strings
+type MachinesSource []string
+
+// DecodeMapstructure implements custom decoding for multiple input types
+func (m *MachinesSource) DecodeMapstructure(value interface{}) error {
+	switch v := value.(type) {
+	case *MachinesSource:
+		// Handle case where compose-go passes a pointer to an already created instance
+		*m = *v
+		return nil
+	case MachinesSource:
+		// Handle case where compose-go passes a direct instance
+		*m = v
+		return nil
+	case string:
+		// Support single string value or comma-separated values
+		// x-machines: my-machine or x-machines: "machine-1,machine-2"
+		machines, err := parseMachineNames(v)
+		if err != nil {
+			return err
+		}
+		*m = MachinesSource(machines)
+		return nil
+	case []string:
+		// Support string array: x-machines: ["machine-1", "machine-2"]
+		machines, err := validateMachineNames(v)
+		if err != nil {
+			return err
+		}
+		*m = MachinesSource(machines)
+		return nil
+	case []interface{}:
+		// Support interface array that may come from YAML parsing
+		machineNames := make([]string, 0, len(v))
+		for i, machine := range v {
+			str, ok := machine.(string)
+			if !ok {
+				return fmt.Errorf("x-machines[%d] is not a string, got %T", i, machine)
+			}
+			machineNames = append(machineNames, str)
+		}
+		machines, err := validateMachineNames(machineNames)
+		if err != nil {
+			return err
+		}
+		*m = MachinesSource(machines)
+		return nil
+	default:
+		return fmt.Errorf("x-machines must be a string or list of strings, got %T", value)
+	}
+}
+
+// parseMachineNames parses a single string that may contain comma-separated machine names
+func parseMachineNames(machinesStr string) ([]string, error) {
+	// Split by comma and process each machine name, works for both single and multiple values
+	parts := strings.Split(machinesStr, ",")
+	machines := make([]string, 0, len(parts))
+	for _, part := range parts {
+		machines = append(machines, strings.TrimSpace(part))
+	}
+	return validateMachineNames(machines)
+}
+
+// validateMachineNames validates machine names to ensure they are not empty and contain valid characters.
+func validateMachineNames(machines []string) ([]string, error) {
+	for i, machine := range machines {
+		machine = strings.TrimSpace(machine)
+		if machine == "" {
+			return nil, fmt.Errorf("x-machines[%d] cannot be empty", i)
+		}
+		machines[i] = machine
+	}
+	return machines, nil
+}