make the process of registered available hosts less clunky

host/descriptor.go

@@ -0,0 +1,31 @@
+package host
+
+import (
+	"errors"
+
+	"github.com/kidoman/embd/gpio"
+	"github.com/kidoman/embd/i2c"
+)
+
+type Descriptor struct {
+	GPIO func() gpio.GPIO
+	I2C  func() i2c.I2C
+}
+
+type Describer func(rev int) *Descriptor
+
+var Describers = map[Host]Describer{}
+
+func Describe() (*Descriptor, error) {
+	host, rev, err := Detect()
+	if err != nil {
+		return nil, err
+	}
+
+	describer, ok := Describers[host]
+	if !ok {
+		return nil, errors.New("host: invalid host")
+	}
+
+	return describer(rev), nil
+}