refactor: raise checker to be a subpackage of lib

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/checker/checker.go

@@ -0,0 +1,47 @@
+// Package checker defines the Checker interface and a helper utility to avoid import cycles.
+package checker
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/TecharoHQ/anubis/internal"
+)
+
+var (
+	ErrUnparseableConfig = errors.New("checker: config is unparseable")
+	ErrInvalidConfig     = errors.New("checker: config is invalid")
+)
+
+type Interface interface {
+	Check(*http.Request) (matches bool, err error)
+	Hash() string
+}
+
+type List []Interface
+
+func (l List) Check(r *http.Request) (bool, error) {
+	for _, c := range l {
+		ok, err := c.Check(r)
+		if err != nil {
+			return ok, err
+		}
+		if ok {
+			return ok, nil
+		}
+	}
+
+	return false, nil
+}
+
+func (l List) Hash() string {
+	var sb strings.Builder
+
+	for _, c := range l {
+		fmt.Fprintln(&sb, c.Hash())
+	}
+
+	return internal.FastHash(sb.String())
+}