Put command access checks on the command level

Checking using `settings.Allowed` is odd. Not all commands are related
to setting configuration settings. Admin commands are coming in the
future, for which this is certainly not the case.

We now do access checks early on (during command processing), so command
handlers can be clean of access checks. If we're inside of a command
handler, the user is privileged to run it.

bot/access.go

@@ -0,0 +1,37 @@
+package bot
+
+import (
+	"fmt"
+
+	"maunium.net/go/mautrix/id"
+
+	"gitlab.com/etke.cc/postmoogle/utils"
+)
+
+type accessCheckerFunc func(id.UserID, id.RoomID) (bool, error)
+
+func (b *Bot) allowAnyone(actorID id.UserID, targetRoomID id.RoomID) (bool, error) {
+	return true, nil
+}
+
+func (b *Bot) allowOwner(actorID id.UserID, targetRoomID id.RoomID) (bool, error) {
+	if !utils.Match(actorID.String(), b.allowedUsers) {
+		return false, nil
+	}
+
+	if b.noowner {
+		return true, nil
+	}
+
+	cfg, err := b.getSettings(targetRoomID)
+	if err != nil {
+		return false, fmt.Errorf("failed to retrieve settings: %v", err)
+	}
+
+	owner := cfg.Owner()
+	if owner == "" {
+		return true, nil
+	}
+
+	return owner == actorID.String(), nil
+}