1 files changed, 205 insertions, 0 deletions
diff --git a/backend.go b/backend.go
new file mode 100644
index 0000000..0291ffa
--- /dev/null
+++ b/backend.go
@@ -0,0 +1,205 @@
+package main
+
+import (
+	"errors"
+	"strconv"
+	"strings"
+
+	"github.com/dustin/go-nntp"
+	nntpserver "github.com/dustin/go-nntp/server"
+	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
+)
+
+func NewMetaBackend(logger log.Logger, backends ...nntpserver.Backend) (nntpserver.Backend, error) {
+	mb := &metaBackend{logger: logger, groups: make(map[string]int)}
+	for _, b := range backends {
+		if err := mb.add(b); err != nil {
+			return nil, err
+		}
+	}
+
+	return mb, nil
+}
+
+type metaBackend struct {
+	logger   log.Logger
+	backends []nntpserver.Backend
+	groups   map[string]int
+}
+
+func (mb metaBackend) debug(keyvals ...any) error { return level.Debug(mb.logger).Log(keyvals...) }
+func (mb metaBackend) info(keyvals ...any) error  { return level.Info(mb.logger).Log(keyvals...) }
+func (mb metaBackend) warn(keyvals ...any) error  { return level.Warn(mb.logger).Log(keyvals...) }
+func (mb metaBackend) err(keyvals ...any) error   { return level.Error(mb.logger).Log(keyvals...) }
+
+func (mb *metaBackend) add(b nntpserver.Backend) error {
+	grps, err := b.ListGroups(1_000_000)
+	if err != nil {
+		return err
+	}
+
+	_ = mb.info("msg", "adding backend", "group_count", len(grps))
+
+	i := len(mb.backends)
+	mb.backends = append(mb.backends, b)
+	for _, grp := range grps {
+		mb.groups[grp.Name] = i
+	}
+
+	return nil
+}
+
+func (mb metaBackend) ListGroups(max int) ([]*nntp.Group, error) {
+	var groups []*nntp.Group
+	for _, b := range mb.backends {
+		grps, err := b.ListGroups(max - len(groups))
+		if err != nil {
+			return nil, err
+		}
+		groups = append(groups, grps...)
+
+		if len(groups) == max {
+			break
+		}
+	}
+
+	_ = mb.info(
+		"msg", "metaBackend method",
+		"method", "ListGroups",
+		"count", len(groups),
+	)
+	return groups, nil
+}
+
+func (mb metaBackend) GetGroup(name string) (*nntp.Group, error) {
+	b, err := mb.backendFor(name)
+	if err != nil {
+		return nil, err
+	}
+
+	grp, err := b.GetGroup(name)
+	_ = mb.info(
+		"msg", "metaBackend method",
+		"method", "GetGroup",
+		"name", name,
+		"err", err,
+	)
+	return grp, err
+}
+
+func (mb metaBackend) GetArticles(group *nntp.Group, from, to int64) ([]nntpserver.NumberedArticle, error) {
+	b, err := mb.backendFor(group.Name)
+	if err != nil {
+		return nil, err
+	}
+
+	articles, err := b.GetArticles(group, from, to)
+	_ = mb.info(
+		"msg", "metaBackend method",
+		"method", "GetArticles",
+		"group", group.Name,
+		"from-to", strconv.Itoa(int(from))+"-"+strconv.Itoa(int(to)),
+		"count", len(articles),
+		"err", err,
+	)
+	return articles, err
+}
+
+func (mb metaBackend) GetArticle(group *nntp.Group, messageID string) (*nntp.Article, error) {
+	b, err := mb.backendFor(group.Name)
+	if err != nil {
+		return nil, err
+	}
+
+	article, err := b.GetArticle(group, messageID)
+	_ = mb.info(
+		"msg", "metaBackend method",
+		"method", "GetArticle",
+		"group", group.Name,
+		"messageID", messageID,
+		"err", err,
+	)
+	return article, err
+}
+
+func (mb metaBackend) Post(article *nntp.Article) error {
+	groupNames := strings.Split(article.Header.Get("Newsgroups"), ",")
+	for i := range groupNames {
+		groupNames[i] = strings.Trim(groupNames[i], " ")
+	}
+
+	bes, err := mb.backendsFor(groupNames)
+	if err != nil {
+		return err
+	}
+
+	var errs []error
+	for _, b := range bes {
+		// TODO: need to filter the "Newsgroups" header to only the
+		//       groups relevant to each backend?
+		errs = append(errs, b.Post(article))
+	}
+
+	err = errors.Join(errs...)
+	_ = mb.info(
+		"msg", "metaBackend method",
+		"method", "Post",
+		"groups", article.Header.Get("Newsgroups"),
+		"backends", len(bes),
+		"err", err,
+	)
+	return err
+}
+
+func (mb metaBackend) Authorized() bool {
+	_ = mb.info(
+		"msg", "metaBackend method",
+		"method", "Authorized",
+	)
+	return true
+}
+
+func (mb metaBackend) AllowPost() bool {
+	_ = mb.info(
+		"msg", "metaBackend method",
+		"method", "AllowPost",
+	)
+	return true
+}
+
+func (mb metaBackend) Authenticate(user, _ string) (nntpserver.Backend, error) {
+	_ = mb.info(
+		"msg", "metaBackend method",
+		"method", "Authenticate",
+		"user", user,
+	)
+	return nil, nil
+}
+
+func (mb metaBackend) backendFor(name string) (nntpserver.Backend, error) {
+	i, ok := mb.groups[name]
+	if !ok {
+		return nil, nntpserver.ErrNoSuchGroup
+	}
+	return mb.backends[i], nil
+}
+
+func (mb metaBackend) backendsFor(names []string) ([]nntpserver.Backend, error) {
+	tbl := make([]bool, len(mb.backends))
+	for _, name := range names {
+		i, ok := mb.groups[name]
+		if !ok {
+			return nil, nntpserver.ErrNoSuchGroup
+		}
+		tbl[i] = true
+	}
+
+	backends := make([]nntpserver.Backend, 0, len(mb.backends))
+	for i, y := range tbl {
+		if y {
+			backends = append(backends, mb.backends[i])
+		}
+	}
+	return backends, nil
+}