Implement LAST command

README.md

@@ -36,7 +36,7 @@
 - :construction: Group and Article Selection
   - :heavy_check_mark: `GROUP`
   - :heavy_check_mark: `LISTGROUP`
-  - :x: `LAST`
+  - :heavy_check_mark: `LAST`
   - :x: `NEXT`
 - :construction: The LIST Commands
   - :heavy_check_mark: `LIST ACTIVE`

internal/backend/sqlite/sqlite.go

@@ -173,6 +173,17 @@ func (sb *SQLiteBackend) GetArticleNumbers(g *models.Group, low, high int64) ([]
 	return numbers, nil
 }
 
+func (sb *SQLiteBackend) GetLastArticleByNum(g *models.Group, a *models.Article) (models.Article, error) {
+	var lastArticle models.Article
+	if err := sb.db.Get(&lastArticle, "SELECT articles.* FROM articles INNER JOIN articles_to_groups atg on atg.article_id = articles.id WHERE atg.article_number < ? AND atg.group_id = ? LIMIT 1", a.ArticleNumber, g.ID); err != nil {
+		return lastArticle, err
+	}
+	if err := sb.db.Get(&a.ArticleNumber, "SELECT article_number FROM articles_to_groups WHERE article_id = ?", a.ID); err != nil {
+		return lastArticle, err
+	}
+	return lastArticle, json.Unmarshal([]byte(a.HeaderRaw), &a.Header)
+}
+
 func (sb *SQLiteBackend) GetNewArticlesSince(timestamp int64) ([]string, error) {
 	var articleIds []string
 	return articleIds, sb.db.Select(&articleIds, "SELECT json_extract(articles.header, '$.Message-Id[0]') FROM articles WHERE created_at > datetime(?, 'unixepoch')", timestamp)

internal/backend/storage_backend.go

@@ -19,4 +19,5 @@ type StorageBackend interface {
 	GetArticleByNumber(g *models.Group, num int) (models.Article, error)
 	GetArticleNumbers(g *models.Group, low, high int64) ([]int64, error)
 	GetNewArticlesSince(timestamp int64) ([]string, error)
+	GetLastArticleByNum(g *models.Group, a *models.Article) (models.Article, error)
 }

internal/protocol/constants.go

@@ -62,6 +62,7 @@ const (
 	CommandStat         = "STAT"
 	CommandHelp         = "HELP"
 	CommandNewNews      = "NEWNEWS"
+	CommandLast         = "LAST"
 )
 
 const (

internal/server/handler.go

@@ -42,6 +42,7 @@ func NewHandler(b backend.StorageBackend, serverDomain string) *Handler {
 		protocol.CommandStat:         h.handleArticle,
 		protocol.CommandHelp:         h.handleHelp,
 		protocol.CommandNewNews:      h.handleNewNews,
+		protocol.CommandLast:         h.handleLast,
 	}
 	h.serverDomain = serverDomain
 	return h
@@ -626,6 +627,42 @@ func (h *Handler) handleNewNews(s *Session, command string, arguments []string,
 	return dw.Close()
 }
 
+func (h *Handler) handleLast(s *Session, command string, arguments []string, id uint) error {
+	s.tconn.StartResponse(id)
+	defer s.tconn.EndResponse(id)
+
+	if len(arguments) != 0 {
+		return s.tconn.PrintfLine(protocol.ErrSyntaxError.String())
+	}
+
+	if s.currentGroup == nil {
+		return s.tconn.PrintfLine(protocol.NNTPResponse{Code: 412, Message: "no newsgroup selected"}.String())
+	}
+
+	if s.currentArticle == nil {
+		return s.tconn.PrintfLine(protocol.NNTPResponse{Code: 420, Message: "No current article selected"}.String())
+	}
+
+	low, err := h.backend.GetGroupLowWaterMark(s.currentGroup)
+	if err != nil {
+		return err
+	}
+
+	if s.currentArticle.ArticleNumber == low {
+		return s.tconn.PrintfLine(protocol.NNTPResponse{Code: 422, Message: "No previous article to retrieve"}.String())
+	}
+
+	a, err := h.backend.GetLastArticleByNum(s.currentGroup, s.currentArticle)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return s.tconn.PrintfLine(protocol.NNTPResponse{Code: 422, Message: "No previous article to retrieve"}.String())
+		}
+		return err
+	}
+
+	return s.tconn.PrintfLine(protocol.NNTPResponse{Code: 223, Message: fmt.Sprintf("%d %s retrieved", a.ArticleNumber, a.Header.Get("Message-ID"))}.String())
+}
+
 func (h *Handler) Handle(s *Session, message string, id uint) error {
 	splittedMessage := strings.Split(message, " ")
 	for i, v := range splittedMessage {