feat(backend): add Store.Get and bookmark view helpers

backend/store.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"database/sql"
+	"errors"
 	"fmt"
 	"strings"
 
@@ -28,6 +29,22 @@ type Bookmark struct {
 	UpdatedAt        int64    `json:"updated_at"`         // unix ms; see Upsert
 }
 
+// HasNewChapter reports whether the site has published past the read point.
+// A nil LatestChapterNum means nothing has been captured yet, which is not the
+// same as "nothing new".
+func (b Bookmark) HasNewChapter() bool {
+	return b.LatestChapterNum != nil && *b.LatestChapterNum > b.LastChapterNum
+}
+
+// ContinueURL is where the Continue button points: the chapter last read, or
+// the series page when no chapter URL was ever captured.
+func (b Bookmark) ContinueURL() string {
+	if b.LastChapterURL != "" {
+		return b.LastChapterURL
+	}
+	return b.SeriesURL
+}
+
 const schema = `
 CREATE TABLE IF NOT EXISTS bookmarks (
   key                TEXT PRIMARY KEY,
@@ -182,6 +199,21 @@ func (s *Store) List() ([]Bookmark, error) {
 	return out, rows.Err()
 }
 
+// Get returns one bookmark by key. A missing key is not an error: ok is false
+// and err is nil. UI mutations read-modify-write through this so they preserve
+// the fields they do not touch.
+func (s *Store) Get(key string) (Bookmark, bool, error) {
+	b, err := scanBookmark(s.db.QueryRow(
+		`SELECT `+bookmarkColumns+` FROM bookmarks WHERE key = ?`, key).Scan)
+	if errors.Is(err, sql.ErrNoRows) {
+		return Bookmark{}, false, nil
+	}
+	if err != nil {
+		return Bookmark{}, false, fmt.Errorf("get %q: %w", key, err)
+	}
+	return b, true, nil
+}
+
 // Upsert inserts or replaces a bookmark by key (last-write-wins) and returns
 // the row as actually stored.
 //