Add metric for "inbox" flag of tags

Enable reproduction of the "Documents in inbox" count reported on
Paperless-ngx' main page when combined with the document count per tag.

Relates to issue #39.

tag.go

@@ -17,6 +17,7 @@ type tagCollector struct {
 
 	infoDesc     *prometheus.Desc
 	docCountDesc *prometheus.Desc
+	inboxDesc    *prometheus.Desc
 }
 
 func newTagCollector(cl tagClient) *tagCollector {
@@ -29,12 +30,16 @@ func newTagCollector(cl tagClient) *tagCollector {
 		docCountDesc: prometheus.NewDesc("paperless_tag_document_count",
 			"Number of documents associated with a tag.",
 			[]string{"id"}, nil),
+		inboxDesc: prometheus.NewDesc("paperless_tag_inbox",
+			"Whether the tag is marked as an inbox tag.",
+			[]string{"id"}, nil),
 	}
 }
 
 func (c *tagCollector) describe(ch chan<- *prometheus.Desc) {
 	ch <- c.infoDesc
 	ch <- c.docCountDesc
+	ch <- c.inboxDesc
 }
 
 func (c *tagCollector) collect(ctx context.Context, ch chan<- prometheus.Metric) error {
@@ -54,6 +59,15 @@ func (c *tagCollector) collect(ctx context.Context, ch chan<- prometheus.Metric)
 		ch <- prometheus.MustNewConstMetric(c.docCountDesc, prometheus.GaugeValue,
 			float64(tag.DocumentCount), id)
 
+		isInboxTag := 0
+
+		if tag.IsInboxTag {
+			isInboxTag = 1
+		}
+
+		ch <- prometheus.MustNewConstMetric(c.inboxDesc, prometheus.GaugeValue,
+			float64(isInboxTag), id)
+
 		return nil
 	})
 }

tag_test.go

@@ -80,18 +80,27 @@ func TestTagCollect(t *testing.T) {
 	cl.items = append(cl.items, []client.Tag{
 		{ID: 8463, Name: "aaa", Slug: "aslug"},
 		{ID: 338, Name: "three-three-eight", DocumentCount: 13},
+		{ID: 2930, Name: "mybox", Slug: "mb", IsInboxTag: true},
 		{ID: 26429, Name: "last"},
 	}...)
 
 	testutil.CollectAndCompare(t, c, `
 # HELP paperless_tag_document_count Number of documents associated with a tag.
 # TYPE paperless_tag_document_count gauge
 paperless_tag_document_count{id="26429"} 0
+paperless_tag_document_count{id="2930"} 0
 paperless_tag_document_count{id="338"} 13
 paperless_tag_document_count{id="8463"} 0
+# HELP paperless_tag_inbox Whether the tag is marked as an inbox tag.
+# TYPE paperless_tag_inbox gauge
+paperless_tag_inbox{id="26429"} 0
+paperless_tag_inbox{id="2930"} 1
+paperless_tag_inbox{id="338"} 0
+paperless_tag_inbox{id="8463"} 0
 # HELP paperless_tag_info Static information about a tag.
 # TYPE paperless_tag_info gauge
 paperless_tag_info{id="26429",name="last",slug=""} 1
+paperless_tag_info{id="2930",name="mybox",slug="mb"} 1
 paperless_tag_info{id="338",name="three-three-eight",slug=""} 1
 paperless_tag_info{id="8463",name="aaa",slug="aslug"} 1
 `)