adding sequence marker to get topics to support staggard loading

doc/api.oa3

@@ -2485,7 +2485,7 @@ paths:
     get:
       tags:
         - content
-      description: Get channel topic slots. If revision set, detail fields omitted in response
+      description: Get channel topic slots. If revision set, detail fields omitted in response. Staggered loading supported through sequnce marker. Initially count can be used to limit the topics returned. The sequence marker returned in the header must be used in subsequent queries for the same topic window.
       operationId: get-channel-topics
       security:
         - bearerAuth: []
@@ -2501,16 +2501,43 @@ paths:
           description: return updated topics since revision 
           required: false
           schema:
-            type: string
+            type: integer
+            format: int64
+        - name: count
+          in: query
+          description: limit number of topics from latest when revision not set
+          required: false
+          schema:
+            type: integer
+            format: int64
+        - name: begin
+          in: query
+          description: return topics after and including sequence marker
+          required: false
+          schema:
+            type: integer
+            format: int64
+        - name: end
+          in: query
+          description: return topics before and not including sequence marker
+          required: false
+          schema:
+            type: integer
+            format: int64
       responses:
         '200':
           description: successful operation
           headers:
-            X-Topic-Revision:
+            Topic-Revision:
               schema:
                 type: integer
                 format: int64
               description: current topic revision
+            Topic-Marker:
+              schema:
+                type: integer
+                format: int64
+              description: sequnce marker of first topic when count set
           content:
             application/json:
               schema:

net/server/internal/api_getChannelTopics.go

@@ -6,9 +6,23 @@ import (
   "databag/internal/store"
 )
 
+func reverse(input []store.TopicSlot) []store.TopicSlot {
+  var output []store.TopicSlot
+  for i := len(input) - 1; i >= 0; i-- {
+    output = append(output, input[i])
+  }
+  return output
+}
+
 func GetChannelTopics(w http.ResponseWriter, r *http.Request) {
   var revisionSet bool
   var revision int64
+  var beginSet bool
+  var begin int64
+  var endSet bool
+  var end int64
+  var countSet bool
+  var count int
 
   channelSlot, _, err, code := getChannelSlot(r, false)
   if err != nil {
@@ -25,24 +39,102 @@ func GetChannelTopics(w http.ResponseWriter, r *http.Request) {
     }
   }
 
+  cnt := r.FormValue("count")
+  if cnt != "" {
+    countSet = true
+    if count, err = strconv.Atoi(cnt); err != nil {
+      ErrResponse(w, http.StatusBadRequest, err)
+      return
+    }
+  }
+
+  bn := r.FormValue("begin")
+  if bn != "" {
+    beginSet = true
+    if begin, err = strconv.ParseInt(bn, 10, 64); err != nil {
+      ErrResponse(w, http.StatusBadRequest, err)
+      return
+    }
+  }
+
+  en := r.FormValue("end")
+  if en != "" {
+    endSet = true
+    if end, err = strconv.ParseInt(en, 10, 64); err != nil {
+      ErrResponse(w, http.StatusBadRequest, err)
+      return
+    }
+  }
+
   response := []*Topic{}
   if revisionSet {
     var slots []store.TopicSlot
-    if err := store.DB.Preload("Topic").Where("channel_id = ? AND revision > ?", channelSlot.Channel.ID, revision).Find(&slots).Error; err != nil {
+    if beginSet && !endSet {
-      ErrResponse(w, http.StatusInternalServerError, err)
+      if err := store.DB.Preload("Topic").Where("channel_id = ? AND revision > ? AND id >= ?", channelSlot.Channel.ID, revision, begin).Find(&slots).Error; err != nil {
-      return
+        ErrResponse(w, http.StatusInternalServerError, err)
+        return
+      }
+    } else if !beginSet && endSet {
+      if err := store.DB.Preload("Topic").Where("channel_id = ? AND revision > ? AND id < ?", channelSlot.Channel.ID, revision, end).Find(&slots).Error; err != nil {
+        ErrResponse(w, http.StatusInternalServerError, err)
+        return
+      }
+    } else if beginSet && endSet {
+      if err := store.DB.Preload("Topic").Where("channel_id = ? AND revision > ? AND id >= ? AND id < ?", channelSlot.Channel.ID, revision, begin, end).Find(&slots).Error; err != nil {
+        ErrResponse(w, http.StatusInternalServerError, err)
+        return
+      }
+    } else {
+      if err := store.DB.Preload("Topic").Where("channel_id = ? AND revision > ?", channelSlot.Channel.ID, revision).Find(&slots).Error; err != nil {
+        ErrResponse(w, http.StatusInternalServerError, err)
+        return
+      }
     }
     for _, slot := range slots {
       response = append(response, getTopicRevisionModel(&slot))
     }
   } else {
     var slots []store.TopicSlot
-    if err := store.DB.Preload("Topic.Assets").Where("channel_id = ?", channelSlot.Channel.ID).Find(&slots).Error; err != nil {
+    if countSet {
-      ErrResponse(w, http.StatusInternalServerError, err)
+      if !endSet {
-      return
+        if err := store.DB.Preload("Topic.Assets").Where("channel_id = ?", channelSlot.Channel.ID).Order("id desc").Limit(count).Find(&slots).Error; err != nil {
+          ErrResponse(w, http.StatusInternalServerError, err)
+          return
+        }
+      } else {
+        if err := store.DB.Preload("Topic.Assets").Where("channel_id = ? AND id < ?", channelSlot.Channel.ID, end).Order("id desc").Limit(count).Find(&slots).Error; err != nil {
+          ErrResponse(w, http.StatusInternalServerError, err)
+          return
+        }
+      }
+      slots = reverse(slots)
+    } else if beginSet && !endSet {
+      if err := store.DB.Preload("Topic.Assets").Where("channel_id = ? AND id >= ?", channelSlot.Channel.ID, begin).Find(&slots).Error; err != nil {
+        ErrResponse(w, http.StatusInternalServerError, err)
+        return
+      }
+    } else if !beginSet && endSet {
+      if err := store.DB.Preload("Topic.Assets").Where("channel_id = ? AND id < ?", channelSlot.Channel.ID, end).Find(&slots).Error; err != nil {
+        ErrResponse(w, http.StatusInternalServerError, err)
+        return
+      }
+    } else if beginSet && endSet {
+      if err := store.DB.Preload("Topic.Assets").Where("channel_id = ? AND id >= ? AND id < ?", channelSlot.Channel.ID, begin, end).Find(&slots).Error; err != nil {
+        ErrResponse(w, http.StatusInternalServerError, err)
+        return
+      }
+    } else {
+      if err := store.DB.Preload("Topic.Assets").Where("channel_id = ?", channelSlot.Channel.ID).Find(&slots).Error; err != nil {
+        ErrResponse(w, http.StatusInternalServerError, err)
+        return
+      }
     }
     for _, slot := range slots {
       if slot.Topic != nil {
+        if countSet {
+          w.Header().Set("Topic-Index", strconv.FormatUint(uint64(slot.ID), 10))
+          countSet = false
+        }
         response = append(response, getTopicModel(&slot))
       }
     }