From d552528ce744f439f44f8ccda386f8b37e2a9e1f Mon Sep 17 00:00:00 2001
From: Zaptoss <zaptosgg@gmail.com>
Date: Mon, 12 Aug 2024 11:51:34 +0300
Subject: [PATCH] Improve pagination

---
 internal/service/handlers/leaderboard.go |  9 +++++++-
 internal/service/handlers/list_events.go | 26 +++++++++++-------------
 internal/service/page/offset_params.go   | 11 ++++++++--
 3 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/internal/service/handlers/leaderboard.go b/internal/service/handlers/leaderboard.go
index ec3b8f2..38a729c 100644
--- a/internal/service/handlers/leaderboard.go
+++ b/internal/service/handlers/leaderboard.go
@@ -24,8 +24,15 @@ func Leaderboard(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	leadersCount, err := BalancesQ(r).Count()
+	if err != nil {
+		Log(r).WithError(err).Error("Failed to leaders count")
+		ape.RenderErr(w, problems.InternalError())
+		return
+	}
+
 	resp := newLeaderboardResponse(leaders)
-	resp.Links = req.GetLinks(r)
+	resp.Links = req.GetLinks(r, uint64(leadersCount))
 	if req.Count {
 		leadersCount, err := BalancesQ(r).FilterDisabled().Count()
 		if err != nil {
diff --git a/internal/service/handlers/list_events.go b/internal/service/handlers/list_events.go
index 8dd40c1..b28d1b6 100644
--- a/internal/service/handlers/list_events.go
+++ b/internal/service/handlers/list_events.go
@@ -75,19 +75,17 @@ func ListEvents(w http.ResponseWriter, r *http.Request) {
 	}
 
 	var eventsCount int
-	if req.Count {
-		eventsCount, err = EventsQ(r).
-			FilterByNullifier(*req.FilterNullifier).
-			FilterByStatus(req.FilterStatus...).
-			FilterByType(req.FilterType...).
-			FilterInactiveNotClaimed(inactiveTypes...).
-			Count()
-		if err != nil {
-			Log(r).WithError(err).Errorf("Failed to count filtered events: nullifier=%s status=%v type=%v",
-				*req.FilterNullifier, req.FilterStatus, req.FilterType)
-			ape.RenderErr(w, problems.InternalError())
-			return
-		}
+	eventsCount, err = EventsQ(r).
+		FilterByNullifier(*req.FilterNullifier).
+		FilterByStatus(req.FilterStatus...).
+		FilterByType(req.FilterType...).
+		FilterInactiveNotClaimed(inactiveTypes...).
+		Count()
+	if err != nil {
+		Log(r).WithError(err).Errorf("Failed to count filtered events: nullifier=%s status=%v type=%v",
+			*req.FilterNullifier, req.FilterStatus, req.FilterType)
+		ape.RenderErr(w, problems.InternalError())
+		return
 	}
 
 	meta, err := getOrderedEventsMeta(events, r)
@@ -98,7 +96,7 @@ func ListEvents(w http.ResponseWriter, r *http.Request) {
 	}
 
 	resp := newEventsResponse(events, meta)
-	resp.Links = req.OffsetParams.GetLinks(r)
+	resp.Links = req.OffsetParams.GetLinks(r, uint64(eventsCount))
 	if req.Count {
 		_ = resp.PutMeta(struct {
 			EventsCount int `json:"events_count"`
diff --git a/internal/service/page/offset_params.go b/internal/service/page/offset_params.go
index 03e144c..6292b78 100644
--- a/internal/service/page/offset_params.go
+++ b/internal/service/page/offset_params.go
@@ -25,10 +25,17 @@ func (p *OffsetParams) Validate() error {
 	}.Filter()
 }
 
-func (p *OffsetParams) GetLinks(r *http.Request) *resources.Links {
+func (p *OffsetParams) GetLinks(r *http.Request, resourceCount uint64) *resources.Links {
 	result := resources.Links{
 		Self: p.getLink(r, p.PageNumber),
-		Next: p.getLink(r, p.PageNumber+1),
+	}
+
+	if p.PageNumber != 0 {
+		result.Prev = p.getLink(r, p.PageNumber-1)
+	}
+
+	if p.Limit*p.PageNumber < resourceCount {
+		result.Next = p.getLink(r, p.PageNumber+1)
 	}
 	return &result
 }