[feature] add paging to account follows, followers and follow requests endpoints (#2186)

internal/db/bundb/util.go

@@ -20,7 +20,9 @@ package bundb
 import (
 	"strings"
 
+	"github.com/superseriousbusiness/gotosocial/internal/cache"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/paging"
 	"github.com/uptrace/bun"
 )
 
@@ -83,6 +85,29 @@ func whereStartsLike(
 	)
 }
 
+// loadPagedIDs loads a page of IDs from given SliceCache by `key`, resorting to `loadDESC` if required. Uses `page` to sort + page resulting IDs.
+// NOTE: IDs returned from `cache` / `loadDESC` MUST be in descending order, otherwise paging will not work correctly / return things out of order.
+func loadPagedIDs(cache *cache.SliceCache[string], key string, page *paging.Page, loadDESC func() ([]string, error)) ([]string, error) {
+	// Check cache for IDs, else load.
+	ids, err := cache.Load(key, loadDESC)
+	if err != nil {
+		return nil, err
+	}
+
+	// Our cached / selected IDs are ALWAYS
+	// fetched from `loadDESC` in descending
+	// order. Depending on the paging requested
+	// this may be an unexpected order.
+	if page.GetOrder().Ascending() {
+		ids = paging.Reverse(ids)
+	}
+
+	// Page the resulting IDs.
+	ids = page.Page(ids)
+
+	return ids, nil
+}
+
 // updateWhere parses []db.Where and adds it to the given update query.
 func updateWhere(q *bun.UpdateQuery, where []db.Where) {
 	for _, w := range where {