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backend/node_modules/bullmq/dist/esm/commands/includes/findPage.lua

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+--[[
+  Function to achieve pagination for a set or hash.
+  This function simulates pagination in the most efficient way possible
+  for a set using sscan or hscan.
+
+  The main limitation is that sets are not order preserving, so the
+  pagination is not stable. This means that if the set is modified
+  between pages, the same element may appear in different pages.
+]] -- Maximum number of elements to be returned by sscan per iteration.
+local maxCount = 100
+
+-- Finds the cursor, and returns the first elements available for the requested page.
+local function findPage(key, command, pageStart, pageSize, cursor, offset,
+                        maxIterations, fetchJobs)
+    local items = {}
+    local jobs = {}
+    local iterations = 0
+
+    repeat
+        -- Iterate over the set using sscan/hscan.
+        local result = rcall(command, key, cursor, "COUNT", maxCount)
+
+        cursor = result[1]
+        local members = result[2]
+        local step = 1
+        if command == "HSCAN" then
+            step = 2
+        end
+        
+        if #members == 0 then
+            -- If the result is empty, we can return the result.
+            return cursor, offset, items, jobs
+        end
+
+        local chunkStart = offset
+        local chunkEnd = offset + #members / step
+
+        local pageEnd = pageStart + pageSize
+
+        if chunkEnd < pageStart then
+            -- If the chunk is before the page, we can skip it.
+            offset = chunkEnd
+        elseif chunkStart > pageEnd then
+            -- If the chunk is after the page, we can return the result.
+            return cursor, offset, items, jobs
+        else
+            -- If the chunk is overlapping the page, we need to add the elements to the result.
+            for i = 1, #members, step do
+                if offset >= pageEnd then
+                    return cursor, offset, items, jobs
+                end
+                if offset >= pageStart then
+                    local index = #items + 1
+                    if fetchJobs ~= nil then
+                        jobs[#jobs+1] = rcall("HGETALL", members[i])
+                    end
+                    if step == 2 then
+                        items[index] = {members[i], members[i + 1]}
+                    else
+                        items[index] = members[i]
+                    end
+                end
+                offset = offset + 1
+            end
+        end
+        iterations = iterations + 1
+    until cursor == "0" or iterations >= maxIterations
+
+    return cursor, offset, items, jobs
+end