task sorting might work

server/ajax/task.go

@@ -7,10 +7,16 @@ import (
 	"local/todo-server/server/ajax/form"
 	"local/todo-server/server/ajax/task"
 	"net/http"
+	"sort"
 	"strconv"
 	"strings"
 )
 
+type taskWithDelta struct {
+	task  *task.Task
+	delta int
+}
+
 func (a *Ajax) loadTasks(w http.ResponseWriter, r *http.Request) error {
 	listID, _, _ := a.Cur(r)
 	filterComplete := filterComplete(form.Get(r, "compl"))
@@ -158,8 +164,8 @@ func (a *Ajax) parseTaskStr(w http.ResponseWriter, r *http.Request) error {
 func (a *Ajax) changeOrder(w http.ResponseWriter, r *http.Request) error {
 	order := form.Get(r, "order")
 	orders := strings.Split(order, "&")
-	sum := 0
-	zero := ""
+	modified := make([]taskWithDelta, 0)
+	indices := make([]int, 0)
 	for _, order := range orders {
 		taskIDDelta := strings.Split(order, "=")
 		if len(taskIDDelta) < 2 {
@@ -167,43 +173,34 @@ func (a *Ajax) changeOrder(w http.ResponseWriter, r *http.Request) error {
 		}
 		taskID := taskIDDelta[0]
 		delta, _ := strconv.Atoi(taskIDDelta[1])
-		if delta < 0 {
-			delta = -1
-		} else {
-			delta = 0
-		}
 		task, err := a.storageGetTask(taskID)
 		if err != nil {
 			return err
 		}
-		listID, err := a.taskIDToListID(taskID)
+		modified = append(modified, taskWithDelta{task: task, delta: delta})
+		indices = append(indices, task.Index)
+	}
+	sort.Slice(modified, func(i, j int) bool {
+		if modified[i].delta < modified[j].delta {
+			return true
+		} else if modified[i].delta > modified[j].delta {
+			return false
+		}
+		return modified[i].task.Index < modified[j].task.Index
+	})
+	sort.Ints(indices)
+	for i := 0; i < len(modified); i++ {
+		task := *modified[i].task
+		task.Index = indices[i]
+		listID, err := a.taskIDToListID(task.UUID)
 		if err != nil {
 			return err
 		}
-		task.Index += delta
-		if err := a.storageSetTask(listID, task); err != nil {
+		if err := a.storageSetTask(listID, &task); err != nil {
 			return err
 		}
-		if delta == 0 {
-			zero = taskID
-		}
-		sum += delta
 	}
-	if zero == "" || sum == 0 {
-		return nil
-	}
-	task, err := a.storageGetTask(zero)
-	if err != nil {
-		return err
-	}
-	listID, err := a.taskIDToListID(zero)
-	if err != nil {
-		return err
-	}
-	task.Index -= sum
-	if err := a.storageSetTask(listID, task); err != nil {
-		return err
-	}
-	fmt.Fprint(w, `{"total":1}`)
+
+	fmt.Fprintf(w, `{"total":1}`)
 	return nil
 }