Advanced Priority Sorting (If none, but above 'Z')

model.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"sort"
 	"strings"
 	"time"
 
@@ -189,3 +190,41 @@ func (a *AppState) WriteDoneList() error {
 	}
 	return a.DoneList.WriteToFilename(a.getDoneFile())
 }
+
+func (a *AppState) AdvancedPrioritySort(t1, t2 *todotxt.Task) bool {
+	if t1.HasPriority() && t2.HasPriority() {
+		return t1.Priority < t2.Priority
+	} else if t1.HasPriority() && !t2.HasPriority() {
+		return t1.Priority <= "Y"
+	} else if !t1.HasPriority() && t2.HasPriority() {
+		return "Y" <= t2.Priority
+	}
+	return t1.HasPriority()
+}
+
+type customSort struct {
+	list todotxt.TaskList
+	by   func(t1, t2 *todotxt.Task) bool
+}
+
+func (c *customSort) Len() int {
+	return len(c.list)
+}
+
+func (c *customSort) Swap(l, r int) {
+	c.list[l], c.list[r] = c.list[r], c.list[l]
+}
+
+func (c *customSort) Less(l, r int) bool {
+	return c.by(&c.list[l], &c.list[r])
+}
+
+type By func(t1, t2 *todotxt.Task) bool
+
+func (by By) Sort(list []todotxt.Task) {
+	ts := &customSort{
+		list: list,
+		by:   by,
+	}
+	sort.Sort(ts)
+}