Add `last` template function

`last` allows the user to select the last X items of
and array.

diff --git a/tpl/template_funcs.go b/tpl/template_funcs.go
index 96028b1824bcf324931f1923fd889fc2ab3613de..7849aaae168a1941770b5af2673bbdf99f0cd5d4 100644 (file)
--- a/tpl/template_funcs.go
+++ b/tpl/template_funcs.go
@@ -388,6 +388,42 @@ func First(limit interface{}, seq interface{}) (interface{}, error) {
        return seqv.Slice(0, limitv).Interface(), nil
 }
 
+// Last is exposed to templates, to iterate over the last N items in a
+// rangeable list.
+func Last(limit interface{}, seq interface{}) (interface{}, error) {
+
+       if limit == nil || seq == nil {
+               return nil, errors.New("both limit and seq must be provided")
+       }
+
+       limitv, err := cast.ToIntE(limit)
+
+       if err != nil {
+               return nil, err
+       }
+
+       if limitv < 1 {
+               return nil, errors.New("can't return negative/empty count of items from sequence")
+       }
+
+       seqv := reflect.ValueOf(seq)
+       seqv, isNil := indirect(seqv)
+       if isNil {
+               return nil, errors.New("can't iterate over a nil value")
+       }
+
+       switch seqv.Kind() {
+       case reflect.Array, reflect.Slice, reflect.String:
+               // okay
+       default:
+               return nil, errors.New("can't iterate over " + reflect.ValueOf(seq).Type().String())
+       }
+       if limitv > seqv.Len() {
+               limitv = seqv.Len()
+       }
+       return seqv.Slice(seqv.Len()-limitv, seqv.Len()).Interface(), nil
+}
+
 // After is exposed to templates, to iterate over all the items after N in a
 // rangeable list. It's meant to accompany First
 func After(index interface{}, seq interface{}) (interface{}, error) {
@@ -1288,6 +1324,7 @@ func init() {
                "relURL":      func(a string) template.HTML { return template.HTML(helpers.RelURL(a)) },
                "markdownify": Markdownify,
                "first":       First,
+               "last":        Last,
                "after":       After,
                "where":       Where,
                "delimit":     Delimit,

diff --git a/tpl/template_funcs_test.go b/tpl/template_funcs_test.go
index 2df82457cbeed499a17c93f28ea4d7efa5ef6e6a..573b0fe23ab40d81a263e00a646cb63fefc09e68 100644 (file)
--- a/tpl/template_funcs_test.go
+++ b/tpl/template_funcs_test.go
@@ -253,6 +253,40 @@ func TestFirst(t *testing.T) {
        }
 }
 
+func TestLast(t *testing.T) {
+       for i, this := range []struct {
+               count    interface{}
+               sequence interface{}
+               expect   interface{}
+       }{
+               {int(2), []string{"a", "b", "c"}, []string{"b", "c"}},
+               {int32(3), []string{"a", "b"}, []string{"a", "b"}},
+               {int64(2), []int{100, 200, 300}, []int{200, 300}},
+               {100, []int{100, 200}, []int{100, 200}},
+               {"1", []int{100, 200, 300}, []int{300}},
+               {int64(-1), []int{100, 200, 300}, false},
+               {"noint", []int{100, 200, 300}, false},
+               {1, nil, false},
+               {nil, []int{100}, false},
+               {1, t, false},
+       } {
+               results, err := Last(this.count, this.sequence)
+               if b, ok := this.expect.(bool); ok && !b {
+                       if err == nil {
+                               t.Errorf("[%d] First didn't return an expected error", i)
+                       }
+               } else {
+                       if err != nil {
+                               t.Errorf("[%d] failed: %s", i, err)
+                               continue
+                       }
+                       if !reflect.DeepEqual(results, this.expect) {
+                               t.Errorf("[%d] First %d items, got %v but expected %v", i, this.count, results, this.expect)
+                       }
+               }
+       }
+}
+
 func TestAfter(t *testing.T) {
        for i, this := range []struct {
                count    interface{}