finish empty implementation of Text.Substring

pkg/fetcher/resource_bytes.go

@@ -61,11 +61,11 @@ func (r *BytesResource) Read(start int64, end int64) ([]byte, *ResourceError) {
 
 	// Bounds check
 	length := int64(len(r._bytes))
-	if start > (length - 1) {
-		start = length - 1
+	if start > length {
+		start = length
 	}
-	if end > length {
-		end = length
+	if end > (length - 1) {
+		end = length - 1
 	}
 
 	return r._bytes[start : end+1], nil

pkg/manifest/locator.go

@@ -151,11 +151,29 @@ func TextFromJSON(rawJson map[string]interface{}) (t Text) {
 	return
 }
 
-func (t Text) Substring(start, end uint64) Text {
+func (t Text) Substring(start, end int64) Text {
 	if t.Highlight == "" {
 		return t
 	}
 
+	length := int64(len(t.Highlight))
+	if start > length-1 {
+		start = length
+	}
+	if start < 0 {
+		start = 0
+	}
+	if end > length-1 {
+		end = length - 1
+	}
+	if end < 0 {
+		end = 0
+	}
+
+	t.Before += t.Highlight[:start]
+	t.After = t.Highlight[end+1:] + t.After
+	t.Highlight = t.Highlight[start : end+1]
+
 	return t
 }
 

pkg/manifest/locator_test.go

@@ -245,3 +245,53 @@ func TestTextJSON(t *testing.T) {
 		"after": "Text after"
 	}`, string(s), "JSON objects should be equal")
 }
+
+func TestSubstringFromRange(t *testing.T) {
+	text := Text{
+		Before:    "before",
+		Highlight: "highlight",
+		After:     "after",
+	}
+
+	assert.Equal(t, Text{
+		Before:    "before",
+		Highlight: "h",
+		After:     "ighlightafter",
+	}, text.Substring(0, -1))
+
+	assert.Equal(t, Text{
+		Before:    "before",
+		Highlight: "h",
+		After:     "ighlightafter",
+	}, text.Substring(0, 0))
+
+	assert.Equal(t, Text{
+		Before:    "beforehigh",
+		Highlight: "lig",
+		After:     "htafter",
+	}, text.Substring(4, 6))
+
+	assert.Equal(t, Text{
+		Before:    "before",
+		Highlight: "highlight",
+		After:     "after",
+	}, text.Substring(0, 8))
+
+	assert.Equal(t, Text{
+		Before:    "beforehighli",
+		Highlight: "ght",
+		After:     "after",
+	}, text.Substring(6, 12))
+
+	assert.Equal(t, Text{
+		Before:    "beforehighligh",
+		Highlight: "t",
+		After:     "after",
+	}, text.Substring(8, 12))
+
+	assert.Equal(t, Text{
+		Before:    "beforehighlight",
+		Highlight: "",
+		After:     "after",
+	}, text.Substring(9, 12))
+}