From 0fe5b743194ecce030f9b77d1f739b65352d62d2 Mon Sep 17 00:00:00 2001
From: mappu <mappu04@gmail.com>
Date: Tue, 11 Jul 2017 17:53:06 +1200
Subject: [PATCH] diff: correctness fixes

---
 diff/diff.go | 36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/diff/diff.go b/diff/diff.go
index e6c3213..534f454 100644
--- a/diff/diff.go
+++ b/diff/diff.go
@@ -1,3 +1,7 @@
+// Paul's Simple Diff Algorithm v 0.1
+// (C) Paul Butler 2007 <http://www.paulbutler.org/>
+// May be used and distributed under the zlib/libpng license.
+// https://github.com/paulgb/simplediff/
 package diff
 
 import (
@@ -6,13 +10,6 @@ import (
 	"strings"
 )
 
-/*
-Paul's Simple Diff Algorithm v 0.1
-(C) Paul Butler 2007 <http://www.paulbutler.org/>
-May be used and distributed under the zlib/libpng license.
-https://github.com/paulgb/simplediff/
-*/
-
 var Separator string = "\n"
 
 type Operation int8
@@ -29,17 +26,30 @@ type Instruction struct {
 }
 
 func (this *Instruction) RenderHTML() string {
+	sc := strings.Join(this.Content, Separator)
+	if len(sc) == 0 {
+		return ""
+	}
+
 	switch this.Op {
 	case OP_INSERTED:
-		return `<ins>` + strings.Join(this.Content, Separator) + `</ins>`
+		return `<ins>` + sc + `</ins>`
 	case OP_REMOVED:
-		return `<del>` + strings.Join(this.Content, Separator) + `</del>`
+		return `<del>` + sc + `</del>`
 	default: //OP_UNCHANGED:
-		return strings.Join(this.Content, Separator)
+		return sc
 	}
 }
 
+type twoints struct {
+	O, N int
+}
+
 func Diff(o, n []string) []Instruction {
+	if len(o) == 0 && len(n) == 0 {
+		return []Instruction{}
+	}
+
 	maxl := 0
 	omax := 0
 	nmax := 0
@@ -56,7 +66,7 @@ func Diff(o, n []string) []Instruction {
 		}
 
 		// Build diff matrix
-		for nindex, _ := range n {
+		for nindex, _ := range nkeys {
 			if _, ok := matrix[oindex]; !ok {
 				matrix[oindex] = make(map[int]int, len(n)+1)
 			}
@@ -79,9 +89,9 @@ func Diff(o, n []string) []Instruction {
 
 	ret := Diff(o[0:omax], n[0:nmax])
 	if maxl != nmax {
-		ret = append(ret, Instruction{OP_UNCHANGED, n[nmax:maxl]})
+		ret = append(ret, Instruction{OP_UNCHANGED, n[nmax : maxl-nmax]})
 	}
-	ret = append(ret, Diff(o[0:omax+maxl], n[0:nmax+maxl])...)
+	ret = append(ret, Diff(o[omax+maxl:], n[nmax+maxl:])...)
 
 	return ret
 }