@@ -0,0 +1,99 @@
+package git
+
+import (
+	"fmt"
+	"log"
+	"strings"
+
+	"github.com/bluekeyes/go-gitdiff/gitdiff"
+	"github.com/go-git/go-git/v5/plumbing/object"
+)
+
+type TextFragment struct {
+	Header string
+	Lines  []gitdiff.Line
+}
+
+type Diff struct {
+	Name struct {
+		Old string
+		New string
+	}
+	TextFragments []TextFragment
+}
+
+// A nicer git diff representation.
+type NiceDiff struct {
+	Commit struct {
+		Message string
+		Author  object.Signature
+		This    string
+		Parent  string
+	}
+	Stat struct {
+		FilesChanged int
+		Insertions   int
+		Deletions    int
+	}
+	Diff []Diff
+}
+
+func (g *GitRepo) Diff() (*NiceDiff, error) {
+	c, err := g.r.CommitObject(g.h)
+	if err != nil {
+		return nil, fmt.Errorf("commit object: %w", err)
+	}
+
+	var parent *object.Commit
+	if len(c.ParentHashes) > 0 {
+		parent, err = c.Parent(0)
+		if err != nil {
+			return nil, fmt.Errorf("getting parent: %w", err)
+		}
+	} else {
+		parent = c
+	}
+
+	patch, err := parent.Patch(c)
+	if err != nil {
+		return nil, fmt.Errorf("patch: %w", err)
+	}
+
+	diffs, _, err := gitdiff.Parse(strings.NewReader(patch.String()))
+	if err != nil {
+		log.Println(err)
+	}
+
+	nd := NiceDiff{}
+	nd.Commit.This = c.Hash.String()
+	nd.Commit.Parent = parent.Hash.String()
+	nd.Commit.Author = c.Author
+	nd.Commit.Message = c.Message
+	ndiff := Diff{}
+
+	for _, d := range diffs {
+		ndiff.Name.New = d.NewName
+		ndiff.Name.Old = d.OldName
+
+		for _, tf := range d.TextFragments {
+			ndiff.TextFragments = append(ndiff.TextFragments, TextFragment{
+				Header: tf.Header(),
+				Lines:  tf.Lines,
+			})
+			for _, l := range tf.Lines {
+				switch l.Op {
+				case gitdiff.OpAdd:
+					nd.Stat.Insertions += 1
+				case gitdiff.OpDelete:
+					nd.Stat.Deletions += 1
+				}
+			}
+		}
+
+		nd.Diff = append(nd.Diff, ndiff)
+	}
+
+	nd.Stat.FilesChanged = len(diffs)
+
+	return &nd, nil
+}

@@ -12,6 +12,7 @@ require (
 	github.com/Microsoft/go-winio v0.5.2 // indirect
 	github.com/ProtonMail/go-crypto v0.0.0-20221026131551-cf6655e29de4 // indirect
 	github.com/acomagu/bufpipe v1.0.3 // indirect
+	github.com/bluekeyes/go-gitdiff v0.7.0 // indirect
 	github.com/cloudflare/circl v1.1.0 // indirect
 	github.com/emirpasic/gods v1.18.1 // indirect
 	github.com/go-git/gcfg v1.5.0 // indirect
@@ -22,6 +23,7 @@ github.com/kevinburke/ssh_config v1.2.0 // indirect
 	github.com/pjbgf/sha1cd v0.2.0 // indirect
 	github.com/sergi/go-diff v1.1.0 // indirect
 	github.com/skeema/knownhosts v1.1.0 // indirect
+	github.com/sourcegraph/go-diff v0.6.1 // indirect
 	github.com/xanzy/ssh-agent v0.3.2 // indirect
 	golang.org/x/crypto v0.3.0 // indirect
 	golang.org/x/net v0.2.0 // indirect

@@ -10,6 +10,8 @@ github.com/anmitsu/go-shlex v0.0.0-20200514113438-38f4b401e2be h1:9AeTilPcZAjCFIImctFaOjnTIavg87rW78vTPkQqLI8=
 github.com/anmitsu/go-shlex v0.0.0-20200514113438-38f4b401e2be/go.mod h1:ySMOLuWl6zY27l47sB3qLNK6tF2fkHG55UZxx8oIVo4=
 github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5 h1:0CwZNZbxp69SHPdPJAN/hZIm0C4OItdklCFmMRWYpio=
 github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5/go.mod h1:wHh0iHkYZB8zMSxRWpUBQtwG5a7fFgvEO+odwuTv2gs=
+github.com/bluekeyes/go-gitdiff v0.7.0 h1:w4SrRFcufU0/tEpWx3VurDBAnWfpxsmwS7yWr14meQk=
+github.com/bluekeyes/go-gitdiff v0.7.0/go.mod h1:QpfYYO1E0fTVHVZAZKiRjtSGY9823iCdvGXBcEzHGbM=
 github.com/bwesterb/go-ristretto v1.2.0/go.mod h1:fUIoIZaG73pV5biE2Blr2xEzDoMj7NFEuV9ekS419A0=
 github.com/cloudflare/circl v1.1.0 h1:bZgT/A+cikZnKIwn7xL2OBj012Bmvho/o6RpRvv3GKY=
 github.com/cloudflare/circl v1.1.0/go.mod h1:prBCrKB9DV4poKZY1l9zBXg2QJY7mvgRvtMxxK7fi4I=
@@ -29,6 +31,7 @@ github.com/go-git/go-git-fixtures/v4 v4.3.1 h1:y5z6dd3qi8Hl+stezc8p3JxDkoTRqMAlKnXHuzrfjTQ=
 github.com/go-git/go-git-fixtures/v4 v4.3.1/go.mod h1:8LHG1a3SRW71ettAD/jW13h8c6AqjVSeL11RAdgaqpo=
 github.com/go-git/go-git/v5 v5.5.0 h1:StO/ASRvk1Pp74tr7XQ0pQwKlCFignzzTF/NLKdQzUE=
 github.com/go-git/go-git/v5 v5.5.0/go.mod h1:g456XI30HAdt7GQtIf8JR6GDAdULGaR4KtfFtQa0uTg=
+github.com/google/go-cmp v0.5.2/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
 github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/imdario/mergo v0.3.13 h1:lFzP57bqS/wsqKssCGmtLAb8A0wKjLGrve2q3PPVcBk=
@@ -56,9 +59,13 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/sergi/go-diff v1.1.0 h1:we8PVUC3FE2uYfodKH/nBHMSetSfHDR6scGdBi+erh0=
 github.com/sergi/go-diff v1.1.0/go.mod h1:STckp+ISIX8hZLjrqAeVduY0gWCT9IjLuqbuNXdaHfM=
+github.com/shurcooL/go v0.0.0-20180423040247-9e1955d9fb6e/go.mod h1:TDJrrUr11Vxrven61rcy3hJMUqaf/CLWYhHNPmT14Lk=
+github.com/shurcooL/go-goon v0.0.0-20170922171312-37c2f522c041/go.mod h1:N5mDOmsrJOB+vfqUK+7DmDyjhSLIIBnXo9lvZJj3MWQ=
 github.com/sirupsen/logrus v1.7.0/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
 github.com/skeema/knownhosts v1.1.0 h1:Wvr9V0MxhjRbl3f9nMnKnFfiWTJmtECJ9Njkea3ysW0=
 github.com/skeema/knownhosts v1.1.0/go.mod h1:sKFq3RD6/TKZkSWn8boUbDC7Qkgcv+8XXijpFO6roag=
+github.com/sourcegraph/go-diff v0.6.1 h1:hmA1LzxW0n1c3Q4YbrFgg4P99GSnebYa3x8gr0HZqLQ=
+github.com/sourcegraph/go-diff v0.6.1/go.mod h1:iBszgVvyxdc8SFZ7gm69go2KDdt3ag071iBaWPF6cjs=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
@@ -115,6 +122,7 @@ golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20200227125254-8fa46927fb4f/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

@@ -12,5 +12,6 @@ mux.HandleFunc("/:name", d.RepoIndex, "GET")
 	mux.HandleFunc("/:name/tree/:ref/...", d.RepoTree, "GET")
 	mux.HandleFunc("/:name/blob/:ref/...", d.FileContent, "GET")
 	mux.HandleFunc("/:name/log/:ref", d.Log, "GET")
+	mux.HandleFunc("/:name/commit/:ref", d.Diff, "GET")
 	return mux
 }

@@ -127,3 +127,39 @@ log.Println(err)
 		return
 	}
 }
+
+func (d *deps) Diff(w http.ResponseWriter, r *http.Request) {
+	name := flow.Param(r.Context(), "name")
+	ref := flow.Param(r.Context(), "ref")
+
+	path := filepath.Join(d.c.Git.ScanPath, name+".git")
+	gr, err := git.Open(path, ref)
+	if err != nil {
+		Write404(w, *d.c)
+		return
+	}
+
+	diff, err := gr.Diff()
+	if err != nil {
+		Write500(w, *d.c)
+		log.Println(err)
+		return
+	}
+
+	tpath := filepath.Join(d.c.Template.Dir, "*")
+	t := template.Must(template.ParseGlob(tpath))
+
+	data := make(map[string]interface{})
+
+	data["commit"] = diff.Commit
+	data["stat"] = diff.Stat
+	data["diff"] = diff.Diff
+	data["meta"] = d.c.Meta
+	data["name"] = name
+	data["ref"] = ref
+
+	if err := t.ExecuteTemplate(w, "commit", data); err != nil {
+		log.Println(err)
+		return
+	}
+}

@@ -0,0 +1,52 @@
+{{ define "commit" }}
+<html>
+{{ template "head" . }}
+
+  <header>
+    <h1>{{ .meta.Title }}</h1>
+    <h2>{{ .meta.Description }}</h2>
+  </header>
+  <body>
+    {{ template "nav" . }}
+    <main>
+      <section>
+        <p>author: {{ .commit.Author.Name }} <{{ .commit.Author.Email}}> on {{ .commit.Author.When }}</p>
+        <p>commit: <a href="/{{ .name }}/commit/{{ .commit.This }}">
+          {{ .commit.This }}
+        </a>
+        </p>
+        <p>parent: <a href="/{{ .name }}/commit/{{ .commit.Parent }}">
+          {{ .commit.Parent }}
+        </a>
+        </p>
+        <p>{{ .stat.FilesChanged }} files changed,
+          {{ .stat.Insertions }} insertions(+),
+          {{ .stat.Deletions }} deletions(-)
+        </p>
+      </section>
+      <section>
+        {{ range .diff }}
+          {{ if .Name.Old }}
+          <p>{{ .Name.Old }} → {{ .Name.New }}</p>
+          {{ else }}
+          <p>{{.Name.New }}</p>
+          {{- end -}}
+            <pre>
+            {{- range .TextFragments -}}
+            <p>{{- .Header -}}</p>
+              {{- range .Lines -}}
+                {{- if eq .Op.String "+" -}}
+                <span style="color: green">{{ .String }}</span>
+                {{- end -}}
+                {{- if eq .Op.String "-" -}}
+                <span style="color: red">{{ .String }}</span>
+                {{- end -}}
+              {{- end -}}
+            {{- end -}}
+            </pre>
+        {{ end }}
+      </section>
+    </main>
+  </body>
+</html>
+{{ end }}