From 33d7af2229cc4c27e1831f7d44e434e6a91bf6f9 Mon Sep 17 00:00:00 2001
From: itchyny <itchyny@hatena.ne.jp>
Date: Tue, 7 Jan 2020 23:39:39 +0900
Subject: [PATCH] implement cycle renames

---
 mmv.go      | 60 ++++++++++++++++++++++++++++++++++++--
 mmv_test.go | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 141 insertions(+), 2 deletions(-)

diff --git a/mmv.go b/mmv.go
index 4b9f62f..58f2ab4 100644
--- a/mmv.go
+++ b/mmv.go
@@ -1,6 +1,11 @@
 package mmv
 
-import "os"
+import (
+	"fmt"
+	"math/rand"
+	"os"
+	"path/filepath"
+)
 
 // Move multiple files.
 func Move(files map[string]string) error {
@@ -22,8 +27,59 @@ type rename struct {
 
 func buildRenames(files map[string]string) ([]rename, error) {
 	rs := make([]rename, 0, 2*len(files))
+	vs := make(map[string]int, len(files))
+	revs := make(map[string]string, len(files))
 	for src, dst := range files {
-		rs = append(rs, rename{src, dst})
+		revs[dst] = src
+	}
+	var i int
+	for _, dst := range files {
+		if vs[dst] > 0 {
+			continue
+		}
+		i++
+		var cycle bool
+		for {
+			vs[dst] = i
+			if x, ok := files[dst]; ok {
+				dst = x
+				if vs[x] > 0 {
+					cycle = vs[x] == i
+					break
+				}
+			} else {
+				break
+			}
+		}
+		var tmp string
+		if cycle {
+			tmp = randomPath(filepath.Dir(dst))
+			rs = append(rs, rename{dst, tmp})
+			vs[dst]--
+		}
+		for {
+			if src, ok := revs[dst]; ok && (!cycle || vs[src] == i) {
+				rs = append(rs, rename{src, dst})
+				if !cycle {
+					vs[dst] = i
+				}
+				dst = src
+			} else {
+				break
+			}
+		}
+		if cycle {
+			rs = append(rs, rename{tmp, dst})
+		}
 	}
 	return rs, nil
 }
+
+func randomPath(dir string) string {
+	for {
+		path := filepath.Join(dir, fmt.Sprint(rand.Uint64()))
+		if _, err := os.Stat(path); err != nil && os.IsNotExist(err) {
+			return path
+		}
+	}
+}
diff --git a/mmv_test.go b/mmv_test.go
index c06ac22..1128996 100644
--- a/mmv_test.go
+++ b/mmv_test.go
@@ -16,6 +16,7 @@ func TestMove(t *testing.T) {
 		files    map[string]string
 		contents map[string]string
 		expected map[string]string
+		cnt      int
 		err      error
 	}{
 		{
@@ -27,6 +28,7 @@ func TestMove(t *testing.T) {
 			files: map[string]string{
 				"foo": "bar",
 			},
+			cnt: 1,
 			contents: map[string]string{
 				"foo": "0",
 			},
@@ -40,6 +42,7 @@ func TestMove(t *testing.T) {
 				"foo": "qux",
 				"bar": "quxx",
 			},
+			cnt: 2,
 			contents: map[string]string{
 				"foo": "0",
 				"bar": "1",
@@ -51,6 +54,84 @@ func TestMove(t *testing.T) {
 				"baz":  "2",
 			},
 		},
+		{
+			name: "swap two files",
+			files: map[string]string{
+				"foo": "bar",
+				"bar": "foo",
+			},
+			cnt: 3,
+			contents: map[string]string{
+				"foo": "0",
+				"bar": "1",
+				"baz": "2",
+			},
+			expected: map[string]string{
+				"bar": "0",
+				"foo": "1",
+				"baz": "2",
+			},
+		},
+		{
+			name: "two swaps",
+			files: map[string]string{
+				"foo": "bar",
+				"bar": "foo",
+				"baz": "qux",
+				"qux": "baz",
+			},
+			cnt: 6,
+			contents: map[string]string{
+				"foo": "0",
+				"bar": "1",
+				"baz": "2",
+				"qux": "3",
+			},
+			expected: map[string]string{
+				"bar": "0",
+				"foo": "1",
+				"qux": "2",
+				"baz": "3",
+			},
+		},
+		{
+			name: "three files",
+			files: map[string]string{
+				"foo": "bar",
+				"bar": "baz",
+				"baz": "qux",
+			},
+			cnt: 3,
+			contents: map[string]string{
+				"foo": "0",
+				"bar": "1",
+				"baz": "2",
+			},
+			expected: map[string]string{
+				"bar": "0",
+				"baz": "1",
+				"qux": "2",
+			},
+		},
+		{
+			name: "cycle three files",
+			files: map[string]string{
+				"foo": "bar",
+				"bar": "baz",
+				"baz": "foo",
+			},
+			cnt: 4,
+			contents: map[string]string{
+				"foo": "0",
+				"bar": "1",
+				"baz": "2",
+			},
+			expected: map[string]string{
+				"bar": "0",
+				"baz": "1",
+				"foo": "2",
+			},
+		},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
@@ -59,6 +140,8 @@ func TestMove(t *testing.T) {
 			require.NoError(t, os.Chdir(dir))
 			require.NoError(t, err)
 			require.NoError(t, setupFiles(tc.contents))
+			rs, _ := buildRenames(tc.files)
+			assert.Equal(t, tc.cnt, len(rs))
 			require.NoError(t, Move(tc.files))
 			assert.Equal(t, tc.expected, fileContents("."))
 		})