lib/transform: add transform library and --name-transform flag

lib/transform adds the transform library, supporting advanced path name
transformations for converting and renaming files and directories by applying
prefixes, suffixes, and other alterations.

It also adds the --name-transform flag for use with sync, copy, and move.

Multiple transformations can be used in sequence, applied in the order they are
specified on the command line.

By default --name-transform will only apply to file names. The means only the leaf
file name will be transformed. However some of the transforms would be better
applied to the whole path or just directories. To choose which which part of the
file path is affected some tags can be added to the --name-transform:

file	Only transform the leaf name of files (DEFAULT)
dir	Only transform name of directories - these may appear anywhere in the path
all	Transform the entire path for files and directories

Example syntax:
--name-transform file,prefix=ABC
--name-transform dir,prefix=DEF

lib/transform/transform_test.go

@@ -0,0 +1,142 @@
+package transform
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// sync tests are in fs/sync/sync_transform_test.go to avoid import cycle issues
+
+func newOptions(s ...string) (context.Context, error) {
+	ctx := context.Background()
+	err := SetOptions(ctx, s...)
+	return ctx, err
+}
+
+func TestPath(t *testing.T) {
+	for _, test := range []struct {
+		path string
+		want string
+	}{
+		{"", ""},
+		{"toe/toe/toe", "tictactoe/tictactoe/tictactoe"},
+		{"a/b/c", "tictaca/tictacb/tictacc"},
+	} {
+		ctx, err := newOptions("all,prefix=tac", "all,prefix=tic")
+		require.NoError(t, err)
+
+		got := Path(ctx, test.path, false)
+		assert.Equal(t, test.want, got)
+	}
+}
+
+func TestFileTagOnFile(t *testing.T) {
+	for _, test := range []struct {
+		path string
+		want string
+	}{
+		{"a/b/c.txt", "a/b/1c.txt"},
+	} {
+		ctx, err := newOptions("file,prefix=1")
+		require.NoError(t, err)
+
+		got := Path(ctx, test.path, false)
+		assert.Equal(t, test.want, got)
+	}
+}
+
+func TestDirTagOnFile(t *testing.T) {
+	for _, test := range []struct {
+		path string
+		want string
+	}{
+		{"a/b/c.txt", "1a/1b/c.txt"},
+	} {
+		ctx, err := newOptions("dir,prefix=1")
+		require.NoError(t, err)
+
+		got := Path(ctx, test.path, false)
+		assert.Equal(t, test.want, got)
+	}
+}
+
+func TestAllTag(t *testing.T) {
+	for _, test := range []struct {
+		path string
+		want string
+	}{
+		{"a/b/c.txt", "1a/1b/1c.txt"},
+	} {
+		ctx, err := newOptions("all,prefix=1")
+		require.NoError(t, err)
+
+		got := Path(ctx, test.path, false)
+		assert.Equal(t, test.want, got)
+	}
+}
+
+func TestFileTagOnDir(t *testing.T) {
+	for _, test := range []struct {
+		path string
+		want string
+	}{
+		{"a/b", "a/b"},
+	} {
+		ctx, err := newOptions("file,prefix=1")
+		require.NoError(t, err)
+
+		got := Path(ctx, test.path, true)
+		assert.Equal(t, test.want, got)
+	}
+}
+
+func TestDirTagOnDir(t *testing.T) {
+	for _, test := range []struct {
+		path string
+		want string
+	}{
+		{"a/b", "1a/1b"},
+	} {
+		ctx, err := newOptions("dir,prefix=1")
+		require.NoError(t, err)
+
+		got := Path(ctx, test.path, true)
+		assert.Equal(t, test.want, got)
+	}
+}
+
+func TestVarious(t *testing.T) {
+	for _, test := range []struct {
+		path  string
+		want  string
+		flags []string
+	}{
+		{"stories/The Quick Brown Fox!.txt", "STORIES/THE QUICK BROWN FOX!.TXT", []string{"all,uppercase"}},
+		{"stories/The Quick Brown Fox!.txt", "stories/The Slow Brown Turtle!.txt", []string{"all,replace=Fox:Turtle", "all,replace=Quick:Slow"}},
+		{"stories/The Quick Brown Fox!.txt", "c3Rvcmllcw==/VGhlIFF1aWNrIEJyb3duIEZveCEudHh0", []string{"all,base64encode"}},
+		{"c3Rvcmllcw==/VGhlIFF1aWNrIEJyb3duIEZveCEudHh0", "stories/The Quick Brown Fox!.txt", []string{"all,base64decode"}},
+		{"stories/The Quick Brown 🦊 Fox Went to the Café!.txt", "stories/The Quick Brown 🦊 Fox Went to the Café!.txt", []string{"all,nfc"}},
+		{"stories/The Quick Brown 🦊 Fox Went to the Café!.txt", "stories/The Quick Brown 🦊 Fox Went to the Café!.txt", []string{"all,nfd"}},
+		{"stories/The Quick Brown 🦊 Fox!.txt", "stories/The Quick Brown  Fox!.txt", []string{"all,ascii"}},
+		{"stories/The Quick Brown 🦊 Fox!.txt", "stories/The+Quick+Brown+%F0%9F%A6%8A+Fox%21.txt", []string{"all,url"}},
+		{"stories/The Quick Brown Fox!.txt", "stories/The Quick Brown Fox!", []string{"all,trimsuffix=.txt"}},
+		{"stories/The Quick Brown Fox!.txt", "OLD_stories/OLD_The Quick Brown Fox!.txt", []string{"all,prefix=OLD_"}},
+		{"stories/The Quick Brown 🦊 Fox Went to the Café!.txt", "stories/The Quick Brown _ Fox Went to the Caf_!.txt", []string{"all,charmap=ISO-8859-7"}},
+		{"stories/The Quick Brown Fox: A Memoir [draft].txt", "stories/The Quick Brown Fox： A Memoir ［draft］.txt", []string{"all,encoder=Colon,SquareBracket"}},
+		{"stories/The Quick Brown 🦊 Fox Went to the Café!.txt", "stories/The Quick Brown 🦊 Fox", []string{"all,truncate=21"}},
+		{"stories/The Quick Brown Fox!.txt", "stories/The Quick Brown Fox!.txt", []string{"all,command=echo"}},
+		{"stories/The Quick Brown Fox!.txt", "stories/The Quick Brown Fox!.txt-" + time.Now().Local().Format("20060102"), []string{"date=-{YYYYMMDD}"}},
+		{"stories/The Quick Brown Fox!.txt", "stories/The Quick Brown Fox!.txt-" + time.Now().Local().Format("2006-01-02 0304PM"), []string{"date=-{macfriendlytime}"}},
+		{"stories/The Quick Brown Fox!.txt", "ababababababab/ababab ababababab ababababab ababab!abababab", []string{"all,regex=[\\.\\w]/ab"}},
+	} {
+		ctx, err := newOptions(test.flags...)
+		require.NoError(t, err)
+
+		got := Path(ctx, test.path, false)
+		assert.Equal(t, test.want, got)
+	}
+}