Do a large chunk of the move to go

This commit moves a huge chunk of the code to go. The TODO.md document
indicates what is left to be done.

internal/fsx/copy.go

@@ -0,0 +1,41 @@
+package fsx
+
+import (
+	"errors"
+	"io"
+	"os"
+)
+
+var ErrCopySameFile = errors.New("src and dst must be different files")
+
+// CopyFile copies a file from src to dst.
+// When dst and src are the same file, returns ErrCopySameFile.
+func CopyFile(dst, src string) error {
+	if src == dst {
+		return ErrCopySameFile
+	}
+
+	// open the source
+	srcFile, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer srcFile.Close()
+
+	// stat it to get the mode!
+	srcStat, err := srcFile.Stat()
+	if err != nil {
+		return err
+	}
+
+	// open or create the destination
+	dstFile, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE, srcStat.Mode())
+	if err != nil {
+		return err
+	}
+	defer dstFile.Close()
+
+	// and do the copy!
+	_, err = io.Copy(dstFile, srcFile)
+	return err
+}

internal/fsx/touch.go

@@ -0,0 +1,25 @@
+package fsx
+
+import (
+	"os"
+	"time"
+)
+
+// Touch touches a file
+func Touch(path string) error {
+	_, err := os.Stat(path)
+	switch {
+	case os.IsNotExist(err):
+		f, err := os.Create(path)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+		return nil
+	case err != nil:
+		return err
+	default:
+		now := time.Now().Local()
+		return os.Chtimes(path, now, now)
+	}
+}

internal/fsx/type.go

@@ -0,0 +1,13 @@
+package fsx
+
+import "os"
+
+func IsDirectory(path string) bool {
+	info, err := os.Stat(path)
+	return err == nil && info.Mode().IsDir()
+}
+
+func IsFile(path string) bool {
+	info, err := os.Stat(path)
+	return err == nil && info.Mode().IsRegular()
+}