Refactor Package structure

This commit cleans up the package structure, to make two new top-level
packages `internal` (for internal-use packages) and `pkg` (for general
shared utility code).

pkg/fsx/copy.go

@@ -0,0 +1,107 @@
+package fsx
+
+import (
+	"errors"
+	"io"
+	"os"
+	"path/filepath"
+)
+
+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 SameFile(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
+}
+
+var ErrCopyNoDirectory = errors.New("dst is not a directory")
+
+// CopyDirectory copies the directory src to dst recursively.
+// The destination directory must exist, or an error is returned.
+//
+// onCopy, when not nil, is called for each file or directory being copied.
+func CopyDirectory(dst, src string, onCopy func(dst, src string)) error {
+	// sanity checks
+	if SameFile(src, dst) {
+		return ErrCopySameFile
+	}
+	if !IsDirectory(dst) {
+		return ErrCopyNoDirectory
+	}
+
+	// call onCopy for this directory!
+	if onCopy != nil {
+		onCopy(dst, src)
+	}
+
+	// iterate over the entries or bail out
+	entries, err := os.ReadDir(src)
+	if err != nil {
+		return err
+	}
+
+	for _, entry := range entries {
+		name := entry.Name()
+		eDest := filepath.Join(dst, name)
+		eSrc := filepath.Join(src, name)
+
+		// it is not a directory => Use CopyFile
+		if !entry.IsDir() {
+			if onCopy != nil {
+				onCopy(eDest, eSrc)
+			}
+
+			// do the copy!
+			if err := CopyFile(eDest, eSrc); err != nil {
+				return err
+			}
+
+			continue
+		}
+
+		// find out the mode of the entry
+		eInfo, err := entry.Info()
+		if err != nil {
+			return err
+		}
+
+		// make the target directory
+		if err := os.Mkdir(eDest, eInfo.Mode()); err != nil {
+			return err
+		}
+
+		// do the copy!
+		if err := CopyDirectory(eDest, eSrc, onCopy); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}

pkg/fsx/same.go

@@ -0,0 +1,87 @@
+package fsx
+
+import (
+	"os"
+	"path/filepath"
+)
+
+// SameFile checks if path1 and path2 refer to the same file.
+// If both files exist, they are compared using [os.SameFile].
+// If both files do not exist, the paths are first compared syntactically and then via recursion on [filepath.Dir].
+func SameFile(path1, path2 string) bool {
+
+	// initial attempt: check if directly
+	same, certain := couldBeSameFile(path1, path2)
+	if certain {
+		return same
+	}
+
+	// second attempt: find the directory names and base paths
+	d1, n1 := filepath.Dir(path1), filepath.Base(path1)
+	d2, n2 := filepath.Dir(path2), filepath.Base(path2)
+
+	// if we have different file names (and they don't exist)
+	// we don't need to continue
+	if n1 != n2 {
+		return false
+	}
+
+	// compare the base names!
+	{
+		same, _ := couldBeSameFile(d1, d2)
+		return same
+	}
+}
+
+// couldBeSameFile checks if path1 might be the same as path2.
+//
+// If both files exist, compares using [os.SameFile].
+// Otherwise compares absolute paths using string comparison.
+//
+// same indicates if they might be the same file.
+// authorative indiciates if the result is authorative.
+func couldBeSameFile(path1, path2 string) (same, authorative bool) {
+	{
+		// stat both files
+		info1, err1 := os.Stat(path1)
+		info2, err2 := os.Stat(path2)
+
+		// both files exist => check using os.SameFile
+		// the result is always authorative
+		if err1 == nil && err2 == nil {
+			same = os.SameFile(info1, info2)
+			authorative = true
+			return
+		}
+
+		// only 1 file errored => they could be different
+		if (err1 == nil) != (err2 == nil) {
+			return
+		}
+
+		// only 1 file does not exist => they could be different
+		if os.IsNotExist(err1) != os.IsNotExist(err2) {
+			return
+		}
+	}
+
+	{
+		// resolve paths absolutely
+		rpath1, err1 := filepath.Abs(path1)
+		rpath2, err2 := filepath.Abs(path2)
+
+		// if either path could not be resolved absolutely
+		// fallback to just using clean!
+		if err1 != nil {
+			rpath1 = filepath.Clean(path1)
+		}
+		if err2 != nil {
+			rpath2 = filepath.Clean(path2)
+		}
+
+		// compare using strings
+		same = rpath1 == rpath2
+		authorative = same // positive result is authorative!
+		return
+	}
+}

pkg/fsx/touch.go

@@ -0,0 +1,29 @@
+package fsx
+
+import (
+	"os"
+	"time"
+)
+
+// Touch touches a file.
+// It is similar to the unix 'touch' command.
+//
+// If the file does not exist exists, it is created using [os.Create].
+// If the file does exist, it's access and modification times are updated to the current time.
+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)
+	}
+}

pkg/fsx/type.go

@@ -0,0 +1,24 @@
+// Package fsx provides convenient abstractions to work with the filesystem.
+package fsx
+
+import (
+	"os"
+)
+
+// Exists checks if the given path exists
+func Exists(path string) bool {
+	_, err := os.Stat(path)
+	return err == nil
+}
+
+// IsDirectory checks if the provided path exists and is a directory
+func IsDirectory(path string) bool {
+	info, err := os.Stat(path)
+	return err == nil && info.Mode().IsDir()
+}
+
+// IsFile checks if the provided path exists and is a regular file
+func IsFile(path string) bool {
+	info, err := os.Stat(path)
+	return err == nil && info.Mode().IsRegular()
+}