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.

distillery/resources.go

@@ -0,0 +1,120 @@
+// TODO: Rename this to resources oncen finished
+package distillery
+
+import (
+	"embed"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+
+	"github.com/pkg/errors"
+)
+
+// resourceEmbed contains all the resources required by the WissKI-Distillery package.
+//go:embed all:resources
+var resourceEmbed embed.FS
+
+// InstallResource install a resource src into dest.
+// When it encounters a directory, recursively installs the directory is called.
+// For each installation item, onInstallFile is called, unless onInstallFile is nil.
+//
+// If src points to a file, dst must either be an existing file, or not exist.
+// If src points to a directory, dst must either be an existing directory, or not exist.
+func InstallResource(dst, src string, onInstallFile func(dst, src string)) error {
+	return installFile(dst, resourceEmbed, src, onInstallFile)
+}
+
+var errExpectedFileButGotDirectory = errors.New("Expected a file, but got a directory")
+var errExpectedDirectoryButGotFile = errors.New("Expected a directory, but got a file")
+
+func installFile(dst string, fsys embed.FS, src string, onInstallFile func(dst, src string)) error {
+	// call the on-install file path
+	if onInstallFile != nil {
+		onInstallFile(dst, src)
+	}
+
+	// open the source file!
+	srcFile, err := fsys.Open(src)
+	if err != nil {
+		return errors.Wrapf(err, "Error opening source file %s", src)
+	}
+	defer srcFile.Close()
+
+	// stat the source file to install
+	srcStat, srcErr := srcFile.Stat()
+	if srcErr != nil {
+		return errors.Wrapf(srcErr, "Error calling stat on source %s", src)
+	}
+
+	// if it is a directory, we should recurse!
+	if srcStat.IsDir() {
+		return installDir(dst, srcStat, srcFile, fsys, src, onInstallFile)
+	}
+
+	// determine if we need to create the destination file, or if it already exists
+	dstStat, dstErr := os.Stat(dst)
+	flag := os.O_WRONLY
+	switch {
+	case os.IsNotExist(dstErr):
+		flag |= os.O_CREATE
+	case dstErr != nil:
+		return errors.Wrapf(dstErr, "Error calling stat on destination %s", dst)
+	case dstStat.IsDir():
+		return errors.Wrapf(errExpectedFileButGotDirectory, "Error processing destination %s", dst)
+	}
+
+	// Open the file
+	dstFile, err := os.OpenFile(dst, flag, srcStat.Mode())
+	if err != nil {
+		return errors.Wrapf(err, "Error opening destination %s", dst)
+	}
+	defer dstFile.Close()
+
+	// copy over the content
+	_, err = io.Copy(dstFile, srcFile)
+	return errors.Wrapf(err, "Error writing to destination %s", dst)
+
+}
+
+func installDir(dst string, srcStat fs.FileInfo, srcFile fs.File, fsys embed.FS, src string, onInstallFile func(dst, src string)) error {
+	// make sure it is a directory!
+	dir, ok := srcFile.(fs.ReadDirFile)
+	if !ok {
+		return errExpectedDirectoryButGotFile
+	}
+
+	// create the destination
+	dstStat, dstErr := os.Stat(dst)
+	switch {
+	case os.IsNotExist(dstErr):
+		if err := os.MkdirAll(dst, srcStat.Mode()); err != nil {
+			return errors.Wrapf(err, "Error creating destination directory %s", dst)
+		}
+	case dstErr != nil:
+		return errors.Wrapf(dstErr, "Error calling stat on destination %s", dst)
+	case !dstStat.IsDir():
+		return errors.Wrapf(errExpectedDirectoryButGotFile, "Error opening destination %s", dst)
+	case dstErr == nil:
+	}
+
+	// read the directory
+	entries, err := dir.ReadDir(-1)
+	if err != nil {
+		return errors.Wrapf(err, "Error reading source directory %s", srcFile)
+	}
+
+	// iterate over all the children
+	for _, entry := range entries {
+		if err := func(dst, src string) error {
+			return installFile(dst, fsys, src, onInstallFile)
+		}(
+			filepath.Join(dst, entry.Name()),
+			filepath.Join(src, entry.Name()),
+		); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}