embed: Begin refactor to use clearer paths

internal/unpack/unpack.go

@@ -0,0 +1,65 @@
+// Package unpack unpacks files and templates to a target directory
+package unpack
+
+import (
+	"bytes"
+	"errors"
+	"io/fs"
+)
+
+var errExpectedFileButGotDirectory = errors.New("expected a file, but got a directory")
+var errExpectedDirectoryButGotFile = errors.New("expected a directory, but got a file")
+
+// InstallResource installs the resource at src within fsys to dst.
+//
+// OnInstallFile is called for each source and destination file.
+// OnInstallFile may be nil.
+//
+// See [InstallDir] or [InstallFile].
+func InstallResource(dst string, src string, fsys fs.FS, onInstallFile func(dst, src string)) error {
+	// open the srcFile
+	srcFile, err := fsys.Open(src)
+	if err != nil {
+		return err
+	}
+	defer srcFile.Close()
+
+	// stat it!
+	srcInfo, err := srcFile.Stat()
+	if err != nil {
+		return err
+	}
+
+	// call the hook (if any)
+	if onInstallFile != nil {
+		onInstallFile(dst, src)
+	}
+
+	// this is a directory, so the cast is safe!
+	if srcInfo.IsDir() {
+		return installDir(dst, srcInfo, srcFile.(fs.ReadDirFile), src, fsys, onInstallFile)
+	}
+
+	// this is a regular file!
+	return installFile(dst, srcInfo, srcFile)
+}
+
+// UnpackTemplate unpacks the given file template and template.
+// See [WriteTemplate] for possible errors.
+func UnpackTemplate(context map[string]string, src fs.File) ([]byte, fs.FileMode, error) {
+	// stat the source file to install
+	srcStat, srcErr := src.Stat()
+	if srcErr != nil {
+		return nil, 0, srcErr
+	}
+
+	// should not be a directory
+	if srcStat.IsDir() {
+		return nil, 0, errExpectedFileButGotDirectory
+	}
+
+	// read all the bytes into a buffer
+	var buffer bytes.Buffer
+	err := WriteTemplate(&buffer, context, src)
+	return buffer.Bytes(), srcStat.Mode(), err
+}