Cleanup internal packages

internal/unpack/template.go

@@ -5,6 +5,8 @@ import (
 	"bufio"
 	"fmt"
 	"io"
+	"io/fs"
+	"os"
 	"strings"
 
 	"golang.org/x/exp/maps"
@@ -194,3 +196,38 @@ parseloop:
 
 	return nil
 }
+
+// InstallTemplate unpacks the resource located at src in fsys, then processes it as a template, and eventually writes it to dst.
+// Any existing file is truncated and overwritten.
+//
+// See [WriteTemplate] for possible errors.
+func InstallTemplate(dst string, context map[string]string, src string, fsys fs.FS) 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
+	}
+
+	// check if it is a directory
+	if srcInfo.IsDir() {
+		return errExpectedFileButGotDirectory
+	}
+
+	// open the destination file
+	file, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, srcInfo.Mode())
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	// write the file!
+	return WriteTemplate(file, context, srcFile)
+}