Introduce templateutil for common template functionality

templateutil/defaults.go

@@ -0,0 +1,45 @@
+package templateutil
+
+import (
+	"encoding/base64"
+	"text/template"
+	"unicode"
+
+	"github.com/symflower/pretty"
+	"github.com/zimmski/osutil/bytesutil"
+)
+
+// DefaultFuncMap holds common template functions.
+var DefaultFuncMap = template.FuncMap{
+	"base64": func(in string) string {
+		return base64.StdEncoding.EncodeToString([]byte(in))
+	},
+	"prefixContinuationLinesWith": bytesutil.PrefixContinuationLinesWith,
+	"lowerFirst": func(s string) string {
+		return string(unicode.ToLower(rune(s[0]))) + s[1:]
+	},
+	"pretty": func(data any) string {
+		return pretty.Sprintf("%# v", data)
+	},
+	"prettyLazy": func(data any) string {
+		return pretty.LazySprintf("%# v", data)
+	},
+	"quote": func(data any) string {
+		return pretty.Sprintf("%q", data)
+	},
+}
+
+// MergeFuncMaps returns all functions of "a" and all functions of "b" in a new function mapping.
+// For entries that are defined in both maps the entry defined in b is chosen.
+func MergeFuncMaps(a template.FuncMap, b template.FuncMap) template.FuncMap {
+	c := template.FuncMap{}
+
+	for n, f := range a {
+		c[n] = f
+	}
+	for n, f := range b {
+		c[n] = f
+	}
+
+	return c
+}

templateutil/file.go

@@ -0,0 +1,53 @@
+package templateutil
+
+import (
+	"bytes"
+	"errors"
+	"os"
+	"path/filepath"
+	"text/template"
+
+	pkgerrors "github.com/pkg/errors"
+	"github.com/symflower/pretty"
+)
+
+// WriteTemplateToFile executes a template with the given data and saves the result into a file.
+func WriteTemplateToFile(filePath string, tmpl *template.Template, data any) error {
+	var driver bytes.Buffer
+
+	err := tmpl.Execute(&driver, data)
+	if err != nil {
+		return pkgerrors.Wrap(err, pretty.LazySprintf("%# v", data))
+	}
+
+	err = os.WriteFile(filePath, driver.Bytes(), 0640)
+	if err != nil {
+		return pkgerrors.Wrap(err, filePath)
+	}
+
+	return nil
+}
+
+// RewriteFileAsTemplate read in a file, execute it as a template with the given data and save the result into the same file.
+func RewriteFileAsTemplate(filePath string, funcMap template.FuncMap, data any) (err error) {
+	tmpl, err := template.New(filepath.Base(filePath)).Funcs(funcMap).ParseFiles(filePath) // REMARK Use the file name as template identifier because otherwise `template.ParseFiles` fails.
+	if err != nil {
+		return pkgerrors.Wrap(err, filePath)
+	}
+
+	f, err := os.Create(filePath)
+	if err != nil {
+		return pkgerrors.Wrap(err, filePath)
+	}
+	defer func() {
+		if e := f.Close(); e != nil {
+			err = errors.Join(err, e)
+		}
+	}()
+
+	if err := tmpl.Execute(f, data); err != nil {
+		return pkgerrors.Wrap(err, filePath)
+	}
+
+	return nil
+}