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engine.go
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engine.go
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package mail
import (
"bytes"
"fmt"
htmlTemplate "html/template"
"io"
"io/ioutil"
"path/filepath"
"strings"
textTemplate "text/template"
)
type MissingVar int
const (
HaltOnError MissingVar = iota
ContinueOnError
ZeroValueOnError
)
// templateEngine combines html/template and text/template and calls functions
// based on extension of given template name.
type templateEngine struct {
leftDelim, rightDelim string
funcMap map[string]interface{}
missingVar MissingVar
htmlTemplate *htmlTemplate.Template
textTemplate *textTemplate.Template
}
func newTemplateEngine() *templateEngine {
return &templateEngine{
leftDelim: "{{",
rightDelim: "}}",
missingVar: HaltOnError,
}
}
func (t *templateEngine) ExecuteTemplate(name string, vars Vars) ([]byte, error) {
if !t.Exists(name) {
return nil, fmt.Errorf("template '%v' not found", name)
}
var buf bytes.Buffer
switch filepath.Ext(name) {
case "." + HTMLExtension:
if err := t.htmlTemplate.ExecuteTemplate(&buf, name, vars); err != nil {
return nil, err
}
case "." + TextExtension:
if err := t.textTemplate.ExecuteTemplate(&buf, name, vars); err != nil {
return nil, err
}
}
return buf.Bytes(), nil
}
func (t *templateEngine) Exists(name string) bool {
switch filepath.Ext(name) {
case "." + HTMLExtension:
for _, v := range t.htmlTemplate.Templates() {
if name == v.Name() {
return true
}
}
case "." + TextExtension:
for _, v := range t.textTemplate.Templates() {
if name == v.Name() {
return true
}
}
}
return false
}
func (t *templateEngine) ParseFiles(files Files) error {
var err error
t.textTemplate, err = parseTextFiles(files, t.leftDelim, t.rightDelim, t.funcMap)
if err != nil {
return err
}
t.htmlTemplate, err = parseHTMLFiles(files, t.leftDelim, t.rightDelim, t.funcMap)
if err != nil {
return err
}
switch t.missingVar {
case ContinueOnError:
t.textTemplate = t.textTemplate.Option("missingkey=default")
t.htmlTemplate = t.htmlTemplate.Option("missingkey=default")
case ZeroValueOnError:
t.textTemplate = t.textTemplate.Option("missingkey=zero")
t.htmlTemplate = t.htmlTemplate.Option("missingkey=zero")
default:
fallthrough
case HaltOnError:
t.textTemplate = t.textTemplate.Option("missingkey=error")
t.htmlTemplate = t.htmlTemplate.Option("missingkey=error")
}
return nil
}
// TODO: try to combine parseTextFiles and parseHTMLFiles using an interface{}
// parseTextFiles is a modified copy of:
// https://godoc.org/github.com/golang/go/src/html/template#Template.ParseFiles
func parseTextFiles(files Files, leftDelim, rightDelim string, funcMap textTemplate.FuncMap) (*textTemplate.Template, error) {
var t *textTemplate.Template
err := files.Walk(func(name string, body io.ReadCloser) error {
defer body.Close()
if !strings.HasSuffix(name, "."+TextExtension) {
return nil
}
// read full body
b, err := ioutil.ReadAll(body)
if err != nil {
return err
}
// create new template if necessary
if t == nil {
t = textTemplate.New(name).Delims(leftDelim, rightDelim).Funcs(funcMap)
}
// parse template
var tmpl *textTemplate.Template
if name == t.Name() {
tmpl = t
} else {
tmpl = t.New(name)
}
_, err = tmpl.Parse(string(b))
return err
})
if err != nil {
return nil, err
}
return t, nil
}
// parseHTMLFiles is a modified copy of:
// https://godoc.org/github.com/golang/go/src/html/template#Template.ParseFiles
func parseHTMLFiles(files Files, leftDelim, rightDelim string, funcMap htmlTemplate.FuncMap) (*htmlTemplate.Template, error) {
var t *htmlTemplate.Template
err := files.Walk(func(name string, body io.ReadCloser) error {
defer body.Close()
if !strings.HasSuffix(name, "."+HTMLExtension) {
return nil
}
// read full body
b, err := ioutil.ReadAll(body)
if err != nil {
return err
}
// create new template if necessary
if t == nil {
t = htmlTemplate.New(name).Delims(leftDelim, rightDelim).Funcs(funcMap)
}
// parse template
var tmpl *htmlTemplate.Template
if name == t.Name() {
tmpl = t
} else {
tmpl = t.New(name)
}
_, err = tmpl.Parse(string(b))
return err
})
if err != nil {
return nil, err
}
return t, nil
}