Restructure language loading to support incomplete translations

On startup, files are scanned and any missing values are replaced with
the english version.

lang.go

@@ -1,5 +1,7 @@
 package main
 
+import "strings"
+
 type langMeta struct {
 	Name string `json:"name"`
 }
@@ -9,14 +11,80 @@ type quantityString struct {
 	Plural   string `json:"plural"`
 }
 
+type adminLangs map[string]adminLang
+
+func (ls *adminLangs) getOptions(chosen string) (string, []string) {
+	opts := make([]string, len(*ls))
+	chosenLang := (*ls)[chosen].Meta.Name
+	i := 0
+	for _, lang := range *ls {
+		opts[i] = lang.Meta.Name
+	}
+	return chosenLang, opts
+}
+
 type adminLang struct {
 	Meta            langMeta                  `json:"meta"`
-	Strings         map[string]string         `json:"strings"`
-	Notifications   map[string]string         `json:"notifications"`
+	Strings         langSection               `json:"strings"`
+	Notifications   langSection               `json:"notifications"`
 	QuantityStrings map[string]quantityString `json:"quantityStrings"`
+	JSON            string
+}
+
+type formLangs map[string]formLang
+
+func (ls *formLangs) getOptions(chosen string) (string, []string) {
+	opts := make([]string, len(*ls))
+	chosenLang := (*ls)[chosen].Meta.Name
+	i := 0
+	for _, lang := range *ls {
+		opts[i] = lang.Meta.Name
+	}
+	return chosenLang, opts
 }
 
 type formLang struct {
-	Strings           map[string]string         `json:"strings"`
-	ValidationStrings map[string]quantityString `json:"validationStrings"`
+	Meta                  langMeta                  `json:"meta"`
+	Strings               langSection               `json:"strings"`
+	ValidationStrings     map[string]quantityString `json:"validationStrings"`
+	validationStringsJSON string
+}
+
+type emailLangs map[string]emailLang
+
+func (ls *emailLangs) getOptions(chosen string) (string, []string) {
+	opts := make([]string, len(*ls))
+	chosenLang := (*ls)[chosen].Meta.Name
+	i := 0
+	for _, lang := range *ls {
+		opts[i] = lang.Meta.Name
+	}
+	return chosenLang, opts
+}
+
+type emailLang struct {
+	Meta          langMeta    `json:"meta"`
+	UserCreated   langSection `json:"userCreated"`
+	InviteExpiry  langSection `json:"inviteExpiry"`
+	PasswordReset langSection `json:"passwordReset"`
+	UserDeleted   langSection `json:"userDeleted"`
+	InviteEmail   langSection `json:"inviteEmail"`
+}
+
+type langSection map[string]string
+
+func (el *langSection) format(field string, vals ...string) string {
+	text := el.get(field)
+	for _, val := range vals {
+		text = strings.Replace(text, "{n}", val, 1)
+	}
+	return text
+}
+
+func (el *langSection) get(field string) string {
+	t, ok := (*el)[field]
+	if !ok {
+		return ""
+	}
+	return t
 }