From b751118d09289824e8a63fad77725f161d083760 Mon Sep 17 00:00:00 2001
From: Oleg Kovalov <oleg@hey.com>
Date: Sat, 21 May 2022 13:01:05 +0200
Subject: [PATCH] Add TextMarshaler

---
 example_test.go | 17 +++++++++++++++++
 flagx.go        | 15 +++++++++++++++
 utils.go        | 44 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+)
 create mode 100644 utils.go

diff --git a/example_test.go b/example_test.go
index 12d67fb..0a56834 100644
--- a/example_test.go
+++ b/example_test.go
@@ -2,6 +2,7 @@ package flagx_test
 
 import (
 	"fmt"
+	"net"
 	"os"
 	"time"
 
@@ -22,3 +23,19 @@ func ExampleFlagSet() {
 		panic(fmt.Sprintf("got %v want %v", d, 20*time.Second))
 	}
 }
+
+func ExampleTextVar() {
+	fs := flagx.NewFlagSet("ExampleTextVar", os.Stdout)
+
+	var ip net.IP
+	fs.Text(&ip, "ip", "", net.IPv4(192, 168, 0, 100), "`IP address` to parse")
+
+	err := fs.Parse([]string{"-ip", "127.0.0.1"})
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("{ip: %v}\n\n", ip)
+
+	// Output:
+	// {ip: 127.0.0.1}
+}
diff --git a/flagx.go b/flagx.go
index e1f98d0..725ad89 100644
--- a/flagx.go
+++ b/flagx.go
@@ -1,6 +1,7 @@
 package flagx
 
 import (
+	"encoding"
 	"flag"
 	"io"
 	"time"
@@ -80,6 +81,20 @@ func (f *FlagSet) Func(name, alias, usage string, fn func(string) error) {
 	}
 }
 
+// Text defines a flag with the specified name and usage string.
+// The argument p must be a pointer to a variable that will hold the value
+// of the flag, and p must implement encoding.TextUnmarshaler.
+// If the flag is used, the flag value will be passed to p's UnmarshalText method.
+// The type of the default value must be the same as the type of p.
+// Empty string for alias means no alias will be created.
+func (f *FlagSet) Text(p encoding.TextUnmarshaler, name, alias string, value encoding.TextMarshaler, usage string) {
+	// TODO(cristaloleg): for Go 1.19 this can be f.fs.TextVar(...)
+	f.fs.Var(newTextValue(value, p), name, usage)
+	if alias != "" {
+		f.fs.Var(newTextValue(value, p), alias, usage)
+	}
+}
+
 // Bool defines a bool flag with specified name, alias, default value, and usage string.
 // The argument p points to a bool variable in which to store the value of the flag.
 // Empty string for alias means no alias will be created.
diff --git a/utils.go b/utils.go
new file mode 100644
index 0000000..1c7dc05
--- /dev/null
+++ b/utils.go
@@ -0,0 +1,44 @@
+package flagx
+
+import (
+	"encoding"
+	"fmt"
+	"reflect"
+)
+
+type textValue struct {
+	val encoding.TextUnmarshaler
+}
+
+func newTextValue(val encoding.TextMarshaler, p encoding.TextUnmarshaler) textValue {
+	ptrVal := reflect.ValueOf(p)
+	if ptrVal.Kind() != reflect.Ptr {
+		panic("flagx: variable value type must be a pointer")
+	}
+	defVal := reflect.ValueOf(val)
+	if defVal.Kind() == reflect.Ptr {
+		defVal = defVal.Elem()
+	}
+	if defVal.Type() != ptrVal.Type().Elem() {
+		panic(fmt.Sprintf("flagx: default type does not match variable type: %v != %v", defVal.Type(), ptrVal.Type().Elem()))
+	}
+	ptrVal.Elem().Set(defVal)
+	return textValue{p}
+}
+
+func (v textValue) Set(s string) error {
+	return v.val.UnmarshalText([]byte(s))
+}
+
+func (v textValue) Get() interface{} {
+	return v.val
+}
+
+func (v textValue) String() string {
+	if m, ok := v.val.(encoding.TextMarshaler); ok {
+		if b, err := m.MarshalText(); err == nil {
+			return string(b)
+		}
+	}
+	return ""
+}