From 6d96051dadb29d11442d7a14eae150003a6b0f9f Mon Sep 17 00:00:00 2001
From: Radek Simko <radek.simko@gmail.com>
Date: Wed, 3 Aug 2016 23:35:43 +0100
Subject: [PATCH] Add support for omitempty tag option

---
 struct.go      | 35 ++++++++++++++++++++++++++++++++++-
 struct_test.go | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/struct.go b/struct.go
index f4620af..a1efa17 100644
--- a/struct.go
+++ b/struct.go
@@ -19,6 +19,7 @@ import (
 	"errors"
 	"fmt"
 	"reflect"
+	"strings"
 	"time"
 	"unicode"
 )
@@ -323,6 +324,26 @@ func reflectWithProperType(t reflect.Type, key *Key, field reflect.Value, delim
 	return nil
 }
 
+func isEmptyValue(v reflect.Value) bool {
+	switch v.Kind() {
+	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
+		return v.Len() == 0
+	case reflect.Bool:
+		return !v.Bool()
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return v.Int() == 0
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return v.Uint() == 0
+	case reflect.Float32, reflect.Float64:
+		return v.Float() == 0
+	case reflectTime:
+		return v.Interface().(time.Time).IsZero()
+	case reflect.Interface, reflect.Ptr:
+		return v.IsNil()
+	}
+	return false
+}
+
 func (s *Section) reflectFrom(val reflect.Value) error {
 	if val.Kind() == reflect.Ptr {
 		val = val.Elem()
@@ -338,7 +359,19 @@ func (s *Section) reflectFrom(val reflect.Value) error {
 			continue
 		}
 
-		fieldName := s.parseFieldName(tpField.Name, tag)
+		opts := strings.Split(tag, ",")
+		if len(opts) > 2 {
+			return fmt.Errorf("Expected max. 2 comma-separated values in a tag, %d given", len(opts))
+		}
+
+		if len(opts) == 2 {
+			v := opts[1]
+			if v == "omitempty" && isEmptyValue(field) {
+				continue
+			}
+		}
+
+		fieldName := s.parseFieldName(tpField.Name, opts[0])
 		if len(fieldName) == 0 || !field.CanSet() {
 			continue
 		}
diff --git a/struct_test.go b/struct_test.go
index b3f5d46..39763c1 100644
--- a/struct_test.go
+++ b/struct_test.go
@@ -269,6 +269,38 @@ None        =
 		Convey("Reflect from non-point struct", func() {
 			So(ReflectFrom(cfg, Author{}), ShouldNotBeNil)
 		})
+
+		Convey("Reflect from struct with omitempty", func() {
+			cfg := Empty()
+			type SpecialStruct struct {
+				FirstName  string    `ini:"first_name"`
+				LastName   string    `ini:"last_name"`
+				JustOmitMe string    `ini:"omitempty"`
+				LastLogin  time.Time `ini:"last_login,omitempty"`
+				LastLogin2 time.Time `ini:",omitempty"`
+				NotEmpty   int       `ini:"omitempty"`
+			}
+
+			So(ReflectFrom(cfg, &SpecialStruct{FirstName: "John", LastName: "Doe", NotEmpty: 9}), ShouldBeNil)
+
+			var buf bytes.Buffer
+			_, err = cfg.WriteTo(&buf)
+			So(buf.String(), ShouldEqual, `first_name = John
+last_name  = Doe
+omitempty  = 9
+
+`)
+		})
+
+		Convey("Reflect from struct with too many opts in a tag", func() {
+			cfg := Empty()
+			type SpecialStruct struct {
+				TooManyOpts string `ini:"first_name,second,third"`
+				LastName    string `ini:"last_name"`
+			}
+
+			So(ReflectFrom(cfg, &SpecialStruct{TooManyOpts: "John", LastName: "Doe"}), ShouldNotBeNil)
+		})
 	})
 }