From 6111341a3c36a596d9c1506fab2297e6fd36bffa Mon Sep 17 00:00:00 2001
From: Nikita Tokarchuk <tokarchuk+bitbucket@nevisq.com>
Date: Tue, 24 Mar 2020 21:26:28 +0100
Subject: [PATCH] Check for nil interface correctly

---
 mongox/base/getid.go         |  3 ++-
 mongox/database/deleteone.go |  3 ++-
 mongox/query/compose.go      |  3 ++-
 mongox/utils/isnil.go        | 21 +++++++++++++++++++++
 mongox/utils/isnil_test.go   | 32 ++++++++++++++++++++++++++++++++
 5 files changed, 59 insertions(+), 3 deletions(-)
 create mode 100644 mongox/utils/isnil.go
 create mode 100644 mongox/utils/isnil_test.go

diff --git a/mongox/base/getid.go b/mongox/base/getid.go
index 6209db6..f5f4bd8 100644
--- a/mongox/base/getid.go
+++ b/mongox/base/getid.go
@@ -6,6 +6,7 @@ import (
 	"go.mongodb.org/mongo-driver/bson/primitive"
 
 	"github.com/mainnika/mongox-go-driver/v2/mongox"
+	"github.com/mainnika/mongox-go-driver/v2/mongox/utils"
 )
 
 // GetID returns source document id
@@ -62,7 +63,7 @@ func getObjectOrPanic(source mongox.JSONBased) (id primitive.D) {
 func getInterfaceOrPanic(source mongox.InterfaceBased) (id interface{}) {
 
 	id = source.GetID()
-	if id != nil {
+	if !utils.IsNil(id) {
 		return id
 	}
 
diff --git a/mongox/database/deleteone.go b/mongox/database/deleteone.go
index 95b360e..76462fb 100644
--- a/mongox/database/deleteone.go
+++ b/mongox/database/deleteone.go
@@ -10,6 +10,7 @@ import (
 	"github.com/mainnika/mongox-go-driver/v2/mongox"
 	"github.com/mainnika/mongox-go-driver/v2/mongox/base"
 	"github.com/mainnika/mongox-go-driver/v2/mongox/query"
+	"github.com/mainnika/mongox-go-driver/v2/mongox/utils"
 )
 
 // DeleteOne removes a document from a database and then returns it into target
@@ -22,7 +23,7 @@ func (d *Database) DeleteOne(target interface{}, filters ...interface{}) error {
 
 	opts.Sort = composed.Sorter()
 
-	if target != nil {
+	if !utils.IsNil(target) {
 		composed.And(primitive.M{"_id": base.GetID(target)})
 	}
 
diff --git a/mongox/query/compose.go b/mongox/query/compose.go
index afa5d3d..382f463 100644
--- a/mongox/query/compose.go
+++ b/mongox/query/compose.go
@@ -7,6 +7,7 @@ import (
 	"go.mongodb.org/mongo-driver/bson/primitive"
 
 	"github.com/mainnika/mongox-go-driver/v2/mongox/base/protection"
+	"github.com/mainnika/mongox-go-driver/v2/mongox/utils"
 )
 
 // Compose is a function to compose filters into a single query
@@ -26,7 +27,7 @@ func Compose(filters ...interface{}) *Query {
 // Push applies single filter to a query
 func Push(q *Query, f interface{}) bool {
 
-	if f == nil {
+	if utils.IsNil(f) {
 		return true
 	}
 
diff --git a/mongox/utils/isnil.go b/mongox/utils/isnil.go
new file mode 100644
index 0000000..9c32162
--- /dev/null
+++ b/mongox/utils/isnil.go
@@ -0,0 +1,21 @@
+package utils
+
+import (
+	"unsafe"
+)
+
+// IsNil function evaluates the interface value to nil
+func IsNil(i interface{}) bool {
+
+	type iface struct {
+		_   *interface{}
+		ptr unsafe.Pointer
+	}
+
+	unpacked := (*iface)(unsafe.Pointer(&i))
+	if unpacked.ptr == nil {
+		return true
+	}
+
+	return *(*unsafe.Pointer)(unpacked.ptr) == nil
+}
diff --git a/mongox/utils/isnil_test.go b/mongox/utils/isnil_test.go
new file mode 100644
index 0000000..a6d1ced
--- /dev/null
+++ b/mongox/utils/isnil_test.go
@@ -0,0 +1,32 @@
+package utils
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIsNil(t *testing.T) {
+
+	testvalues := []struct {
+		i     interface{}
+		isnil bool
+	}{
+		{nil, true},
+		{(*string)(nil), true},
+		{([]string)(nil), true},
+		{(map[string]string)(nil), true},
+		{(func() bool)(nil), true},
+		{(chan func() bool)(nil), true},
+		{"", true},
+		{0, true},
+		{append(([]string)(nil), ""), false},
+		{[]string{}, false},
+		{1, false},
+		{"1", false},
+	}
+
+	for _, tt := range testvalues {
+		assert.Equal(t, tt.isnil, IsNil(tt.i))
+	}
+}