From 059bf34e9518ede0d410fb52cea596b754b66410 Mon Sep 17 00:00:00 2001
From: Phillip Dominy <pdominy@taxslayer.com>
Date: Sun, 22 Apr 2018 16:31:26 -0400
Subject: [PATCH] Add BSON marshalling

---
 decimal.go      | 28 +++++++++++++++++
 decimal_test.go | 80 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 108 insertions(+)

diff --git a/decimal.go b/decimal.go
index ad92a901..dbfffb2d 100644
--- a/decimal.go
+++ b/decimal.go
@@ -25,6 +25,8 @@ import (
 	"math/big"
 	"strconv"
 	"strings"
+
+	"gopkg.in/mgo.v2/bson"
 )
 
 // DivisionPrecision is the number of decimal places in the result when it
@@ -874,6 +876,32 @@ func (d Decimal) MarshalBinary() (data []byte, err error) {
 	return
 }
 
+// GetBSON implements the bson.Getter interface
+func (d Decimal) GetBSON() (interface{}, error) {
+	// Pass through string to create Mongo Decimal128 type
+	dec128, err := bson.ParseDecimal128(d.String())
+	if err != nil {
+		return nil, err
+	}
+	return dec128, nil
+}
+
+// SetBSON implements the bson.Setter interface
+func (d *Decimal) SetBSON(raw bson.Raw) error {
+	// Unmarshal as Mongo Decimal128 first then pass through string to obtain Decimal
+	var dec128 bson.Decimal128
+	berr := raw.Unmarshal(&dec128)
+	if berr != nil {
+		return berr
+	}
+	dec, derr := NewFromString(dec128.String())
+	if derr != nil {
+		return derr
+	}
+	*d = dec
+	return nil
+}
+
 // Scan implements the sql.Scanner interface for database deserialization.
 func (d *Decimal) Scan(value interface{}) error {
 	// first try to see if the data is stored in database as a Numeric datatype
diff --git a/decimal_test.go b/decimal_test.go
index ac800896..6b0cefe9 100644
--- a/decimal_test.go
+++ b/decimal_test.go
@@ -12,6 +12,8 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"gopkg.in/mgo.v2/bson"
 )
 
 type testEnt struct {
@@ -2284,3 +2286,81 @@ func TestRoundBankAnomaly(t *testing.T) {
 		t.Errorf("Expected bank rounding %s to equal %s, but it was %s", b, expected, bRounded)
 	}
 }
+
+func TestBSON(t *testing.T) {
+	// Capture positive and negative cases of floating numbers and whole numbers in various bit ranges; also copied scientific notation
+	// test cases from above
+	tests := []string{
+		"3.14159",
+		"42",
+		"42949672960",
+		"18446744073709551616000",
+		"-3.14159",
+		"-42",
+		"-42949672960",
+		"-18446744073709551616000",
+		"0",
+		"1e9",
+		"2.41E-3",
+		"24.2E-4",
+		"243E-5",
+		"1e-5",
+		"245E3",
+		"1.2345E-1",
+		"0e5",
+		"0e-5",
+		"123.456e0",
+		"123.456e2",
+		"123.456e10",
+	}
+
+	type decStruct struct {
+		Dec Decimal
+	}
+
+	// For each test the idea is that the String output of the original parsed decimal should match the String output of the
+	// decimal after it has been marshalled and unmarshalled into BSON
+	for i := range tests {
+		d, errD := NewFromString(tests[i])
+		if errD != nil {
+			t.Errorf("TestBSON failed decimal parsing for case %v because of parse error - %v", tests[i], errD)
+		}
+		exp := d.String()
+
+		// Test structure marshalling first
+		s1 := decStruct{Dec: d}
+		data, err := bson.Marshal(s1)
+		if err != nil {
+			t.Errorf("TestBSON failed structure marshalling for case %v because of marshal error - %v", tests[i], err)
+		}
+		s2 := decStruct{}
+		err = bson.Unmarshal(data, &s2)
+		if err != nil {
+			t.Errorf("TestBSON failed structure marshalling for case %v because of unmarshal error - %v", tests[i], err)
+		}
+		res := s2.Dec.String()
+		if exp != res {
+			t.Errorf("TestBSON failed structure marshalling for case %v got %v expected %v", tests[i], res, exp)
+		}
+
+		// Next test map marshalling
+		m := bson.M{"dec": d}
+		data2, err2 := bson.Marshal(m)
+		if err2 != nil {
+			t.Errorf("TestBSON failed map marshalling for case %v because of marshal error - %v", tests[i], err2)
+		}
+		m2 := make(bson.M)
+		err2 = bson.Unmarshal(data2, m2)
+		if err2 != nil {
+			t.Errorf("TestBSON failed map marshalling for case %v because of unmarshal error - %v", tests[i], err2)
+		}
+		d2, errD2 := NewFromString(m2["dec"].(bson.Decimal128).String())
+		if errD2 != nil {
+			t.Errorf("TestBSON failed map marshalling for case %v because of parse error - %v", tests[i], errD2)
+		}
+		res2 := d2.String()
+		if exp != res2 {
+			t.Errorf("TestBSON failed map marshalling for case %v got %v expected %v", tests[i], res2, exp)
+		}
+	}
+}