From 1d11247e33d4884325f79d0459d2cd81e852be20 Mon Sep 17 00:00:00 2001
From: Mark Sagi-Kazar <mark.sagikazar@gmail.com>
Date: Tue, 20 Jul 2021 01:04:13 +0200
Subject: [PATCH] feat(encoding): add dotenv codec

Signed-off-by: Mark Sagi-Kazar <mark.sagikazar@gmail.com>
---
 internal/encoding/dotenv/codec.go      | 61 +++++++++++++++++++++++++
 internal/encoding/dotenv/codec_test.go | 63 ++++++++++++++++++++++++++
 internal/encoding/dotenv/map_utils.go  | 41 +++++++++++++++++
 3 files changed, 165 insertions(+)
 create mode 100644 internal/encoding/dotenv/codec.go
 create mode 100644 internal/encoding/dotenv/codec_test.go
 create mode 100644 internal/encoding/dotenv/map_utils.go

diff --git a/internal/encoding/dotenv/codec.go b/internal/encoding/dotenv/codec.go
new file mode 100644
index 0000000..4485063
--- /dev/null
+++ b/internal/encoding/dotenv/codec.go
@@ -0,0 +1,61 @@
+package dotenv
+
+import (
+	"bytes"
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/subosito/gotenv"
+)
+
+const keyDelimiter = "_"
+
+// Codec implements the encoding.Encoder and encoding.Decoder interfaces for encoding data containing environment variables
+// (commonly called as dotenv format).
+type Codec struct{}
+
+func (Codec) Encode(v map[string]interface{}) ([]byte, error) {
+	flattened := map[string]interface{}{}
+
+	flattened = flattenAndMergeMap(flattened, v, "", keyDelimiter)
+
+	keys := make([]string, 0, len(flattened))
+
+	for key := range flattened {
+		keys = append(keys, key)
+	}
+
+	sort.Strings(keys)
+
+	var buf bytes.Buffer
+
+	for _, key := range keys {
+		_, err := buf.WriteString(fmt.Sprintf("%v=%v\n", strings.ToUpper(key), flattened[key]))
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return buf.Bytes(), nil
+}
+
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	var buf bytes.Buffer
+
+	_, err := buf.Write(b)
+	if err != nil {
+		return err
+	}
+
+	env, err := gotenv.StrictParse(&buf)
+	if err != nil {
+		return err
+	}
+
+	for key, value := range env {
+		v[key] = value
+	}
+
+	return nil
+}
diff --git a/internal/encoding/dotenv/codec_test.go b/internal/encoding/dotenv/codec_test.go
new file mode 100644
index 0000000..d297071
--- /dev/null
+++ b/internal/encoding/dotenv/codec_test.go
@@ -0,0 +1,63 @@
+package dotenv
+
+import (
+	"reflect"
+	"testing"
+)
+
+// original form of the data
+const original = `# key-value pair
+KEY=value
+`
+
+// encoded form of the data
+const encoded = `KEY=value
+`
+
+// Viper's internal representation
+var data = map[string]interface{}{
+	"KEY": "value",
+}
+
+func TestCodec_Encode(t *testing.T) {
+	codec := Codec{}
+
+	b, err := codec.Encode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if encoded != string(b) {
+		t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+	}
+}
+
+func TestCodec_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(original), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(data, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", v, data)
+		}
+	})
+
+	t.Run("InvalidData", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(`invalid data`), v)
+		if err == nil {
+			t.Fatal("expected decoding to fail")
+		}
+
+		t.Logf("decoding failed as expected: %s", err)
+	})
+}
diff --git a/internal/encoding/dotenv/map_utils.go b/internal/encoding/dotenv/map_utils.go
new file mode 100644
index 0000000..ce6e6ef
--- /dev/null
+++ b/internal/encoding/dotenv/map_utils.go
@@ -0,0 +1,41 @@
+package dotenv
+
+import (
+	"strings"
+
+	"github.com/spf13/cast"
+)
+
+// flattenAndMergeMap recursively flattens the given map into a new map
+// Code is based on the function with the same name in tha main package.
+// TODO: move it to a common place
+func flattenAndMergeMap(shadow map[string]interface{}, m map[string]interface{}, prefix string, delimiter string) map[string]interface{} {
+	if shadow != nil && prefix != "" && shadow[prefix] != nil {
+		// prefix is shadowed => nothing more to flatten
+		return shadow
+	}
+	if shadow == nil {
+		shadow = make(map[string]interface{})
+	}
+
+	var m2 map[string]interface{}
+	if prefix != "" {
+		prefix += delimiter
+	}
+	for k, val := range m {
+		fullKey := prefix + k
+		switch val.(type) {
+		case map[string]interface{}:
+			m2 = val.(map[string]interface{})
+		case map[interface{}]interface{}:
+			m2 = cast.ToStringMap(val)
+		default:
+			// immediate value
+			shadow[strings.ToLower(fullKey)] = val
+			continue
+		}
+		// recursively merge to shadow map
+		shadow = flattenAndMergeMap(shadow, m2, fullKey, delimiter)
+	}
+	return shadow
+}