From 0cbe3e235747c1137436e912875da7b7882fc7c4 Mon Sep 17 00:00:00 2001
From: Mihir Gandhi <mihir20121997@gmail.com>
Date: Tue, 21 May 2024 18:44:56 +0530
Subject: [PATCH] chore: optimise function config.ConfigKeyToEnv (#475)

---
 config/config.go      |  9 +--------
 config/config_test.go | 13 +++++++++++++
 config/env.go         | 37 ++++++++++++++++++++++++++++++++++---
 3 files changed, 48 insertions(+), 11 deletions(-)

diff --git a/config/config.go b/config/config.go
index 72bc17b2..fdec58b3 100644
--- a/config/config.go
+++ b/config/config.go
@@ -35,7 +35,6 @@ package config
 
 import (
 	"fmt"
-	"regexp"
 	"strconv"
 	"strings"
 	"sync"
@@ -46,12 +45,6 @@ import (
 
 const DefaultEnvPrefix = "RSERVER"
 
-// regular expression matching lowercase letter followed by an uppercase letter
-var camelCaseMatch = regexp.MustCompile("([a-z0-9])([A-Z])")
-
-// regular expression matching uppercase letters contained in environment variable names
-var upperCaseMatch = regexp.MustCompile("^[A-Z0-9_]+$")
-
 // Default is the singleton config instance
 var Default *Config
 
@@ -341,7 +334,7 @@ func getOrCreatePointer[T configTypes](
 // the replacer cannot detect camelCase keys.
 func (c *Config) bindEnv(key string) {
 	envVar := key
-	if !upperCaseMatch.MatchString(key) {
+	if !isUpperCaseConfigKey(key) {
 		envVar = ConfigKeyToEnv(c.envPrefix, key)
 	}
 	// bind once
diff --git a/config/config_test.go b/config/config_test.go
index 94db77d5..5cdf1fbd 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -494,6 +494,9 @@ func TestConfigKeyToEnv(t *testing.T) {
 	require.Equal(t, expected, ConfigKeyToEnv(DefaultEnvPrefix, "KeyVar1Var2"))
 	require.Equal(t, expected, ConfigKeyToEnv(DefaultEnvPrefix, "RSERVER_KEY_VAR1_VAR2"))
 	require.Equal(t, "KEY_VAR1_VAR2", ConfigKeyToEnv(DefaultEnvPrefix, "KEY_VAR1_VAR2"))
+	require.Equal(t, expected, ConfigKeyToEnv(DefaultEnvPrefix, "Key_Var1.Var2"))
+	require.Equal(t, expected, ConfigKeyToEnv(DefaultEnvPrefix, "key_Var1_Var2"))
+	require.Equal(t, "RSERVER_KEY_VAR_1_VAR2", ConfigKeyToEnv(DefaultEnvPrefix, "Key_Var.1.Var2"))
 }
 
 func TestGetEnvThroughViper(t *testing.T) {
@@ -724,3 +727,13 @@ func TestConfigLoad(t *testing.T) {
 		require.Error(t, err)
 	})
 }
+
+// Benchmark for the original ConfigKeyToEnv function
+func BenchmarkConfigKeyToEnv(b *testing.B) {
+	envPrefix := "MYAPP"
+	configKey := "myConfig.KeyName"
+	for i := 0; i < b.N; i++ {
+		_ = ConfigKeyToEnv(envPrefix, configKey)
+	}
+	b.ReportAllocs()
+}
diff --git a/config/env.go b/config/env.go
index cd67c68d..e726e335 100644
--- a/config/env.go
+++ b/config/env.go
@@ -4,15 +4,46 @@ package config
 import (
 	"os"
 	"strings"
+	"unicode"
 )
 
+func isUpperCaseConfigKey(s string) bool {
+	for _, ch := range s {
+		if !(ch == '_' || unicode.IsUpper(ch) || unicode.IsDigit(ch)) {
+			return false
+		}
+	}
+	return true
+}
+
 // ConfigKeyToEnv gets the env variable name from a given config key
 func ConfigKeyToEnv(envPrefix, s string) string {
-	if upperCaseMatch.MatchString(s) {
+	// Check if the string is already in upper case format
+	if isUpperCaseConfigKey(s) {
 		return s
 	}
-	snake := camelCaseMatch.ReplaceAllString(s, "${1}_${2}")
-	return envPrefix + "_" + strings.ToUpper(strings.ReplaceAll(snake, ".", "_"))
+
+	// convert camelCase to snake_case
+	var builder strings.Builder
+
+	// Add the prefix
+	builder.WriteString(envPrefix)
+	builder.WriteByte('_')
+
+	// Transform the input string to the desired format
+	for i, r := range s {
+		if r >= 'A' && r <= 'Z' && i > 0 && (s[i-1] >= 'a' && s[i-1] <= 'z' || s[i-1] >= '0' && s[i-1] <= '9') {
+			builder.WriteByte('_')
+		} else if r == '.' {
+			r = '_'
+		}
+		if unicode.IsLetter(r) {
+			r = unicode.ToUpper(r)
+		}
+		builder.WriteRune(r)
+	}
+
+	return builder.String()
 }
 
 // getEnv returns the environment value stored in key variable