feat(api): add Delete and Sub methods, update CI workflows

- Add Delete(key) to remove keys from all config layers
- Add Sub(key) to get a scoped ConfigManager for nested sections
- Update CodeQL workflow actions to v4/v5/v3
- Update govulncheck workflow checkout to v4
- Remove boilerplate comments from CodeQL workflow
- Add comprehensive tests for both new methods
- Update README with Sub() usage example and API docs

.github/workflows/codeql-analysis.yml

@@ -36,31 +36,20 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Install Go
-      uses: actions/setup-go@v4
+      uses: actions/setup-go@v5
       with:
         go-version-file: go.mod
 
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@v2
+      uses: github/codeql-action/init@v3
       with:
         languages: ${{ matrix.language }}
 
     - name: Autobuild
-      uses: github/codeql-action/autobuild@v2
-
-    # ℹ️ Command-line programs to run using the OS shell.
-    # 📚 https://git.io/JvXDl
-
-    # ✏️ If the Autobuild fails above, remove it and uncomment the following three lines
-    #    and modify them (or add more) to build your code if your project
-    #    uses a compiled language
-
-    #- run: |
-    #   make bootstrap
-    #   make release
+      uses: github/codeql-action/autobuild@v3
 
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@v2
+      uses: github/codeql-action/analyze@v3

.github/workflows/govulncheck.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Run govulncheck
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - id: govulncheck
         uses: golang/govulncheck-action@v1
         with:

.github/workflows/test.yml

@@ -0,0 +1,19 @@
+name: test
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.26"
+      - run: go test -race -count=1 ./...
+      - run: go vet ./...
+      - run: go install honnef.co/go/tools/cmd/staticcheck@latest && staticcheck ./...

README.md

@@ -1,9 +1,161 @@
 # JETY
 
-JSON, ENV, YAML, TOML
+[![test](https://github.com/taigrr/jety/actions/workflows/test.yml/badge.svg)](https://github.com/taigrr/jety/actions/workflows/test.yml)
+[![govulncheck](https://github.com/taigrr/jety/actions/workflows/govulncheck.yml/badge.svg)](https://github.com/taigrr/jety/actions/workflows/govulncheck.yml)
 
-This is a package for collapsing multiple configuration stores (env+json, env+yaml, env+toml) and writing them back to a centralized config.
+JSON, ENV, TOML, YAML
 
-It should behave similarly to the AutomaticEnv functionality of viper, but without some of the extra heft of the depedendencies it carries.
+A lightweight Go configuration management library supporting JSON, ENV, TOML, and YAML formats.
+It provides viper-like `AutomaticEnv` functionality with fewer dependencies.
+Originally built to support [grlx](http://github.com/gogrlx/grlx).
 
-The inital purpose of this repo is to support the configuration requirements of [grlx](http://github.com/gogrlx/grlx), but development may continue to expand until more viper use cases and functionality are covered.
+## Installation
+
+```bash
+go get github.com/taigrr/jety
+```
+
+Requires Go 1.26.1 or later.
+
+## Quick Start
+
+```go
+package main
+
+import "github.com/taigrr/jety"
+
+func main() {
+    // Set defaults
+    jety.SetDefault("port", 8080)
+    jety.SetDefault("host", "localhost")
+
+    // Environment variables are loaded automatically
+    // e.g., PORT=9000 overrides the default
+
+    // Read from config file
+    jety.SetConfigFile("config.toml")
+    jety.SetConfigType("toml")
+    if err := jety.ReadInConfig(); err != nil {
+        // handle error
+    }
+
+    // Get values (Set > env > config file > default)
+    port := jety.GetInt("port")
+    host := jety.GetString("host")
+}
+```
+
+## Features
+
+- **Multiple formats**: JSON, TOML, YAML
+- **Automatic env loading**: Environment variables loaded on init
+- **Prefix filtering**: Filter env vars by prefix (e.g., `MYAPP_`)
+- **Case-insensitive keys**: Keys normalized to lowercase
+- **Type coercion**: Getters handle type conversion gracefully
+- **Thread-safe**: Safe for concurrent access
+- **Config precedence**: Set() > environment > config file > defaults
+
+## Nested Configuration
+
+For nested config structures like:
+
+```toml
+[services.cloud]
+var = "xyz"
+timeout = "30s"
+
+[services.cloud.auth]
+client_id = "abc123"
+```
+
+Use `Sub()` to get a scoped ConfigManager for a nested section:
+
+```go
+cloud := jety.Sub("services")
+if cloud != nil {
+    inner := cloud.Sub("cloud")
+    if inner != nil {
+        varValue := inner.GetString("var")      // "xyz"
+        timeout := inner.GetDuration("timeout")  // 30s
+    }
+}
+```
+
+Or access nested values directly with `GetStringMap` and type assertions:
+
+```go
+services := jety.GetStringMap("services")
+cloud := services["cloud"].(map[string]any)
+varValue := cloud["var"].(string)  // "xyz"
+```
+
+### Environment Variable Overrides
+
+Environment variables use uppercase keys. For nested config, the env var name is the key in uppercase:
+
+```bash
+# Override top-level key
+export PORT=9000
+
+# For nested keys, use the full key name in uppercase
+export SERVICES_CLOUD_VAR=override_value
+```
+
+With a prefix:
+
+```go
+cm := jety.NewConfigManager().WithEnvPrefix("MYAPP_")
+```
+
+```bash
+export MYAPP_PORT=9000
+export MYAPP_SERVICES_CLOUD_VAR=override_value
+```
+
+**Note**: Environment variables override both defaults and config file values for registered keys (keys that appear in defaults or the config file).
+
+## API
+
+### Configuration
+
+| Function              | Description                                   |
+| --------------------- | --------------------------------------------- |
+| `SetConfigFile(path)` | Set config file path                          |
+| `SetConfigDir(dir)`   | Set config directory                          |
+| `SetConfigName(name)` | Set config file name (without extension)      |
+| `SetConfigType(type)` | Set config type: `"toml"`, `"yaml"`, `"json"` |
+| `ReadInConfig()`      | Read config file                              |
+| `WriteConfig()`       | Write config to file                          |
+
+### Values
+
+| Function                 | Description              |
+| ------------------------ | ------------------------ |
+| `Set(key, value)`        | Set a value              |
+| `SetDefault(key, value)` | Set a default value      |
+| `Delete(key)`            | Remove a key             |
+| `Sub(key)`               | Get scoped sub-config    |
+| `Get(key)`               | Get raw value            |
+| `GetString(key)`         | Get as string            |
+| `GetInt(key)`            | Get as int               |
+| `GetInt64(key)`          | Get as int64             |
+| `GetFloat64(key)`        | Get as float64           |
+| `GetBool(key)`           | Get as bool              |
+| `GetDuration(key)`       | Get as time.Duration     |
+| `GetStringSlice(key)`    | Get as []string          |
+| `GetIntSlice(key)`       | Get as []int             |
+| `GetStringMap(key)`      | Get as map[string]any    |
+| `IsSet(key)`             | Check if key has a value |
+| `AllKeys()`              | List all known keys      |
+| `AllSettings()`          | Get all values as a map  |
+
+### Environment
+
+| Function                | Description                                         |
+| ----------------------- | --------------------------------------------------- |
+| `WithEnvPrefix(prefix)` | Filter env vars by prefix (strips prefix from keys) |
+| `SetEnvPrefix(prefix)`  | Set prefix for env var lookups                      |
+
+## License
+
+See [LICENSE](LICENSE) file.

default.go

@@ -1,4 +1,4 @@
-package config
+package jety
 
 import "time"
 
@@ -20,6 +20,14 @@ func SetConfigName(name string) {
 	defaultConfigManager.SetConfigName(name)
 }
 
+func GetFloat64(key string) float64 {
+	return defaultConfigManager.GetFloat64(key)
+}
+
+func GetInt64(key string) int64 {
+	return defaultConfigManager.GetInt64(key)
+}
+
 func GetInt(key string) int {
 	return defaultConfigManager.GetInt(key)
 }
@@ -40,8 +48,8 @@ func Set(key string, value any) {
 	defaultConfigManager.Set(key, value)
 }
 
-func WriteConfig() {
-	defaultConfigManager.WriteConfig()
+func WriteConfig() error {
+	return defaultConfigManager.WriteConfig()
 }
 
 func ConfigFileUsed() string {
@@ -67,3 +75,43 @@ func GetStringMap(key string) map[string]any {
 func GetStringSlice(key string) []string {
 	return defaultConfigManager.GetStringSlice(key)
 }
+
+func Get(key string) any {
+	return defaultConfigManager.Get(key)
+}
+
+func SetBool(key string, value bool) {
+	defaultConfigManager.SetBool(key, value)
+}
+
+func SetString(key string, value string) {
+	defaultConfigManager.SetString(key, value)
+}
+
+func Delete(key string) {
+	defaultConfigManager.Delete(key)
+}
+
+func Sub(key string) *ConfigManager {
+	return defaultConfigManager.Sub(key)
+}
+
+func SetConfigDir(path string) {
+	defaultConfigManager.SetConfigDir(path)
+}
+
+func WithEnvPrefix(prefix string) *ConfigManager {
+	return defaultConfigManager.WithEnvPrefix(prefix)
+}
+
+func IsSet(key string) bool {
+	return defaultConfigManager.IsSet(key)
+}
+
+func AllKeys() []string {
+	return defaultConfigManager.AllKeys()
+}
+
+func AllSettings() map[string]any {
+	return defaultConfigManager.AllSettings()
+}

doc.go

@@ -0,0 +1,31 @@
+// Package jety provides configuration management supporting JSON, ENV, TOML, and YAML formats.
+//
+// It offers viper-like AutomaticEnv functionality with minimal dependencies, allowing
+// configuration to be loaded from files and environment variables with automatic merging.
+//
+// Configuration sources are layered with the following precedence (highest to lowest):
+//   - Values set via Set() or SetString()/SetBool()
+//   - Environment variables (optionally filtered by prefix)
+//   - Values from config file via ReadInConfig()
+//   - Default values set via SetDefault()
+//
+// Basic usage:
+//
+//	jety.SetConfigFile("/etc/myapp/config.yaml")
+//	jety.SetConfigType("yaml")
+//	jety.SetEnvPrefix("MYAPP_")
+//	jety.SetDefault("port", 8080)
+//
+//	if err := jety.ReadInConfig(); err != nil {
+//	    log.Fatal(err)
+//	}
+//
+//	port := jety.GetInt("port")
+//
+// For multiple independent configurations, create separate ConfigManager instances:
+//
+//	cm := jety.NewConfigManager()
+//	cm.SetConfigFile("/etc/myapp/config.toml")
+//	cm.SetConfigType("toml")
+//	cm.ReadInConfig()
+package jety

getters.go

@@ -1,4 +1,4 @@
-package config
+package jety
 
 import (
 	"fmt"
@@ -7,15 +7,24 @@ import (
 	"time"
 )
 
+// resolve looks up a key in combinedConfig, falling back to envConfig.
+func (c *ConfigManager) resolve(key string) (ConfigMap, bool) {
+	lower := strings.ToLower(key)
+	if v, ok := c.combinedConfig[lower]; ok {
+		return v, true
+	}
+	if v, ok := c.envConfig[lower]; ok {
+		return v, true
+	}
+	return ConfigMap{}, false
+}
+
 func (c *ConfigManager) Get(key string) any {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return nil
-		}
+		return nil
 	}
 	return v.Value
 }
@@ -23,53 +32,37 @@ func (c *ConfigManager) Get(key string) any {
 func (c *ConfigManager) GetBool(key string) bool {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return false
-		}
+		return false
 	}
 	val := v.Value
 	switch val := val.(type) {
 	case bool:
 		return val
 	case string:
-		if strings.ToLower(val) == "true" {
-			return true
-		}
-		return false
+		return strings.EqualFold(val, "true")
 	case int:
-		if val == 0 {
-			return false
-		}
-		return true
-	case float32, float64:
-		if val == 0 {
-			return false
-		}
-		return true
+		return val != 0
+	case float32:
+		return val != 0
+	case float64:
+		return val != 0
+	case time.Duration:
+		return val > 0
 	case nil:
 		return false
-	case time.Duration:
-		if val == 0 || val < 0 {
-			return false
-		}
-		return true
 	default:
-		return val.(bool)
+		return false
 	}
 }
 
 func (c *ConfigManager) GetDuration(key string) time.Duration {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return 0
-		}
+		return 0
 	}
 	val := v.Value
 	switch val := val.(type) {
@@ -83,6 +76,8 @@ func (c *ConfigManager) GetDuration(key string) time.Duration {
 		return d
 	case int:
 		return time.Duration(val)
+	case int64:
+		return time.Duration(val)
 	case float32:
 		return time.Duration(val)
 	case float64:
@@ -90,20 +85,16 @@ func (c *ConfigManager) GetDuration(key string) time.Duration {
 	case nil:
 		return 0
 	default:
-		return val.(time.Duration)
-
+		return 0
 	}
 }
 
 func (c *ConfigManager) GetString(key string) string {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return ""
-		}
+		return ""
 	}
 
 	switch val := v.Value.(type) {
@@ -117,12 +108,9 @@ func (c *ConfigManager) GetString(key string) string {
 func (c *ConfigManager) GetStringMap(key string) map[string]any {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return nil
-		}
+		return nil
 	}
 	switch val := v.Value.(type) {
 	case map[string]any:
@@ -135,34 +123,99 @@ func (c *ConfigManager) GetStringMap(key string) map[string]any {
 func (c *ConfigManager) GetStringSlice(key string) []string {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return nil
-		}
+		return nil
 	}
 	switch val := v.Value.(type) {
 	case []string:
 		return val
+	case []any:
+		var ret []string
+		for _, v := range val {
+			switch v := v.(type) {
+			case string:
+				ret = append(ret, v)
+			default:
+				ret = append(ret, fmt.Sprintf("%v", v))
+			}
+		}
+		return ret
 	default:
 		return nil
 	}
 }
 
+func (c *ConfigManager) GetFloat64(key string) float64 {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	v, ok := c.resolve(key)
+	if !ok {
+		return 0
+	}
+	switch val := v.Value.(type) {
+	case float64:
+		return val
+	case float32:
+		return float64(val)
+	case int:
+		return float64(val)
+	case int64:
+		return float64(val)
+	case string:
+		f, err := strconv.ParseFloat(val, 64)
+		if err != nil {
+			return 0
+		}
+		return f
+	case nil:
+		return 0
+	default:
+		return 0
+	}
+}
+
+func (c *ConfigManager) GetInt64(key string) int64 {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	v, ok := c.resolve(key)
+	if !ok {
+		return 0
+	}
+	switch val := v.Value.(type) {
+	case int64:
+		return val
+	case int:
+		return int64(val)
+	case string:
+		i, err := strconv.ParseInt(val, 10, 64)
+		if err != nil {
+			return 0
+		}
+		return i
+	case float32:
+		return int64(val)
+	case float64:
+		return int64(val)
+	case nil:
+		return 0
+	default:
+		return 0
+	}
+}
+
 func (c *ConfigManager) GetInt(key string) int {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return 0
-		}
+		return 0
 	}
 	switch val := v.Value.(type) {
 	case int:
 		return val
+	case int64:
+		return int(val)
 	case string:
 		i, err := strconv.Atoi(val)
 		if err != nil {
@@ -183,16 +236,38 @@ func (c *ConfigManager) GetInt(key string) int {
 func (c *ConfigManager) GetIntSlice(key string) []int {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return nil
-		}
+		return nil
 	}
 	switch val := v.Value.(type) {
 	case []int:
 		return val
+	case []any:
+		var ret []int
+		for _, v := range val {
+			switch v := v.(type) {
+			case int:
+				ret = append(ret, v)
+			case int64:
+				ret = append(ret, int(v))
+			case string:
+				i, err := strconv.Atoi(v)
+				if err != nil {
+					continue
+				}
+				ret = append(ret, i)
+			case float32:
+				ret = append(ret, int(v))
+			case float64:
+				ret = append(ret, int(v))
+			case nil:
+				continue
+			default:
+				continue
+			}
+		}
+		return ret
 	default:
 		return nil
 	}

go.mod

@@ -1,8 +1,8 @@
 module github.com/taigrr/jety
 
-go 1.21.3
+go 1.26.1
 
 require (
-	github.com/BurntSushi/toml v1.3.2
+	github.com/BurntSushi/toml v1.6.0
 	gopkg.in/yaml.v3 v3.0.1
 )

go.sum

@@ -1,5 +1,5 @@
-github.com/BurntSushi/toml v1.3.2 h1:o7IhLm0Msx3BaB+n3Ag7L8EVlByGnpq14C4YWiu/gL8=
-github.com/BurntSushi/toml v1.3.2/go.mod h1:CxXYINrC8qIiEnFrOxCa7Jy5BFHlXnUU2pbicEuybxQ=
+github.com/BurntSushi/toml v1.6.0 h1:dRaEfpa2VI55EwlIW72hMRHdWouJeRF7TPYhI+AUQjk=
+github.com/BurntSushi/toml v1.6.0/go.mod h1:ukJfTF/6rtPPRCnwkur4qwRxa8vTRFBF0uk2lLoLwho=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

jety.go

@@ -1,10 +1,11 @@
-package config
+package jety
 
 import (
 	"encoding/json"
 	"errors"
 	"fmt"
 	"os"
+	"path/filepath"
 	"strings"
 	"sync"
 
@@ -21,58 +22,74 @@ const (
 type (
 	configType string
 
+	// ConfigMap holds a configuration entry with its original key name and value.
 	ConfigMap struct {
 		Key   string
 		Value any
 	}
 
+	// ConfigManager manages layered configuration from defaults, files,
+	// environment variables, and programmatic overrides.
 	ConfigManager struct {
-		configName       string
-		configPath       string
-		configFileUsed   string
-		configType       configType
-		envPrefix        string
-		mapConfig        map[string]ConfigMap
-		defaultConfig    map[string]ConfigMap
-		envConfig        map[string]ConfigMap
-		combinedConfig   map[string]ConfigMap
-		mutex            sync.RWMutex
-		explicitDefaults bool
+		configName     string
+		configPath     string
+		configFileUsed string
+		configType     configType
+		overrideConfig map[string]ConfigMap
+		fileConfig     map[string]ConfigMap
+		defaultConfig  map[string]ConfigMap
+		envConfig      map[string]ConfigMap
+		combinedConfig map[string]ConfigMap
+		mutex          sync.RWMutex
 	}
 )
 
-var ErrConfigFileNotFound = errors.New("config File Not Found")
+var (
+	ErrConfigFileNotFound = errors.New("config file not found")
+	ErrConfigFileEmpty    = errors.New("config file is empty")
+)
 
-func NewConfigManager() *ConfigManager {
-	cm := ConfigManager{}
-	cm.envConfig = make(map[string]ConfigMap)
-	cm.mapConfig = make(map[string]ConfigMap)
-	cm.defaultConfig = make(map[string]ConfigMap)
-	cm.combinedConfig = make(map[string]ConfigMap)
-	cm.envPrefix = ""
-	envSet := os.Environ()
-	for _, env := range envSet {
-		kv := strings.Split(env, "=")
-		lower := strings.ToLower(kv[0])
-		cm.envConfig[lower] = ConfigMap{Key: kv[0], Value: kv[1]}
+// parseEnv reads environment variables, optionally filtering by prefix,
+// and returns a map keyed by lowercased (and prefix-stripped) variable names.
+func parseEnv(prefix string) map[string]ConfigMap {
+	result := make(map[string]ConfigMap)
+	for _, env := range os.Environ() {
+		key, value, found := strings.Cut(env, "=")
+		if !found {
+			continue
+		}
+		if prefix != "" {
+			stripped, ok := strings.CutPrefix(key, prefix)
+			if !ok {
+				continue
+			}
+			key = stripped
+		}
+		result[strings.ToLower(key)] = ConfigMap{Key: key, Value: value}
 	}
-	return &cm
+	return result
 }
 
+// NewConfigManager creates a new ConfigManager with all environment
+// variables loaded. Use [ConfigManager.WithEnvPrefix] or
+// [ConfigManager.SetEnvPrefix] to filter by prefix.
+func NewConfigManager() *ConfigManager {
+	return &ConfigManager{
+		envConfig:      parseEnv(""),
+		overrideConfig: make(map[string]ConfigMap),
+		fileConfig:     make(map[string]ConfigMap),
+		defaultConfig:  make(map[string]ConfigMap),
+		combinedConfig: make(map[string]ConfigMap),
+	}
+}
+
+// WithEnvPrefix filters environment variables to only those starting with
+// the given prefix, stripping the prefix from key names. Returns the
+// ConfigManager for chaining.
 func (c *ConfigManager) WithEnvPrefix(prefix string) *ConfigManager {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
-	c.envPrefix = prefix
-	envSet := os.Environ()
-	c.envConfig = make(map[string]ConfigMap)
-	for _, env := range envSet {
-		kv := strings.Split(env, "=")
-		if strings.HasPrefix(kv[0], prefix) {
-			withoutPrefix := strings.TrimPrefix(kv[0], prefix)
-			lower := strings.ToLower(withoutPrefix)
-			c.envConfig[lower] = ConfigMap{Key: withoutPrefix, Value: kv[1]}
-		}
-	}
+	c.envConfig = parseEnv(prefix)
 	return c
 }
 
@@ -82,23 +99,69 @@ func (c *ConfigManager) ConfigFileUsed() string {
 	return c.configFileUsed
 }
 
-func (c *ConfigManager) UseExplicitDefaults(enable bool) {
-	c.mutex.Lock()
-	defer c.mutex.Unlock()
-	c.explicitDefaults = enable
+// IsSet checks whether a key has been set in any configuration source.
+func (c *ConfigManager) IsSet(key string) bool {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	lower := strings.ToLower(key)
+	if _, ok := c.combinedConfig[lower]; ok {
+		return true
+	}
+	_, ok := c.envConfig[lower]
+	return ok
+}
+
+// AllKeys returns all keys from all configuration sources, deduplicated.
+func (c *ConfigManager) AllKeys() []string {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	seen := make(map[string]struct{})
+	var keys []string
+	for k := range c.combinedConfig {
+		if _, ok := seen[k]; !ok {
+			seen[k] = struct{}{}
+			keys = append(keys, k)
+		}
+	}
+	for k := range c.envConfig {
+		if _, ok := seen[k]; !ok {
+			seen[k] = struct{}{}
+			keys = append(keys, k)
+		}
+	}
+	return keys
+}
+
+// AllSettings returns all settings as a flat map of key to value.
+func (c *ConfigManager) AllSettings() map[string]any {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	result := make(map[string]any, len(c.combinedConfig))
+	for k, v := range c.combinedConfig {
+		result[k] = v.Value
+	}
+	return result
 }
 
 func (c *ConfigManager) collapse() {
-	c.mutex.RLock()
-	defer c.mutex.RUnlock()
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
 	ccm := make(map[string]ConfigMap)
+	// Precedence (highest to lowest): overrides (Set) > env > file > defaults
 	for k, v := range c.defaultConfig {
 		ccm[k] = v
-		if _, ok := c.envConfig[k]; ok {
-			ccm[k] = c.envConfig[k]
+	}
+	for k, v := range c.fileConfig {
+		ccm[k] = v
+	}
+	for k, v := range c.envConfig {
+		if _, inDefaults := c.defaultConfig[k]; inDefaults {
+			ccm[k] = v
+		} else if _, inFile := c.fileConfig[k]; inFile {
+			ccm[k] = v
 		}
 	}
-	for k, v := range c.mapConfig {
+	for k, v := range c.overrideConfig {
 		ccm[k] = v
 	}
 	c.combinedConfig = ccm
@@ -107,6 +170,9 @@ func (c *ConfigManager) collapse() {
 func (c *ConfigManager) WriteConfig() error {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
+	if c.configFileUsed == "" {
+		return errors.New("no config file specified")
+	}
 	flattenedConfig := make(map[string]any)
 	for _, v := range c.combinedConfig {
 		flattenedConfig[v.Key] = v.Value
@@ -128,8 +194,10 @@ func (c *ConfigManager) WriteConfig() error {
 		}
 		defer f.Close()
 		enc := yaml.NewEncoder(f)
-		err = enc.Encode(flattenedConfig)
-		return err
+		if err = enc.Encode(flattenedConfig); err != nil {
+			return err
+		}
+		return enc.Close()
 	case ConfigTypeJSON:
 		f, err := os.Create(c.configFileUsed)
 		if err != nil {
@@ -143,8 +211,10 @@ func (c *ConfigManager) WriteConfig() error {
 	}
 }
 
-func (c *ConfigManager) SetConfigType(configType string) error {
-	switch configType {
+func (c *ConfigManager) SetConfigType(ct string) error {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+	switch ct {
 	case "toml":
 		c.configType = ConfigTypeTOML
 	case "yaml":
@@ -152,20 +222,42 @@ func (c *ConfigManager) SetConfigType(configType string) error {
 	case "json":
 		c.configType = ConfigTypeJSON
 	default:
-		return fmt.Errorf("config type %s not supported", configType)
+		return fmt.Errorf("config type %s not supported", ct)
 	}
 	return nil
 }
 
+// SetEnvPrefix filters environment variables to only those starting with
+// the given prefix, stripping the prefix from key names.
 func (c *ConfigManager) SetEnvPrefix(prefix string) {
-	c.envPrefix = prefix
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+	c.envConfig = parseEnv(prefix)
 }
 
 func (c *ConfigManager) ReadInConfig() error {
-	c.mutex.Lock()
-	defer c.mutex.Unlock()
-	// assume config = map[string]any
-	confFileData, err := readFile(c.configFileUsed, c.configType)
+	c.mutex.RLock()
+	configFile := c.configFileUsed
+	if configFile == "" && c.configPath != "" && c.configName != "" {
+		ext := ""
+		switch c.configType {
+		case ConfigTypeTOML:
+			ext = ".toml"
+		case ConfigTypeYAML:
+			ext = ".yaml"
+		case ConfigTypeJSON:
+			ext = ".json"
+		}
+		configFile = filepath.Join(c.configPath, c.configName+ext)
+	}
+	configType := c.configType
+	c.mutex.RUnlock()
+
+	if configFile == "" {
+		return errors.New("no config file specified: use SetConfigFile or SetConfigDir + SetConfigName")
+	}
+
+	confFileData, err := readFile(configFile, configType)
 	if err != nil {
 		return err
 	}
@@ -174,38 +266,73 @@ func (c *ConfigManager) ReadInConfig() error {
 		lower := strings.ToLower(k)
 		conf[lower] = ConfigMap{Key: k, Value: v}
 	}
-	c.mapConfig = conf
+	c.mutex.Lock()
+	c.fileConfig = conf
+	c.configFileUsed = configFile
+	c.mutex.Unlock()
+	c.collapse()
 	return nil
 }
 
 func readFile(filename string, fileType configType) (map[string]any, error) {
+	f, err := os.Open(filename)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, ErrConfigFileNotFound
+		}
+		return nil, err
+	}
+	defer f.Close()
+
+	info, err := f.Stat()
+	if err != nil {
+		return nil, err
+	}
+	if info.Size() == 0 {
+		return nil, ErrConfigFileEmpty
+	}
+
 	fileData := make(map[string]any)
 	switch fileType {
 	case ConfigTypeTOML:
-		_, err := toml.DecodeFile(filename, &fileData)
+		_, err := toml.NewDecoder(f).Decode(&fileData)
 		return fileData, err
 	case ConfigTypeYAML:
-		f, err := os.Open(filename)
-		if err != nil {
-			return nil, err
-		}
-		defer f.Close()
-		d := yaml.NewDecoder(f)
-		err = d.Decode(&fileData)
+		err := yaml.NewDecoder(f).Decode(&fileData)
 		return fileData, err
 	case ConfigTypeJSON:
-		f, err := os.Open(filename)
-		if err != nil {
-			return nil, err
-		}
-		defer f.Close()
-		err = json.NewDecoder(f).Decode(&fileData)
+		err := json.NewDecoder(f).Decode(&fileData)
 		return fileData, err
 	default:
 		return nil, fmt.Errorf("config type %s not supported", fileType)
 	}
 }
 
+// Sub returns a new ConfigManager rooted at the given key. The key must
+// refer to a map value (e.g., from a nested TOML/YAML/JSON section).
+// The returned ConfigManager has the nested map loaded as its default
+// config, and does not inherit the parent's environment prefix, overrides,
+// or config file. Returns nil if the key does not exist or is not a map.
+func (c *ConfigManager) Sub(key string) *ConfigManager {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	v, ok := c.resolve(key)
+	if !ok {
+		return nil
+	}
+	m, ok := v.Value.(map[string]any)
+	if !ok {
+		return nil
+	}
+	sub := NewConfigManager()
+	for k, val := range m {
+		lower := strings.ToLower(k)
+		sub.defaultConfig[lower] = ConfigMap{Key: k, Value: val}
+		sub.combinedConfig[lower] = ConfigMap{Key: k, Value: val}
+	}
+	return sub
+}
+
 func (c *ConfigManager) SetConfigDir(path string) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()

setters.go

@@ -1,4 +1,4 @@
-package config
+package jety
 
 import (
 	"strings"
@@ -8,7 +8,7 @@ func (c *ConfigManager) SetBool(key string, value bool) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	lower := strings.ToLower(key)
-	c.mapConfig[lower] = ConfigMap{Key: key, Value: value}
+	c.overrideConfig[lower] = ConfigMap{Key: key, Value: value}
 	c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
 }
 
@@ -16,7 +16,7 @@ func (c *ConfigManager) SetString(key string, value string) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	lower := strings.ToLower(key)
-	c.mapConfig[lower] = ConfigMap{Key: key, Value: value}
+	c.overrideConfig[lower] = ConfigMap{Key: key, Value: value}
 	c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
 }
 
@@ -24,19 +24,36 @@ func (c *ConfigManager) Set(key string, value any) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	lower := strings.ToLower(key)
-	c.mapConfig[lower] = ConfigMap{Key: key, Value: value}
+	c.overrideConfig[lower] = ConfigMap{Key: key, Value: value}
 	c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
 }
 
+// Delete removes a key from all configuration layers (overrides, file,
+// defaults) and rebuilds the combined configuration. Environment variables
+// are not affected since they are loaded from the process environment.
+func (c *ConfigManager) Delete(key string) {
+	c.mutex.Lock()
+	lower := strings.ToLower(key)
+	delete(c.overrideConfig, lower)
+	delete(c.fileConfig, lower)
+	delete(c.defaultConfig, lower)
+	delete(c.combinedConfig, lower)
+	c.mutex.Unlock()
+}
+
 func (c *ConfigManager) SetDefault(key string, value any) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	lower := strings.ToLower(key)
 	c.defaultConfig[lower] = ConfigMap{Key: key, Value: value}
-	if _, ok := c.mapConfig[lower]; !ok {
-		if envVal, ok := c.envConfig[lower]; !ok {
-			c.mapConfig[lower] = envVal
-			c.combinedConfig[lower] = envVal
-		}
+	// Update combinedConfig respecting precedence: override > env > file > default
+	if v, ok := c.overrideConfig[lower]; ok {
+		c.combinedConfig[lower] = v
+	} else if v, ok := c.envConfig[lower]; ok {
+		c.combinedConfig[lower] = ConfigMap{Key: key, Value: v.Value}
+	} else if v, ok := c.fileConfig[lower]; ok {
+		c.combinedConfig[lower] = v
+	} else {
+		c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
 	}
 }