improve manager options workflow

- Break out ManagerOpts type
- Add default configuration values system
- Add WithOpts method
- Rename WithPrefix to WithEnvOverride

config.go

@@ -10,7 +10,29 @@ import (
 	"github.com/spf13/viper"
 )
 
-// Manager is the top-level configuration schema and viper instance.
+// ManagerOpts defines options for the configuration manager.
+type ManagerOpts[T any] struct {
+	// PreLoad is an optional function that is called before loading the
+	// configuration file.
+	PreLoad func(*Manager[T]) error
+
+	// PostLoad is an optional function that is called after loading the
+	// configuration file.
+	PostLoad func(*Manager[T]) error
+
+	// EnvPrefix is an optional environment variable prefix that will be used
+	// to override configuration values from environment variables. If set,
+	// viper will automatically read environment variables with this prefix.
+	EnvPrefix string
+
+	// Defaults is a map of default values for the configuration.
+	Defaults map[string]any
+}
+
+// Manager is the top-level configuration schema and viper instance. Always use
+// the C() method to access the loaded configuration. Always use NewManager to
+// create a new configuration manager. The type parameter T is the configuration
+// schema that will be used to unmarshal the configuration file.
 type Manager[T any] struct {
 	// PreLoad is an optional function that is called before loading the
 	// configuration file.
@@ -49,9 +71,33 @@ func NewManager[T any](configName, configType, configPath string) *Manager[T] {
 	return m
 }
 
-// WithPrefix sets the environment variable prefix for the viper instance. Must
+// WithOpts sets additional options for the Manager.
-// be set in order to use environment variables for configuration.
+func (m *Manager[T]) WithOpts(opts *ManagerOpts[T]) *Manager[T] {
-func (m *Manager[T]) WithPrefix(prefix string) *Manager[T] {
+	if opts == nil {
+		return m
+	}
+
+	if opts.PreLoad != nil {
+		m.PreLoad = opts.PreLoad
+	}
+	if opts.PostLoad != nil {
+		m.PostLoad = opts.PostLoad
+	}
+	if opts.Defaults != nil {
+		for key, value := range opts.Defaults {
+			m.viper.SetDefault(key, value)
+		}
+	}
+	if opts.EnvPrefix != "" {
+		m.WithEnvOverride(opts.EnvPrefix)
+	}
+
+	return m
+}
+
+// WithEnvOverride sets the environment variable prefix for the viper instance
+// and configures viper to automatically read environment variables.
+func (m *Manager[T]) WithEnvOverride(prefix string) *Manager[T] {
 	m.viper.SetEnvPrefix(prefix)
 	m.viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
 	m.viper.AutomaticEnv()

go.mod

@@ -8,20 +8,20 @@ require (
 )
 
 require (
-	github.com/fsnotify/fsnotify v1.8.0 // indirect
+	github.com/fsnotify/fsnotify v1.9.0 // indirect
-	github.com/gabriel-vasile/mimetype v1.4.8 // indirect
+	github.com/gabriel-vasile/mimetype v1.4.9 // indirect
 	github.com/go-playground/locales v0.14.1 // indirect
 	github.com/go-playground/universal-translator v0.18.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
 	github.com/google/go-cmp v0.7.0 // indirect
 	github.com/leodido/go-urn v1.4.0 // indirect
 	github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e // indirect
-	github.com/pelletier/go-toml/v2 v2.2.3 // indirect
+	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
 	github.com/rogpeppe/go-internal v1.14.1 // indirect
-	github.com/sagikazarmark/locafero v0.7.0 // indirect
+	github.com/sagikazarmark/locafero v0.9.0 // indirect
 	github.com/sourcegraph/conc v0.3.0 // indirect
-	github.com/spf13/afero v1.12.0 // indirect
+	github.com/spf13/afero v1.14.0 // indirect
-	github.com/spf13/cast v1.7.1 // indirect
+	github.com/spf13/cast v1.9.2 // indirect
 	github.com/spf13/pflag v1.0.6 // indirect
 	github.com/subosito/gotenv v1.6.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect

go.sum

@@ -2,10 +2,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/frankban/quicktest v1.14.6 h1:7Xjx+VpznH+oBnejlPUj8oUpdxnVs4f8XU8WnHkI4W8=
 github.com/frankban/quicktest v1.14.6/go.mod h1:4ptaffx2x8+WTWXmUCuVU6aPUX1/Mz7zb5vbUoiM6w0=
-github.com/fsnotify/fsnotify v1.8.0 h1:dAwr6QBTBZIkG8roQaJjGof0pp0EeF+tNV7YBP3F/8M=
+github.com/fsnotify/fsnotify v1.9.0 h1:2Ml+OJNzbYCTzsxtv8vKSFD9PbJjmhYF14k/jKC7S9k=
-github.com/fsnotify/fsnotify v1.8.0/go.mod h1:8jBTzvmWwFyi3Pb8djgCCO5IBqzKJ/Jwo8TRcHyHii0=
+github.com/gabriel-vasile/mimetype v1.4.9 h1:5k+WDwEsD9eTLL8Tz3L0VnmVh9QxGjRmjBvAG7U/oYY=
-github.com/gabriel-vasile/mimetype v1.4.8 h1:FfZ3gj38NjllZIeJAmMhr+qKL8Wu+nOoI3GqacKw1NM=
-github.com/gabriel-vasile/mimetype v1.4.8/go.mod h1:ByKUIKGjh1ODkGM1asKUbQZOLGrPjydw3hYPU2YU9t8=
 github.com/go-playground/assert/v2 v2.2.0 h1:JvknZsQTYeFEAhQwI4qEt9cyV5ONwRHC+lYKSsYSR8s=
 github.com/go-playground/assert/v2 v2.2.0/go.mod h1:VDjEfimB/XKnb+ZQfWdccd7VUvScMdVu0Titje2rxJ4=
 github.com/go-playground/locales v0.14.1 h1:EWaQ/wswjilfKLTECiXz7Rh+3BjFhfDFKv/oXslEjJA=
@@ -24,19 +22,15 @@ github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 github.com/leodido/go-urn v1.4.0 h1:WT9HwE9SGECu3lg4d/dIA+jxlljEa1/ffXKmRjqdmIQ=
 github.com/leodido/go-urn v1.4.0/go.mod h1:bvxc+MVxLKB4z00jd1z+Dvzr47oO32F/QSNjSBOlFxI=
 github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e h1:fD57ERR4JtEqsWbfPhv4DMiApHyliiK5xCTNVSPiaAs=
-github.com/pelletier/go-toml/v2 v2.2.3 h1:YmeHyLY8mFWbdkNWwpr+qIL2bEqT0o95WSdkNHvL12M=
+github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0t5Ec4=
-github.com/pelletier/go-toml/v2 v2.2.3/go.mod h1:MfCQTFTvCcUyyvvwm1+G6H/jORL20Xlb6rzQu9GuUkc=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/rogpeppe/go-internal v1.14.1 h1:UQB4HGPB6osV0SQTLymcB4TgvyWu6ZyliaW0tI/otEQ=
-github.com/sagikazarmark/locafero v0.7.0 h1:5MqpDsTGNDhY8sGp0Aowyf0qKsPrhewaLSsFaodPcyo=
+github.com/sagikazarmark/locafero v0.9.0 h1:GbgQGNtTrEmddYDSAH9QLRyfAHY12md+8YFTqyMTC9k=
-github.com/sagikazarmark/locafero v0.7.0/go.mod h1:2za3Cg5rMaTMoG/2Ulr9AwtFaIppKXTRYnozin4aB5k=
 github.com/sourcegraph/conc v0.3.0 h1:OQTbbt6P72L20UqAkXXuLOj79LfEanQ+YQFNpLA9ySo=
 github.com/sourcegraph/conc v0.3.0/go.mod h1:Sdozi7LEKbFPqYX2/J+iBAM6HpqSLTASQIKqDmF7Mt0=
-github.com/spf13/afero v1.12.0 h1:UcOPyRBYczmFn6yvphxkn9ZEOY65cpwGKb5mL36mrqs=
+github.com/spf13/afero v1.14.0 h1:9tH6MapGnn/j0eb0yIXiLjERO8RB6xIVZRDCX7PtqWA=
-github.com/spf13/afero v1.12.0/go.mod h1:ZTlWwG4/ahT8W7T0WQ5uYmjI9duaLQGy3Q2OAl4sk/4=
+github.com/spf13/cast v1.9.2 h1:SsGfm7M8QOFtEzumm7UZrZdLLquNdzFYfIbEXntcFbE=
-github.com/spf13/cast v1.7.1 h1:cuNEagBQEHWN1FnbGEjCXL2szYEXqfJPbP2HNUaca9Y=
-github.com/spf13/cast v1.7.1/go.mod h1:ancEpBxwJDODSW/UG4rDrAqiKolqNNh2DX3mk86cAdo=
 github.com/spf13/pflag v1.0.6 h1:jFzHGLGAlb3ruxLB8MhbI6A8+AQX/2eW4qeyNZXNp2o=
 github.com/spf13/pflag v1.0.6/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/spf13/viper v1.20.1 h1:ZMi+z/lvLyPSCoNtFCpqjy0S4kPbirhpTMwl8BkW9X4=