Move to yaml-based configuration

This commit updates the configuration to be yaml-based and updates the
configuration to read in a yaml file.

internal/config/read.go

@@ -2,60 +2,31 @@ package config
 
 import (
 	"io"
-	"reflect"
 
+	"github.com/FAU-CDI/wisski-distillery/internal/config/validators"
 	"github.com/FAU-CDI/wisski-distillery/pkg/environment"
-	"github.com/FAU-CDI/wisski-distillery/pkg/envreader"
-	"github.com/FAU-CDI/wisski-distillery/pkg/stringparser"
-	"github.com/pkg/errors"
+	"github.com/FAU-CDI/wisski-distillery/pkg/validator"
+	"gopkg.in/yaml.v3"
 )
 
-// Unmarshal updates this configuration from the provided [io.Reader].
-//
-// Data is read using the [envreader.ReadAll] method, see the appropriate documentation for the file format.
-//
-// The `env` and `parser` reflect tags of the [Config] struct determine the keys to read from, and the types to expect.
-// When a key is missing, it is set to the default value.
-//
-// See also [stringparser.Parse].
+// Unmarshal reads configuration from the provided io.Reader, and then validates it.
+// Configuration is read in yaml format.
 func (config *Config) Unmarshal(env environment.Environment, src io.Reader) error {
-	// read all the values!
-	values, err := envreader.ReadAll(src)
-	if err != nil {
-		return err
-	}
-
-	vConfig := reflect.ValueOf(config).Elem()
-	tConfig := vConfig.Type()
-
-	// iterate over the types
-	numValues := tConfig.NumField()
-	for i := 0; i < numValues; i++ {
-		tField := tConfig.Field(i)
-		vField := vConfig.FieldByName(tField.Name)
-
-		tEnv := tField.Tag.Get("env")
-		tDefault := tField.Tag.Get("default")
-		tParser := tField.Tag.Get("parser")
-
-		// skip it if it isn't loaded!
-		if tEnv == "" {
-			continue
-		}
-
-		// read the value with a default
-		value, ok := values[tEnv]
-		if !ok || value == "" {
-			if tDefault != "" {
-				value = tDefault
-			}
-		}
-
-		// parse the value!
-		if err := stringparser.Parse(env, tParser, value, vField); err != nil {
-			return errors.Errorf("Config.Unmarshal: Setting %q, Parser %q: %s", tEnv, tParser, err)
+	// read yaml!
+	{
+		decoder := yaml.NewDecoder(src)
+		decoder.KnownFields(true)
+		if err := decoder.Decode(config); err != nil {
+			return err
 		}
 	}
 
-	return nil
+	// do the validator
+	return validator.Validate(config, validators.New(env))
+}
+
+func (config *Config) Marshal(dest io.Writer) error {
+	encoder := yaml.NewEncoder(dest)
+	encoder.SetIndent(4)
+	return encoder.Encode(config)
 }