feat: Support multiple configuration files (#396)

* Revert "Revert "feat: Support multiple configuration files" (#395)"

This reverts commit 87740e74a6.

* feat: Properly implement support for config directory

vendor/github.com/TwiN/deepmerge/yaml.go

@@ -0,0 +1,83 @@
+package deepmerge
+
+import (
+	"errors"
+
+	"gopkg.in/yaml.v3"
+)
+
+var (
+	ErrDeepMergeDuplicatePrimitiveKey = errors.New("error deep merging YAML files due to duplicate primitive key: only maps and slices/arrays can be merged, which means you cannot have define the same key twice for parameters that are not maps or slices/arrays")
+)
+
+type Config struct {
+	// PreventDuplicateKeysWithPrimitiveValue causes YAML to return an error if dst and src define the same key if
+	// said key has a value with a primitive type
+	// This does not apply to slices or maps. Defaults to true
+	PreventDuplicateKeysWithPrimitiveValue bool
+}
+
+// YAML merges the contents of src into dst
+func YAML(dst, src []byte, optionalConfig ...Config) ([]byte, error) {
+	var cfg Config
+	if len(optionalConfig) > 0 {
+		cfg = optionalConfig[0]
+	} else {
+		cfg = Config{PreventDuplicateKeysWithPrimitiveValue: true}
+	}
+	var dstMap, srcMap map[string]interface{}
+	err := yaml.Unmarshal(dst, &dstMap)
+	if err != nil {
+		return nil, err
+	}
+	err = yaml.Unmarshal(src, &srcMap)
+	if err != nil {
+		return nil, err
+	}
+	if dstMap == nil {
+		dstMap = make(map[string]interface{})
+	}
+	if err = deepMerge(dstMap, srcMap, cfg); err != nil {
+		return nil, err
+	}
+	return yaml.Marshal(dstMap)
+}
+
+func deepMerge(dst, src map[string]interface{}, config Config) error {
+	for srcKey, srcValue := range src {
+		if srcValueAsMap, ok := srcValue.(map[string]interface{}); ok { // handle maps
+			if dstValue, ok := dst[srcKey]; ok {
+				if dstValueAsMap, ok := dstValue.(map[string]interface{}); ok {
+					err := deepMerge(dstValueAsMap, srcValueAsMap, config)
+					if err != nil {
+						return err
+					}
+					continue
+				}
+			} else {
+				dst[srcKey] = make(map[string]interface{})
+			}
+			err := deepMerge(dst[srcKey].(map[string]interface{}), srcValueAsMap, config)
+			if err != nil {
+				return err
+			}
+		} else if srcValueAsSlice, ok := srcValue.([]interface{}); ok { // handle slices
+			if dstValue, ok := dst[srcKey]; ok {
+				if dstValueAsSlice, ok := dstValue.([]interface{}); ok {
+					// If both src and dst are slices, we'll copy the elements from that src slice over to the dst slice
+					dst[srcKey] = append(dstValueAsSlice, srcValueAsSlice...)
+					continue
+				}
+			}
+			dst[srcKey] = srcValueAsSlice
+		} else { // handle primitives
+			if config.PreventDuplicateKeysWithPrimitiveValue {
+				if _, ok := dst[srcKey]; ok {
+					return ErrDeepMergeDuplicatePrimitiveKey
+				}
+			}
+			dst[srcKey] = srcValue
+		}
+	}
+	return nil
+}