MM-28859 Add feature flag managment system using split.io and remove viper. (#15954)

* Add feature flag managment system using split.io and remove viper.

* Fixing tests.

* Attempt to fix postgres tests.

* Fix watch filepath for advanced logging.

* Review fixes.

* Some error wrapping.

* Remove unessisary store interface.

* Desanitize SplitKey

* Simplify.

* Review feedback.

* Rename split mlog adatper to split logger.

* fsInner

* Style.

* Restore oldcfg test.

* Downgrading non-actionable feature flag errors to warnings.

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

config/environment.go

@@ -4,11 +4,122 @@
 package config
 
 import (
+	"os"
 	"reflect"
+	"strconv"
+	"strings"
 
 	"github.com/mattermost/mattermost-server/v5/model"
 )
 
+func GetEnvironment() map[string]string {
+	mmenv := make(map[string]string)
+	for _, env := range os.Environ() {
+		kv := strings.SplitN(env, "=", 2)
+		key := strings.ToUpper(kv[0])
+		if strings.HasPrefix(key, "MM") {
+			mmenv[key] = kv[1]
+		}
+	}
+
+	return mmenv
+}
+
+func applyEnvKey(key, value string, rValueSubject reflect.Value) {
+	keyParts := strings.SplitN(key, "_", 2)
+	if len(keyParts) < 1 {
+		return
+	}
+	rFieldValue := rValueSubject.FieldByNameFunc(func(candidate string) bool {
+		candidateUpper := strings.ToUpper(candidate)
+		return candidateUpper == keyParts[0]
+	})
+
+	if !rFieldValue.IsValid() {
+		return
+	}
+
+	if rFieldValue.Kind() == reflect.Ptr {
+		rFieldValue = rFieldValue.Elem()
+		if !rFieldValue.IsValid() {
+			return
+		}
+	}
+
+	switch rFieldValue.Kind() {
+	case reflect.Struct:
+		// If we have only one part left, we can't deal with a struct
+		// the env var is incomplete so give up.
+		if len(keyParts) < 2 {
+			return
+		}
+		applyEnvKey(keyParts[1], value, rFieldValue)
+	case reflect.String:
+		rFieldValue.Set(reflect.ValueOf(value))
+	case reflect.Bool:
+		boolVal, err := strconv.ParseBool(value)
+		if err == nil {
+			rFieldValue.Set(reflect.ValueOf(boolVal))
+		}
+	case reflect.Int:
+		intVal, err := strconv.ParseInt(value, 10, 0)
+		if err == nil {
+			rFieldValue.Set(reflect.ValueOf(int(intVal)))
+		}
+	case reflect.Int64:
+		intVal, err := strconv.ParseInt(value, 10, 0)
+		if err == nil {
+			rFieldValue.Set(reflect.ValueOf(intVal))
+		}
+	case reflect.SliceOf(reflect.TypeOf("")).Kind():
+		rFieldValue.Set(reflect.ValueOf(strings.Split(value, " ")))
+	}
+}
+
+func applyEnvironmentMap(inputConfig *model.Config, env map[string]string) *model.Config {
+	appliedConfig := inputConfig.Clone()
+
+	rvalConfig := reflect.ValueOf(appliedConfig).Elem()
+	for envKey, envValue := range env {
+		applyEnvKey(strings.TrimPrefix(envKey, "MM_"), envValue, rvalConfig)
+	}
+
+	return appliedConfig
+}
+
+// generateEnvironmentMap creates a map[string]interface{} containing true at the leaves mirroring the
+// configuration structure so the client can know which env variables are overridden
+func generateEnvironmentMap(env map[string]string) map[string]interface{} {
+	rType := reflect.TypeOf(model.Config{})
+	return generateEnvironmentMapWithBaseKey(env, rType, "MM")
+}
+
+func generateEnvironmentMapWithBaseKey(env map[string]string, rType reflect.Type, base string) map[string]interface{} {
+	if rType.Kind() != reflect.Struct {
+		return nil
+	}
+
+	mapRepresentation := make(map[string]interface{})
+	for i := 0; i < rType.NumField(); i++ {
+		rField := rType.Field(i)
+		if rField.Type.Kind() == reflect.Struct {
+			if val := generateEnvironmentMapWithBaseKey(env, rField.Type, base+"_"+rField.Name); val != nil {
+				mapRepresentation[rField.Name] = val
+			}
+		} else {
+			if _, ok := env[strings.ToUpper(base+"_"+rField.Name)]; ok {
+				mapRepresentation[rField.Name] = true
+			}
+		}
+	}
+
+	if len(mapRepresentation) == 0 {
+		return nil
+	}
+
+	return mapRepresentation
+}
+
 // removeEnvOverrides returns a new config without the given environment overrides.
 // If a config variable has an environment override, that variable is set to the value that was
 // read from the store.