Refactor system setting (#27000)

This PR reduces the complexity of the system setting system.

It only needs one line to introduce a new option, and the option can be
used anywhere out-of-box.

It is still high-performant (and more performant) because the config
values are cached in the config system.

3 files changed, 185 insertions, 0 deletions

diff --git a/modules/setting/config.go b/modules/setting/config.go
new file mode 100644
index 0000000000..db189f44ac
--- /dev/null
+++ b/modules/setting/config.go
@@ -0,0 +1,55 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package setting
+
+import (
+	"sync"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting/config"
+)
+
+type PictureStruct struct {
+	DisableGravatar       *config.Value[bool]
+	EnableFederatedAvatar *config.Value[bool]
+}
+
+type ConfigStruct struct {
+	Picture *PictureStruct
+}
+
+var (
+	defaultConfig     *ConfigStruct
+	defaultConfigOnce sync.Once
+)
+
+func initDefaultConfig() {
+	config.SetCfgSecKeyGetter(&cfgSecKeyGetter{})
+	defaultConfig = &ConfigStruct{
+		Picture: &PictureStruct{
+			DisableGravatar:       config.Bool(false, config.CfgSecKey{Sec: "picture", Key: "DISABLE_GRAVATAR"}, "picture.disable_gravatar"),
+			EnableFederatedAvatar: config.Bool(false, config.CfgSecKey{Sec: "picture", Key: "ENABLE_FEDERATED_AVATAR"}, "picture.enable_federated_avatar"),
+		},
+	}
+}
+
+func Config() *ConfigStruct {
+	defaultConfigOnce.Do(initDefaultConfig)
+	return defaultConfig
+}
+
+type cfgSecKeyGetter struct{}
+
+func (c cfgSecKeyGetter) GetValue(sec, key string) (v string, has bool) {
+	cfgSec, err := CfgProvider.GetSection(sec)
+	if err != nil {
+		log.Error("Unable to get config section: %q", sec)
+		return "", false
+	}
+	cfgKey := ConfigSectionKey(cfgSec, key)
+	if cfgKey == nil {
+		return "", false
+	}
+	return cfgKey.Value(), true
+}
diff --git a/modules/setting/config/getter.go b/modules/setting/config/getter.go
new file mode 100644
index 0000000000..99f9a4775a
--- /dev/null
+++ b/modules/setting/config/getter.go
@@ -0,0 +1,49 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package config
+
+import (
+	"context"
+	"sync"
+)
+
+var getterMu sync.RWMutex
+
+type CfgSecKeyGetter interface {
+	GetValue(sec, key string) (v string, has bool)
+}
+
+var cfgSecKeyGetterInternal CfgSecKeyGetter
+
+func SetCfgSecKeyGetter(p CfgSecKeyGetter) {
+	getterMu.Lock()
+	cfgSecKeyGetterInternal = p
+	getterMu.Unlock()
+}
+
+func GetCfgSecKeyGetter() CfgSecKeyGetter {
+	getterMu.RLock()
+	defer getterMu.RUnlock()
+	return cfgSecKeyGetterInternal
+}
+
+type DynKeyGetter interface {
+	GetValue(ctx context.Context, key string) (v string, has bool)
+	GetRevision(ctx context.Context) int
+	InvalidateCache()
+}
+
+var dynKeyGetterInternal DynKeyGetter
+
+func SetDynGetter(p DynKeyGetter) {
+	getterMu.Lock()
+	dynKeyGetterInternal = p
+	getterMu.Unlock()
+}
+
+func GetDynGetter() DynKeyGetter {
+	getterMu.RLock()
+	defer getterMu.RUnlock()
+	return dynKeyGetterInternal
+}
diff --git a/modules/setting/config/value.go b/modules/setting/config/value.go
new file mode 100644
index 0000000000..817fcdb786
--- /dev/null
+++ b/modules/setting/config/value.go
@@ -0,0 +1,81 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package config
+
+import (
+	"context"
+	"strconv"
+	"sync"
+)
+
+type CfgSecKey struct {
+	Sec, Key string
+}
+
+type Value[T any] struct {
+	mu sync.RWMutex
+
+	cfgSecKey CfgSecKey
+	dynKey    string
+
+	def, value T
+	revision   int
+}
+
+func (value *Value[T]) parse(s string) (v T) {
+	switch any(v).(type) {
+	case bool:
+		b, _ := strconv.ParseBool(s)
+		return any(b).(T)
+	default:
+		panic("unsupported config type, please complete the code")
+	}
+}
+
+func (value *Value[T]) Value(ctx context.Context) (v T) {
+	dg := GetDynGetter()
+	if dg == nil {
+		// this is an edge case: the database is not initialized but the system setting is going to be used
+		// it should panic to avoid inconsistent config values (from config / system setting) and fix the code
+		panic("no config dyn value getter")
+	}
+
+	rev := dg.GetRevision(ctx)
+
+	// if the revision in database doesn't change, use the last value
+	value.mu.RLock()
+	if rev == value.revision {
+		v = value.value
+		value.mu.RUnlock()
+		return v
+	}
+	value.mu.RUnlock()
+
+	// try to parse the config and cache it
+	var valStr *string
+	if dynVal, has := dg.GetValue(ctx, value.dynKey); has {
+		valStr = &dynVal
+	} else if cfgVal, has := GetCfgSecKeyGetter().GetValue(value.cfgSecKey.Sec, value.cfgSecKey.Key); has {
+		valStr = &cfgVal
+	}
+	if valStr == nil {
+		v = value.def
+	} else {
+		v = value.parse(*valStr)
+	}
+
+	value.mu.Lock()
+	value.value = v
+	value.revision = rev
+	value.mu.Unlock()
+	return v
+}
+
+func (value *Value[T]) DynKey() string {
+	return value.dynKey
+}
+
+func Bool(def bool, cfgSecKey CfgSecKey, dynKey string) *Value[bool] {
+	return &Value[bool]{def: def, cfgSecKey: cfgSecKey, dynKey: dynKey}
+}