From f9fc3be7168c545a097771a0cd3601ee32dcb239 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=B8ren=20Rasmussen?= <sr@joco.dk>
Date: Thu, 29 Aug 2024 12:36:48 +0200
Subject: [PATCH] add viperconfig

---
 viperconfig/configuration_manager.go | 108 +++++++++++++++++++++++++++
 viperconfig/context.go               |  26 +++++++
 2 files changed, 134 insertions(+)
 create mode 100644 viperconfig/configuration_manager.go
 create mode 100644 viperconfig/context.go

diff --git a/viperconfig/configuration_manager.go b/viperconfig/configuration_manager.go
new file mode 100644
index 0000000..4603b50
--- /dev/null
+++ b/viperconfig/configuration_manager.go
@@ -0,0 +1,108 @@
+package configuration_manager
+
+import (
+	"bytes"
+	"log/slog"
+	"os"
+	"strings"
+	"sync"
+
+	"github.com/fsnotify/fsnotify"
+	"github.com/spf13/pflag"
+	"github.com/spf13/viper"
+)
+
+// ConfigurationManager[T any] manages Viper for the specified configuration struct
+type ConfigurationManager[T any] struct {
+	name     string
+	config   T
+	defaults []byte
+	lock     *sync.RWMutex
+	vc       *viper.Viper
+}
+
+// New[T any] creates a new configuration manager for the specified configuration struct
+func New[T any](name string, defaults []byte) *ConfigurationManager[T] {
+	// Initialize
+	p := &ConfigurationManager[T]{
+		name:     name,
+		defaults: defaults,
+		lock:     &sync.RWMutex{},
+		vc:       viper.New(),
+	}
+
+	// Load defaults
+	vd := viper.New()
+	buf := bytes.NewBuffer(p.defaults)
+	if err := vd.ReadConfig(buf); err != nil {
+		slog.Error("Error loading default configuration", "error", err)
+		os.Exit(1)
+	}
+
+	// Create Viper instance
+	p.vc = viper.New()
+	p.vc.AddConfigPath("/secrets")
+	p.vc.AddConfigPath("/etc/joco")
+	p.vc.AddConfigPath("/etc")
+	p.vc.AddConfigPath(".")
+	p.vc.SetConfigName(p.name)
+	p.vc.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
+	p.vc.SetEnvPrefix(p.name)
+	p.vc.AutomaticEnv()
+	p.vc.OnConfigChange(p.onConfigChange)
+
+	// Set defaults from embedded configuration file
+	for k, v := range vd.AllSettings() {
+		p.vc.SetDefault(k, v)
+	}
+
+	// Load the configuration (ignore file not found)
+	if err := p.load(); err != nil {
+		slog.Error("Error loading configuration", "error", err)
+		os.Exit(1)
+	}
+
+	p.vc.BindPFlags(pflag.CommandLine)
+
+	// Monitor changes to the configuration
+	p.vc.WatchConfig()
+
+	return p
+}
+
+func (p *ConfigurationManager[T]) Get() T {
+	p.lock.RLock()
+	defer p.lock.RUnlock()
+
+	return p.config
+}
+
+func (p *ConfigurationManager[T]) load() error {
+	if err := p.vc.ReadInConfig(); err != nil {
+		if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
+			return err
+		}
+	}
+
+	var cfg T
+	if err := viper.Unmarshal(&cfg); err != nil {
+		return err
+	}
+
+	p.lock.Lock()
+	p.config = cfg
+	p.lock.Unlock()
+
+	return nil
+}
+
+func (p *ConfigurationManager[T]) onConfigChange(in fsnotify.Event) {
+	if err := p.load(); err != nil {
+		slog.Error("Error re-loading configuration", "error", err)
+	}
+}
+
+// SaveToFile saves the embedded default configuration to the specified file
+func (p *ConfigurationManager[T]) SaveToFile(path string) error {
+	return os.WriteFile(path, p.defaults, os.ModeExclusive)
+}
diff --git a/viperconfig/context.go b/viperconfig/context.go
new file mode 100644
index 0000000..9908196
--- /dev/null
+++ b/viperconfig/context.go
@@ -0,0 +1,26 @@
+package configuration_manager
+
+import "context"
+
+type contextKey struct{}
+
+var (
+	ConfigurationKey = contextKey{}
+)
+
+// GetConfigFromContext[T any] returns the current configuration extracted from the passed context
+func GetConfigFromContext[T any](ctx context.Context) T {
+	cm := GetConfigMgrFromContext[T](ctx)
+
+	return cm.Get()
+}
+
+// GetConfigMgrFromContext[T any] returns the configuration manager stored in the passed context
+func GetConfigMgrFromContext[T any](ctx context.Context) ConfigurationManager[T] {
+	return ctx.Value(ConfigurationKey).(ConfigurationManager[T])
+}
+
+// SetConfigMgrOnContext[T any] stores the passed configuration manager on the passed context
+func SetConfigMgrOnContext[T any](ctx context.Context, value T) context.Context {
+	return context.WithValue(ctx, ConfigurationKey, value)
+}