feat(refactor): moving configuration and api to proper packages

internal/config/config.go

@@ -0,0 +1,67 @@
+package config
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/spf13/viper"
+)
+
+// Config holds all configuration for the application.
+type Config struct {
+	Database DatabaseConfig `mapstructure:"database"`
+	Server   ServerConfig   `mapstructure:"server"`
+}
+
+// DatabaseConfig holds database connection configuration.
+type DatabaseConfig struct {
+	User     string `mapstructure:"user"`
+	Password string `mapstructure:"password"`
+	Dbname   string `mapstructure:"dbname"`
+	Host     string `mapstructure:"host"`
+	Port     int    `mapstructure:"port"`
+	Sslmode  string `mapstructure:"sslmode"`
+}
+
+// ServerConfig holds server-specific configuration.
+type ServerConfig struct {
+	Address string `mapstructure:"address"`
+}
+
+// Load reads configuration from file and environment variables.
+func Load() (*Config, error) {
+	// 0. Configuration for environment variables
+	viper.SetEnvPrefix("APP") // Variables must start with "APP_" (e.g., APP_SERVER_ADDRESS)
+
+	// 1. Base configuration file
+	viper.SetConfigName("config") // config.yaml
+	viper.SetConfigType("yaml")
+	viper.AddConfigPath(".")
+
+	// Read the base file. Don't stop if it's not found.
+	if err := viper.ReadInConfig(); err != nil {
+		if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
+			return nil, fmt.Errorf("error reading base config file config.yaml: %w", err)
+		}
+	}
+
+	// 2. Override with environment-specific file (via APP_ENV)
+	if env := os.Getenv("APP_ENV"); env != "" {
+		viper.SetConfigName("config." + env) // e.g., config.prod.yaml
+		if err := viper.MergeInConfig(); err != nil {
+			log.Printf("Warning: could not load config file for environment '%s': %v", env, err)
+		}
+	}
+
+	viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
+	viper.AutomaticEnv()
+
+	var cfg Config
+	if err := viper.Unmarshal(&cfg); err != nil {
+		return nil, fmt.Errorf("unable to decode config into struct: %w", err)
+	}
+
+	return &cfg, nil
+}