Add core modules (SSH args parser, cache, resolver, NetBox client) with tests

internal/config/config.go

@@ -0,0 +1,76 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/spf13/viper"
+)
+
+type Config struct {
+	NetBox   NetBoxConfig   `mapstructure:"netbox"`
+	Resolver ResolverConfig `mapstructure:"resolver"`
+	Cache    CacheConfig    `mapstructure:"cache"`
+	SSH      SSHConfig      `mapstructure:"ssh"`
+}
+
+type NetBoxConfig struct {
+	URL   string `mapstructure:"url"`
+	Token string `mapstructure:"token"`
+}
+
+type ResolverConfig struct {
+	Strategies        []string `mapstructure:"strategies"`
+	ManagementSubnets []string `mapstructure:"management_subnets"`
+	InterfaceName     string   `mapstructure:"interface_name"`
+}
+
+type CacheConfig struct {
+	TTL  int    `mapstructure:"ttl"`
+	Path string `mapstructure:"path"`
+}
+
+type SSHConfig struct {
+	DefaultUser string `mapstructure:"default_user"`
+}
+
+func Load() (*Config, error) {
+	v := viper.New()
+
+	v.SetDefault("resolver.strategies", []string{"management_subnet", "primary_ip"})
+	v.SetDefault("resolver.management_subnets", []string{})
+	v.SetDefault("cache.ttl", 3600)
+
+	configDir, err := os.UserConfigDir()
+	if err == nil {
+		v.SetConfigName("netssh")
+		v.SetConfigType("yaml")
+		v.AddConfigPath(filepath.Join(configDir))
+		v.AddConfigPath(".")
+	}
+
+	v.SetEnvPrefix("NETSSH")
+	v.AutomaticEnv()
+
+	if err := v.ReadInConfig(); err != nil {
+		if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
+			return nil, fmt.Errorf("reading config: %w", err)
+		}
+	}
+
+	var cfg Config
+	if err := v.Unmarshal(&cfg); err != nil {
+		return nil, fmt.Errorf("parsing config: %w", err)
+	}
+
+	if cfg.Cache.Path == "" {
+		cacheDir, err := os.UserCacheDir()
+		if err != nil {
+			cacheDir = filepath.Join(os.Getenv("HOME"), ".cache")
+		}
+		cfg.Cache.Path = filepath.Join(cacheDir, "netssh", "hosts.json")
+	}
+
+	return &cfg, nil
+}