package config

import (
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"strings"

	"github.com/spf13/viper"
)

// DefaultJWTSecret is a development-only placeholder. Load replaces it with
// an ephemeral secret before returning a usable Config.
const DefaultJWTSecret = "dev-secret-do-not-use-in-production"

// LoadInfo describes runtime decisions made while loading configuration.
type LoadInfo struct {
	// EphemeralJWTSecret is true when a placeholder jwt.secret was replaced
	// with a random in-memory value for the current process.
	EphemeralJWTSecret bool
}

func defaults(v *viper.Viper) {
	v.SetDefault("server.host", "0.0.0.0")
	v.SetDefault("server.port", 10086)

	v.SetDefault("database.driver", "sqlite3")
	v.SetDefault("database.sqlite.path", "data/mygo.db")
	v.SetDefault("database.postgres.host", "localhost")
	v.SetDefault("database.postgres.port", 5432)
	v.SetDefault("database.postgres.user", "mygo")
	v.SetDefault("database.postgres.password", "")
	v.SetDefault("database.postgres.dbname", "mygo")
	v.SetDefault("database.postgres.sslmode", "disable")

	v.SetDefault("storage.driver", "local")
	v.SetDefault("storage.local.path", "data/files")

	v.SetDefault("jwt.secret", DefaultJWTSecret)
	v.SetDefault("jwt.access_ttl", "15m")
	v.SetDefault("jwt.refresh_ttl", "168h")

	v.SetDefault("log.level", "info")
	v.SetDefault("log.file_path", "")
	v.SetDefault("log.file_level", "debug")
}

func New() *viper.Viper {
	v := viper.New()
	v.SetEnvPrefix("MYGO")
	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
	v.AutomaticEnv()
	defaults(v)
	return v
}

func Load(v *viper.Viper, cfgFile string) (*Config, LoadInfo, error) {
	if cfgFile != "" {
		v.SetConfigFile(cfgFile)
	} else {
		v.SetConfigName("config")
		v.SetConfigType("yaml")
		v.AddConfigPath(".")
	}

	if err := v.ReadInConfig(); err != nil {
		var notFound viper.ConfigFileNotFoundError
		if !errors.As(err, &notFound) {
			return nil, LoadInfo{}, fmt.Errorf("read config: %w", err)
		}
	}

	var cfg Config
	if err := v.Unmarshal(&cfg); err != nil {
		return nil, LoadInfo{}, fmt.Errorf("unmarshal config: %w", err)
	}

	info, err := hardenRuntimeSecrets(&cfg)
	if err != nil {
		return nil, LoadInfo{}, err
	}

	if err := cfg.Validate(); err != nil {
		return nil, LoadInfo{}, fmt.Errorf("validate config: %w", err)
	}

	return &cfg, info, nil
}

func hardenRuntimeSecrets(cfg *Config) (LoadInfo, error) {
	if !isWeakJWTSecret(cfg.JWT.Secret) {
		return LoadInfo{}, nil
	}

	secret, err := generateEphemeralJWTSecret()
	if err != nil {
		return LoadInfo{}, fmt.Errorf("generate ephemeral jwt secret: %w", err)
	}

	cfg.JWT.Secret = secret
	return LoadInfo{EphemeralJWTSecret: true}, nil
}

func isWeakJWTSecret(secret string) bool {
	switch secret {
	case DefaultJWTSecret, "change-me-in-production", "changeme-in-production":
		return true
	default:
		return false
	}
}

func generateEphemeralJWTSecret() (string, error) {
	var secret [32]byte
	if _, err := rand.Read(secret[:]); err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(secret[:]), nil
}