package config

import (
	"crypto/sha256"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"runtime"

	"gopkg.in/yaml.v3"
)

// Config holds all application configuration.
type Config struct {
	Database DatabaseConfig `yaml:"database"`
	Port     string         `yaml:"port"`
	Path     string         `yaml:"path"`
	Secret   string         `yaml:"secret"`
}

// DatabaseConfig holds database-specific configuration.
type DatabaseConfig struct {
	Type string `yaml:"type"` // "sqlite" (default) or "mysql"
	DSN  string `yaml:"dsn"`  // MySQL connection string (required when type is "mysql")
}

const defaultPort = "8080"

// mysqlExampleDSN is written into new config files as a reference.
const mysqlExampleDSN = "user:password@tcp(127.0.0.1:3306)/blog_go?charset=utf8mb4&parseTime=True&loc=Local"

// getConfigPath returns the OS-aware config directory and config file path.
func getConfigPath() (dir, file string) {
	switch runtime.GOOS {
	case "windows":
		dir = filepath.Join(".", "win", "etc", "blog_go")
	case "darwin":
		dir = filepath.Join(".", "mac", "etc", "blog_go")
	default:
		dir = filepath.Join("/", "etc", "blog_go")
	}
	file = filepath.Join(dir, "config.yaml")
	return
}

// getDefaultStoragePath returns the OS-aware default storage path.
func getDefaultStoragePath() string {
	switch runtime.GOOS {
	case "windows":
		return filepath.Join(".", "win", "srv", "blog_go")
	case "darwin":
		return filepath.Join(".", "mac", "srv", "blog_go")
	default:
		return filepath.Join("/", "srv", "blog_go")
	}
}

// generateSecret returns a random-ish hex string for the session secret.
func generateSecret() string {
	hostname, _ := os.Hostname()
	input := fmt.Sprintf("%s-%d", hostname, os.Getpid())
	hash := sha256.Sum256([]byte(input))
	return fmt.Sprintf("%x", hash)
}

// LoadConfig reads the config file or creates one with defaults.
func LoadConfig() *Config {
	configDir, configFile := getConfigPath()
	defaultPath := getDefaultStoragePath()

	// Check if config file exists; create with defaults if not.
	if _, err := os.Stat(configFile); os.IsNotExist(err) {
		log.Printf("Config file not found at %s, creating with defaults...", configFile)
		if err := os.MkdirAll(configDir, 0755); err != nil {
			log.Fatalf("Failed to create config directory %s: %v", configDir, err)
		}

		cfg := &Config{
			Database: DatabaseConfig{
				Type: "sqlite",
				DSN:  mysqlExampleDSN,
			},
			Port:   defaultPort,
			Path:   defaultPath,
			Secret: generateSecret(),
		}

		data, err := yaml.Marshal(cfg)
		if err != nil {
			log.Fatalf("Failed to marshal default config: %v", err)
		}

		if err := os.WriteFile(configFile, data, 0644); err != nil {
			log.Fatalf("Failed to write config file %s: %v", configFile, err)
		}
		log.Printf("Default config created at %s", configFile)
		return cfg
	}

	// Read existing config file.
	data, err := os.ReadFile(configFile)
	if err != nil {
		log.Printf("Warning: could not read config file %s: %v, using defaults", configFile, err)
		cfg := &Config{}
		return applyDefaults(cfg, defaultPath)
	}

	cfg := &Config{}
	if err := yaml.Unmarshal(data, cfg); err != nil {
		log.Printf("Warning: malformed config file %s: %v, using defaults", configFile, err)
	}

	return applyDefaults(cfg, defaultPath)
}

// applyDefaults fills zero-value fields with sensible defaults.
func applyDefaults(cfg *Config, defaultPath string) *Config {
	if cfg.Port == "" {
		cfg.Port = defaultPort
	}
	if cfg.Database.Type == "" {
		cfg.Database.Type = "sqlite"
	}
	if cfg.Path == "" {
		cfg.Path = defaultPath
	}
	if cfg.Secret == "" {
		cfg.Secret = generateSecret()
	}
	return cfg
}