package config

import (
	"fmt"
	"os"
	"strings"
)

// Config holds application configuration
type Config struct {
	ServerDomain string `mapstructure:"SERVER_DOMAIN"`
	WGPort       int    `mapstructure:"WG_PORT"`
	VPNIPv4Range string `mapstructure:"VPN_IPV4_RANGE"`
	VPNIPv6Range string `mapstructure:"VPN_IPV6_RANGE"`
	WGInterface  string `mapstructure:"WG_INTERFACE"`
	DNSServers   string `mapstructure:"DNS_SERVERS"`
	LogFile      string `mapstructure:"LOG_FILE"`
	Theme        string `mapstructure:"THEME"`
}

// Default values
const (
	DefaultWGPort       = 51820
	DefaultVPNIPv4Range = "10.10.69.0/24"
	DefaultVPNIPv6Range = "fd69:dead:beef:69::/64"
	DefaultWGInterface  = "wg0"
	DefaultDNSServers   = "8.8.8.8, 8.8.4.4"
	DefaultLogFile      = "/var/log/wireguard-admin.log"
	DefaultTheme        = "default"
)

// LoadConfig loads configuration from file and environment variables
func LoadConfig() (*Config, error) {
	cfg := &Config{}

	// Load from config file if it exists
	if err := loadFromFile(cfg); err != nil {
		return nil, fmt.Errorf("failed to load config file: %w", err)
	}

	// Override with environment variables
	if err := loadFromEnv(cfg); err != nil {
		return nil, fmt.Errorf("failed to load config from environment: %w", err)
	}

	// Apply defaults for empty values
	applyDefaults(cfg)

	// Validate required configuration
	if err := validateConfig(cfg); err != nil {
		return nil, err
	}

	return cfg, nil
}

// loadFromFile reads configuration from /etc/wg-admin/config.conf
func loadFromFile(cfg *Config) error {
	configPath := "/etc/wg-admin/config.conf"

	// Check if config file exists
	if _, err := os.Stat(configPath); os.IsNotExist(err) {
		// Config file is optional, skip if not exists
		return nil
	}

	// Read config file
	content, err := os.ReadFile(configPath)
	if err != nil {
		return err
	}

	// Parse key=value pairs
	lines := strings.Split(string(content), "\n")
	for _, line := range lines {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}

		parts := strings.SplitN(line, "=", 2)
		if len(parts) != 2 {
			continue
		}

		key := strings.TrimSpace(parts[0])
		value := strings.TrimSpace(parts[1])

		// Set value using mapstructure tags
		switch key {
		case "SERVER_DOMAIN":
			cfg.ServerDomain = value
		case "WG_PORT":
			var port int
			if _, err := fmt.Sscanf(value, "%d", &port); err == nil {
				cfg.WGPort = port
			}
		case "VPN_IPV4_RANGE":
			cfg.VPNIPv4Range = value
		case "VPN_IPV6_RANGE":
			cfg.VPNIPv6Range = value
		case "WG_INTERFACE":
			cfg.WGInterface = value
		case "DNS_SERVERS":
			cfg.DNSServers = value
		case "LOG_FILE":
			cfg.LogFile = value
		case "THEME":
			cfg.Theme = value
		}
	}

	return nil
}

// loadFromEnv loads configuration from environment variables
func loadFromEnv(cfg *Config) error {
	// Read environment variables
	if val := os.Getenv("SERVER_DOMAIN"); val != "" {
		cfg.ServerDomain = val
	}
	if val := os.Getenv("WG_PORT"); val != "" {
		var port int
		if _, err := fmt.Sscanf(val, "%d", &port); err == nil {
			cfg.WGPort = port
		}
	}
	if val := os.Getenv("VPN_IPV4_RANGE"); val != "" {
		cfg.VPNIPv4Range = val
	}
	if val := os.Getenv("VPN_IPV6_RANGE"); val != "" {
		cfg.VPNIPv6Range = val
	}
	if val := os.Getenv("WG_INTERFACE"); val != "" {
		cfg.WGInterface = val
	}
	if val := os.Getenv("DNS_SERVERS"); val != "" {
		cfg.DNSServers = val
	}
	if val := os.Getenv("LOG_FILE"); val != "" {
		cfg.LogFile = val
	}
	if val := os.Getenv("THEME"); val != "" {
		cfg.Theme = val
	}

	return nil
}

// applyDefaults sets default values for empty configuration
func applyDefaults(cfg *Config) {
	if cfg.WGPort == 0 {
		cfg.WGPort = DefaultWGPort
	}
	if cfg.VPNIPv4Range == "" {
		cfg.VPNIPv4Range = DefaultVPNIPv4Range
	}
	if cfg.VPNIPv6Range == "" {
		cfg.VPNIPv6Range = DefaultVPNIPv6Range
	}
	if cfg.WGInterface == "" {
		cfg.WGInterface = DefaultWGInterface
	}
	if cfg.DNSServers == "" {
		cfg.DNSServers = DefaultDNSServers
	}
	if cfg.LogFile == "" {
		cfg.LogFile = DefaultLogFile
	}
	if cfg.Theme == "" {
		cfg.Theme = DefaultTheme
	}
}

// validateConfig checks that required configuration is present
func validateConfig(cfg *Config) error {
	if cfg.ServerDomain == "" {
		return fmt.Errorf("SERVER_DOMAIN is required. Set it in /etc/wg-admin/config.conf or via environment variable.")
	}

	// Validate port range
	if cfg.WGPort < 1 || cfg.WGPort > 65535 {
		return fmt.Errorf("WG_PORT must be between 1 and 65535, got: %d", cfg.WGPort)
	}

	// Validate CIDR format for IPv4 range
	if !isValidCIDR(cfg.VPNIPv4Range, true) {
		return fmt.Errorf("Invalid VPN_IPV4_RANGE format: %s", cfg.VPNIPv4Range)
	}

	// Validate CIDR format for IPv6 range
	if !isValidCIDR(cfg.VPNIPv6Range, false) {
		return fmt.Errorf("Invalid VPN_IPV6_RANGE format: %s", cfg.VPNIPv6Range)
	}

	return nil
}

// isValidCIDR performs basic CIDR validation
func isValidCIDR(cidr string, isIPv4 bool) bool {
	if cidr == "" {
		return false
	}

	// Split address and prefix
	parts := strings.Split(cidr, "/")
	if len(parts) != 2 {
		return false
	}

	// Basic validation - more comprehensive validation could be added
	if isIPv4 {
		// IPv4 CIDR should have address like x.x.x.x
		return true // Simplified validation
	}

	// IPv6 CIDR
	return true // Simplified validation
}

// GetVPNIPv4Network extracts the IPv4 network from CIDR (e.g., "10.10.69.0" from "10.10.69.0/24")
func (c *Config) GetVPNIPv4Network() string {
	parts := strings.Split(c.VPNIPv4Range, "/")
	if len(parts) == 0 {
		return ""
	}
	return strings.TrimSuffix(parts[0], "0")
}

// GetVPNIPv6Network extracts the IPv6 network from CIDR (e.g., "fd69:dead:beef:69::" from "fd69:dead:beef:69::/64")
func (c *Config) GetVPNIPv6Network() string {
	parts := strings.Split(c.VPNIPv6Range, "/")
	if len(parts) == 0 {
		return ""
	}
	return strings.TrimSuffix(parts[0], "::")
}