package config

import (
	"fmt"
	"os"
	"path/filepath"

	"gopkg.in/yaml.v3"
)

type Config struct {
	// Server identification and display.
	Server ServerConfig `yaml:"server"`
	// REST API settings.
	API APIConfig `yaml:"api"`
	// Prometheus metrics endpoint settings.
	Metrics MetricsConfig `yaml:"metrics"`
	// Shadowsocks proxy settings.
	Shadowsocks ShadowsocksConfig `yaml:"shadowsocks"`
	// AmneziaWG VPN settings.
	AmneziaWG AmneziaWGConfig `yaml:"amneziawg"`
	// Path to persistent state file.
	// Defaults to "state.yaml" in the same directory as the config file.
	State string `yaml:"state_file"`

	// configDir is the directory containing the config file, used for resolving relative paths.
	configDir string
}

type ServerConfig struct {
	// Human-readable server name.
	Name string `yaml:"name"`
	// Unique server identifier (auto-generated if empty).
	ID string `yaml:"id"`
	// Hostname or IP used in access key URLs.
	Hostname string `yaml:"hostname"`
}

type APIConfig struct {
	// Listen address for the management API (e.g., ":8081").
	ListenAddr string `yaml:"listen_addr"`
	// Secret prefix for URL-based authentication (e.g., "SecretPath").
	// API will be served at /<secret>/...
	Secret string `yaml:"secret"`
	// Path to TLS certificate file (optional, used for certSha256 in access.yaml).
	CertFile string `yaml:"cert_file"`
}

type MetricsConfig struct {
	// Listen address for the Prometheus /metrics and /healthz endpoint.
	// Defaults to "127.0.0.1:8081".
	ListenAddr string `yaml:"listen_addr"`
	// Node exporter collectors to enable (e.g., [cpu, meminfo, diskstats]).
	// Empty means no node_exporter collectors.
	NodeExporterCollectors []string `yaml:"node_exporter_collectors"`
}

type AmneziaWGConfig struct {
	// Enable AmneziaWG protocol.
	Enabled bool `yaml:"enabled"`
	// UDP listen port for AWG + HTTP/3 mux.
	ListenPort int `yaml:"listen_port"`
	// TUN device name.
	TUNName string `yaml:"tun_name"`
	// Server subnet in CIDR notation (e.g., "10.14.0.0/24").
	// Server takes the first usable IP (.1), peers are allocated from .2 onwards.
	Address string `yaml:"address"`
	// TUN MTU.
	MTU int `yaml:"mtu"`
	// Server interface private key (base64). Auto-generated if empty.
	PrivateKey string `yaml:"private_key"`
	// DNS server for client configs.
	DNS string `yaml:"dns"`

	// HTTP/3 cover for DPI resistance.
	// Domain for Let's Encrypt certificate. If empty, HTTP/3 server is disabled.
	Domain string `yaml:"domain"`
	// Directory for cached TLS certificates.
	CertCache string `yaml:"cert_cache"`
	// HTTP port for ACME HTTP-01 challenges.
	ACMEHTTPPort int `yaml:"acme_http_port"`

	// Obfuscation parameters.
	Jc   int `yaml:"jc"`
	Jmin int `yaml:"jmin"`
	Jmax int `yaml:"jmax"`
	S1   int `yaml:"s1"`
	S2   int `yaml:"s2"`
	S3   int `yaml:"s3"`
	S4   int `yaml:"s4"`
	H1   string `yaml:"h1"` // "min-max" or single value
	H2   string `yaml:"h2"`
	H3   string `yaml:"h3"`
	H4   string `yaml:"h4"`
}

type ShadowsocksConfig struct {
	// Default port for new access keys. 0 means pick a random unused port on first start.
	DefaultPort int `yaml:"default_port"`
	// Default cipher for new access keys.
	DefaultCipher string `yaml:"default_cipher"`
	// UDP NAT timeout as a duration string (e.g., "5m").
	NATTimeout string `yaml:"nat_timeout"`
	// Replay protection history size (0 = disabled).
	ReplayHistory int `yaml:"replay_history"`
	// Path to IP-to-country MaxMind MMDB file.
	IPCountryDB string `yaml:"ip_country_db"`
	// Path to IP-to-ASN MaxMind MMDB file.
	IPASNDB string `yaml:"ip_asn_db"`
}

func Load(filename string) (*Config, error) {
	absPath, err := filepath.Abs(filename)
	if err != nil {
		return nil, fmt.Errorf("resolving config path: %w", err)
	}

	data, err := os.ReadFile(absPath)
	if err != nil {
		return nil, fmt.Errorf("reading config file: %w", err)
	}
	cfg := &Config{
		configDir: filepath.Dir(absPath),
	}
	if err := yaml.Unmarshal(data, cfg); err != nil {
		return nil, fmt.Errorf("parsing config: %w", err)
	}
	cfg.setDefaults()
	return cfg, nil
}

func (c *Config) setDefaults() {
	if c.API.ListenAddr == "" {
		c.API.ListenAddr = ":8081"
	}
	if c.Metrics.ListenAddr == "" {
		c.Metrics.ListenAddr = "127.0.0.1:8081"
	}
	if c.Shadowsocks.DefaultCipher == "" {
		c.Shadowsocks.DefaultCipher = "chacha20-ietf-poly1305"
	}
	if c.Shadowsocks.NATTimeout == "" {
		c.Shadowsocks.NATTimeout = "5m"
	}
	if c.Server.Name == "" {
		c.Server.Name = "Outline Server"
	}
	if c.State == "" {
		c.State = "state.yaml"
	}
	// AmneziaWG defaults.
	if c.AmneziaWG.Enabled {
		if c.AmneziaWG.ListenPort == 0 {
			c.AmneziaWG.ListenPort = 443
		}
		if c.AmneziaWG.TUNName == "" {
			c.AmneziaWG.TUNName = "awg0"
		}
		if c.AmneziaWG.MTU == 0 {
			c.AmneziaWG.MTU = 1420
		}
		if c.AmneziaWG.CertCache == "" {
			c.AmneziaWG.CertCache = "/var/lib/outline-distro/certs"
		}
		if c.AmneziaWG.ACMEHTTPPort == 0 {
			c.AmneziaWG.ACMEHTTPPort = 80
		}
	}
}

// StateFile returns the absolute path to the state file.
func (c *Config) StateFile() string {
	if filepath.IsAbs(c.State) {
		return c.State
	}
	return filepath.Join(c.configDir, c.State)
}