package ctrld

import (
	"context"
	"crypto/tls"
	"net"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	"github.com/Control-D-Inc/ctrld/internal/dnsrcode"
	"github.com/go-playground/validator/v10"
	"github.com/lucas-clemente/quic-go"
	"github.com/lucas-clemente/quic-go/http3"
	"github.com/miekg/dns"
	"github.com/spf13/viper"
)

// SetConfigName set the config name that ctrld will look for.
func SetConfigName(v *viper.Viper, name string) {
	v.SetConfigName(name)

	configPath := "$HOME"
	// viper has its own way to get user home directory:  https://github.com/spf13/viper/blob/v1.14.0/util.go#L134
	// To be consistent, we prefer os.UserHomeDir instead.
	if homeDir, err := os.UserHomeDir(); err == nil {
		configPath = homeDir
	}
	v.AddConfigPath(configPath)
	v.AddConfigPath(".")
}

// InitConfig initializes default config values for given *viper.Viper instance.
func InitConfig(v *viper.Viper, name string) {
	SetConfigName(v, name)

	v.SetDefault("listener", map[string]*ListenerConfig{
		"0": {
			IP:   "127.0.0.1",
			Port: 53,
		},
	})
	v.SetDefault("network", map[string]*NetworkConfig{
		"0": {
			Name:  "Network 0",
			Cidrs: []string{"0.0.0.0/0"},
		},
	})
	v.SetDefault("upstream", map[string]*UpstreamConfig{
		"0": {
			BootstrapIP: "76.76.2.11",
			Name:        "Control D - Anti-Malware",
			Type:        ResolverTypeDOH,
			Endpoint:    "https://freedns.controld.com/p1",
			Timeout:     5000,
		},
		"1": {
			BootstrapIP: "76.76.2.11",
			Name:        "Control D - No Ads",
			Type:        ResolverTypeDOQ,
			Endpoint:    "p2.freedns.controld.com",
			Timeout:     3000,
		},
	})
}

// Config represents ctrld supported configuration.
type Config struct {
	Service  ServiceConfig              `mapstructure:"service" toml:"service,omitempty"`
	Network  map[string]*NetworkConfig  `mapstructure:"network" toml:"network" validate:"min=1,dive"`
	Upstream map[string]*UpstreamConfig `mapstructure:"upstream" toml:"upstream" validate:"min=1,dive"`
	Listener map[string]*ListenerConfig `mapstructure:"listener" toml:"listener" validate:"min=1,dive"`
}

// ServiceConfig specifies the general ctrld config.
type ServiceConfig struct {
	LogLevel         string `mapstructure:"log_level" toml:"log_level,omitempty"`
	LogPath          string `mapstructure:"log_path" toml:"log_path,omitempty"`
	CacheEnable      bool   `mapstructure:"cache_enable" toml:"cache_enable,omitempty"`
	CacheSize        int    `mapstructure:"cache_size" toml:"cache_size,omitempty"`
	CacheTTLOverride int    `mapstructure:"cache_ttl_override" toml:"cache_ttl_override,omitempty"`
	CacheServeStale  bool   `mapstructure:"cache_serve_stale" toml:"cache_serve_stale,omitempty"`
	Daemon           bool   `mapstructure:"-" toml:"-"`
	AllocateIP       bool   `mapstructure:"-" toml:"-"`
}

// NetworkConfig specifies configuration for networks where ctrld will handle requests.
type NetworkConfig struct {
	Name   string       `mapstructure:"name" toml:"name,omitempty"`
	Cidrs  []string     `mapstructure:"cidrs" toml:"cidrs,omitempty" validate:"dive,cidr"`
	IPNets []*net.IPNet `mapstructure:"-" toml:"-"`
}

// UpstreamConfig specifies configuration for upstreams that ctrld will forward requests to.
type UpstreamConfig struct {
	Name              string              `mapstructure:"name" toml:"name,omitempty"`
	Type              string              `mapstructure:"type" toml:"type,omitempty" validate:"oneof=doh doh3 dot doq os legacy"`
	Endpoint          string              `mapstructure:"endpoint" toml:"endpoint,omitempty" validate:"required_unless=Type os"`
	BootstrapIP       string              `mapstructure:"bootstrap_ip" toml:"bootstrap_ip,omitempty"`
	Domain            string              `mapstructure:"-" toml:"-"`
	Timeout           int                 `mapstructure:"timeout" toml:"timeout,omitempty" validate:"gte=0"`
	transport         *http.Transport     `mapstructure:"-" toml:"-"`
	http3RoundTripper *http3.RoundTripper `mapstructure:"-" toml:"-"`
}

// ListenerConfig specifies the networks configuration that ctrld will run on.
type ListenerConfig struct {
	IP         string                `mapstructure:"ip" toml:"ip,omitempty" validate:"ip"`
	Port       int                   `mapstructure:"port" toml:"port,omitempty" validate:"gt=0"`
	Restricted bool                  `mapstructure:"restricted" toml:"restricted,omitempty"`
	Policy     *ListenerPolicyConfig `mapstructure:"policy" toml:"policy,omitempty"`
}

// ListenerPolicyConfig specifies the policy rules for ctrld to filter incoming requests.
type ListenerPolicyConfig struct {
	Name                 string   `mapstructure:"name" toml:"name,omitempty"`
	Networks             []Rule   `mapstructure:"networks" toml:"networks,omitempty,inline,multiline" validate:"dive,len=1"`
	Rules                []Rule   `mapstructure:"rules" toml:"rules,omitempty,inline,multiline" validate:"dive,len=1"`
	FailoverRcodes       []string `mapstructure:"failover_rcodes" toml:"failover_rcodes,omitempty" validate:"dive,dnsrcode"`
	FailoverRcodeNumbers []int    `mapstructure:"-" toml:"-"`
}

// Rule is a map from source to list of upstreams.
// ctrld uses rule to perform requests matching and forward
// the request to corresponding upstreams if it's matched.
type Rule map[string][]string

// Init initialized necessary values for an UpstreamConfig.
func (uc *UpstreamConfig) Init() {
	if u, err := url.Parse(uc.Endpoint); err == nil {
		uc.Domain = u.Host
	}
	if uc.Domain != "" {
		return
	}

	if !strings.Contains(uc.Endpoint, ":") {
		uc.Domain = uc.Endpoint
		uc.Endpoint = net.JoinHostPort(uc.Endpoint, defaultPortFor(uc.Type))
	}
	host, _, _ := net.SplitHostPort(uc.Endpoint)
	uc.Domain = host
	if net.ParseIP(uc.Domain) != nil {
		uc.BootstrapIP = uc.Domain
	}
}

// SetupTransport initializes the network transport used to connect to upstream server.
// For now, only DoH upstream is supported.
func (uc *UpstreamConfig) SetupTransport() {
	switch uc.Type {
	case ResolverTypeDOH:
		uc.setupDOHTransport()
	case ResolverTypeDOH3:
		uc.setupDOH3Transport()
	}
}

func (uc *UpstreamConfig) setupDOHTransport() {
	uc.transport = http.DefaultTransport.(*http.Transport).Clone()
	uc.transport.DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
		dialer := &net.Dialer{
			Timeout:   10 * time.Second,
			KeepAlive: 10 * time.Second,
		}
		Log(ctx, ProxyLog.Debug(), "debug dial context %s - %s - %s", addr, network, bootstrapDNS)
		// if we have a bootstrap ip set, use it to avoid DNS lookup
		if uc.BootstrapIP != "" {
			if _, port, _ := net.SplitHostPort(addr); port != "" {
				addr = net.JoinHostPort(uc.BootstrapIP, port)
			}
			Log(ctx, ProxyLog.Debug(), "sending doh request to: %s", addr)
		}
		return dialer.DialContext(ctx, network, addr)
	}

	uc.pingUpstream()
}

func (uc *UpstreamConfig) setupDOH3Transport() {
	uc.http3RoundTripper = &http3.RoundTripper{}
	uc.http3RoundTripper.Dial = func(ctx context.Context, addr string, tlsCfg *tls.Config, cfg *quic.Config) (quic.EarlyConnection, error) {
		host := addr
		ProxyLog.Debug().Msgf("debug dial context D0H3 %s - %s", addr, bootstrapDNS)
		// if we have a bootstrap ip set, use it to avoid DNS lookup
		if uc.BootstrapIP != "" {
			if _, port, _ := net.SplitHostPort(addr); port != "" {
				addr = net.JoinHostPort(uc.BootstrapIP, port)
			}
			ProxyLog.Debug().Msgf("sending doh3 request to: %s", addr)
		}
		remoteAddr, err := net.ResolveUDPAddr("udp", addr)
		if err != nil {
			return nil, err
		}

		udpConn, err := net.ListenUDP("udp", nil)
		if err != nil {
			return nil, err
		}
		return quic.DialEarlyContext(ctx, udpConn, remoteAddr, host, tlsCfg, cfg)
	}

	uc.pingUpstream()
}

func (uc *UpstreamConfig) pingUpstream() {
	// Warming up the transport by querying a test packet.
	dnsResolver, err := NewResolver(uc)
	if err != nil {
		ProxyLog.Error().Err(err).Msgf("failed to create resolver for upstream: %s", uc.Name)
		return
	}
	msg := new(dns.Msg)
	msg.SetQuestion(".", dns.TypeNS)
	msg.MsgHdr.RecursionDesired = true
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	_, _ = dnsResolver.Resolve(ctx, msg)
}

// Init initialized necessary values for an ListenerConfig.
func (lc *ListenerConfig) Init() {
	if lc.Policy != nil {
		lc.Policy.FailoverRcodeNumbers = make([]int, len(lc.Policy.FailoverRcodes))
		for i, rcode := range lc.Policy.FailoverRcodes {
			lc.Policy.FailoverRcodeNumbers[i] = dnsrcode.FromString(rcode)
		}
	}
}

// ValidateConfig validates the given config.
func ValidateConfig(validate *validator.Validate, cfg *Config) error {
	_ = validate.RegisterValidation("dnsrcode", validateDnsRcode)
	return validate.Struct(cfg)
}

func validateDnsRcode(fl validator.FieldLevel) bool {
	return dnsrcode.FromString(fl.Field().String()) != -1
}

func defaultPortFor(typ string) string {
	switch typ {
	case ResolverTypeDOH, ResolverTypeDOH3:
		return "443"
	case ResolverTypeDOQ, ResolverTypeDOT:
		return "853"
	case ResolverTypeLegacy:
		return "53"
	}
	return "53"
}