package config

import (
	"fmt"
	"io/ioutil"
	"net"

	"git.wntrmute.dev/kyle/kdhcp/log"
	"gopkg.in/yaml.v2"
)

const (
	CurrentVersion = 1
)

func ensureV4(ip net.IP) (net.IP, error) {
	ip4 := ip.To4()
	if ip4 == nil {
		return ip4, fmt.Errorf("%s isn't an IPv4 address", ip)
	}

	return ip4, nil
}

type IPRange struct {
	Start net.IP
	End   net.IP
}

func (r *IPRange) ensureV4() (err error) {
	if r.Start, err = ensureV4(r.Start); err != nil {
		return fmt.Errorf("config: range start address %w", err)
	}

	if r.End, err = ensureV4(r.End); err != nil {
		return fmt.Errorf("config: range end address %w", err)
	}

	return nil
}

type Network struct {
	Gateway   net.IP   `yaml:"gateway"`
	Mask      net.IP   `yaml:"mask"`
	Broadcast net.IP   `yaml:"broadcast"`
	DNS       []net.IP `yaml:"dns"`
	Domain    string   `yaml:"domain"`
}

func (n *Network) ensureV4() (err error) {
	n.Gateway, err = ensureV4(n.Gateway)
	if err != nil {
		return fmt.Errorf("config: gateway %w", err)
	}

	n.Mask, err = ensureV4(n.Mask)
	if err != nil {
		return fmt.Errorf("config: mask  %w", err)
	}

	n.Broadcast, err = ensureV4(n.Broadcast)
	if err != nil {
		return fmt.Errorf("config: broadcast  %w", err)
	}

	for i := range n.DNS {
		n.DNS[i], err = ensureV4(n.DNS[i])
		if err != nil {
			return fmt.Errorf("config: DNS address %w", err)
		}
	}

	return nil
}

type ConfigFile struct {
	Server *Config `yaml:"kdhcp"`
}

type Config struct {
	Version   int                 `yaml:"version"`
	Interface string              `yaml:"interface"`
	LeaseFile string              `yaml:"lease_file"`
	Network   *Network            `yaml:"network"`
	Pools     map[string]*IPRange `yaml:"pools"`
	Statics   map[string]net.IP   `yaml:"statics"`
	Device    *net.Interface
}

func (cfg *Config) process() (err error) {
	switch {
	case cfg.Version == 0:
		log.Warningln("config: Version is 0, which indicates it hasn't been set. The config may be invalid.")
	case cfg.Version > CurrentVersion:
		log.Warningf("config: Version is greater than the current version %d. The config may not behave as expected.", CurrentVersion)
	}

	cfg.Device, err = net.InterfaceByName(cfg.Interface)
	if err != nil {
		return fmt.Errorf("config: while looking up interface %s: %w", cfg.Interface, err)
	}

	err = cfg.Network.ensureV4()
	if err != nil {
		return err
	}

	for k, v := range cfg.Pools {
		if err = v.ensureV4(); err != nil {
			return fmt.Errorf("config: pool %s %w", k, err)
		}

		cfg.Pools[k] = v
	}

	for k, v := range cfg.Statics {
		cfg.Statics[k], err = ensureV4(v)
		if err != nil {
			return fmt.Errorf("config: %s %w", k, err)
		}
	}

	return nil
}

func Load(path string) (*Config, error) {
	data, err := ioutil.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("config: loading %s: %w", path, err)
	}

	configFile := &ConfigFile{}
	err = yaml.Unmarshal(data, configFile)
	if err != nil {
		return nil, fmt.Errorf("config: while unmarshaling %s: %w", path, err)
	}

	if configFile.Server == nil {
		log.Fatal("missing `kdhcp` section of config")
	}
	config := configFile.Server
	if err = config.process(); err != nil {
		return nil, err
	}

	return config, nil
}