package nebula

import (
	"context"
	"errors"
	"fmt"
	"io/ioutil"
	"net"
	"os"
	"os/signal"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"syscall"
	"time"

	"github.com/imdario/mergo"
	"github.com/sirupsen/logrus"
	"gopkg.in/yaml.v2"
)

type Config struct {
	path        string
	files       []string
	Settings    map[interface{}]interface{}
	oldSettings map[interface{}]interface{}
	callbacks   []func(*Config)
	l           *logrus.Logger
}

func NewConfig(l *logrus.Logger) *Config {
	return &Config{
		Settings: make(map[interface{}]interface{}),
		l:        l,
	}
}

// Load will find all yaml files within path and load them in lexical order
func (c *Config) Load(path string) error {
	c.path = path
	c.files = make([]string, 0)

	err := c.resolve(path, true)
	if err != nil {
		return err
	}

	if len(c.files) == 0 {
		return fmt.Errorf("no config files found at %s", path)
	}

	sort.Strings(c.files)

	err = c.parse()
	if err != nil {
		return err
	}

	return nil
}

func (c *Config) LoadString(raw string) error {
	if raw == "" {
		return errors.New("Empty configuration")
	}
	return c.parseRaw([]byte(raw))
}

// RegisterReloadCallback stores a function to be called when a config reload is triggered. The functions registered
// here should decide if they need to make a change to the current process before making the change. HasChanged can be
// used to help decide if a change is necessary.
// These functions should return quickly or spawn their own go routine if they will take a while
func (c *Config) RegisterReloadCallback(f func(*Config)) {
	c.callbacks = append(c.callbacks, f)
}

// HasChanged checks if the underlying structure of the provided key has changed after a config reload. The value of
// k in both the old and new settings will be serialized, the result of the string comparison is returned.
// If k is an empty string the entire config is tested.
// It's important to note that this is very rudimentary and susceptible to configuration ordering issues indicating
// there is change when there actually wasn't any.
func (c *Config) HasChanged(k string) bool {
	if c.oldSettings == nil {
		return false
	}

	var (
		nv interface{}
		ov interface{}
	)

	if k == "" {
		nv = c.Settings
		ov = c.oldSettings
		k = "all settings"
	} else {
		nv = c.get(k, c.Settings)
		ov = c.get(k, c.oldSettings)
	}

	newVals, err := yaml.Marshal(nv)
	if err != nil {
		c.l.WithField("config_path", k).WithError(err).Error("Error while marshaling new config")
	}

	oldVals, err := yaml.Marshal(ov)
	if err != nil {
		c.l.WithField("config_path", k).WithError(err).Error("Error while marshaling old config")
	}

	return string(newVals) != string(oldVals)
}

// CatchHUP will listen for the HUP signal in a go routine and reload all configs found in the
// original path provided to Load. The old settings are shallow copied for change detection after the reload.
func (c *Config) CatchHUP(ctx context.Context) {
	ch := make(chan os.Signal, 1)
	signal.Notify(ch, syscall.SIGHUP)

	go func() {
		for {
			select {
			case <-ctx.Done():
				signal.Stop(ch)
				close(ch)
				return
			case <-ch:
				c.l.Info("Caught HUP, reloading config")
				c.ReloadConfig()
			}
		}
	}()
}

func (c *Config) ReloadConfig() {
	c.oldSettings = make(map[interface{}]interface{})
	for k, v := range c.Settings {
		c.oldSettings[k] = v
	}

	err := c.Load(c.path)
	if err != nil {
		c.l.WithField("config_path", c.path).WithError(err).Error("Error occurred while reloading config")
		return
	}

	for _, v := range c.callbacks {
		v(c)
	}
}

// GetString will get the string for k or return the default d if not found or invalid
func (c *Config) GetString(k, d string) string {
	r := c.Get(k)
	if r == nil {
		return d
	}

	return fmt.Sprintf("%v", r)
}

// GetStringSlice will get the slice of strings for k or return the default d if not found or invalid
func (c *Config) GetStringSlice(k string, d []string) []string {
	r := c.Get(k)
	if r == nil {
		return d
	}

	rv, ok := r.([]interface{})
	if !ok {
		return d
	}

	v := make([]string, len(rv))
	for i := 0; i < len(v); i++ {
		v[i] = fmt.Sprintf("%v", rv[i])
	}

	return v
}

// GetMap will get the map for k or return the default d if not found or invalid
func (c *Config) GetMap(k string, d map[interface{}]interface{}) map[interface{}]interface{} {
	r := c.Get(k)
	if r == nil {
		return d
	}

	v, ok := r.(map[interface{}]interface{})
	if !ok {
		return d
	}

	return v
}

// GetInt will get the int for k or return the default d if not found or invalid
func (c *Config) GetInt(k string, d int) int {
	r := c.GetString(k, strconv.Itoa(d))
	v, err := strconv.Atoi(r)
	if err != nil {
		return d
	}

	return v
}

// GetBool will get the bool for k or return the default d if not found or invalid
func (c *Config) GetBool(k string, d bool) bool {
	r := strings.ToLower(c.GetString(k, fmt.Sprintf("%v", d)))
	v, err := strconv.ParseBool(r)
	if err != nil {
		switch r {
		case "y", "yes":
			return true
		case "n", "no":
			return false
		}
		return d
	}

	return v
}

// GetDuration will get the duration for k or return the default d if not found or invalid
func (c *Config) GetDuration(k string, d time.Duration) time.Duration {
	r := c.GetString(k, "")
	v, err := time.ParseDuration(r)
	if err != nil {
		return d
	}
	return v
}

func (c *Config) GetLocalAllowList(k string) (*LocalAllowList, error) {
	var nameRules []AllowListNameRule
	handleKey := func(key string, value interface{}) (bool, error) {
		if key == "interfaces" {
			var err error
			nameRules, err = c.getAllowListInterfaces(k, value)
			if err != nil {
				return false, err
			}

			return true, nil
		}
		return false, nil
	}

	al, err := c.GetAllowList(k, handleKey)
	if err != nil {
		return nil, err
	}
	return &LocalAllowList{AllowList: al, nameRules: nameRules}, nil
}

func (c *Config) GetRemoteAllowList(k, rangesKey string) (*RemoteAllowList, error) {
	al, err := c.GetAllowList(k, nil)
	if err != nil {
		return nil, err
	}
	remoteAllowRanges, err := c.getRemoteAllowRanges(rangesKey)
	if err != nil {
		return nil, err
	}
	return &RemoteAllowList{AllowList: al, insideAllowLists: remoteAllowRanges}, nil
}

func (c *Config) getRemoteAllowRanges(k string) (*CIDR6Tree, error) {
	value := c.Get(k)
	if value == nil {
		return nil, nil
	}

	remoteAllowRanges := NewCIDR6Tree()

	rawMap, ok := value.(map[interface{}]interface{})
	if !ok {
		return nil, fmt.Errorf("config `%s` has invalid type: %T", k, value)
	}
	for rawKey, rawValue := range rawMap {
		rawCIDR, ok := rawKey.(string)
		if !ok {
			return nil, fmt.Errorf("config `%s` has invalid key (type %T): %v", k, rawKey, rawKey)
		}

		allowList, err := c.getAllowList(fmt.Sprintf("%s.%s", k, rawCIDR), rawValue, nil)
		if err != nil {
			return nil, err
		}

		_, cidr, err := net.ParseCIDR(rawCIDR)
		if err != nil {
			return nil, fmt.Errorf("config `%s` has invalid CIDR: %s", k, rawCIDR)
		}

		remoteAllowRanges.AddCIDR(cidr, allowList)
	}

	return remoteAllowRanges, nil
}

// If the handleKey func returns true, the rest of the parsing is skipped
// for this key. This allows parsing of special values like `interfaces`.
func (c *Config) GetAllowList(k string, handleKey func(key string, value interface{}) (bool, error)) (*AllowList, error) {
	r := c.Get(k)
	if r == nil {
		return nil, nil
	}

	return c.getAllowList(k, r, handleKey)
}

// If the handleKey func returns true, the rest of the parsing is skipped
// for this key. This allows parsing of special values like `interfaces`.
func (c *Config) getAllowList(k string, raw interface{}, handleKey func(key string, value interface{}) (bool, error)) (*AllowList, error) {
	rawMap, ok := raw.(map[interface{}]interface{})
	if !ok {
		return nil, fmt.Errorf("config `%s` has invalid type: %T", k, raw)
	}

	tree := NewCIDR6Tree()

	// Keep track of the rules we have added for both ipv4 and ipv6
	type allowListRules struct {
		firstValue     bool
		allValuesMatch bool
		defaultSet     bool
		allValues      bool
	}
	rules4 := allowListRules{firstValue: true, allValuesMatch: true, defaultSet: false}
	rules6 := allowListRules{firstValue: true, allValuesMatch: true, defaultSet: false}

	for rawKey, rawValue := range rawMap {
		rawCIDR, ok := rawKey.(string)
		if !ok {
			return nil, fmt.Errorf("config `%s` has invalid key (type %T): %v", k, rawKey, rawKey)
		}

		if handleKey != nil {
			handled, err := handleKey(rawCIDR, rawValue)
			if err != nil {
				return nil, err
			}
			if handled {
				continue
			}
		}

		value, ok := rawValue.(bool)
		if !ok {
			return nil, fmt.Errorf("config `%s` has invalid value (type %T): %v", k, rawValue, rawValue)
		}

		_, cidr, err := net.ParseCIDR(rawCIDR)
		if err != nil {
			return nil, fmt.Errorf("config `%s` has invalid CIDR: %s", k, rawCIDR)
		}

		// TODO: should we error on duplicate CIDRs in the config?
		tree.AddCIDR(cidr, value)

		maskBits, maskSize := cidr.Mask.Size()

		var rules *allowListRules
		if maskSize == 32 {
			rules = &rules4
		} else {
			rules = &rules6
		}

		if rules.firstValue {
			rules.allValues = value
			rules.firstValue = false
		} else {
			if value != rules.allValues {
				rules.allValuesMatch = false
			}
		}

		// Check if this is 0.0.0.0/0 or ::/0
		if maskBits == 0 {
			rules.defaultSet = true
		}
	}

	if !rules4.defaultSet {
		if rules4.allValuesMatch {
			_, zeroCIDR, _ := net.ParseCIDR("0.0.0.0/0")
			tree.AddCIDR(zeroCIDR, !rules4.allValues)
		} else {
			return nil, fmt.Errorf("config `%s` contains both true and false rules, but no default set for 0.0.0.0/0", k)
		}
	}

	if !rules6.defaultSet {
		if rules6.allValuesMatch {
			_, zeroCIDR, _ := net.ParseCIDR("::/0")
			tree.AddCIDR(zeroCIDR, !rules6.allValues)
		} else {
			return nil, fmt.Errorf("config `%s` contains both true and false rules, but no default set for ::/0", k)
		}
	}

	return &AllowList{cidrTree: tree}, nil
}

func (c *Config) getAllowListInterfaces(k string, v interface{}) ([]AllowListNameRule, error) {
	var nameRules []AllowListNameRule

	rawRules, ok := v.(map[interface{}]interface{})
	if !ok {
		return nil, fmt.Errorf("config `%s.interfaces` is invalid (type %T): %v", k, v, v)
	}

	firstEntry := true
	var allValues bool
	for rawName, rawAllow := range rawRules {
		name, ok := rawName.(string)
		if !ok {
			return nil, fmt.Errorf("config `%s.interfaces` has invalid key (type %T): %v", k, rawName, rawName)
		}
		allow, ok := rawAllow.(bool)
		if !ok {
			return nil, fmt.Errorf("config `%s.interfaces` has invalid value (type %T): %v", k, rawAllow, rawAllow)
		}

		nameRE, err := regexp.Compile("^" + name + "$")
		if err != nil {
			return nil, fmt.Errorf("config `%s.interfaces` has invalid key: %s: %v", k, name, err)
		}

		nameRules = append(nameRules, AllowListNameRule{
			Name:  nameRE,
			Allow: allow,
		})

		if firstEntry {
			allValues = allow
			firstEntry = false
		} else {
			if allow != allValues {
				return nil, fmt.Errorf("config `%s.interfaces` values must all be the same true/false value", k)
			}
		}
	}

	return nameRules, nil
}

func (c *Config) Get(k string) interface{} {
	return c.get(k, c.Settings)
}

func (c *Config) IsSet(k string) bool {
	return c.get(k, c.Settings) != nil
}

func (c *Config) get(k string, v interface{}) interface{} {
	parts := strings.Split(k, ".")
	for _, p := range parts {
		m, ok := v.(map[interface{}]interface{})
		if !ok {
			return nil
		}

		v, ok = m[p]
		if !ok {
			return nil
		}
	}

	return v
}

// direct signifies if this is the config path directly specified by the user,
// versus a file/dir found by recursing into that path
func (c *Config) resolve(path string, direct bool) error {
	i, err := os.Stat(path)
	if err != nil {
		return nil
	}

	if !i.IsDir() {
		c.addFile(path, direct)
		return nil
	}

	paths, err := readDirNames(path)
	if err != nil {
		return fmt.Errorf("problem while reading directory %s: %s", path, err)
	}

	for _, p := range paths {
		err := c.resolve(filepath.Join(path, p), false)
		if err != nil {
			return err
		}
	}

	return nil
}

func (c *Config) addFile(path string, direct bool) error {
	ext := filepath.Ext(path)

	if !direct && ext != ".yaml" && ext != ".yml" {
		return nil
	}

	ap, err := filepath.Abs(path)
	if err != nil {
		return err
	}

	c.files = append(c.files, ap)
	return nil
}

func (c *Config) parseRaw(b []byte) error {
	var m map[interface{}]interface{}

	err := yaml.Unmarshal(b, &m)
	if err != nil {
		return err
	}

	c.Settings = m
	return nil
}

func (c *Config) parse() error {
	var m map[interface{}]interface{}

	for _, path := range c.files {
		b, err := ioutil.ReadFile(path)
		if err != nil {
			return err
		}

		var nm map[interface{}]interface{}
		err = yaml.Unmarshal(b, &nm)
		if err != nil {
			return err
		}

		// We need to use WithAppendSlice so that firewall rules in separate
		// files are appended together
		err = mergo.Merge(&nm, m, mergo.WithAppendSlice)
		m = nm
		if err != nil {
			return err
		}
	}

	c.Settings = m
	return nil
}

func readDirNames(path string) ([]string, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}

	paths, err := f.Readdirnames(-1)
	f.Close()
	if err != nil {
		return nil, err
	}

	sort.Strings(paths)
	return paths, nil
}

func configLogger(c *Config) error {
	// set up our logging level
	logLevel, err := logrus.ParseLevel(strings.ToLower(c.GetString("logging.level", "info")))
	if err != nil {
		return fmt.Errorf("%s; possible levels: %s", err, logrus.AllLevels)
	}
	c.l.SetLevel(logLevel)

	disableTimestamp := c.GetBool("logging.disable_timestamp", false)
	timestampFormat := c.GetString("logging.timestamp_format", "")
	fullTimestamp := (timestampFormat != "")
	if timestampFormat == "" {
		timestampFormat = time.RFC3339
	}

	logFormat := strings.ToLower(c.GetString("logging.format", "text"))
	switch logFormat {
	case "text":
		c.l.Formatter = &logrus.TextFormatter{
			TimestampFormat:  timestampFormat,
			FullTimestamp:    fullTimestamp,
			DisableTimestamp: disableTimestamp,
		}
	case "json":
		c.l.Formatter = &logrus.JSONFormatter{
			TimestampFormat:  timestampFormat,
			DisableTimestamp: disableTimestamp,
		}
	default:
		return fmt.Errorf("unknown log format `%s`. possible formats: %s", logFormat, []string{"text", "json"})
	}

	return nil
}