package validate

import (
	"encoding/base64"
	"fmt"
	"regexp"
	"strings"

	"jarl/internal/catalog"
	"jarl/internal/dnsname"
	"jarl/internal/model"
	"jarl/internal/namedconf"
)

// TSIGAlgorithms are the algorithms named supports, with the minimum
// recommended secret length in bytes (the hash output size).
var TSIGAlgorithms = map[string]int{
	"hmac-md5":    16,
	"hmac-sha1":   20,
	"hmac-sha224": 28,
	"hmac-sha256": 32,
	"hmac-sha384": 48,
	"hmac-sha512": 64,
}

var reViewName = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9_.-]{0,63}$`)

func (c *checker) checkSettings() {
	st := c.s.Settings
	for _, ns := range st.Nameservers {
		if !dnsname.IsHostname(ns, false) {
			c.errf("settings_invalid", "settings", 0, "default name server %q is not a valid host name", dnsname.Display(ns))
		}
	}
	if st.RName != "" && !dnsname.IsMailbox(st.RName) {
		c.errf("settings_invalid", "settings", 0, "default SOA contact %q is not a valid mailbox name", st.RName)
	}
	if st.DefaultTTL > maxTTL {
		c.errf("settings_invalid", "settings", 0, "default TTL %d is larger than 2147483647", st.DefaultTTL)
	}
	switch st.SerialPolicy {
	case model.SerialDate, model.SerialIncrement, model.SerialUnixtime:
	default:
		c.errf("settings_invalid", "settings", 0, "unknown serial policy %q", st.SerialPolicy)
	}
}

func (c *checker) checkKeys() {
	seen := map[string]bool{}
	for _, k := range c.s.SortedKeys() {
		label := "TSIG key " + k.Name
		if seen[k.Name] {
			c.errf("key_duplicate", "key", k.ID, "%s is defined more than once", label)
		}
		seen[k.Name] = true
		if k.Name == "" {
			c.errf("key_name_invalid", "key", k.ID, "TSIG key has no name")
		} else if err := dnsname.CheckZoneName(dnsname.Fqdn(k.Name)); err != nil {
			c.errf("key_name_invalid", "key", k.ID, "%s: invalid name: %v", label, err)
		} else if strings.HasPrefix(strings.ToLower(k.Name), model.ViewKeyPrefix) {
			c.errf("key_name_reserved", "key", k.ID, "%s: names starting with %s are kept for the keys Jarl gives views", label, model.ViewKeyPrefix)
		}
		minLen, ok := TSIGAlgorithms[k.Algorithm]
		if !ok {
			c.errf("key_algorithm_invalid", "key", k.ID, "%s: unsupported algorithm %q (use one of hmac-sha256, hmac-sha512, ...)", label, k.Algorithm)
		}
		b, err := base64.StdEncoding.DecodeString(k.Secret)
		if err != nil || len(b) == 0 {
			c.errf("key_secret_invalid", "key", k.ID, "%s: secret is not valid base64", label)
		} else if ok && len(b) < minLen {
			c.warnf("key_secret_weak", "key", k.ID, "%s: secret is only %d bytes; %d or more are recommended for %s", label, len(b), minLen, k.Algorithm)
		}
		if k.Algorithm == "hmac-md5" || k.Algorithm == "hmac-sha1" {
			c.warnf("key_algorithm_weak", "key", k.ID, "%s: %s is outdated; prefer hmac-sha256", label, k.Algorithm)
		}
	}
}

// parseElements parses ACL-style element strings, reporting errors.
func (c *checker) parseElements(elems []string, report func(err error, elem string)) []namedconf.AMElement {
	var out []namedconf.AMElement
	for _, s := range elems {
		e, err := namedconf.ParseAMElement(s)
		if err != nil {
			report(err, s)
			continue
		}
		out = append(out, e)
	}
	return out
}

// checkRefs reports references to ACLs and keys that don't exist.
func (c *checker) checkRefs(elems []namedconf.AMElement, where string, objType string, id int64) {
	acls, keys := namedconf.AMRefs(elems)
	for _, a := range acls {
		if c.s.ACLByName(a) == nil {
			c.errf("acl_ref_missing", objType, id, "%s refers to ACL %q, which does not exist", where, a)
		}
	}
	for _, k := range keys {
		if !c.keyNames[model.NormalizeKeyName(k)] && !c.opts.ExternalKeysUnknown {
			c.errf("key_ref_missing", objType, id, "%s refers to TSIG key %q, which does not exist", where, k)
		}
	}
}

func (c *checker) checkACLs() {
	seen := map[string]bool{}
	for _, a := range c.s.SortedACLs() {
		label := "ACL " + a.Name
		lname := strings.ToLower(a.Name)
		if seen[lname] {
			c.errf("acl_duplicate", "acl", a.ID, "%s is defined more than once (ACL names are case-insensitive)", label)
		}
		seen[lname] = true
		if namedconf.BuiltinACLs[lname] {
			c.errf("acl_name_invalid", "acl", a.ID, "%q is a built-in ACL name and can't be redefined", a.Name)
		} else if err := namedconf.CheckACLName(a.Name); err != nil {
			c.errf("acl_name_invalid", "acl", a.ID, "%v", err)
		}
		elems := c.parseElements(a.Elements, func(err error, s string) {
			c.errf("acl_element_invalid", "acl", a.ID, "%s: element %q: %v", label, s, err)
		})
		if len(a.Elements) == 0 {
			c.warnf("acl_empty", "acl", a.ID, "%s is empty and matches nothing", label)
		}
		c.checkRefs(elems, label, "acl", a.ID)
		for _, w := range namedconf.Shadowed(elems) {
			c.warnf("acl_shadowed", "acl", a.ID, "%s: %s", label, w)
		}
	}
	// Cycles between ACLs.
	state := map[string]int{} // 0 unvisited, 1 visiting, 2 done
	var visit func(a *model.ACL, path []string)
	visit = func(a *model.ACL, path []string) {
		n := strings.ToLower(a.Name)
		switch state[n] {
		case 1:
			c.errf("acl_cycle", "acl", a.ID, "ACLs refer to each other in a loop: %s", strings.Join(append(path, a.Name), " -> "))
			return
		case 2:
			return
		}
		state[n] = 1
		var elems []namedconf.AMElement
		for _, s := range a.Elements {
			if e, err := namedconf.ParseAMElement(s); err == nil {
				elems = append(elems, e)
			}
		}
		refs, _ := namedconf.AMRefs(elems)
		for _, r := range refs {
			if next := c.s.ACLByName(r); next != nil {
				visit(next, append(path, a.Name))
			}
		}
		state[n] = 2
	}
	for _, a := range c.s.SortedACLs() {
		visit(a, nil)
	}
}

func (c *checker) checkViews() {
	seen := map[string]bool{}
	for _, v := range c.s.OrderedViews() {
		label := "view " + v.Name
		ln := strings.ToLower(v.Name)
		if seen[ln] {
			c.errf("view_duplicate", "view", v.ID, "%s is defined more than once", label)
		}
		seen[ln] = true
		if !reViewName.MatchString(v.Name) {
			c.errf("view_name_invalid", "view", v.ID, "view name %q must start with a letter or digit and contain only letters, digits, '_', '-' and '.'", v.Name)
		}
		for field, list := range map[string][]string{"match-clients": v.MatchClients, "match-destinations": v.MatchDestinations} {
			elems := c.parseElements(list, func(err error, s string) {
				c.errf("view_acl_invalid", "view", v.ID, "%s: %s element %q: %v", label, field, s, err)
			})
			c.checkRefs(elems, label+" "+field, "view", v.ID)
			for _, w := range namedconf.Shadowed(elems) {
				c.warnf("acl_shadowed", "view", v.ID, "%s %s: %s", label, field, w)
			}
		}
	}
	// Views that can never match because an earlier view matches every
	// client.
	views := c.s.OrderedViews()
	for i, v := range views {
		if !c.viewMatchesEveryone(v) {
			continue
		}
		for _, later := range views[i+1:] {
			c.warnf("view_unreachable", "view", later.ID, "view %s is never used: view %s before it matches every client", later.Name, v.Name)
		}
		break
	}
}

// viewMatchesEveryone reports whether a view matches all clients and
// destinations (and not just recursive queries).
func (c *checker) viewMatchesEveryone(v *model.View) bool {
	if v.MatchRecursiveOnly != nil && *v.MatchRecursiveOnly {
		return false
	}
	return c.listMatchesEveryone(v.MatchClients, true) && c.listMatchesEveryone(v.MatchDestinations, true)
}

// listMatchesEveryone reports whether an element list matches every
// address. emptyIsAny is true for lists that default to "any".
func (c *checker) listMatchesEveryone(list []string, emptyIsAny bool) bool {
	if len(list) == 0 {
		return emptyIsAny
	}
	return namedconf.ContainsAny(c.flatten(list, 0))
}

// flatten parses elements and expands references to user ACLs.
func (c *checker) flatten(list []string, depth int) []namedconf.AMElement {
	var out []namedconf.AMElement
	for _, s := range list {
		e, err := namedconf.ParseAMElement(s)
		if err != nil {
			continue
		}
		if e.Kind == namedconf.AMName && !e.IsBuiltin() && depth < 10 {
			if a := c.s.ACLByName(e.Name); a != nil {
				inner := c.flatten(a.Elements, depth+1)
				if e.Negated {
					// A negated ACL reference: treat as a single
					// negated element (restrictive).
					out = append(out, namedconf.AMElement{Negated: true, Kind: namedconf.AMOther, Raw: "!" + e.Name})
					continue
				}
				out = append(out, inner...)
				continue
			}
		}
		out = append(out, e)
	}
	return out
}

// optionScope maps an option to its catalog scope.
func (c *checker) optionScope(o *model.Option) (string, string, bool) {
	switch o.Scope {
	case model.ScopeOptions:
		return catalog.ScopeOptions, "server options", true
	case model.ScopeTopLevel:
		return catalog.ScopeTop, "top-level statements", true
	case model.ScopeView:
		v := c.s.Views[o.ScopeID]
		if v == nil {
			return "", "", false
		}
		return catalog.ScopeView, "view " + v.Name, true
	case model.ScopeZone:
		z := c.s.Zones[o.ScopeID]
		if z == nil {
			return "", "", false
		}
		return catalog.ZoneScope(z.Type), "zone " + c.zoneLabel(z), true
	}
	return "", "", false
}

func (c *checker) checkOptions() {
	cat := catalog.Default()
	type key struct {
		scope string
		id    int64
		name  string
	}
	counts := map[key]int{}
	var opts []*model.Option
	for _, o := range c.s.Options {
		opts = append(opts, o)
	}
	sortOptions(opts)
	for _, o := range opts {
		scope, where, ok := c.optionScope(o)
		if !ok {
			c.errf("option_scope_invalid", "option", o.ID, "option %s belongs to a %s that does not exist", o.Name, o.Scope)
			continue
		}
		name := strings.ToLower(o.Name)
		st, known := cat.Lookup(scope, name)
		if !known {
			if o.Scope == model.ScopeZone {
				z := c.s.Zones[o.ScopeID]
				c.errf("option_unknown", "option", o.ID, "%s: %q is not a valid option for %s zones", where, o.Name, z.Type)
			} else {
				c.errf("option_unknown", "option", o.ID, "%s: unknown option %q", where, o.Name)
			}
			continue
		}
		if st.Managed {
			c.errf("option_managed", "option", o.ID, "%s: %q can't be set as an option; it is managed through %s", where, o.Name, st.ManagedBy)
			continue
		}
		switch st.Status {
		case "deprecated":
			c.warnf("option_deprecated", "option", o.ID, "%s: %q is deprecated in BIND 9.20", where, o.Name)
		case "obsolete":
			c.warnf("option_obsolete", "option", o.ID, "%s: %q is obsolete and has no effect (or is rejected) in BIND 9.20", where, o.Name)
		case "experimental":
			c.infof("option_experimental", "option", o.ID, "%s: %q is experimental", where, o.Name)
		case "test only", "not configured":
			c.warnf("option_unavailable", "option", o.ID, "%s: %q is %s in this BIND build", where, o.Name, st.Status)
		}
		k := key{o.Scope, o.ScopeID, st.Name}
		counts[k]++
		if counts[k] == 2 && !st.Multiple {
			c.errf("option_duplicate", "option", o.ID, "%s: %q may only be set once", where, o.Name)
		}
		stmt, err := namedconf.ParseOptionValue(o.Name, o.Value)
		if err != nil {
			if strings.TrimSpace(o.Value) == "" && (name == "null" || name == "stderr") {
				continue
			}
			c.errf("option_syntax", "option", o.ID, "%s: %s: %v", where, o.Name, err)
			continue
		}
		if err := checkKind(st, stmt); err != nil {
			c.errf("option_value_invalid", "option", o.ID, "%s: %s: %v (expected: %s)", where, o.Name, err, st.Grammar)
			continue
		}
		label := where + " " + o.Name
		if strings.Contains(st.Grammar, "<address_match_element>") && !strings.Contains(st.Grammar, "\n") {
			if b := stmt.FirstBlock(); b != nil {
				elems, err := namedconf.ParseAMList(b)
				if err != nil {
					c.errf("option_value_invalid", "option", o.ID, "%s: %v", label, err)
				} else {
					c.checkRefs(elems, label, "option", o.ID)
					for _, w := range namedconf.Shadowed(elems) {
						c.warnf("acl_shadowed", "option", o.ID, "%s: %s", label, w)
					}
				}
			}
		}
		for _, kn := range keyRefs(stmt) {
			if !c.keyNames[model.NormalizeKeyName(kn)] && !c.opts.ExternalKeysUnknown {
				c.errf("key_ref_missing", "option", o.ID, "%s refers to TSIG key %q, which does not exist", label, kn)
			}
		}
	}
}

func sortOptions(opts []*model.Option) {
	for i := 1; i < len(opts); i++ {
		for j := i; j > 0 && optLess(opts[j], opts[j-1]); j-- {
			opts[j], opts[j-1] = opts[j-1], opts[j]
		}
	}
}

func optLess(a, b *model.Option) bool {
	if a.Scope != b.Scope {
		return a.Scope < b.Scope
	}
	if a.ScopeID != b.ScopeID {
		return a.ScopeID < b.ScopeID
	}
	if a.Position != b.Position {
		return a.Position < b.Position
	}
	return a.ID < b.ID
}

var (
	reDuration = regexp.MustCompile(`(?i)^(\d+|(\d+[wdhms])+|P(\d+[YMWD])*(T(\d+[HMS])+)?)$`)
	reInteger  = regexp.MustCompile(`^\d+$`)
)

// checkKind does quick checks on simple option values. Anything it does
// not understand is left to named-checkconf.
func checkKind(st *catalog.Statement, stmt *namedconf.Stmt) error {
	args := stmt.Items[1:]
	single := func() (*namedconf.Value, error) {
		if len(args) != 1 || args[0].Value == nil {
			return nil, fmt.Errorf("expected a single value")
		}
		return args[0].Value, nil
	}
	switch st.Kind {
	case catalog.KindBool:
		v, err := single()
		if err != nil {
			return err
		}
		switch strings.ToLower(v.Text) {
		case "yes", "no", "true", "false", "1", "0":
			return nil
		}
		return fmt.Errorf("%q is not a boolean (use yes or no)", v.Text)
	case catalog.KindInt:
		v, err := single()
		if err != nil {
			return err
		}
		if !reInteger.MatchString(v.Text) {
			return fmt.Errorf("%q is not a number", v.Text)
		}
	case catalog.KindDuration:
		v, err := single()
		if err != nil {
			return err
		}
		if !reDuration.MatchString(v.Text) {
			return fmt.Errorf("%q is not a duration (e.g. 3600, 1h30m or PT1H)", v.Text)
		}
	case catalog.KindString, catalog.KindWord:
		if _, err := single(); err != nil {
			return err
		}
	case catalog.KindEnum:
		v, err := single()
		if err != nil {
			return err
		}
		for _, ch := range st.Choices {
			if strings.EqualFold(ch, v.Text) {
				return nil
			}
		}
		if lv := strings.ToLower(v.Text); contains(st.Choices, "yes") && (lv == "true" || lv == "false" || lv == "1" || lv == "0") {
			return nil
		}
		return fmt.Errorf("%q is not one of %s", v.Text, strings.Join(st.Choices, ", "))
	case catalog.KindACL:
		if len(args) != 1 || args[0].Block == nil {
			return fmt.Errorf("expected an address match list in braces, e.g. { 192.168.0.0/16; localhost; }")
		}
	}
	return nil
}

func contains(list []string, s string) bool {
	for _, x := range list {
		if x == s {
			return true
		}
	}
	return false
}

// keyRefs finds TSIG key references in a statement: "key NAME" and
// "keys { NAME; ... }" / "keys NAME" anywhere in it.
func keyRefs(st *namedconf.Stmt) []string {
	var out []string
	var walk func(items []namedconf.Item)
	walk = func(items []namedconf.Item) {
		for i, it := range items {
			if it.Value != nil && !it.Value.Quoted && i+1 < len(items) {
				switch strings.ToLower(it.Value.Text) {
				case "key":
					if n := items[i+1].Value; n != nil {
						out = append(out, n.Text)
					}
				case "keys":
					if n := items[i+1].Value; n != nil {
						out = append(out, n.Text)
					} else if b := items[i+1].Block; b != nil {
						for _, s := range b.Stmts {
							if len(s.Items) > 0 && s.Items[0].Value != nil {
								out = append(out, s.Items[0].Value.Text)
							}
						}
					}
				}
			}
			if it.Block != nil {
				for _, s := range it.Block.Stmts {
					walk(s.Items)
				}
			}
		}
	}
	if st.Keyword() == "key" { // a key definition, not a reference
		return nil
	}
	walk(st.Items)
	return out
}

// effectiveAML finds the first of names set in the view (if any) or in the
// global options, returning its elements (with ACL references expanded).
func (c *checker) effectiveAML(v *model.View, names ...string) ([]namedconf.AMElement, string, bool) {
	for _, n := range names {
		if v != nil {
			if o := c.s.FindOption(model.ScopeView, v.ID, n); o != nil {
				return c.amlOf(o), n, true
			}
		}
		if o := c.s.FindOption(model.ScopeOptions, 0, n); o != nil {
			return c.amlOf(o), n, true
		}
	}
	return nil, "", false
}

func (c *checker) amlOf(o *model.Option) []namedconf.AMElement {
	st, err := namedconf.ParseOptionValue(o.Name, o.Value)
	if err != nil || st.FirstBlock() == nil {
		return nil
	}
	var list []string
	for _, s := range st.FirstBlock().Stmts {
		list = append(list, namedconf.Compact(s.Items))
	}
	return c.flatten(list, 0)
}

func (c *checker) effectiveBool(v *model.View, name string, def bool) bool {
	var o *model.Option
	if v != nil {
		o = c.s.FindOption(model.ScopeView, v.ID, name)
	}
	if o == nil {
		o = c.s.FindOption(model.ScopeOptions, 0, name)
	}
	if o == nil {
		return def
	}
	switch strings.ToLower(strings.TrimSpace(o.Value)) {
	case "yes", "true", "1":
		return true
	case "no", "false", "0":
		return false
	}
	return def
}

// checkSecurity looks for configurations that are dangerous on an
// internet-facing server.
func (c *checker) checkSecurity() {
	views := c.s.OrderedViews()
	type ctx struct {
		v     *model.View
		label string
	}
	var ctxs []ctx
	if len(views) == 0 {
		ctxs = append(ctxs, ctx{nil, "the server"})
	}
	for _, v := range views {
		ctxs = append(ctxs, ctx{v, "view " + v.Name})
	}
	for _, x := range ctxs {
		// A view only reachable from some clients (e.g. "internal") can
		// recurse for everyone inside it without being an open resolver.
		if x.v != nil && !c.listMatchesEveryone(x.v.MatchClients, true) {
			continue
		}
		if c.effectiveBool(x.v, "recursion", true) {
			aml, from, set := c.effectiveAML(x.v, "allow-recursion", "allow-query-cache", "allow-query")
			if set && namedconf.ContainsAny(aml) {
				p := c.warnf("security_open_resolver", "view", viewID(x.v),
					"%s offers recursion to any client (via %s), making it an open resolver that can be abused for DDoS amplification; set allow-recursion to your own networks", x.label, from)
				if x.v != nil {
					p.View = x.v.Name
				}
			}
		}
		if aml, _, set := c.effectiveAML(x.v, "allow-transfer"); set && namedconf.ContainsAny(aml) {
			p := c.warnf("security_open_transfer", "view", viewID(x.v), "%s allows zone transfers (AXFR) to anyone; restrict allow-transfer to your secondaries or a TSIG key", x.label)
			if x.v != nil {
				p.View = x.v.Name
			}
		}
	}
	// Dynamic updates would be lost when Jarl rewrites zone files.
	for _, z := range c.s.SortedZones() {
		if z.Type != model.ZonePrimary {
			continue
		}
		v := c.s.Views[z.ViewID]
		if o := c.s.FindOption(model.ScopeZone, z.ID, "update-policy"); o != nil {
			p := c.errf("dynamic_update_unsupported", "zone", z.ID, "update-policy makes the zone dynamic, but Jarl rewrites zone files and would discard dynamic updates; manage records through Jarl instead")
			p.Zone, p.View = z.Name, c.s.ViewName(z)
			continue
		}
		var aml []namedconf.AMElement
		set := false
		if o := c.s.FindOption(model.ScopeZone, z.ID, "allow-update"); o != nil {
			aml, set = c.amlOf(o), true
		} else {
			aml, _, set = c.effectiveAML(v, "allow-update")
		}
		if set && !onlyNone(aml) {
			p := c.errf("dynamic_update_unsupported", "zone", z.ID, "allow-update makes the zone dynamic, but Jarl rewrites zone files and would discard dynamic updates; remove allow-update (or set it to { none; }) and manage records through Jarl")
			p.Zone, p.View = z.Name, c.s.ViewName(z)
		}
		if o := c.s.FindOption(model.ScopeZone, z.ID, "allow-transfer"); o != nil && namedconf.ContainsAny(c.amlOf(o)) {
			p := c.warnf("security_open_transfer", "zone", z.ID, "allows zone transfers (AXFR) to anyone; restrict allow-transfer to your secondaries or a TSIG key")
			p.Zone, p.View = z.Name, c.s.ViewName(z)
		}
	}
}

func onlyNone(elems []namedconf.AMElement) bool {
	for _, e := range elems {
		if !(e.Kind == namedconf.AMName && e.Name == "none" && !e.Negated) {
			return false
		}
	}
	return true
}

func viewID(v *model.View) int64 {
	if v == nil {
		return 0
	}
	return v.ID
}