package kubesource

import (
	"fmt"
	"net"
	"net/netip"
	"strings"
	"time"

	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	"k8s.io/apimachinery/pkg/runtime"

	"git.k8s-git-k6n.net/mats/fancy-dns/internal/config"
	"git.k8s-git-k6n.net/mats/fancy-dns/internal/localzone"
)

// maxZoneRecords bounds one DNSZone. An object is capped near 1.5 MiB by etcd
// anyway; this keeps a hostile or runaway one from costing a render.
const maxZoneRecords = 5000

// group is a converted ClientGroup with its ordering key.
type group struct {
	cfg      config.Group
	priority int32
}

// zone is a converted DNSZone: the apex and the rendered master file.
type zone struct {
	apex string
	text string
}

func spec(u *unstructured.Unstructured, into any) error {
	raw, ok := u.Object["spec"].(map[string]any)
	if !ok {
		return fmt.Errorf("the object has no spec")
	}
	return runtime.DefaultUnstructuredConverter.FromUnstructured(raw, into)
}

func convertGroup(u *unstructured.Unstructured) (group, error) {
	var s ClientGroupSpec
	if err := spec(u, &s); err != nil {
		return group{}, err
	}
	return groupFromSpec(u.GetName(), s)
}

// CheckGroup validates a ClientGroup spec the way the runtime will, so an
// editor can refuse a bad one before it is written.
func CheckGroup(name string, s ClientGroupSpec) (config.Group, error) {
	g, err := groupFromSpec(name, s)
	return g.cfg, err
}

func groupFromSpec(name string, s ClientGroupSpec) (group, error) {
	g := config.Group{
		Name:          name,
		Comment:       s.Comment,
		Match:         s.Match,
		Policy:        s.Policy,
		AllowDomains:  s.AllowDomains,
		DenyDomains:   s.DenyDomains,
		SkipBlocklist: s.SkipBlocklist,
		SkipCache:     s.SkipCache,
		RateLimit:     s.RateLimit,
		MaxConcurrent: s.MaxConcurrent,
		LogQueries:    s.LogQueries,
		Upstreams:     s.Upstreams,
	}
	switch g.Policy {
	case "allow", "deny", "block_only":
	default:
		return group{}, fmt.Errorf("policy must be allow, deny or block_only (got %q)", g.Policy)
	}
	for _, cidr := range g.Match.CIDRs {
		if _, _, err := net.ParseCIDR(cidr); err != nil {
			return group{}, fmt.Errorf("bad CIDR %q", cidr)
		}
	}
	// Copy before normalising: the slice belongs to the decoded object.
	g.Match.PTRSuffixes = append([]string(nil), g.Match.PTRSuffixes...)
	for i, s := range g.Match.PTRSuffixes {
		if !strings.HasSuffix(s, ".") {
			g.Match.PTRSuffixes[i] = s + "."
		}
	}
	if !g.Match.Any && len(g.Match.CIDRs) == 0 && len(g.Match.PTRSuffixes) == 0 && len(g.Match.Tags) == 0 {
		return group{}, fmt.Errorf("match selects no clients: set cidrs, ptr_suffixes, tags or any")
	}
	if g.Match.Any && len(g.Match.CIDRs) == 0 && len(g.Match.PTRSuffixes) == 0 && len(g.Match.Tags) == 0 {
		// config.Validate refuses this shape for every group. Refusing it here
		// rejects one object instead of the whole merged configuration.
		return group{}, fmt.Errorf("match.any alone is not accepted; use a catch-all in the YAML acl.groups")
	}
	if g.RateLimit < 0 || g.MaxConcurrent < 0 {
		return group{}, fmt.Errorf("rate_limit and max_concurrent must not be negative")
	}
	return group{cfg: g, priority: s.Priority}, nil
}

func convertList(u *unstructured.Unstructured) (config.ListSource, error) {
	var s BlockListSpec
	if err := spec(u, &s); err != nil {
		return config.ListSource{}, err
	}
	return listFromSpec(u.GetName(), s)
}

// CheckList validates a BlockList spec the way the runtime will.
func CheckList(name string, s BlockListSpec) (config.ListSource, error) {
	return listFromSpec(name, s)
}

func listFromSpec(name string, s BlockListSpec) (config.ListSource, error) {
	l := config.ListSource{
		Name:                  name,
		Format:                s.Format,
		URL:                   s.URL,
		Mirror:                s.Mirror,
		Enabled:               !s.Disabled,
		MaxBytes:              s.MaxBytes,
		Categories:            s.Categories,
		Comment:               s.Comment,
		InsecureSkipTLSVerify: s.InsecureSkipTLSVerify,
	}
	if !isHTTP(l.URL) {
		return config.ListSource{}, fmt.Errorf("url must be http(s) (got %q)", l.URL)
	}
	for _, m := range l.Mirror {
		if !isHTTP(m) {
			return config.ListSource{}, fmt.Errorf("mirror must be http(s) (got %q)", m)
		}
	}
	switch l.Format {
	case "", "auto", "hosts", "adblock", "plain", "rpz":
	default:
		return config.ListSource{}, fmt.Errorf("unknown format %q", l.Format)
	}
	var err error
	if l.Refresh, err = duration(s.Refresh); err != nil {
		return config.ListSource{}, fmt.Errorf("refresh: %w", err)
	}
	if l.Timeout, err = duration(s.Timeout); err != nil {
		return config.ListSource{}, fmt.Errorf("timeout: %w", err)
	}
	if l.MaxBytes < 0 {
		return config.ListSource{}, fmt.Errorf("max_bytes must not be negative")
	}
	return l, nil
}

func isHTTP(u string) bool {
	return strings.HasPrefix(u, "https://") || strings.HasPrefix(u, "http://")
}

func duration(s string) (config.Duration, error) {
	if s == "" {
		return 0, nil
	}
	d, err := time.ParseDuration(s)
	if err != nil {
		return 0, err
	}
	if d < 0 {
		return 0, fmt.Errorf("must not be negative")
	}
	return config.Duration(d), nil
}

func convertZone(u *unstructured.Unstructured) (zone, error) {
	var s DNSZoneSpec
	if err := spec(u, &s); err != nil {
		return zone{}, err
	}
	return zoneFromSpec(s, u.GetGeneration())
}

// CheckZone validates a DNSZone spec by rendering it exactly as the runtime
// will, and returns the master file.
func CheckZone(s DNSZoneSpec) (string, error) {
	z, err := zoneFromSpec(s, 1)
	return z.text, err
}

func zoneFromSpec(s DNSZoneSpec, generation int64) (zone, error) {
	if s.Zone == "" {
		return zone{}, fmt.Errorf("spec.zone is required")
	}
	if len(s.Records) > maxZoneRecords {
		return zone{}, fmt.Errorf("%d records exceeds the limit of %d", len(s.Records), maxZoneRecords)
	}
	apex, err := localzone.NormalizeOrigin(s.Zone)
	if err != nil {
		return zone{}, fmt.Errorf("spec.zone: %w", err)
	}
	var ns []string
	recs := make([]localzone.Record, 0, len(s.Records))
	for _, r := range s.Records {
		name := r.Name
		if name == "@" {
			name = apex
		}
		recs = append(recs, localzone.Record{Name: name, Type: r.Type, TTL: r.TTL, Value: r.Value})
		if strings.EqualFold(r.Type, "NS") && name == apex {
			ns = append(ns, r.Value)
		}
	}
	if s.SOA == "" && len(ns) == 0 {
		return zone{}, fmt.Errorf("a zone needs an apex NS record (name \"@\") or an explicit soa")
	}
	// The generation changes exactly when the spec does, so every replica
	// renders the same bytes for the same object version.
	serial := uint32(generation)
	if serial == 0 {
		serial = 1
	}
	text, err := localzone.RenderZone(apex, localzone.ZoneDefaults{TTL: s.TTL, Soa: s.SOA}, recs, serial)
	if err != nil {
		return zone{}, err
	}
	return zone{apex: apex, text: text}, nil
}

// Override is a converted AddressOverride.
type Override struct {
	Domain    string   `json:"domain"`
	Addresses []string `json:"addresses"`
}

// Rules is a converted DomainRule.
type Rules struct {
	Action string   `json:"action"`
	Names  []string `json:"names"`
}

func convertOverride(u *unstructured.Unstructured) (Override, error) {
	var s AddressOverrideSpec
	if err := spec(u, &s); err != nil {
		return Override{}, err
	}
	return CheckOverride(s)
}

// CheckOverride validates an AddressOverride spec and returns it in canonical
// form (lower-case name without the trailing dot, addresses as printed by
// netip).
func CheckOverride(s AddressOverrideSpec) (Override, error) {
	domain := strings.TrimSuffix(strings.ToLower(strings.TrimSpace(s.Domain)), ".")
	if err := checkRuleName(domain, false); err != nil {
		return Override{}, fmt.Errorf("domain: %w", err)
	}
	if len(s.Addresses) == 0 {
		return Override{}, fmt.Errorf("at least one address is required")
	}
	out := Override{Domain: domain}
	seen := map[string]bool{}
	for _, raw := range s.Addresses {
		ip, err := netip.ParseAddr(strings.TrimSpace(raw))
		if err != nil {
			return Override{}, fmt.Errorf("%q is not an IPv4 or IPv6 address", raw)
		}
		ip = ip.Unmap()
		if !seen[ip.String()] {
			seen[ip.String()] = true
			out.Addresses = append(out.Addresses, ip.String())
		}
	}
	return out, nil
}

func convertRules(u *unstructured.Unstructured) (Rules, error) {
	var s DomainRuleSpec
	if err := spec(u, &s); err != nil {
		return Rules{}, err
	}
	return CheckRules(s)
}

// CheckRules validates a DomainRule spec.
func CheckRules(s DomainRuleSpec) (Rules, error) {
	if s.Action != "block" && s.Action != "allow" {
		return Rules{}, fmt.Errorf("action must be block or allow (got %q)", s.Action)
	}
	if len(s.Names) > maxRuleNames {
		return Rules{}, fmt.Errorf("%d names exceeds the limit of %d; use a BlockList for large sets", len(s.Names), maxRuleNames)
	}
	out := Rules{Action: s.Action}
	for _, n := range s.Names {
		n = strings.ToLower(strings.TrimSpace(n))
		if err := checkRuleName(n, true); err != nil {
			return Rules{}, fmt.Errorf("name %q: %w", n, err)
		}
		out.Names = append(out.Names, n)
	}
	return out, nil
}

// maxRuleNames bounds one DomainRule; an object is capped near 1.5 MiB by etcd
// anyway, and a bigger set belongs in a BlockList that is fetched.
const maxRuleNames = 5000

// checkRuleName accepts only what a DNS name or a wildcard pattern can contain.
// This is a security check, not tidiness: names are joined into the blocklist
// parser's line-oriented input, so a newline or a comment character in a name
// could smuggle in a rule of its own.
func checkRuleName(n string, wildcard bool) error {
	if n == "" {
		return fmt.Errorf("a name is required")
	}
	if wildcard {
		n = strings.TrimPrefix(strings.TrimPrefix(n, "**."), "*.")
	}
	n = strings.TrimSuffix(n, ".")
	if n == "" || len(n) > 253 {
		return fmt.Errorf("not a valid DNS name")
	}
	for _, label := range strings.Split(n, ".") {
		if label == "" || len(label) > 63 {
			return fmt.Errorf("not a valid DNS name")
		}
		for _, c := range label {
			ok := c >= 'a' && c <= 'z' || c >= '0' && c <= '9' || c == '-' || c == '_'
			if !ok {
				return fmt.Errorf("not a valid DNS name (only letters, digits, '-' and '_' are allowed)")
			}
		}
	}
	return nil
}

// RenderRPZ renders the overrides as the RPZ text the blocklist manager reads:
// one "name A address" line per address, applying to the name and everything
// under it.
func RenderRPZ(in []Override) string {
	var b strings.Builder
	b.WriteString("$TTL 60\n")
	for _, o := range in {
		for _, a := range o.Addresses {
			typ := "A"
			if strings.Contains(a, ":") {
				typ = "AAAA"
			}
			fmt.Fprintf(&b, "%s %s %s\n", o.Domain, typ, a)
		}
	}
	return b.String()
}