package auth

import (
	"fmt"
	"regexp"
	"sort"
	"strings"
	"sync"

	"jarl/internal/model"
)

// Resources that grants apply to.
const (
	ResZones    = "zones"   // zone definitions and zone options
	ResRecords  = "records" // records in zones
	ResViews    = "views"   // views and view options
	ResACLs     = "acls"
	ResTSIG     = "tsig"     // TSIG keys
	ResOptions  = "options"  // server options, top-level statements, settings
	ResAudit    = "audit"    // audit log and everyone's changesets
	ResStats    = "stats"    // query statistics
	ResBlocking = "blocking" // blocklists and block/allow rules
	// ResCerts is certificates for other hosts (jarl cert get), by the
	// names in them. It is never part of "*": it hands out private keys.
	ResCerts = "certificates"
	ResAll   = "*"
)

// Resources lists the resources in display order.
var Resources = []string{ResZones, ResRecords, ResViews, ResACLs, ResTSIG, ResOptions, ResAudit, ResStats, ResBlocking, ResCerts}

// Access levels.
const (
	Read  = "read"
	Write = "write"
)

// DefaultViewName is used for matching view filters against zones that
// are not in a view.
const DefaultViewName = "_default"

// ValidateGrant checks a grant and normalizes it.
func ValidateGrant(g *model.Grant) error {
	g.Resource = strings.ToLower(strings.TrimSpace(g.Resource))
	g.Access = strings.ToLower(strings.TrimSpace(g.Access))
	ok := g.Resource == ResAll
	for _, r := range Resources {
		ok = ok || g.Resource == r
	}
	if !ok {
		return fmt.Errorf("unknown resource %q (use one of %s or *)", g.Resource, strings.Join(Resources, ", "))
	}
	if g.Access != Read && g.Access != Write {
		return fmt.Errorf("access must be read or write, not %q", g.Access)
	}
	norm := func(list []string, lower bool, trimDot bool) []string {
		var out []string
		for _, s := range list {
			s = strings.TrimSpace(s)
			if lower {
				s = strings.ToLower(s)
			}
			if trimDot && s != "." {
				s = strings.TrimSuffix(s, ".")
			}
			if s != "" {
				out = append(out, s)
			}
		}
		return out
	}
	g.Zones = norm(g.Zones, true, true)
	g.Views = norm(g.Views, false, false)
	g.Names = norm(g.Names, true, true)
	g.Types = norm(g.Types, false, false)
	for i, t := range g.Types {
		g.Types[i] = strings.ToUpper(t)
	}
	if len(g.Types) > 0 && g.Resource != ResRecords {
		return fmt.Errorf("the types filter only applies to the records resource")
	}
	if len(g.Names) > 0 && g.Resource != ResRecords && g.Resource != ResCerts {
		return fmt.Errorf("the names filter only applies to the records and certificates resources")
	}
	if (len(g.Zones) > 0 || len(g.Views) > 0) && g.Resource != ResRecords && g.Resource != ResZones && g.Resource != ResViews {
		return fmt.Errorf("zone and view filters only apply to the zones, records and views resources")
	}
	for _, p := range append(append(append([]string{}, g.Zones...), g.Names...), g.Views...) {
		if strings.ContainsAny(p, " \t\n") {
			return fmt.Errorf("invalid pattern %q", p)
		}
	}
	return nil
}

// ParseGrant parses the compact grant syntax used by the CLI and docs:
//
//	resource:access [zones=a,b] [views=x] [names=pattern] [types=TXT,CNAME]
//
// For example "records:write zones=example.com names=_acme-challenge.* types=TXT".
func ParseGrant(s string) (model.Grant, error) {
	var g model.Grant
	fields := strings.Fields(s)
	if len(fields) == 0 {
		return g, fmt.Errorf("empty grant")
	}
	res, acc, ok := strings.Cut(fields[0], ":")
	if !ok {
		return g, fmt.Errorf("grant %q must start with resource:access, e.g. records:write", s)
	}
	g.Resource, g.Access = res, acc
	for _, f := range fields[1:] {
		k, v, ok := strings.Cut(f, "=")
		if !ok || v == "" {
			return g, fmt.Errorf("invalid filter %q (use key=value)", f)
		}
		vals := strings.Split(v, ",")
		switch strings.ToLower(k) {
		case "zone", "zones":
			g.Zones = append(g.Zones, vals...)
		case "view", "views":
			g.Views = append(g.Views, vals...)
		case "name", "names":
			g.Names = append(g.Names, vals...)
		case "type", "types":
			g.Types = append(g.Types, vals...)
		default:
			return g, fmt.Errorf("unknown filter %q (use zones, views, names or types)", k)
		}
	}
	return g, ValidateGrant(&g)
}

// FormatGrant returns the compact form of a grant.
func FormatGrant(g model.Grant) string {
	parts := []string{g.Resource + ":" + g.Access}
	add := func(k string, vals []string) {
		if len(vals) > 0 {
			parts = append(parts, k+"="+strings.Join(vals, ","))
		}
	}
	add("zones", g.Zones)
	add("views", g.Views)
	add("names", g.Names)
	add("types", g.Types)
	return strings.Join(parts, " ")
}

// Action is something a principal wants to do.
type Action struct {
	Resource string
	Write    bool
	Zone     string // zone FQDN (zones, records)
	View     string // view name ("" for zones without a view)
	Name     string // record owner FQDN (records)
	Type     string // record type (records)
}

func (a Action) String() string {
	acc := Read
	if a.Write {
		acc = Write
	}
	s := a.Resource + ":" + acc
	if a.Zone != "" {
		s += " zone " + strings.TrimSuffix(a.Zone, ".")
	}
	if a.View != "" {
		s += " view " + a.View
	}
	if a.Name != "" {
		s += " name " + strings.TrimSuffix(a.Name, ".")
	}
	if a.Type != "" {
		s += " type " + a.Type
	}
	return s
}

var globCache sync.Map // pattern -> *regexp.Regexp

func globMatch(pattern, s string) bool {
	if pattern == "*" {
		return true
	}
	if !strings.ContainsAny(pattern, "*?") {
		return pattern == s
	}
	v, ok := globCache.Load(pattern)
	if !ok {
		var sb strings.Builder
		sb.WriteString("^")
		for _, c := range pattern {
			switch c {
			case '*':
				sb.WriteString(".*")
			case '?':
				sb.WriteString(".")
			default:
				sb.WriteString(regexp.QuoteMeta(string(c)))
			}
		}
		sb.WriteString("$")
		v, _ = globCache.LoadOrStore(pattern, regexp.MustCompile(sb.String()))
	}
	return v.(*regexp.Regexp).MatchString(s)
}

func matchAny(patterns []string, s string, fold bool) bool {
	if len(patterns) == 0 {
		return true
	}
	if fold {
		s = strings.ToLower(s)
	}
	for _, p := range patterns {
		if globMatch(p, s) {
			return true
		}
	}
	return false
}

func trimName(n string) string {
	if n == "." {
		return n
	}
	return strings.TrimSuffix(strings.ToLower(n), ".")
}

// GrantAllows reports whether g allows action a.
func GrantAllows(g model.Grant, a Action) bool {
	if g.Resource != ResAll && g.Resource != a.Resource {
		return false
	}
	if g.Resource == ResAll && a.Resource == ResCerts {
		return false // only an explicit certificates grant
	}
	if a.Write && g.Access != Write {
		return false
	}
	if a.Zone != "" && !matchAny(g.Zones, trimName(a.Zone), true) {
		return false
	}
	view := a.View
	if view == "" {
		view = DefaultViewName
	}
	if (a.Zone != "" || a.Resource == ResViews) && !matchAny(g.Views, view, false) {
		return false
	}
	if a.Name != "" && !matchAny(g.Names, trimName(a.Name), true) {
		return false
	}
	if a.Type != "" && len(g.Types) > 0 {
		found := false
		for _, t := range g.Types {
			if strings.EqualFold(t, a.Type) {
				found = true
				break
			}
		}
		if !found {
			return false
		}
	}
	return true
}

// GrantsAllow reports whether any grant allows a.
func GrantsAllow(gs []model.Grant, a Action) bool {
	for _, g := range gs {
		if GrantAllows(g, a) {
			return true
		}
	}
	return false
}

// Principal is an authenticated identity.
type Principal struct {
	User   *model.User
	Token  *model.Token // nil for sessions and local CLI use
	Method string       // session, token, local
	IP     string
	Agent  string
}

// System is the principal used for internal operations.
var System = &Principal{User: &model.User{ID: 0, Username: "system", Admin: true}, Method: "local"}

// Name returns a display name for the principal.
func (p *Principal) Name() string {
	if p == nil || p.User == nil {
		return ""
	}
	return p.User.Username
}

// IsAdmin reports whether the principal has admin rights. Admin rights
// are never available through a restricted token.
func (p *Principal) IsAdmin() bool {
	if p == nil || p.User == nil || !p.User.Admin {
		return false
	}
	return p.Token == nil || p.Token.Grants == nil
}

// Can reports whether the principal may perform a.
func (p *Principal) Can(a Action) bool {
	if p == nil || p.User == nil || p.User.Disabled {
		return false
	}
	userOK := p.User.Admin || GrantsAllow(p.User.Grants, a)
	if !userOK {
		return false
	}
	if p.Token != nil && p.Token.Grants != nil {
		return GrantsAllow(p.Token.Grants, a)
	}
	return true
}

// CanSeeZone reports whether the principal may see that a zone exists:
// any read access to the zone definition or to some of its records.
func (p *Principal) CanSeeZone(zone, view string) bool {
	if p.Can(Action{Resource: ResZones, Zone: zone, View: view}) {
		return true
	}
	// Records access with name/type filters still reveals the zone.
	check := func(gs []model.Grant) bool {
		for _, g := range gs {
			if g.Resource != ResAll && g.Resource != ResRecords && g.Resource != ResZones {
				continue
			}
			ng := g
			ng.Names, ng.Types = nil, nil
			if GrantAllows(ng, Action{Resource: g.Resource, Zone: zone, View: view}) {
				return true
			}
		}
		return false
	}
	if p.User == nil || p.User.Disabled {
		return false
	}
	if !p.User.Admin && !check(p.User.Grants) {
		return false
	}
	if p.Token != nil && p.Token.Grants != nil {
		return check(p.Token.Grants)
	}
	return true
}

// Summary describes effective permissions for display.
func (p *Principal) Summary() []string {
	if p.IsAdmin() {
		return []string{"admin (everything)"}
	}
	var out []string
	gs := p.User.Grants
	if p.User.Admin {
		gs = []model.Grant{{Resource: ResAll, Access: Write}}
	}
	for _, g := range gs {
		out = append(out, FormatGrant(g))
	}
	if p.Token != nil && p.Token.Grants != nil {
		var tg []string
		for _, g := range p.Token.Grants {
			tg = append(tg, FormatGrant(g))
		}
		out = append(out, "restricted by token to: "+strings.Join(tg, "; "))
	}
	sort.Strings(out)
	return out
}

// RoleTemplates are ready-made grant sets offered in the UI and CLI.
var RoleTemplates = map[string][]model.Grant{
	"readonly": {{Resource: ResAll, Access: Read}},
	"dns-editor": {
		{Resource: ResZones, Access: Write},
		{Resource: ResRecords, Access: Write},
		{Resource: ResViews, Access: Read},
		{Resource: ResACLs, Access: Read},
		{Resource: ResOptions, Access: Read},
		{Resource: ResBlocking, Access: Read},
	},
	"operator": {{Resource: ResAll, Access: Write}},
	"acme":     {{Resource: ResRecords, Access: Write, Names: []string{"_acme-challenge.*"}, Types: []string{"TXT"}}},
	// certificates for other hosts (jarl cert get): narrow it with names=
	// to the host's own.
	"certificates": {{Resource: ResCerts, Access: Write}},
}