// Package tokeycloak transforms a canonical KeyCape export into a Keycloak realm
// import JSON file (spec §7 — migration contract, Keycloak expansion path).
package tokeycloak

import (
	"context"
	"fmt"
	"sort"
	"strings"
	"time"

	"keycape/internal/domain"
	"keycape/internal/migration/lldapexport"
	"keycape/internal/server/telemetry"
)

// ---------------------------------------------------------------------------
// Keycloak realm import types
// ---------------------------------------------------------------------------

// KeycloakRealm is the top-level realm import JSON structure.
type KeycloakRealm struct {
	Realm                     string                `json:"realm"`
	DisplayName               string                `json:"displayName,omitempty"`
	Enabled                   bool                  `json:"enabled"`
	SsoSessionMaxLifespan     int                   `json:"ssoSessionMaxLifespan,omitempty"`
	DefaultSignatureAlgorithm string                `json:"defaultSignatureAlgorithm,omitempty"`
	IdentityProviders         []interface{}         `json:"identityProviders"`
	Clients                   []KeycloakClient      `json:"clients"`
	Users                     []KeycloakUser        `json:"users"`
	Groups                    []KeycloakGroup       `json:"groups"`
	Roles                     KeycloakRoles         `json:"roles"`
	ClientScopes              []KeycloakClientScope `json:"clientScopes"`
}

// KeycloakClient represents a registered client in the Keycloak realm.
type KeycloakClient struct {
	ClientID                  string                   `json:"clientId"`
	Name                      string                   `json:"name,omitempty"`
	Enabled                   bool                     `json:"enabled"`
	PublicClient              bool                     `json:"publicClient"`
	StandardFlowEnabled       bool                     `json:"standardFlowEnabled"`
	ImplicitFlowEnabled       bool                     `json:"implicitFlowEnabled"`
	DirectAccessGrantsEnabled bool                     `json:"directAccessGrantsEnabled"`
	ServiceAccountsEnabled    bool                     `json:"serviceAccountsEnabled"`
	RedirectUris              []string                 `json:"redirectUris"`
	DefaultClientScopes       []string                 `json:"defaultClientScopes"`
	Attributes                map[string]string        `json:"attributes,omitempty"`
	ProtocolMappers           []KeycloakProtocolMapper `json:"protocolMappers,omitempty"`
}

// KeycloakProtocolMapper carries a claim into the tokens Keycloak issues.
// KeyCape emits the claims of the NetKingdom IAM profile that Keycloak has no
// native concept for — tenant, principal type, resource audience — as mappers,
// since without them a migrated realm issues tokens the profile does not accept.
type KeycloakProtocolMapper struct {
	Name           string            `json:"name"`
	Protocol       string            `json:"protocol"`
	ProtocolMapper string            `json:"protocolMapper"`
	Config         map[string]string `json:"config"`
}

// KeycloakUser represents a user in the Keycloak realm.
type KeycloakUser struct {
	Username    string               `json:"username"`
	Email       string               `json:"email,omitempty"`
	FirstName   string               `json:"firstName,omitempty"`
	LastName    string               `json:"lastName,omitempty"`
	Enabled     bool                 `json:"enabled"`
	Groups      []string             `json:"groups,omitempty"`
	RealmRoles  []string             `json:"realmRoles,omitempty"`
	Credentials []KeycloakCredential `json:"credentials,omitempty"`
	Attributes  map[string][]string  `json:"attributes,omitempty"`
}

// KeycloakCredential holds a single credential entry (e.g. hashed password placeholder).
type KeycloakCredential struct {
	Type      string `json:"type"`
	Value     string `json:"value"`
	Temporary bool   `json:"temporary"`
}

// KeycloakGroup represents a user group in the Keycloak realm.
type KeycloakGroup struct {
	Name       string              `json:"name"`
	Path       string              `json:"path"`
	Attributes map[string][]string `json:"attributes,omitempty"`
}

// KeycloakRoles is the realm-level roles container.
type KeycloakRoles struct {
	Realm []KeycloakRole `json:"realm"`
}

// KeycloakRole represents a single realm role.
type KeycloakRole struct {
	Name string `json:"name"`
}

// KeycloakClientScope represents a client scope in the realm.
type KeycloakClientScope struct {
	Name     string `json:"name"`
	Protocol string `json:"protocol"`
}

// ---------------------------------------------------------------------------
// Transformer
// ---------------------------------------------------------------------------

// Config holds realm-level configuration for the transformation.
type Config struct {
	RealmName string
	Issuer    string
}

// Transformer converts a canonical lldapexport.ExportResult into a KeycloakRealm.
type Transformer struct {
	cfg     Config
	emitter telemetry.Emitter

	// unpreserved accumulates every field the last transform could not carry
	// into the realm. ValidationReport surfaces it.
	unpreserved []string
}

// New creates a new Transformer with the given configuration and telemetry emitter.
func New(cfg Config, emitter telemetry.Emitter) *Transformer {
	return &Transformer{cfg: cfg, emitter: emitter}
}

// Transform converts a canonical export with no client registrations. The
// resulting realm has no clients, which is recorded as an unpreserved item —
// an empty clients array is otherwise indistinguishable from a realm that
// genuinely has none.
func (t *Transformer) Transform(export *lldapexport.ExportResult) (*KeycloakRealm, error) {
	return t.TransformWithClients(export, nil)
}

// TransformWithClients converts a canonical export plus an explicit client list
// into a Keycloak realm import structure.
func (t *Transformer) TransformWithClients(export *lldapexport.ExportResult, clients []domain.Client) (*KeycloakRealm, error) {
	t.unpreserved = nil

	realm := &KeycloakRealm{
		Realm:             t.cfg.RealmName,
		Enabled:           true,
		IdentityProviders: []interface{}{},
	}

	// ProfileVersion "0.1" → RS256.
	if export.ProfileVersion == "0.1" {
		realm.DefaultSignatureAlgorithm = "RS256"
	}

	// Map users.
	realm.Users = make([]KeycloakUser, 0, len(export.Users))
	for _, u := range export.Users {
		realm.Users = append(realm.Users, mapUser(u))
	}

	// Map groups.
	realm.Groups = make([]KeycloakGroup, 0, len(export.Groups))
	for _, g := range export.Groups {
		realm.Groups = append(realm.Groups, mapGroup(g))
	}

	// Map clients, collecting every registration field that could not be
	// carried across so the caller can report it.
	realm.Clients = make([]KeycloakClient, 0, len(clients))
	for _, c := range clients {
		mapped, dropped := mapClient(c)
		realm.Clients = append(realm.Clients, mapped)
		t.unpreserved = append(t.unpreserved, dropped...)
	}
	if len(clients) == 0 {
		t.unpreserved = append(t.unpreserved,
			"no client registrations were supplied: the realm carries no clients, so the service-identity, "+
				"audience, tenant/role, MFA and lifetime contract is not migrated")
	}

	// Realm roles and client scopes are derived from the identities and
	// registrations actually present. Emitting empty containers made a realm
	// that drops every role look like one that has none.
	realm.Roles = KeycloakRoles{Realm: realmRoles(export.Users, clients)}
	realm.ClientScopes = clientScopes(clients)

	// Credential material is out of scope for an artifact generator, but its
	// absence must be stated: an operator who imports this realm and finds
	// nobody can log in should learn that here, not there.
	if len(export.Users) > 0 {
		t.unpreserved = append(t.unpreserved,
			"passwords and MFA credentials are not migrated: every user in this realm requires credential "+
				"re-establishment and factor re-enrolment")
		t.unpreserved = append(t.unpreserved,
			"subject continuity is not established: the canonical ID is an LLDAP DN carried as the "+
				"keycape.canonicalId attribute, while Keycloak mints its own sub, so relying parties keyed "+
				"on sub will not recognise migrated users")
	}

	// Emit migration telemetry. A transform that could not carry part of the
	// contract is partial, matching what the LLDAP export reports (KEY-WP-0018):
	// an operator scanning events should not see "success" for an artifact that
	// still needs manual work.
	outcome := "success"
	if len(t.unpreserved) > 0 {
		outcome = "partial"
	}
	t.emitter.Emit(context.Background(), telemetry.Event{
		Timestamp: time.Now().UTC(),
		EventType: telemetry.EventMigration,
		Endpoint:  "keycape-to-keycloak",
		Result:    outcome,
	})

	return realm, nil
}

// UnpreservedReport lists what the last transform could not carry into the
// realm. These are not defects in the generated file — they are the parts of the
// KeyCape contract an operator still has to establish by hand.
//
// It is deliberately separate from ValidationReport: an empty validation report
// means the realm is consistent with the canonical data, which is not the same
// as a complete migration, and collapsing the two would make one of those
// questions unanswerable.
func (t *Transformer) UnpreservedReport() []string {
	return t.unpreserved
}

// ValidationReport compares a canonical export against a produced Keycloak realm
// and returns a list of incompatibility descriptions.
// An empty slice means the import is consistent with the canonical data — see
// UnpreservedReport for what consistency does not cover.
func (t *Transformer) ValidationReport(export *lldapexport.ExportResult, realm *KeycloakRealm) []string {
	var issues []string

	// Any pre-existing incompatibilities from the canonical export propagate.
	for _, inc := range export.IncompatibilityReport {
		issues = append(issues, "canonical export incompatibility: "+inc)
	}

	// User count must match.
	if len(realm.Users) != len(export.Users) {
		issues = append(issues, "user count mismatch: canonical has "+
			itoa(len(export.Users))+" users but realm has "+itoa(len(realm.Users)))
	}

	// Group count must match.
	if len(realm.Groups) != len(export.Groups) {
		issues = append(issues, "group count mismatch: canonical has "+
			itoa(len(export.Groups))+" groups but realm has "+itoa(len(realm.Groups)))
	}

	// Identity providers must be empty per the NetKingdom IAM profile.
	if len(realm.IdentityProviders) != 0 {
		issues = append(issues, "identity providers must be empty per NetKingdom IAM profile")
	}

	return issues
}

// ---------------------------------------------------------------------------
// Mapping helpers
// ---------------------------------------------------------------------------

// mapUser carries a canonical user into a Keycloak user. The canonical ID and
// tenant become attributes: Keycloak mints its own sub, so the KeyCape subject
// survives only as data something downstream can map, never as the subject.
func mapUser(u domain.User) KeycloakUser {
	ku := KeycloakUser{
		Username:   u.Username,
		Email:      u.Email,
		Enabled:    u.Enabled,
		RealmRoles: u.Roles,
		Attributes: map[string][]string{},
	}
	if u.ID != "" {
		ku.Attributes["keycape.canonicalId"] = []string{u.ID}
	}
	if u.Tenant != "" {
		ku.Attributes["tenant"] = []string{u.Tenant}
	}
	if len(ku.Attributes) == 0 {
		ku.Attributes = nil
	}

	// Split DisplayName at first space → FirstName + LastName.
	ku.FirstName, ku.LastName = splitDisplayName(u.DisplayName)

	// Convert group names to Keycloak paths: "/groupname".
	if len(u.Groups) > 0 {
		ku.Groups = make([]string, len(u.Groups))
		for i, g := range u.Groups {
			ku.Groups[i] = "/" + g
		}
	}

	return ku
}

func mapGroup(g domain.Group) KeycloakGroup {
	return KeycloakGroup{
		Name: g.Name,
		Path: "/" + g.Name,
	}
}

// mapClient carries a KeyCape registration into a Keycloak client, and appends
// to unpreserved every field it could not represent. A caller that ignores the
// second return value produces a realm that silently differs from the KeyCape
// contract, which is the defect this signature exists to make awkward.
func mapClient(c domain.Client) (KeycloakClient, []string) {
	var unpreserved []string

	kc := KeycloakClient{
		ClientID:     c.ClientID,
		Name:         c.DisplayName,
		Enabled:      true,
		PublicClient: c.ClientType == "public",
		// Flows follow the declared grants. Enabling the standard flow for a
		// service-only client would widen it during migration.
		StandardFlowEnabled:       hasGrant(c.GrantTypes, "authorization_code"),
		ServiceAccountsEnabled:    hasGrant(c.GrantTypes, "client_credentials"),
		ImplicitFlowEnabled:       false, // never — per NetKingdom IAM profile
		DirectAccessGrantsEnabled: false, // never — per NetKingdom IAM profile
		RedirectUris:              c.RedirectURIs,
		DefaultClientScopes:       c.AllowedScopes,
		Attributes:                map[string]string{},
	}
	if kc.RedirectUris == nil {
		kc.RedirectUris = []string{}
	}
	if kc.DefaultClientScopes == nil {
		kc.DefaultClientScopes = []string{}
	}

	// The resource audience is a claim Keycloak will not produce on its own.
	if c.Audience != "" {
		kc.ProtocolMappers = append(kc.ProtocolMappers, audienceMapper(c.Audience))
	}
	if c.Tenant != "" {
		kc.ProtocolMappers = append(kc.ProtocolMappers, hardcodedClaim("tenant", c.Tenant))
	}
	if c.ServiceSubject != "" {
		// Keycloak derives a service account's subject from its own user; the
		// configured subject cannot be imposed, so carry it as a mapper and
		// say that the subject itself will differ.
		kc.ProtocolMappers = append(kc.ProtocolMappers, hardcodedClaim("service_subject", c.ServiceSubject))
		unpreserved = append(unpreserved, fmt.Sprintf(
			"client %q: serviceSubject %q is carried as a claim, but Keycloak mints its own service-account sub; "+
				"tokens after migration will not carry the KeyCape subject",
			c.ClientID, c.ServiceSubject))
	}
	if len(c.Roles) > 0 {
		kc.ProtocolMappers = append(kc.ProtocolMappers, hardcodedClaim("roles", strings.Join(c.Roles, " ")))
	}
	if c.TokenLifetime > 0 {
		kc.Attributes["access.token.lifespan"] = itoa(int(c.TokenLifetime.Seconds()))
	}
	if c.SecretRef != "" {
		// The reference, never the value: a realm import file is not a secret
		// custody boundary.
		kc.Attributes["keycape.secretRef"] = c.SecretRef
		unpreserved = append(unpreserved, fmt.Sprintf(
			"client %q: secret is not migrated; secretRef %q is recorded as an attribute and must be "+
				"resolved and set on the Keycloak client out of band",
			c.ClientID, c.SecretRef))
	}
	if c.RegistrationURL != "" {
		kc.Attributes["keycape.registrationUrl"] = c.RegistrationURL
	}
	if c.EnrollmentURL != "" {
		kc.Attributes["keycape.enrollmentUrl"] = c.EnrollmentURL
	}
	if c.MFARequired != nil && *c.MFARequired {
		// Keycloak expresses this as an authentication flow binding, which a
		// realm import cannot synthesise from a boolean.
		kc.Attributes["keycape.mfaRequired"] = "true"
		unpreserved = append(unpreserved, fmt.Sprintf(
			"client %q: mfaRequired is not enforceable by import; a Keycloak authentication flow "+
				"requiring a second factor must be bound to this client manually",
			c.ClientID))
	}
	if len(kc.Attributes) == 0 {
		kc.Attributes = nil
	}
	return kc, unpreserved
}

// hasGrant reports whether the registration declares the given grant type.
func hasGrant(grants []string, want string) bool {
	for _, g := range grants {
		if g == want {
			return true
		}
	}
	return false
}

// audienceMapper produces the resource audience on the access token, matching
// KeyCape's split where the ID token keeps the client audience.
func audienceMapper(audience string) KeycloakProtocolMapper {
	return KeycloakProtocolMapper{
		Name:           "keycape-audience",
		Protocol:       "openid-connect",
		ProtocolMapper: "oidc-audience-mapper",
		Config: map[string]string{
			"included.custom.audience": audience,
			"access.token.claim":       "true",
			"id.token.claim":           "false",
		},
	}
}

// hardcodedClaim produces a fixed claim on both tokens.
func hardcodedClaim(claim, value string) KeycloakProtocolMapper {
	return KeycloakProtocolMapper{
		Name:           "keycape-" + claim,
		Protocol:       "openid-connect",
		ProtocolMapper: "oidc-hardcoded-claim-mapper",
		Config: map[string]string{
			"claim.name":         claim,
			"claim.value":        value,
			"access.token.claim": "true",
			"id.token.claim":     "true",
			"jsonType.label":     "String",
		},
	}
}

// splitDisplayName splits a display name at the first space.
// "Alice Liddell" → ("Alice", "Liddell")
// "Bob"           → ("Bob", "")
// "Alice M Smith" → ("Alice", "M Smith")
func splitDisplayName(displayName string) (first, last string) {
	idx := strings.Index(displayName, " ")
	if idx < 0 {
		return displayName, ""
	}
	return displayName[:idx], displayName[idx+1:]
}

// itoa converts an int to its decimal string representation without importing strconv.
func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	neg := n < 0
	if neg {
		n = -n
	}
	buf := make([]byte, 0, 10)
	for n > 0 {
		buf = append([]byte{byte('0' + n%10)}, buf...)
		n /= 10
	}
	if neg {
		buf = append([]byte{'-'}, buf...)
	}
	return string(buf)
}

// realmRoles collects every role named by a user or a client registration.
// Roles referenced by a token but absent from the realm would be silently
// dropped by Keycloak at issuance.
func realmRoles(users []domain.User, clients []domain.Client) []KeycloakRole {
	seen := map[string]bool{}
	var names []string
	add := func(role string) {
		if role == "" || seen[role] {
			return
		}
		seen[role] = true
		names = append(names, role)
	}
	for _, u := range users {
		for _, r := range u.Roles {
			add(r)
		}
	}
	for _, c := range clients {
		for _, r := range c.Roles {
			add(r)
		}
	}
	sort.Strings(names)
	roles := make([]KeycloakRole, 0, len(names))
	for _, n := range names {
		roles = append(roles, KeycloakRole{Name: n})
	}
	return roles
}

// clientScopes collects every scope any registration allows, so the realm can
// grant what KeyCape granted.
func clientScopes(clients []domain.Client) []KeycloakClientScope {
	seen := map[string]bool{}
	var names []string
	for _, c := range clients {
		for _, s := range c.AllowedScopes {
			if s == "" || seen[s] {
				continue
			}
			seen[s] = true
			names = append(names, s)
		}
	}
	sort.Strings(names)
	scopes := make([]KeycloakClientScope, 0, len(names))
	for _, n := range names {
		scopes = append(scopes, KeycloakClientScope{Name: n, Protocol: "openid-connect"})
	}
	return scopes
}