package licensing

import (
	"context"
	"crypto/ed25519"
	"crypto/rand"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"math"
	"os"
	"sort"
	"strings"
	"sync"
	"time"
)

// Public key for license validation (Ed25519).
// This will be embedded at build time or set via SetPublicKey.
// For development, leave empty to skip validation.
var (
	publicKeyMu sync.RWMutex
	publicKey   ed25519.PublicKey
)

// SetPublicKey sets the public key for license validation.
// This should be called during initialization with the production key.
func SetPublicKey(key ed25519.PublicKey) {
	publicKeyMu.Lock()
	defer publicKeyMu.Unlock()

	if len(key) == 0 {
		publicKey = nil
		return
	}

	keyCopy := make(ed25519.PublicKey, len(key))
	copy(keyCopy, key)
	publicKey = keyCopy
}

func currentPublicKey() ed25519.PublicKey {
	publicKeyMu.RLock()
	defer publicKeyMu.RUnlock()

	if len(publicKey) == 0 {
		return nil
	}

	keyCopy := make(ed25519.PublicKey, len(publicKey))
	copy(keyCopy, publicKey)
	return keyCopy
}

// License errors
var (
	ErrInvalidLicense     = errors.New("invalid license key")
	ErrExpiredLicense     = errors.New("license has expired")
	ErrMalformedLicense   = errors.New("malformed license key")
	ErrSignatureInvalid   = errors.New("license signature invalid")
	ErrFeatureNotIncluded = errors.New("feature not included in license")
	ErrNoPublicKey        = errors.New("no public key configured for validation")
)

// Service manages license validation and feature gating.
type Service struct {
	mu      sync.RWMutex
	license *License

	// Grace period duration when license validation fails
	gracePeriod time.Duration

	// Callback when license changes
	onLicenseChange func(*License)

	// Optional canonical evaluator for B2 entitlement checks.
	// When set and no JWT license is active, HasFeature/Status/SubscriptionState
	// delegate to evaluator primitives (capabilities/limits/subscription state).
	// When nil, falls through to existing tier-based logic.
	evaluator *Evaluator

	// Optional subscription state machine hook.
	// Only tracks whether a hook is configured; current derivation remains claim/license based.
	stateMachineConfigured bool

	// Activation-key license server fields.
	serverClient    *LicenseServerClient // HTTP client for license server
	activationState *ActivationState     // Current activation state (nil if using legacy JWT)
	grantRefresh    *grantRefreshLoop    // Background refresh loop (nil until started)
	revocationPoll  *revocationPollLoop  // Background revocation feed poller (nil until started)

	// Persistence reference for activation state save/load. Set via SetPersistence.
	persistence *Persistence
}

// DefaultGracePeriod is the duration after license expiration during which
// features remain available. All grace period logic MUST use this constant.
const DefaultGracePeriod = 7 * 24 * time.Hour

// NewService creates a new license service.
func NewService() *Service {
	return &Service{
		gracePeriod: DefaultGracePeriod,
	}
}

// ensureGracePeriodEnd sets the grace period end time on the license if not already set.
// Must be called while holding s.mu.
func (s *Service) ensureGracePeriodEnd() {
	if s.license != nil && s.license.GracePeriodEnd == nil {
		gracePeriodEnd := time.Unix(s.license.Claims.ExpiresAt, 0).Add(s.gracePeriod)
		s.license.GracePeriodEnd = &gracePeriodEnd
	}
}

// SetLicenseChangeCallback sets a callback for license change events.
func (s *Service) SetLicenseChangeCallback(cb func(*License)) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.onLicenseChange = cb
}

// SetEvaluator overrides the entitlement evaluator.
// In normal operation, Activate and Clear manage the evaluator automatically.
// This method exists for testing; production code should not call it directly.
func (s *Service) SetEvaluator(eval *Evaluator) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.evaluator = eval
}

// SetStateMachine sets the optional subscription state machine hook.
// This is nil-safe and does not alter feature entitlement behavior.
func (s *Service) SetStateMachine(sm any) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.stateMachineConfigured = sm != nil
}

// Evaluator returns the current evaluator, or nil if not set.
func (s *Service) Evaluator() *Evaluator {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.evaluator
}

// Activate validates and activates a license key.
// Activation keys (ppk_live_...) are routed to ActivateWithKey.
// Legacy JWT activation is only allowed in explicit dev mode for test fixtures.
func (s *Service) Activate(licenseKey string) (*License, error) {
	licenseKey = strings.TrimSpace(licenseKey)
	if strings.HasPrefix(licenseKey, ActivationKeyPrefix) {
		return s.ActivateWithKey(licenseKey)
	}
	if !isLicenseValidationDevMode() {
		if !looksLikeLegacyJWTLicense(licenseKey) {
			return nil, fmt.Errorf("license key is not a supported v6 activation key or migratable v5 license")
		}
		return s.ActivateLegacyLicense(licenseKey)
	}

	license, err := ValidateLicense(licenseKey)
	if err != nil {
		return nil, fmt.Errorf("validate license: %w", err)
	}

	// JWT validated successfully — now safe to tear down any existing activation.
	s.StopGrantRefresh()
	s.StopRevocationPoll()

	s.mu.Lock()
	s.license = cloneLicense(license)
	source := NewTokenSource(&s.license.Claims)
	s.evaluator = NewEvaluator(source)
	// Clear any activation state — this is now a legacy JWT license.
	s.activationState = nil
	cb := s.onLicenseChange
	snapshot := cloneLicense(s.license)
	persistence := s.persistence
	s.mu.Unlock()

	// Remove persisted activation state if present.
	if persistence != nil {
		_ = persistence.ClearActivationState()
	}

	if cb != nil {
		cb(snapshot)
	}

	// Keep legacy mutability in explicit dev-mode to avoid breaking existing
	// test fixtures that patch claims after activation. In production mode,
	// callers receive an immutable snapshot to prevent state tampering.
	if isLicenseValidationDevMode() {
		return s.license, nil
	}
	return snapshot, nil
}

func looksLikeLegacyJWTLicense(licenseKey string) bool {
	parts := strings.Split(strings.TrimSpace(licenseKey), ".")
	return len(parts) == 3 && parts[0] != "" && parts[1] != "" && parts[2] != ""
}

// IsLicenseValidationDevMode reports whether legacy JWT validation is enabled
// for development and test fixtures.
func IsLicenseValidationDevMode() bool {
	return isLicenseValidationDevMode()
}

// ActivateWithKey activates a license using an activation key from the license server.
// It creates an installation, receives a relay grant, parses it, and sets the
// resulting license as active. The activation state is persisted for background refresh.
func (s *Service) ActivateWithKey(activationKey string) (*License, error) {
	s.mu.RLock()
	client := s.serverClient
	persistence := s.persistence
	s.mu.RUnlock()

	if client == nil {
		return nil, fmt.Errorf("activation unavailable: license server client not configured")
	}

	// Generate a stable fingerprint for this installation.
	fingerprint, err := generateFingerprint()
	if err != nil {
		return nil, fmt.Errorf("generate instance fingerprint: %w", err)
	}

	hostname, _ := os.Hostname()
	req := ActivateInstallationRequest{
		ActivationKey:       activationKey,
		InstanceFingerprint: fingerprint,
		InstanceName:        hostname,
	}

	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
	defer cancel()

	resp, err := client.Activate(ctx, req)
	if err != nil {
		return nil, fmt.Errorf("activation failed: %w", err)
	}

	return s.applyActivationResponse(resp, fingerprint, client.BaseURL(), persistence)
}

// ActivateLegacyLicense exchanges a legacy v5 JWT-style license for a v6 activation.
func (s *Service) ActivateLegacyLicense(legacyLicenseKey string) (*License, error) {
	s.mu.RLock()
	client := s.serverClient
	persistence := s.persistence
	s.mu.RUnlock()

	if client == nil {
		return nil, fmt.Errorf("activation unavailable: license server client not configured")
	}

	fingerprint, err := generateFingerprint()
	if err != nil {
		return nil, fmt.Errorf("generate instance fingerprint: %w", err)
	}

	hostname, _ := os.Hostname()
	req := ExchangeLegacyLicenseRequest{
		LegacyLicenseKey:    legacyLicenseKey,
		InstanceFingerprint: fingerprint,
		InstanceName:        hostname,
	}

	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
	defer cancel()

	resp, err := client.ExchangeLegacyLicense(ctx, req)
	if err != nil {
		return nil, fmt.Errorf("activation failed: %w", err)
	}

	return s.applyActivationResponse(resp, fingerprint, client.BaseURL(), persistence)
}

func (s *Service) applyActivationResponse(
	resp *ActivateInstallationResponse,
	fingerprint string,
	serverURL string,
	persistence *Persistence,
) (*License, error) {
	// Parse the grant JWT to extract claims.
	gc, err := verifyAndParseGrantJWT(resp.Grant.JWT)
	if err != nil {
		return nil, fmt.Errorf("parse grant from activation: %w", err)
	}

	// Build the license from grant claims.
	lic := grantClaimsToLicense(gc, resp.Grant.JWT)

	// Build activation state for persistence and refresh.
	now := time.Now().Unix()
	state := &ActivationState{
		InstallationID:      resp.Installation.InstallationID,
		InstallationToken:   resp.Installation.InstallationToken,
		LicenseID:           resp.License.LicenseID,
		GrantJWT:            resp.Grant.JWT,
		GrantJTI:            resp.Grant.JTI,
		GrantExpiresAt:      resp.Grant.ParseExpiresAt(),
		InstanceFingerprint: fingerprint,
		LicenseServerURL:    serverURL,
		ActivatedAt:         now,
		LastRefreshedAt:     now,
	}

	s.mu.Lock()
	s.license = cloneLicense(lic)
	source := NewTokenSource(&s.license.Claims)
	s.evaluator = NewEvaluator(source)
	s.activationState = state
	cb := s.onLicenseChange
	snapshot := cloneLicense(s.license)
	s.mu.Unlock()

	// Apply refresh hints from the server.
	s.SetRefreshHints(resp.RefreshPolicy)

	// Persist activation state.
	if persistence != nil {
		if err := persistence.SaveActivationState(state); err != nil {
			// Log but don't fail — the activation succeeded.
			// The grant won't survive restarts without persistence, but that's a degraded mode.
			fmt.Fprintf(os.Stderr, "warning: failed to persist activation state: %v\n", err)
		}
	}

	if cb != nil {
		cb(snapshot)
	}

	return snapshot, nil
}

// IsActivated returns true if the service has an active activation-key license.
func (s *Service) IsActivated() bool {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.activationState != nil
}

// GetActivationState returns a copy of the current activation state, or nil.
func (s *Service) GetActivationState() *ActivationState {
	s.mu.RLock()
	defer s.mu.RUnlock()
	if s.activationState == nil {
		return nil
	}
	stateCopy := *s.activationState
	return &stateCopy
}

// SetLicenseServerClient sets the HTTP client for license server communication.
func (s *Service) SetLicenseServerClient(client *LicenseServerClient) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.serverClient = client
}

// SetPersistence sets the persistence reference for activation state save/load.
func (s *Service) SetPersistence(p *Persistence) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.persistence = p
}

// RestoreActivation restores the license from persisted activation state.
// Called during startup to resume an activation without re-activating.
// Even if the grant is expired, the refresh loop will renew it.
func (s *Service) RestoreActivation(state *ActivationState) error {
	if state == nil {
		return nil
	}

	gc, err := verifyAndParseGrantJWT(state.GrantJWT)
	if err != nil {
		return fmt.Errorf("parse persisted grant: %w", err)
	}

	lic := grantClaimsToLicense(gc, state.GrantJWT)

	s.mu.Lock()
	s.license = cloneLicense(lic)
	source := NewTokenSource(&s.license.Claims)
	s.evaluator = NewEvaluator(source)
	s.activationState = state
	cb := s.onLicenseChange
	snapshot := cloneLicense(s.license)
	s.mu.Unlock()

	if cb != nil {
		cb(snapshot)
	}

	return nil
}

// Clear removes the current license.
// If an activation-key license is present, it also stops the refresh loop and clears the state.
func (s *Service) Clear() {
	// Stop background loops first (outside the lock to avoid deadlock).
	s.StopGrantRefresh()
	s.StopRevocationPoll()

	s.mu.Lock()
	s.license = nil
	s.evaluator = nil
	persistence := s.persistence
	hadActivation := s.activationState != nil
	s.activationState = nil
	cb := s.onLicenseChange
	s.mu.Unlock()

	// Clear persisted activation state if it existed.
	if hadActivation && persistence != nil {
		if err := persistence.ClearActivationState(); err != nil {
			fmt.Fprintf(os.Stderr, "warning: failed to clear activation state: %v\n", err)
		}
	}

	if cb != nil {
		cb(nil)
	}
}

// Current returns the current license, or nil if none.
func (s *Service) Current() *License {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return cloneLicense(s.license)
}

// SetCurrentForTesting injects a license pointer directly into service state.
// This is intended for deterministic unit tests.
func (s *Service) SetCurrentForTesting(license *License) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.license = license
}

// CurrentUnsafeForTesting returns the internal license pointer for in-place mutation.
// This is intended for deterministic unit tests.
func (s *Service) CurrentUnsafeForTesting() *License {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.license
}

// IsValid returns true if a valid, non-expired license is active.
func (s *Service) IsValid() bool {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.license == nil {
		return false
	}

	state := s.currentJWTSubscriptionStateLocked(time.Now())
	return subscriptionStateHasPaidFeatures(state)
}

// HasFeature checks if the current license grants a feature.
func (s *Service) HasFeature(feature string) bool {
	// In demo mode or dev mode, grant all Pro features
	if isDemoMode() || isDevMode() {
		return true
	}

	s.mu.Lock() // Need write lock since we may update grace period
	defer s.mu.Unlock()

	if s.license == nil {
		// Hosted path: evaluator drives entitlements when no JWT is present.
		if s.evaluator != nil {
			// Always include free-tier features, regardless of evaluator state.
			if TierHasFeature(TierFree, feature) {
				return true
			}

			// Only grant paid capabilities when the subscription state permits it.
			if !subscriptionStateHasPaidFeatures(s.evaluator.SubscriptionState()) {
				return false
			}
			return s.evaluator.HasCapability(feature)
		}
		// No license activated — still grant free tier features
		return TierHasFeature(TierFree, feature)
	}

	// JWT takes precedence whenever a license is present (including hybrid mode).
	if !subscriptionStateHasPaidFeatures(s.currentJWTSubscriptionStateLocked(time.Now())) {
		return TierHasFeature(TierFree, feature)
	}

	return s.license.HasFeature(feature)
}

// isDemoMode, isDevMode, and isLicenseValidationDevMode are defined in
// dev_mode_dev.go (default builds) and dev_mode_release.go (release builds).
// In release builds these always return false, preventing env-var bypass of
// feature gating and license signature validation.

const (
	maxLicenseKeyLength     = 16 << 10 // 16 KiB
	maxLicenseSegmentLength = 8 << 10  // 8 KiB
	maxLicensePayloadSize   = 8 << 10  // 8 KiB decoded JSON
)

// GetLicenseState returns the current license state and the license itself
func (s *Service) GetLicenseState() (LicenseState, *License) {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.license == nil {
		if s.evaluator != nil {
			switch s.evaluator.SubscriptionState() {
			case SubStateActive, SubStateTrial:
				return LicenseStateActive, nil
			case SubStateGrace:
				return LicenseStateGracePeriod, nil
			default:
				// Suspended/canceled/expired (or unknown) are treated as non-entitled.
				return LicenseStateExpired, nil
			}
		}
		return LicenseStateNone, nil
	}

	state := s.currentJWTSubscriptionStateLocked(time.Now())
	switch state {
	case SubStateActive, SubStateTrial:
		return LicenseStateActive, cloneLicense(s.license)
	case SubStateGrace:
		return LicenseStateGracePeriod, cloneLicense(s.license)
	default:
		return LicenseStateExpired, cloneLicense(s.license)
	}
}

// GetLicenseStateString returns the current license state as string and whether features are available
// This implements the LicenseChecker interface for the AI service
func (s *Service) GetLicenseStateString() (string, bool) {
	state, _ := s.GetLicenseState()
	hasFeatures := state == LicenseStateActive || state == LicenseStateGracePeriod
	return string(state), hasFeatures
}

// RequireFeature returns an error if the feature is not available.
// This is the primary method for feature gating.
func (s *Service) RequireFeature(feature string) error {
	if !s.HasFeature(feature) {
		return fmt.Errorf("%w: %s requires Pulse %s or above", ErrFeatureNotIncluded, GetFeatureDisplayName(feature), GetFeatureMinTierName(feature))
	}
	return nil
}

// SubscriptionState returns the current normalized subscription state.
func (s *Service) SubscriptionState() string {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.stateMachineConfigured && s.license != nil && s.license.Claims.SubState != "" {
		return string(s.license.Claims.SubState)
	}

	if s.license == nil && s.evaluator != nil {
		return string(s.evaluator.SubscriptionState())
	}
	if s.license == nil {
		return string(SubStateExpired)
	}

	return string(s.currentJWTSubscriptionStateLocked(time.Now()))
}

// Status returns a summary of the current license status.
func (s *Service) Status() *LicenseStatus {
	s.mu.Lock() // Need write lock since we may update grace period
	defer s.mu.Unlock()

	status := &LicenseStatus{
		Valid:    false,
		Tier:     TierFree,
		Features: append([]string(nil), TierFeatures[TierFree]...),
	}

	if s.license == nil {
		// Hosted path: evaluator drives status when no JWT is present.
		if s.evaluator != nil {
			status.PlanVersion = s.evaluator.PlanVersion()
			subState := s.evaluator.SubscriptionState()
			switch subState {
			case SubStateActive, SubStateTrial, SubStateGrace:
				status.Tier = TierPro // hosted billing-backed tenants are effectively "pro" while entitled
				status.Valid = true
				if subState == SubStateGrace {
					status.InGracePeriod = true
				}
				if subState == SubStateTrial {
					if trialEndsAt := s.evaluator.TrialEndsAt(); trialEndsAt != nil {
						expiresAt := time.Unix(*trialEndsAt, 0).Format(time.RFC3339)
						status.ExpiresAt = &expiresAt
						status.DaysRemaining = remainingDaysCeil(*trialEndsAt, time.Now().Unix())
					}
				}
				status.Features = unionFeatures(TierFeatures[TierFree], evaluatorFeatures(s.evaluator))

				if maxSystems, ok := s.evaluator.GetLimit(MaxMonitoredSystemsLicenseGateKey); ok {
					status.MaxMonitoredSystems = safeIntFromInt64(maxSystems)
				}
				if maxGuests, ok := s.evaluator.GetLimit("max_guests"); ok {
					status.MaxGuests = safeIntFromInt64(maxGuests)
				}
			default:
				status.Tier = TierFree
				status.Valid = false
				// Keep effective capabilities free-tier only when subscription is not entitled.
				status.Features = append([]string(nil), TierFeatures[TierFree]...)
				if defaultSystems := TierMonitoredSystemLimits[TierFree]; defaultSystems > 0 {
					status.MaxMonitoredSystems = defaultSystems
				}
				status.MaxGuests = 0
			}
		} else {
			// No license, no evaluator — apply the free-tier monitored-system limit.
			if defaultSystems := TierMonitoredSystemLimits[TierFree]; defaultSystems > 0 {
				status.MaxMonitoredSystems = defaultSystems
			}
		}
		return status
	}

	status.Email = s.license.Claims.Email
	status.Tier = s.license.Claims.Tier
	status.PlanVersion = s.license.Claims.EntitlementPlanVersion()
	status.IsLifetime = s.license.IsLifetime()
	status.DaysRemaining = s.license.DaysRemaining()
	status.Features = s.license.AllFeatures()

	if maxSystems, ok := s.license.Claims.EffectiveLimits()[MaxMonitoredSystemsLicenseGateKey]; ok {
		status.MaxMonitoredSystems = safeIntFromInt64(maxSystems)
	}
	if maxGuests, ok := s.license.Claims.EffectiveLimits()["max_guests"]; ok {
		status.MaxGuests = safeIntFromInt64(maxGuests)
	}

	// Apply the tier default monitored-system limit when claims don't specify one.
	// For recognized tiers, use their defined limit (0 = unlimited for Cloud/MSP/Enterprise).
	// For unrecognized tiers, fall back to free tier limit to prevent unlimited access.
	if status.MaxMonitoredSystems == 0 {
		if defaultSystems, ok := TierMonitoredSystemLimits[status.Tier]; ok {
			status.MaxMonitoredSystems = defaultSystems
		} else {
			status.MaxMonitoredSystems = TierMonitoredSystemLimits[TierFree]
		}
	}

	if s.license.ExpiresAt() != nil {
		exp := s.license.ExpiresAt().Format(time.RFC3339)
		status.ExpiresAt = &exp
	}

	switch subState := s.currentJWTSubscriptionStateLocked(time.Now()); subState {
	case SubStateActive, SubStateTrial:
		status.Valid = true
	case SubStateGrace:
		status.Valid = true
		status.InGracePeriod = true
		if s.license.GracePeriodEnd != nil {
			graceEnd := s.license.GracePeriodEnd.Format(time.RFC3339)
			status.GracePeriodEnd = &graceEnd
		}
	default:
		status.Valid = false
		status.Features = append([]string(nil), TierFeatures[TierFree]...)
		// Downgrade limits to the free tier when subscription is not entitled.
		if defaultSystems := TierMonitoredSystemLimits[TierFree]; defaultSystems > 0 {
			status.MaxMonitoredSystems = defaultSystems
		} else {
			status.MaxMonitoredSystems = 0
		}
		status.MaxGuests = 0
	}

	return status
}

func (s *Service) currentJWTSubscriptionStateLocked(now time.Time) SubscriptionState {
	if s.license == nil {
		return SubStateExpired
	}

	// Explicit revocation states in JWT claims should always revoke paid access.
	switch s.license.Claims.SubState {
	case SubStateSuspended, SubStateCanceled, SubStateExpired:
		return s.license.Claims.SubState
	}

	// Expiration/grace handling applies regardless of claim substate.
	if s.license.IsExpired() {
		s.ensureGracePeriodEnd()
		if s.license.GracePeriodEnd != nil && now.Before(*s.license.GracePeriodEnd) {
			return SubStateGrace
		}
		return SubStateExpired
	}

	if s.license.Claims.SubState != "" {
		return s.license.Claims.SubState
	}

	return SubStateActive
}

func subscriptionStateHasPaidFeatures(state SubscriptionState) bool {
	switch state {
	case SubStateActive, SubStateTrial, SubStateGrace:
		return true
	default:
		return false
	}
}

func evaluatorFeatures(eval *Evaluator) []string {
	if eval == nil {
		return []string{}
	}

	// Derive a stable, known capability list from the evaluator by enumerating
	// all feature keys currently used by tier-based gating.
	known := make(map[string]struct{}, 32)
	for _, features := range TierFeatures {
		for _, feature := range features {
			known[feature] = struct{}{}
		}
	}

	caps := make([]string, 0, len(known))
	for feature := range known {
		if eval.HasCapability(feature) {
			caps = append(caps, feature)
		}
	}
	sort.Strings(caps)
	return caps
}

func unionFeatures(a, b []string) []string {
	set := make(map[string]struct{}, len(a)+len(b))
	for _, v := range a {
		set[v] = struct{}{}
	}
	for _, v := range b {
		set[v] = struct{}{}
	}

	out := make([]string, 0, len(set))
	for v := range set {
		out = append(out, v)
	}
	sort.Strings(out)
	return out
}

func safeIntFromInt64(v int64) int {
	// Avoid overflow on 32-bit platforms; clamp to max int.
	maxInt := int64(^uint(0) >> 1)
	if v > maxInt {
		return int(maxInt)
	}
	if v < 0 {
		return 0
	}
	return int(v)
}

func remainingDaysCeil(expiresAtUnix, nowUnix int64) int {
	deltaSeconds := expiresAtUnix - nowUnix
	if deltaSeconds <= 0 {
		return 0
	}
	return int(math.Ceil(float64(deltaSeconds) / 86400.0))
}

func cloneLicense(in *License) *License {
	if in == nil {
		return nil
	}

	out := *in
	out.Claims = cloneClaims(in.Claims)
	if in.GracePeriodEnd != nil {
		graceEnd := *in.GracePeriodEnd
		out.GracePeriodEnd = &graceEnd
	}
	return &out
}

func cloneClaims(in Claims) Claims {
	out := in
	if in.Features != nil {
		out.Features = append([]string(nil), in.Features...)
	}
	if in.Capabilities != nil {
		out.Capabilities = append([]string(nil), in.Capabilities...)
	}
	if in.Limits != nil {
		out.Limits = make(map[string]int64, len(in.Limits))
		for key, value := range in.Limits {
			out.Limits[key] = value
		}
	}
	if in.MetersEnabled != nil {
		out.MetersEnabled = append([]string(nil), in.MetersEnabled...)
	}
	return out
}

// ValidateLicense validates a license key and returns the license if valid.
func ValidateLicense(licenseKey string) (*License, error) {
	// Trim whitespace
	licenseKey = strings.TrimSpace(licenseKey)
	if licenseKey == "" {
		return nil, ErrInvalidLicense
	}
	if len(licenseKey) > maxLicenseKeyLength {
		return nil, fmt.Errorf("%w: license key exceeds size limit", ErrMalformedLicense)
	}

	// Parse JWT (base64url.base64url.base64url)
	parts := strings.Split(licenseKey, ".")
	if len(parts) != 3 {
		return nil, ErrMalformedLicense
	}
	for _, part := range parts {
		if part == "" {
			return nil, fmt.Errorf("%w: empty jwt segment", ErrMalformedLicense)
		}
		if len(part) > maxLicenseSegmentLength {
			return nil, fmt.Errorf("%w: jwt segment exceeds size limit", ErrMalformedLicense)
		}
	}

	// Decode header (not used currently, but validate it exists)
	_, err := base64.RawURLEncoding.DecodeString(parts[0])
	if err != nil {
		return nil, fmt.Errorf("%w: invalid header encoding", ErrMalformedLicense)
	}

	// Decode payload
	payloadBytes, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return nil, fmt.Errorf("%w: invalid payload encoding", ErrMalformedLicense)
	}
	if len(payloadBytes) > maxLicensePayloadSize {
		return nil, fmt.Errorf("%w: payload exceeds size limit", ErrMalformedLicense)
	}

	// Decode signature
	signature, err := base64.RawURLEncoding.DecodeString(parts[2])
	if err != nil {
		return nil, fmt.Errorf("%w: invalid signature encoding", ErrMalformedLicense)
	}

	// Verify signature
	// In production, public key MUST be set. In dev mode, we skip signature validation.
	devMode := isLicenseValidationDevMode()
	signedData := []byte(parts[0] + "." + parts[1])
	key := currentPublicKey()

	if len(key) > 0 {
		if !ed25519.Verify(key, signedData, signature) {
			return nil, ErrSignatureInvalid
		}
	} else if !devMode {
		// No public key and not in dev mode - fail validation
		return nil, fmt.Errorf("%w: signature verification required", ErrNoPublicKey)
	}
	// If devMode and no public key, we skip signature verification (for testing only)

	// Parse claims
	var claims Claims
	if err := json.Unmarshal(payloadBytes, &claims); err != nil {
		return nil, fmt.Errorf("%w: invalid claims JSON", ErrMalformedLicense)
	}

	// Validate required fields
	if claims.LicenseID == "" {
		return nil, fmt.Errorf("%w: missing license ID", ErrMalformedLicense)
	}
	if claims.Email == "" {
		return nil, fmt.Errorf("%w: missing email", ErrMalformedLicense)
	}
	if claims.Tier == "" {
		return nil, fmt.Errorf("%w: missing tier", ErrMalformedLicense)
	}

	license := &License{
		Raw:         licenseKey,
		Claims:      claims,
		ValidatedAt: time.Now(),
	}

	// Check expiration with grace period support
	if license.IsExpired() {
		// Calculate how long ago it expired
		expirationTime := time.Unix(claims.ExpiresAt, 0)
		gracePeriodEnd := expirationTime.Add(DefaultGracePeriod)

		if time.Now().Before(gracePeriodEnd) {
			// Within grace period - allow activation but mark as in grace period
			license.GracePeriodEnd = &gracePeriodEnd
			// License is still valid during grace period
		} else {
			// Past grace period - reject
			return nil, fmt.Errorf("%w: expired on %s (grace period ended %s)",
				ErrExpiredLicense,
				expirationTime.Format("2006-01-02"),
				gracePeriodEnd.Format("2006-01-02"))
		}
	}

	return license, nil
}

// generateFingerprint creates a random UUID v4 for identifying this installation.
func generateFingerprint() (string, error) {
	var uuid [16]byte
	if _, err := rand.Read(uuid[:]); err != nil {
		return "", err
	}
	// Set version 4 bits.
	uuid[6] = (uuid[6] & 0x0f) | 0x40
	// Set variant bits.
	uuid[8] = (uuid[8] & 0x3f) | 0x80
	return fmt.Sprintf("%08x-%04x-%04x-%04x-%012x",
		uuid[0:4], uuid[4:6], uuid[6:8], uuid[8:10], uuid[10:16]), nil
}

// GenerateLicenseForTesting creates a test license (DO NOT USE IN PRODUCTION).
// This is only for development/testing without a real license server.
func GenerateLicenseForTesting(email string, tier Tier, expiresIn time.Duration) (string, error) {
	claims := Claims{
		LicenseID: fmt.Sprintf("test_%d", time.Now().UnixNano()),
		Email:     email,
		Tier:      tier,
		IssuedAt:  time.Now().Unix(),
	}
	if expiresIn > 0 {
		claims.ExpiresAt = time.Now().Add(expiresIn).Unix()
	}

	// Create unsigned JWT (for testing only)
	header := base64.RawURLEncoding.EncodeToString([]byte(`{"alg":"EdDSA","typ":"JWT"}`))
	payloadBytes, err := json.Marshal(claims)
	if err != nil {
		return "", fmt.Errorf("marshal test license claims: %w", err)
	}
	payload := base64.RawURLEncoding.EncodeToString(payloadBytes)

	// Fake signature (testing only - real licenses need proper signing)
	signature := base64.RawURLEncoding.EncodeToString([]byte("test-signature-not-valid"))

	return header + "." + payload + "." + signature, nil
}

// GenerateGrantJWTForTesting creates a signed grant JWT and returns the matching
// public key so tests can install it via SetPublicKey before verification.
// DO NOT USE IN PRODUCTION.
func GenerateGrantJWTForTesting(claims GrantClaims) (string, ed25519.PublicKey, error) {
	publicKey, privateKey, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		return "", nil, fmt.Errorf("generate grant test key pair: %w", err)
	}

	header := base64.RawURLEncoding.EncodeToString([]byte(`{"alg":"EdDSA"}`))
	payloadBytes, err := json.Marshal(claims)
	if err != nil {
		return "", nil, fmt.Errorf("marshal grant test claims: %w", err)
	}
	payload := base64.RawURLEncoding.EncodeToString(payloadBytes)
	signedData := []byte(header + "." + payload)
	signature := ed25519.Sign(privateKey, signedData)

	return header + "." + payload + "." + base64.RawURLEncoding.EncodeToString(signature), publicKey, nil
}