// Package entitlementsvc implements the trusted entitlement lifecycle and
// effective-read use cases owned by User Service.
package entitlementsvc

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"strings"
	"time"

	"galaxy/user/internal/domain/common"
	"galaxy/user/internal/domain/entitlement"
	"galaxy/user/internal/ports"
	"galaxy/user/internal/service/shared"
	"galaxy/user/internal/telemetry"
)

const (
	expiryRepairSource     common.Source     = "entitlement_expiry_repair"
	expiryRepairReasonCode common.ReasonCode = "paid_entitlement_expired"
	expiryRepairActorType  common.ActorType  = "service"
	expiryRepairActorID    common.ActorID    = "user-service"

	expiryRepairRetryLimit = 4
)

// ActorInput stores one transport-facing audit actor payload.
type ActorInput struct {
	// Type stores the machine-readable actor type.
	Type string

	// ID stores the optional stable actor identifier.
	ID string
}

// GrantInput stores one trusted entitlement-grant command request.
type GrantInput struct {
	// UserID identifies the user whose current entitlement must be replaced.
	UserID string

	// PlanCode stores the paid plan that must become current.
	PlanCode string

	// Source stores the machine-readable mutation source.
	Source string

	// ReasonCode stores the machine-readable mutation reason.
	ReasonCode string

	// Actor stores the audit actor metadata.
	Actor ActorInput

	// StartsAt stores when the granted paid state becomes effective.
	StartsAt string

	// EndsAt stores the optional finite paid expiry.
	EndsAt string
}

// ExtendInput stores one trusted entitlement-extension command request.
type ExtendInput struct {
	// UserID identifies the user whose current finite paid entitlement must be
	// extended.
	UserID string

	// Source stores the machine-readable mutation source.
	Source string

	// ReasonCode stores the machine-readable mutation reason.
	ReasonCode string

	// Actor stores the audit actor metadata.
	Actor ActorInput

	// EndsAt stores the replacement finite paid expiry.
	EndsAt string
}

// RevokeInput stores one trusted entitlement-revoke command request.
type RevokeInput struct {
	// UserID identifies the user whose current paid entitlement must be
	// revoked.
	UserID string

	// Source stores the machine-readable mutation source.
	Source string

	// ReasonCode stores the machine-readable mutation reason.
	ReasonCode string

	// Actor stores the audit actor metadata.
	Actor ActorInput
}

// CommandResult stores one trusted entitlement mutation result.
type CommandResult struct {
	// UserID identifies the mutated user.
	UserID string

	// Entitlement stores the refreshed current effective snapshot.
	Entitlement entitlement.CurrentSnapshot
}

type effectiveReader interface {
	GetByUserID(ctx context.Context, userID common.UserID) (entitlement.CurrentSnapshot, error)
}

// Reader loads the current effective entitlement snapshot and lazily repairs
// expired finite paid states.
type Reader struct {
	snapshots   ports.EntitlementSnapshotStore
	lifecycle   ports.EntitlementLifecycleStore
	clock       ports.Clock
	idGenerator ports.IDGenerator
	logger      *slog.Logger
	telemetry   *telemetry.Runtime
	publisher   ports.EntitlementChangedPublisher
}

// NewReader constructs one effective entitlement reader.
func NewReader(
	snapshots ports.EntitlementSnapshotStore,
	lifecycle ports.EntitlementLifecycleStore,
	clock ports.Clock,
	idGenerator ports.IDGenerator,
) (*Reader, error) {
	return NewReaderWithObservability(snapshots, lifecycle, clock, idGenerator, nil, nil, nil)
}

// NewReaderWithObservability constructs one effective entitlement reader with
// optional observability hooks.
func NewReaderWithObservability(
	snapshots ports.EntitlementSnapshotStore,
	lifecycle ports.EntitlementLifecycleStore,
	clock ports.Clock,
	idGenerator ports.IDGenerator,
	logger *slog.Logger,
	telemetryRuntime *telemetry.Runtime,
	publisher ports.EntitlementChangedPublisher,
) (*Reader, error) {
	switch {
	case snapshots == nil:
		return nil, fmt.Errorf("entitlement reader: entitlement snapshot store must not be nil")
	case lifecycle == nil:
		return nil, fmt.Errorf("entitlement reader: entitlement lifecycle store must not be nil")
	case clock == nil:
		return nil, fmt.Errorf("entitlement reader: clock must not be nil")
	case idGenerator == nil:
		return nil, fmt.Errorf("entitlement reader: id generator must not be nil")
	default:
		return &Reader{
			snapshots:   snapshots,
			lifecycle:   lifecycle,
			clock:       clock,
			idGenerator: idGenerator,
			logger:      logger,
			telemetry:   telemetryRuntime,
			publisher:   publisher,
		}, nil
	}
}

// GetByUserID returns the current effective entitlement snapshot for userID.
// When the stored snapshot is a naturally expired finite paid state, it
// lazily materializes the replacement free state before returning.
func (service *Reader) GetByUserID(ctx context.Context, userID common.UserID) (snapshot entitlement.CurrentSnapshot, err error) {
	repairOutcome := ""
	userIDString := userID.String()
	defer func() {
		if repairOutcome == "" {
			return
		}
		if service.telemetry != nil {
			service.telemetry.RecordEntitlementMutation(ctx, "expiry_repair", repairOutcome)
		}
		shared.LogServiceOutcome(service.logger, ctx, "entitlement expiry repair completed", err,
			"use_case", "repair_expired_entitlement",
			"command", "expiry_repair",
			"outcome", repairOutcome,
			"user_id", userIDString,
			"source", expiryRepairSource.String(),
			"reason_code", expiryRepairReasonCode.String(),
			"actor_type", expiryRepairActorType.String(),
			"actor_id", expiryRepairActorID.String(),
		)
	}()

	if err := userID.Validate(); err != nil {
		return entitlement.CurrentSnapshot{}, fmt.Errorf("entitlement reader: %w", err)
	}
	if ctx == nil {
		return entitlement.CurrentSnapshot{}, fmt.Errorf("entitlement reader: nil context")
	}

	for attempt := 0; attempt < expiryRepairRetryLimit; attempt++ {
		currentSnapshot, err := service.snapshots.GetByUserID(ctx, userID)
		if err != nil {
			return entitlement.CurrentSnapshot{}, err
		}

		now := service.clock.Now().UTC()
		if !currentSnapshot.IsExpiredAt(now) {
			return currentSnapshot, nil
		}
		if repairOutcome == "" {
			repairOutcome = "conflict"
		}

		recordID, err := service.idGenerator.NewEntitlementRecordID()
		if err != nil {
			repairOutcome = shared.ErrorCodeServiceUnavailable
			return entitlement.CurrentSnapshot{}, err
		}

		freeRecord, freeSnapshot, err := buildExpiryRepairState(currentSnapshot, recordID, now)
		if err != nil {
			repairOutcome = shared.ErrorCodeInternalError
			return entitlement.CurrentSnapshot{}, err
		}

		err = service.lifecycle.RepairExpired(ctx, ports.RepairExpiredEntitlementInput{
			ExpectedExpiredSnapshot: currentSnapshot,
			NewRecord:               freeRecord,
			NewSnapshot:             freeSnapshot,
		})
		switch {
		case err == nil:
			repairOutcome = "success"
			publishEntitlementChanged(ctx, service.publisher, service.telemetry, service.logger, "repair_expired_entitlement", ports.EntitlementChangedOperationExpiredRepaired, freeSnapshot)
			return freeSnapshot, nil
		case errors.Is(err, ports.ErrConflict):
			continue
		default:
			repairOutcome = shared.ErrorCodeServiceUnavailable
			return entitlement.CurrentSnapshot{}, err
		}
	}

	latestSnapshot, err := service.snapshots.GetByUserID(ctx, userID)
	if err != nil {
		repairOutcome = shared.ErrorCodeServiceUnavailable
		return entitlement.CurrentSnapshot{}, err
	}
	if latestSnapshot.IsExpiredAt(service.clock.Now().UTC()) {
		repairOutcome = "conflict"
		return entitlement.CurrentSnapshot{}, fmt.Errorf("entitlement reader: expiry repair retry limit exceeded for user %q", userID)
	}

	return latestSnapshot, nil
}

type commandSupport struct {
	accounts    ports.UserAccountStore
	history     ports.EntitlementHistoryStore
	reader      effectiveReader
	lifecycle   ports.EntitlementLifecycleStore
	clock       ports.Clock
	idGenerator ports.IDGenerator
}

func newCommandSupport(
	accounts ports.UserAccountStore,
	history ports.EntitlementHistoryStore,
	reader effectiveReader,
	lifecycle ports.EntitlementLifecycleStore,
	clock ports.Clock,
	idGenerator ports.IDGenerator,
) (commandSupport, error) {
	switch {
	case accounts == nil:
		return commandSupport{}, fmt.Errorf("user account store must not be nil")
	case history == nil:
		return commandSupport{}, fmt.Errorf("entitlement history store must not be nil")
	case reader == nil:
		return commandSupport{}, fmt.Errorf("effective entitlement reader must not be nil")
	case lifecycle == nil:
		return commandSupport{}, fmt.Errorf("entitlement lifecycle store must not be nil")
	case clock == nil:
		return commandSupport{}, fmt.Errorf("clock must not be nil")
	case idGenerator == nil:
		return commandSupport{}, fmt.Errorf("id generator must not be nil")
	default:
		return commandSupport{
			accounts:    accounts,
			history:     history,
			reader:      reader,
			lifecycle:   lifecycle,
			clock:       clock,
			idGenerator: idGenerator,
		}, nil
	}
}

func (support commandSupport) ensureUserExists(ctx context.Context, userID common.UserID) error {
	exists, err := support.accounts.ExistsByUserID(ctx, userID)
	switch {
	case err != nil:
		return shared.ServiceUnavailable(err)
	case !exists:
		return shared.SubjectNotFound()
	default:
		return nil
	}
}

func (support commandSupport) loadEffectiveSnapshot(
	ctx context.Context,
	userID common.UserID,
) (entitlement.CurrentSnapshot, error) {
	currentSnapshot, err := support.reader.GetByUserID(ctx, userID)
	switch {
	case err == nil:
		return currentSnapshot, nil
	case errors.Is(err, ports.ErrNotFound):
		return entitlement.CurrentSnapshot{}, shared.InternalError(fmt.Errorf("user %q is missing entitlement snapshot", userID))
	default:
		return entitlement.CurrentSnapshot{}, shared.ServiceUnavailable(err)
	}
}

func (support commandSupport) loadCurrentRecord(
	ctx context.Context,
	userID common.UserID,
	now time.Time,
) (entitlement.PeriodRecord, error) {
	historyRecords, err := support.history.ListByUserID(ctx, userID)
	if err != nil {
		return entitlement.PeriodRecord{}, shared.ServiceUnavailable(err)
	}

	currentRecord, ok := currentRecordAt(historyRecords, now)
	if !ok {
		return entitlement.PeriodRecord{}, shared.InternalError(fmt.Errorf("user %q is missing current entitlement history record", userID))
	}

	return currentRecord, nil
}

// GrantService executes the explicit trusted paid-entitlement grant command.
type GrantService struct {
	support   commandSupport
	logger    *slog.Logger
	telemetry *telemetry.Runtime
	publisher ports.EntitlementChangedPublisher
}

// NewGrantService constructs one entitlement-grant use case.
func NewGrantService(
	accounts ports.UserAccountStore,
	history ports.EntitlementHistoryStore,
	reader effectiveReader,
	lifecycle ports.EntitlementLifecycleStore,
	clock ports.Clock,
	idGenerator ports.IDGenerator,
) (*GrantService, error) {
	return NewGrantServiceWithObservability(accounts, history, reader, lifecycle, clock, idGenerator, nil, nil, nil)
}

// NewGrantServiceWithObservability constructs one entitlement-grant use case
// with optional observability hooks.
func NewGrantServiceWithObservability(
	accounts ports.UserAccountStore,
	history ports.EntitlementHistoryStore,
	reader effectiveReader,
	lifecycle ports.EntitlementLifecycleStore,
	clock ports.Clock,
	idGenerator ports.IDGenerator,
	logger *slog.Logger,
	telemetryRuntime *telemetry.Runtime,
	publisher ports.EntitlementChangedPublisher,
) (*GrantService, error) {
	support, err := newCommandSupport(accounts, history, reader, lifecycle, clock, idGenerator)
	if err != nil {
		return nil, fmt.Errorf("entitlement grant service: %w", err)
	}

	return &GrantService{
		support:   support,
		logger:    logger,
		telemetry: telemetryRuntime,
		publisher: publisher,
	}, nil
}

// Execute grants a new current paid entitlement when the current effective
// entitlement is free.
func (service *GrantService) Execute(ctx context.Context, input GrantInput) (result CommandResult, err error) {
	outcome := shared.ErrorCodeInternalError
	userIDString := strings.TrimSpace(input.UserID)
	sourceValue := strings.TrimSpace(input.Source)
	reasonCodeValue := strings.TrimSpace(input.ReasonCode)
	actorTypeValue := strings.TrimSpace(input.Actor.Type)
	actorIDValue := strings.TrimSpace(input.Actor.ID)
	defer func() {
		if service.telemetry != nil {
			service.telemetry.RecordEntitlementMutation(ctx, "grant", outcome)
		}
		shared.LogServiceOutcome(service.logger, ctx, "entitlement grant completed", err,
			"use_case", "grant_entitlement",
			"command", "grant",
			"outcome", outcome,
			"user_id", userIDString,
			"source", sourceValue,
			"reason_code", reasonCodeValue,
			"actor_type", actorTypeValue,
			"actor_id", actorIDValue,
		)
	}()

	if ctx == nil {
		outcome = shared.ErrorCodeInvalidRequest
		return CommandResult{}, shared.InvalidRequest("context must not be nil")
	}

	userID, err := shared.ParseUserID(input.UserID)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	userIDString = userID.String()
	if err := service.support.ensureUserExists(ctx, userID); err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}

	planCode, err := parsePlanCode(input.PlanCode)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	if planCode == entitlement.PlanCodeFree {
		outcome = shared.ErrorCodeInvalidRequest
		return CommandResult{}, shared.InvalidRequest("plan_code must not be \"free\" for grant")
	}
	source, err := parseSource(input.Source)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	sourceValue = source.String()
	reasonCode, err := shared.ParseReasonCode(input.ReasonCode)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	reasonCodeValue = reasonCode.String()
	actor, err := parseActor(input.Actor)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	actorTypeValue = actor.Type.String()
	actorIDValue = actor.ID.String()
	startsAt, err := parseTimestamp("starts_at", input.StartsAt)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	endsAt, err := parseOptionalTimestamp("ends_at", input.EndsAt)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}

	now := service.support.clock.Now().UTC()
	if startsAt.After(now) {
		outcome = shared.ErrorCodeInvalidRequest
		return CommandResult{}, shared.InvalidRequest("starts_at must not be in the future")
	}
	if err := validateGrantBounds(planCode, startsAt, endsAt); err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}

	currentSnapshot, err := service.support.loadEffectiveSnapshot(ctx, userID)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	if currentSnapshot.IsPaid {
		outcome = shared.ErrorCodeConflict
		return CommandResult{}, shared.Conflict()
	}

	currentRecord, err := service.support.loadCurrentRecord(ctx, userID, now)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	if currentRecord.PlanCode != entitlement.PlanCodeFree {
		outcome = shared.ErrorCodeInternalError
		return CommandResult{}, shared.InternalError(fmt.Errorf("user %q current entitlement record must be free before grant", userID))
	}
	if startsAt.Before(currentRecord.StartsAt) {
		outcome = shared.ErrorCodeInvalidRequest
		return CommandResult{}, shared.InvalidRequest("starts_at must not be before the current free entitlement started")
	}

	recordID, err := service.support.idGenerator.NewEntitlementRecordID()
	if err != nil {
		outcome = shared.ErrorCodeServiceUnavailable
		return CommandResult{}, shared.ServiceUnavailable(err)
	}

	updatedCurrentRecord := currentRecord
	updatedCurrentRecord.ClosedAt = &startsAt
	updatedCurrentRecord.ClosedBy = actor
	updatedCurrentRecord.ClosedReasonCode = reasonCode

	newRecord := entitlement.PeriodRecord{
		RecordID:   recordID,
		UserID:     userID,
		PlanCode:   planCode,
		Source:     source,
		Actor:      actor,
		ReasonCode: reasonCode,
		StartsAt:   startsAt,
		EndsAt:     endsAt,
		CreatedAt:  now,
	}
	newSnapshot := entitlement.CurrentSnapshot{
		UserID:     userID,
		PlanCode:   planCode,
		IsPaid:     true,
		StartsAt:   startsAt,
		EndsAt:     endsAt,
		Source:     source,
		Actor:      actor,
		ReasonCode: reasonCode,
		UpdatedAt:  now,
	}

	if err := service.support.lifecycle.Grant(ctx, ports.GrantEntitlementInput{
		ExpectedCurrentSnapshot: currentSnapshot,
		ExpectedCurrentRecord:   currentRecord,
		UpdatedCurrentRecord:    updatedCurrentRecord,
		NewRecord:               newRecord,
		NewSnapshot:             newSnapshot,
	}); err != nil {
		switch {
		case errors.Is(err, ports.ErrConflict):
			outcome = shared.ErrorCodeConflict
			return CommandResult{}, shared.Conflict()
		default:
			outcome = shared.ErrorCodeServiceUnavailable
			return CommandResult{}, shared.ServiceUnavailable(err)
		}
	}
	outcome = "success"
	result = CommandResult{UserID: userID.String(), Entitlement: newSnapshot}
	publishEntitlementChanged(ctx, service.publisher, service.telemetry, service.logger, "grant_entitlement", ports.EntitlementChangedOperationGranted, newSnapshot)

	return result, nil
}

// ExtendService executes the explicit trusted paid-entitlement extend command.
type ExtendService struct {
	support   commandSupport
	logger    *slog.Logger
	telemetry *telemetry.Runtime
	publisher ports.EntitlementChangedPublisher
}

// NewExtendService constructs one entitlement-extend use case.
func NewExtendService(
	accounts ports.UserAccountStore,
	history ports.EntitlementHistoryStore,
	reader effectiveReader,
	lifecycle ports.EntitlementLifecycleStore,
	clock ports.Clock,
	idGenerator ports.IDGenerator,
) (*ExtendService, error) {
	return NewExtendServiceWithObservability(accounts, history, reader, lifecycle, clock, idGenerator, nil, nil, nil)
}

// NewExtendServiceWithObservability constructs one entitlement-extend use
// case with optional observability hooks.
func NewExtendServiceWithObservability(
	accounts ports.UserAccountStore,
	history ports.EntitlementHistoryStore,
	reader effectiveReader,
	lifecycle ports.EntitlementLifecycleStore,
	clock ports.Clock,
	idGenerator ports.IDGenerator,
	logger *slog.Logger,
	telemetryRuntime *telemetry.Runtime,
	publisher ports.EntitlementChangedPublisher,
) (*ExtendService, error) {
	support, err := newCommandSupport(accounts, history, reader, lifecycle, clock, idGenerator)
	if err != nil {
		return nil, fmt.Errorf("entitlement extend service: %w", err)
	}

	return &ExtendService{
		support:   support,
		logger:    logger,
		telemetry: telemetryRuntime,
		publisher: publisher,
	}, nil
}

// Execute extends the current finite paid entitlement by appending a new
// history segment and updating the current snapshot.
func (service *ExtendService) Execute(ctx context.Context, input ExtendInput) (result CommandResult, err error) {
	outcome := shared.ErrorCodeInternalError
	userIDString := strings.TrimSpace(input.UserID)
	sourceValue := strings.TrimSpace(input.Source)
	reasonCodeValue := strings.TrimSpace(input.ReasonCode)
	actorTypeValue := strings.TrimSpace(input.Actor.Type)
	actorIDValue := strings.TrimSpace(input.Actor.ID)
	defer func() {
		if service.telemetry != nil {
			service.telemetry.RecordEntitlementMutation(ctx, "extend", outcome)
		}
		shared.LogServiceOutcome(service.logger, ctx, "entitlement extend completed", err,
			"use_case", "extend_entitlement",
			"command", "extend",
			"outcome", outcome,
			"user_id", userIDString,
			"source", sourceValue,
			"reason_code", reasonCodeValue,
			"actor_type", actorTypeValue,
			"actor_id", actorIDValue,
		)
	}()

	if ctx == nil {
		outcome = shared.ErrorCodeInvalidRequest
		return CommandResult{}, shared.InvalidRequest("context must not be nil")
	}

	userID, err := shared.ParseUserID(input.UserID)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	userIDString = userID.String()
	if err := service.support.ensureUserExists(ctx, userID); err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	source, err := parseSource(input.Source)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	sourceValue = source.String()
	reasonCode, err := shared.ParseReasonCode(input.ReasonCode)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	reasonCodeValue = reasonCode.String()
	actor, err := parseActor(input.Actor)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	actorTypeValue = actor.Type.String()
	actorIDValue = actor.ID.String()
	newEndsAt, err := parseTimestamp("ends_at", input.EndsAt)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}

	now := service.support.clock.Now().UTC()
	currentSnapshot, err := service.support.loadEffectiveSnapshot(ctx, userID)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	if !currentSnapshot.IsPaid || currentSnapshot.EndsAt == nil {
		outcome = shared.ErrorCodeConflict
		return CommandResult{}, shared.Conflict()
	}
	if !newEndsAt.After(*currentSnapshot.EndsAt) {
		outcome = shared.ErrorCodeInvalidRequest
		return CommandResult{}, shared.InvalidRequest("ends_at must be after the current paid entitlement ends_at")
	}

	currentRecord, err := service.support.loadCurrentRecord(ctx, userID, now)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	if currentRecord.PlanCode != currentSnapshot.PlanCode || currentRecord.EndsAt == nil {
		outcome = shared.ErrorCodeInternalError
		return CommandResult{}, shared.InternalError(fmt.Errorf("user %q current entitlement record is inconsistent with current snapshot", userID))
	}

	recordID, err := service.support.idGenerator.NewEntitlementRecordID()
	if err != nil {
		outcome = shared.ErrorCodeServiceUnavailable
		return CommandResult{}, shared.ServiceUnavailable(err)
	}

	segmentStartsAt := currentSnapshot.EndsAt.UTC()
	newRecord := entitlement.PeriodRecord{
		RecordID:   recordID,
		UserID:     userID,
		PlanCode:   currentSnapshot.PlanCode,
		Source:     source,
		Actor:      actor,
		ReasonCode: reasonCode,
		StartsAt:   segmentStartsAt,
		EndsAt:     &newEndsAt,
		CreatedAt:  now,
	}
	newSnapshot := entitlement.CurrentSnapshot{
		UserID:     userID,
		PlanCode:   currentSnapshot.PlanCode,
		IsPaid:     true,
		StartsAt:   currentSnapshot.StartsAt,
		EndsAt:     &newEndsAt,
		Source:     source,
		Actor:      actor,
		ReasonCode: reasonCode,
		UpdatedAt:  now,
	}

	if err := service.support.lifecycle.Extend(ctx, ports.ExtendEntitlementInput{
		ExpectedCurrentSnapshot: currentSnapshot,
		NewRecord:               newRecord,
		NewSnapshot:             newSnapshot,
	}); err != nil {
		switch {
		case errors.Is(err, ports.ErrConflict):
			outcome = shared.ErrorCodeConflict
			return CommandResult{}, shared.Conflict()
		default:
			outcome = shared.ErrorCodeServiceUnavailable
			return CommandResult{}, shared.ServiceUnavailable(err)
		}
	}
	outcome = "success"
	result = CommandResult{UserID: userID.String(), Entitlement: newSnapshot}
	publishEntitlementChanged(ctx, service.publisher, service.telemetry, service.logger, "extend_entitlement", ports.EntitlementChangedOperationExtended, newSnapshot)

	return result, nil
}

// RevokeService executes the explicit trusted paid-entitlement revoke command.
type RevokeService struct {
	support   commandSupport
	logger    *slog.Logger
	telemetry *telemetry.Runtime
	publisher ports.EntitlementChangedPublisher
}

// NewRevokeService constructs one entitlement-revoke use case.
func NewRevokeService(
	accounts ports.UserAccountStore,
	history ports.EntitlementHistoryStore,
	reader effectiveReader,
	lifecycle ports.EntitlementLifecycleStore,
	clock ports.Clock,
	idGenerator ports.IDGenerator,
) (*RevokeService, error) {
	return NewRevokeServiceWithObservability(accounts, history, reader, lifecycle, clock, idGenerator, nil, nil, nil)
}

// NewRevokeServiceWithObservability constructs one entitlement-revoke use case
// with optional observability hooks.
func NewRevokeServiceWithObservability(
	accounts ports.UserAccountStore,
	history ports.EntitlementHistoryStore,
	reader effectiveReader,
	lifecycle ports.EntitlementLifecycleStore,
	clock ports.Clock,
	idGenerator ports.IDGenerator,
	logger *slog.Logger,
	telemetryRuntime *telemetry.Runtime,
	publisher ports.EntitlementChangedPublisher,
) (*RevokeService, error) {
	support, err := newCommandSupport(accounts, history, reader, lifecycle, clock, idGenerator)
	if err != nil {
		return nil, fmt.Errorf("entitlement revoke service: %w", err)
	}

	return &RevokeService{
		support:   support,
		logger:    logger,
		telemetry: telemetryRuntime,
		publisher: publisher,
	}, nil
}

// Execute revokes the current paid entitlement and materializes a new free
// state starting at the revoke timestamp.
func (service *RevokeService) Execute(ctx context.Context, input RevokeInput) (result CommandResult, err error) {
	outcome := shared.ErrorCodeInternalError
	userIDString := strings.TrimSpace(input.UserID)
	sourceValue := strings.TrimSpace(input.Source)
	reasonCodeValue := strings.TrimSpace(input.ReasonCode)
	actorTypeValue := strings.TrimSpace(input.Actor.Type)
	actorIDValue := strings.TrimSpace(input.Actor.ID)
	defer func() {
		if service.telemetry != nil {
			service.telemetry.RecordEntitlementMutation(ctx, "revoke", outcome)
		}
		shared.LogServiceOutcome(service.logger, ctx, "entitlement revoke completed", err,
			"use_case", "revoke_entitlement",
			"command", "revoke",
			"outcome", outcome,
			"user_id", userIDString,
			"source", sourceValue,
			"reason_code", reasonCodeValue,
			"actor_type", actorTypeValue,
			"actor_id", actorIDValue,
		)
	}()

	if ctx == nil {
		outcome = shared.ErrorCodeInvalidRequest
		return CommandResult{}, shared.InvalidRequest("context must not be nil")
	}

	userID, err := shared.ParseUserID(input.UserID)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	userIDString = userID.String()
	if err := service.support.ensureUserExists(ctx, userID); err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	source, err := parseSource(input.Source)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	sourceValue = source.String()
	reasonCode, err := shared.ParseReasonCode(input.ReasonCode)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	reasonCodeValue = reasonCode.String()
	actor, err := parseActor(input.Actor)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	actorTypeValue = actor.Type.String()
	actorIDValue = actor.ID.String()

	now := service.support.clock.Now().UTC()
	currentSnapshot, err := service.support.loadEffectiveSnapshot(ctx, userID)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	if !currentSnapshot.IsPaid {
		outcome = shared.ErrorCodeConflict
		return CommandResult{}, shared.Conflict()
	}

	currentRecord, err := service.support.loadCurrentRecord(ctx, userID, now)
	if err != nil {
		outcome = shared.MetricOutcome(err)
		return CommandResult{}, err
	}
	if currentRecord.PlanCode != currentSnapshot.PlanCode {
		outcome = shared.ErrorCodeInternalError
		return CommandResult{}, shared.InternalError(fmt.Errorf("user %q current entitlement record is inconsistent with current snapshot", userID))
	}

	recordID, err := service.support.idGenerator.NewEntitlementRecordID()
	if err != nil {
		outcome = shared.ErrorCodeServiceUnavailable
		return CommandResult{}, shared.ServiceUnavailable(err)
	}

	updatedCurrentRecord := currentRecord
	updatedCurrentRecord.ClosedAt = &now
	updatedCurrentRecord.ClosedBy = actor
	updatedCurrentRecord.ClosedReasonCode = reasonCode

	newRecord := entitlement.PeriodRecord{
		RecordID:   recordID,
		UserID:     userID,
		PlanCode:   entitlement.PlanCodeFree,
		Source:     source,
		Actor:      actor,
		ReasonCode: reasonCode,
		StartsAt:   now,
		CreatedAt:  now,
	}
	newSnapshot := entitlement.CurrentSnapshot{
		UserID:     userID,
		PlanCode:   entitlement.PlanCodeFree,
		IsPaid:     false,
		StartsAt:   now,
		Source:     source,
		Actor:      actor,
		ReasonCode: reasonCode,
		UpdatedAt:  now,
	}

	if err := service.support.lifecycle.Revoke(ctx, ports.RevokeEntitlementInput{
		ExpectedCurrentSnapshot: currentSnapshot,
		ExpectedCurrentRecord:   currentRecord,
		UpdatedCurrentRecord:    updatedCurrentRecord,
		NewRecord:               newRecord,
		NewSnapshot:             newSnapshot,
	}); err != nil {
		switch {
		case errors.Is(err, ports.ErrConflict):
			outcome = shared.ErrorCodeConflict
			return CommandResult{}, shared.Conflict()
		default:
			outcome = shared.ErrorCodeServiceUnavailable
			return CommandResult{}, shared.ServiceUnavailable(err)
		}
	}
	outcome = "success"
	result = CommandResult{UserID: userID.String(), Entitlement: newSnapshot}
	publishEntitlementChanged(ctx, service.publisher, service.telemetry, service.logger, "revoke_entitlement", ports.EntitlementChangedOperationRevoked, newSnapshot)

	return result, nil
}

func buildExpiryRepairState(
	expiredSnapshot entitlement.CurrentSnapshot,
	recordID entitlement.EntitlementRecordID,
	now time.Time,
) (entitlement.PeriodRecord, entitlement.CurrentSnapshot, error) {
	if !expiredSnapshot.IsExpiredAt(now) {
		return entitlement.PeriodRecord{}, entitlement.CurrentSnapshot{}, fmt.Errorf("expired snapshot repair requires an expired finite paid snapshot")
	}

	freeStartsAt := expiredSnapshot.EndsAt.UTC()
	freeRecord := entitlement.PeriodRecord{
		RecordID:   recordID,
		UserID:     expiredSnapshot.UserID,
		PlanCode:   entitlement.PlanCodeFree,
		Source:     expiryRepairSource,
		Actor:      common.ActorRef{Type: expiryRepairActorType, ID: expiryRepairActorID},
		ReasonCode: expiryRepairReasonCode,
		StartsAt:   freeStartsAt,
		CreatedAt:  now,
	}
	freeSnapshot := entitlement.CurrentSnapshot{
		UserID:     expiredSnapshot.UserID,
		PlanCode:   entitlement.PlanCodeFree,
		IsPaid:     false,
		StartsAt:   freeStartsAt,
		Source:     expiryRepairSource,
		Actor:      common.ActorRef{Type: expiryRepairActorType, ID: expiryRepairActorID},
		ReasonCode: expiryRepairReasonCode,
		UpdatedAt:  now,
	}

	if err := freeRecord.Validate(); err != nil {
		return entitlement.PeriodRecord{}, entitlement.CurrentSnapshot{}, err
	}
	if err := freeSnapshot.Validate(); err != nil {
		return entitlement.PeriodRecord{}, entitlement.CurrentSnapshot{}, err
	}

	return freeRecord, freeSnapshot, nil
}

func currentRecordAt(records []entitlement.PeriodRecord, now time.Time) (entitlement.PeriodRecord, bool) {
	var (
		currentRecord entitlement.PeriodRecord
		found         bool
	)

	for _, record := range records {
		if !record.IsEffectiveAt(now) {
			continue
		}
		if !found || record.StartsAt.After(currentRecord.StartsAt) ||
			(record.StartsAt.Equal(currentRecord.StartsAt) && record.CreatedAt.After(currentRecord.CreatedAt)) {
			currentRecord = record
			found = true
		}
	}

	return currentRecord, found
}

func parsePlanCode(value string) (entitlement.PlanCode, error) {
	planCode := entitlement.PlanCode(shared.NormalizeString(value))
	if !planCode.IsKnown() {
		return "", shared.InvalidRequest("plan_code is unsupported")
	}

	return planCode, nil
}

func parseSource(value string) (common.Source, error) {
	source := common.Source(shared.NormalizeString(value))
	if err := source.Validate(); err != nil {
		return "", shared.InvalidRequest(err.Error())
	}

	return source, nil
}

func parseActor(input ActorInput) (common.ActorRef, error) {
	ref := common.ActorRef{
		Type: common.ActorType(shared.NormalizeString(input.Type)),
		ID:   common.ActorID(shared.NormalizeString(input.ID)),
	}
	if err := ref.Validate(); err != nil {
		switch {
		case ref.Type.IsZero():
			return common.ActorRef{}, shared.InvalidRequest("actor.type must not be empty")
		default:
			return common.ActorRef{}, shared.InvalidRequest(err.Error())
		}
	}

	return ref, nil
}

func parseTimestamp(fieldName string, value string) (time.Time, error) {
	trimmed := shared.NormalizeString(value)
	if trimmed == "" {
		return time.Time{}, shared.InvalidRequest(fieldName + " must not be empty")
	}

	parsed, err := time.Parse(time.RFC3339Nano, trimmed)
	if err != nil {
		return time.Time{}, shared.InvalidRequest(fieldName + " must be a valid RFC 3339 timestamp")
	}

	return parsed.UTC(), nil
}

func parseOptionalTimestamp(fieldName string, value string) (*time.Time, error) {
	trimmed := shared.NormalizeString(value)
	if trimmed == "" {
		return nil, nil
	}

	parsed, err := parseTimestamp(fieldName, trimmed)
	if err != nil {
		return nil, err
	}

	return &parsed, nil
}

func publishEntitlementChanged(
	ctx context.Context,
	publisher ports.EntitlementChangedPublisher,
	telemetryRuntime *telemetry.Runtime,
	logger *slog.Logger,
	useCase string,
	operation ports.EntitlementChangedOperation,
	snapshot entitlement.CurrentSnapshot,
) {
	if publisher == nil {
		return
	}

	event := ports.EntitlementChangedEvent{
		UserID:     snapshot.UserID,
		OccurredAt: snapshot.UpdatedAt.UTC(),
		Source:     snapshot.Source,
		Operation:  operation,
		PlanCode:   snapshot.PlanCode,
		IsPaid:     snapshot.IsPaid,
		StartsAt:   snapshot.StartsAt,
		EndsAt:     snapshot.EndsAt,
		ReasonCode: snapshot.ReasonCode,
		Actor:      snapshot.Actor,
		UpdatedAt:  snapshot.UpdatedAt,
	}
	if err := publisher.PublishEntitlementChanged(ctx, event); err != nil {
		if telemetryRuntime != nil {
			telemetryRuntime.RecordEventPublicationFailure(ctx, ports.EntitlementChangedEventType)
		}
		shared.LogEventPublicationFailure(logger, ctx, ports.EntitlementChangedEventType, err,
			"use_case", useCase,
			"user_id", snapshot.UserID.String(),
			"source", snapshot.Source.String(),
			"reason_code", snapshot.ReasonCode.String(),
			"actor_type", snapshot.Actor.Type.String(),
			"actor_id", snapshot.Actor.ID.String(),
		)
	}
}

func validateGrantBounds(
	planCode entitlement.PlanCode,
	startsAt time.Time,
	endsAt *time.Time,
) error {
	switch {
	case planCode.HasFiniteExpiry():
		if endsAt == nil {
			return shared.InvalidRequest("ends_at must be present for finite paid plans")
		}
	case planCode == entitlement.PlanCodePaidLifetime:
		if endsAt != nil {
			return shared.InvalidRequest("ends_at must be empty for paid_lifetime")
		}
	default:
		return shared.InvalidRequest("plan_code is unsupported")
	}
	if endsAt != nil && !endsAt.After(startsAt) {
		return shared.InvalidRequest("ends_at must be after starts_at")
	}

	return nil
}