package alert_lifecycle

import (
	"context"
	"errors"
	"time"

	"github.com/google/uuid"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

type Actor struct {
	ID         int
	Name, Role string
}
type Detail struct {
	Projection Projection `json:"projection"`
	Timeline   []Fact     `json:"timeline"`
	CanAck     bool       `json:"canAck"`
	CanClose   bool       `json:"canClose"`
}
type Result struct {
	Detail     Detail `json:"detail"`
	Idempotent bool   `json:"idempotent"`
	Won        bool   `json:"won"`
}
type Service struct{ DB *gorm.DB }

func NewService(db *gorm.DB) Service { return Service{DB: db} }

func (s Service) Get(ctx context.Context, alertID string) (Detail, error) {
	if _, err := uuid.Parse(alertID); err != nil {
		return Detail{}, ErrNotFound
	}
	var projection Projection
	if err := s.DB.WithContext(ctx).First(&projection, "id = ?", alertID).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return Detail{}, ErrNotFound
		}
		return Detail{}, err
	}
	facts := make([]Fact, 0)
	if err := s.DB.WithContext(ctx).Where("alert_id = ?", alertID).Order("occurred_at, id").Find(&facts).Error; err != nil {
		return Detail{}, err
	}
	return Detail{Projection: projection, Timeline: facts}, nil
}

func (s Service) Ack(ctx context.Context, alertID string, actor Actor) (Result, error) {
	if _, err := uuid.Parse(alertID); err != nil {
		s.reject(ctx, nil, "ack", actor.ID, "not_found", nil)
		return Result{}, ErrNotFound
	}
	now := time.Now().UTC()
	var projection Projection
	err := s.DB.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
		result := tx.Raw(`UPDATE bell_alerts SET status='acknowledged', acknowledged_by=?, acknowledged_by_name=?, acknowledged_at=?, updated_at=? WHERE id=? AND status='open' RETURNING id,status,acknowledged_by,acknowledged_by_name,acknowledged_at,closed_by,closed_by_name,closed_at,close_outcome,close_note`, actor.ID, actor.Name, now, now, alertID).Scan(&projection)
		if result.Error != nil {
			return result.Error
		}
		if result.RowsAffected == 0 {
			return gorm.ErrRecordNotFound
		}
		return tx.Create(&Fact{ID: uuid.NewString(), AlertID: alertID, Transition: StatusAcknowledged, ActorID: actor.ID, ActorName: actor.Name, OccurredAt: now}).Error
	})
	if err == nil {
		detail, getErr := s.Get(ctx, alertID)
		return Result{Detail: detail, Won: true}, getErr
	}
	if !errors.Is(err, gorm.ErrRecordNotFound) {
		return Result{}, err
	}
	detail, getErr := s.Get(ctx, alertID)
	if getErr != nil {
		return Result{}, getErr
	}
	if detail.Projection.AcknowledgedBy != nil && *detail.Projection.AcknowledgedBy == actor.ID {
		s.reject(ctx, &alertID, "ack", actor.ID, "duplicate", &detail.Projection)
		return Result{Detail: detail, Idempotent: true}, nil
	}
	s.reject(ctx, &alertID, "ack", actor.ID, "already_handled", &detail.Projection)
	return Result{Detail: detail}, ErrAlreadyHandled
}

func (s Service) Close(ctx context.Context, alertID string, input CloseInput, actor Actor) (Result, error) {
	normalized, err := normalizeClose(input)
	if err != nil {
		s.reject(ctx, validAlertID(alertID), "close", actor.ID, "invalid_outcome", nil)
		return Result{}, err
	}
	if _, err = uuid.Parse(alertID); err != nil {
		s.reject(ctx, nil, "close", actor.ID, "not_found", nil)
		return Result{}, ErrNotFound
	}
	var projection Projection
	err = s.DB.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
		if lockErr := tx.Clauses(clause.Locking{Strength: "UPDATE"}).First(&projection, "id = ?", alertID).Error; lockErr != nil {
			return lockErr
		}
		if projection.Status == StatusClosed {
			return ErrInvalidTransition
		}
		if projection.Status != StatusAcknowledged {
			return ErrInvalidTransition
		}
		if actor.Role != "admin" && (projection.AcknowledgedBy == nil || *projection.AcknowledgedBy != actor.ID) {
			return ErrForbidden
		}
		now := time.Now().UTC()
		var note *string
		if normalized.Note != "" {
			note = &normalized.Note
		}
		if updateErr := tx.Model(&projection).Updates(map[string]any{"status": StatusClosed, "closed_by": actor.ID, "closed_by_name": actor.Name, "closed_at": now, "close_outcome": normalized.Outcome, "close_note": note, "updated_at": now}).Error; updateErr != nil {
			return updateErr
		}
		return tx.Create(&Fact{ID: uuid.NewString(), AlertID: alertID, Transition: StatusClosed, ActorID: actor.ID, ActorName: actor.Name, Outcome: &normalized.Outcome, Note: note, OccurredAt: now}).Error
	})
	if err == nil {
		detail, getErr := s.Get(ctx, alertID)
		return Result{Detail: detail, Won: true}, getErr
	}
	if !errors.Is(err, ErrInvalidTransition) && !errors.Is(err, ErrForbidden) && !errors.Is(err, gorm.ErrRecordNotFound) {
		return Result{}, err
	}
	detail, getErr := s.Get(ctx, alertID)
	if getErr != nil {
		return Result{}, getErr
	}
	if detail.Projection.Status == StatusClosed && detail.Projection.ClosedBy != nil && *detail.Projection.ClosedBy == actor.ID && detail.Projection.CloseOutcome != nil && *detail.Projection.CloseOutcome == normalized.Outcome && equalOptional(detail.Projection.CloseNote, normalized.Note) {
		s.reject(ctx, &alertID, "close", actor.ID, "duplicate", &detail.Projection)
		return Result{Detail: detail, Idempotent: true}, nil
	}
	reason := "invalid_transition"
	publicErr := ErrInvalidTransition
	if errors.Is(err, ErrForbidden) {
		reason, publicErr = "forbidden", ErrForbidden
	} else if detail.Projection.Status == StatusClosed {
		reason = "conflicting_replay"
	}
	s.reject(ctx, &alertID, "close", actor.ID, reason, &detail.Projection)
	return Result{Detail: detail}, publicErr
}

func (s Service) reject(ctx context.Context, alertID *string, action string, actorID int, reason string, projection *Projection) {
	audit := RejectionAudit{ID: uuid.NewString(), AlertID: alertID, Action: action, ActorID: actorID, Reason: reason, CreatedAt: time.Now().UTC()}
	if projection != nil {
		audit.ObservedStatus = &projection.Status
		audit.ObservedActor = projection.AcknowledgedBy
	}
	_ = s.DB.WithContext(ctx).Create(&audit).Error
}
func validAlertID(value string) *string {
	if _, err := uuid.Parse(value); err != nil {
		return nil
	}
	return &value
}
func equalOptional(value *string, other string) bool {
	if value == nil {
		return other == ""
	}
	return *value == other
}