package worker

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"slices"
	"time"

	"github.com/google/uuid"

	"github.com/example/remote-access-platform/backend/internal/modules/sessionbroker"
	"github.com/example/remote-access-platform/backend/internal/platform/module"
	workercontracts "github.com/example/remote-access-platform/backend/pkg/contracts/worker"
)

var ErrNoWorkerAvailable = errors.New("no worker available")

type Service struct {
	cfg   module.Config
	store Store
	now   func() time.Time
}

func NewService(deps module.Dependencies, store Store) *Service {
	return &Service{
		cfg:   deps.Config,
		store: store,
		now:   time.Now,
	}
}

func (s *Service) Register(ctx context.Context, registration workercontracts.WorkerRegistration) error {
	if registration.WorkerID == "" {
		return fmt.Errorf("worker id is required")
	}
	registration.LastHeartbeatAt = s.now().UTC()
	return s.store.RegisterWorker(ctx, registration, s.cfg.Worker.HeartbeatTTL)
}

func (s *Service) Heartbeat(ctx context.Context, heartbeat workercontracts.WorkerHeartbeat) error {
	heartbeat.LastHeartbeatAt = s.now().UTC()
	return s.store.TouchWorkerHeartbeat(ctx, heartbeat, s.cfg.Worker.HeartbeatTTL)
}

func (s *Service) Reserve(ctx context.Context, request workercontracts.AttachRequest) (*workercontracts.WorkerLease, error) {
	registration, err := s.reserveWorker(ctx, workercontracts.ProtocolRDP, request.RequiredCapabilities)
	if err != nil {
		return nil, err
	}
	return s.AcquireLease(ctx, registration.WorkerID, request)
}

func (s *Service) reserveWorker(ctx context.Context, protocol workercontracts.Protocol, capabilities []string) (*workercontracts.WorkerRegistration, error) {
	workers, err := s.store.ListWorkers(ctx)
	if err != nil {
		return nil, err
	}
	now := s.now().UTC()
	for _, worker := range workers {
		if worker.Protocol != protocol || worker.Status != workercontracts.StatusOnline {
			continue
		}
		if now.Sub(worker.LastHeartbeatAt) > s.cfg.Worker.StaleLeaseGracePeriod+s.cfg.Worker.HeartbeatTTL {
			continue
		}
		if !hasCapabilities(worker.Capabilities, capabilities) {
			continue
		}
		return &worker, nil
	}
	return nil, ErrNoWorkerAvailable
}

func (s *Service) AcquireLease(ctx context.Context, workerID string, request workercontracts.AttachRequest) (*workercontracts.WorkerLease, error) {
	if request.SessionID == "" {
		request.SessionID = uuid.NewString()
	}
	now := s.now().UTC()
	lease := workercontracts.WorkerLease{
		LeaseID:              uuid.NewString(),
		WorkerID:             workerID,
		Protocol:             workercontracts.ProtocolRDP,
		ResourceID:           request.ResourceID,
		SessionID:            request.SessionID,
		Capabilities:         request.RequiredCapabilities,
		ControlStream:        "worker://control/" + workerID,
		ExpiresAt:            now.Add(s.cfg.Worker.LeaseTTL),
		RenderQualityProfile: normalizeRenderQualityProfile(request.RenderQualityProfile),
	}
	if err := s.store.AcquireLease(ctx, lease, s.cfg.Worker.LeaseTTL); err != nil {
		return nil, err
	}
	return &lease, nil
}

func (s *Service) GetSessionLease(ctx context.Context, sessionID string) (*workercontracts.WorkerLease, error) {
	return s.store.GetLeaseBySession(ctx, sessionID)
}

func (s *Service) RenewLease(ctx context.Context, leaseID string) (*workercontracts.WorkerLease, error) {
	lease, err := s.store.GetLease(ctx, leaseID)
	if err != nil || lease == nil {
		return lease, err
	}
	lease.ExpiresAt = s.now().UTC().Add(s.cfg.Worker.LeaseTTL)
	if err := s.store.RenewLease(ctx, *lease, s.cfg.Worker.LeaseTTL); err != nil {
		return nil, err
	}
	return lease, nil
}

func (s *Service) ReleaseLease(ctx context.Context, leaseID string) error {
	return s.store.ReleaseLease(ctx, leaseID)
}

func (s *Service) ReleaseSessionLease(ctx context.Context, sessionID string) error {
	lease, err := s.store.GetLeaseBySession(ctx, sessionID)
	if err != nil || lease == nil {
		return err
	}
	return s.store.ReleaseLease(ctx, lease.LeaseID)
}

func (s *Service) RecoverStaleLeases(ctx context.Context) ([]workercontracts.WorkerLease, error) {
	leases, err := s.store.ListLeases(ctx)
	if err != nil {
		return nil, err
	}
	var stale []workercontracts.WorkerLease
	now := s.now().UTC()
	for _, lease := range leases {
		registration, err := s.store.GetWorker(ctx, lease.WorkerID)
		if err != nil {
			return nil, err
		}
		if registration == nil || now.Sub(registration.LastHeartbeatAt) > s.cfg.Worker.StaleLeaseGracePeriod+s.cfg.Worker.HeartbeatTTL {
			if err := s.store.ReleaseLease(ctx, lease.LeaseID); err != nil {
				return nil, err
			}
			stale = append(stale, lease)
		}
	}
	return stale, nil
}

func (s *Service) ValidateSessionRuntime(ctx context.Context, sessionID, workerID string) (bool, string, error) {
	lease, err := s.store.GetLeaseBySession(ctx, sessionID)
	if err != nil {
		return false, "", err
	}
	if lease == nil {
		return false, "worker_lease_missing", nil
	}
	if workerID != "" && lease.WorkerID != workerID {
		_ = s.store.ReleaseLease(ctx, lease.LeaseID)
		return false, "worker_binding_mismatch", nil
	}
	now := s.now().UTC()
	if !lease.ExpiresAt.After(now) {
		_ = s.store.ReleaseLease(ctx, lease.LeaseID)
		return false, "worker_lease_expired", nil
	}
	registration, err := s.store.GetWorker(ctx, lease.WorkerID)
	if err != nil {
		return false, "", err
	}
	if registration == nil {
		_ = s.store.ReleaseLease(ctx, lease.LeaseID)
		return false, "worker_registration_missing", nil
	}
	if registration.Status != workercontracts.StatusOnline {
		return false, "worker_not_online", nil
	}
	if now.Sub(registration.LastHeartbeatAt) > s.cfg.Worker.StaleLeaseGracePeriod+s.cfg.Worker.HeartbeatTTL {
		_ = s.store.ReleaseLease(ctx, lease.LeaseID)
		return false, "worker_heartbeat_stale", nil
	}
	return true, "", nil
}

func (s *Service) PublishControl(ctx context.Context, envelope workercontracts.RoutedEnvelope) error {
	return s.store.AppendEnvelope(ctx, envelope)
}

func (s *Service) PublishInput(ctx context.Context, envelope workercontracts.RoutedEnvelope) error {
	return s.store.AppendEnvelope(ctx, envelope)
}

func hasCapabilities(workerCaps, required []string) bool {
	for _, capability := range required {
		if !slices.Contains(workerCaps, capability) {
			return false
		}
	}
	return true
}

func (s *Service) PrepareAttachment(ctx context.Context, session sessionbroker.RemoteSession, attachment sessionbroker.SessionAttachment, runtimeMetadata map[string]any) error {
	renderQualityProfile := normalizeRenderQualityProfile(session.RenderQualityProfile)
	if renderQualityProfile == "balanced" {
		renderQualityProfile = renderQualityProfileFromMetadata(session.Metadata)
	}
	if runtimeMetadata == nil {
		runtimeMetadata = decodeMetadata(session.Metadata)
	}
	return s.store.AppendAssignment(ctx, session.WorkerID, map[string]any{
		"type":                   "session_assignment",
		"session_id":             session.ID,
		"worker_id":              session.WorkerID,
		"attachment_id":          attachment.ID,
		"user_id":                attachment.UserID,
		"device_id":              attachment.DeviceID,
		"takeover_of":            attachment.TakeoverOf,
		"state":                  session.State,
		"render_quality_profile": renderQualityProfile,
		"metadata":               runtimeMetadata,
	})
}

func (s *Service) NotifyDetachment(ctx context.Context, session sessionbroker.RemoteSession, attachment sessionbroker.SessionAttachment) error {
	return s.PublishControl(ctx, workercontracts.RoutedEnvelope{
		SessionID:    session.ID,
		AttachmentID: attachment.ID,
		Type:         "control",
		Payload: map[string]any{
			"action": "detach",
		},
	})
}

func (s *Service) TerminateRemoteSession(ctx context.Context, sessionID, attachmentID string) error {
	return s.PublishControl(ctx, workercontracts.RoutedEnvelope{
		SessionID:    sessionID,
		AttachmentID: attachmentID,
		Type:         "control",
		Payload: map[string]any{
			"action": "terminate",
		},
	})
}

func decodeMetadata(payload []byte) map[string]any {
	var out map[string]any
	if len(payload) == 0 {
		return map[string]any{}
	}
	if err := json.Unmarshal(payload, &out); err != nil {
		return map[string]any{}
	}
	return out
}

func normalizeRenderQualityProfile(profile string) string {
	switch profile {
	case "low_bandwidth", "balanced", "high_quality", "text_priority":
		return profile
	default:
		return "balanced"
	}
}

func renderQualityProfileFromMetadata(metadata []byte) string {
	decoded := decodeMetadata(metadata)
	resource, _ := decoded["resource"].(map[string]any)
	if resource == nil {
		return "balanced"
	}
	if profile, ok := resource["render_quality_profile"].(string); ok && profile != "" {
		return normalizeRenderQualityProfile(profile)
	}
	return "balanced"
}