package notifications

import (
	"context"
	"errors"
	"fmt"
	"time"

	"bookra/apps/backend/internal/config"
	"bookra/apps/backend/internal/db"
	"bookra/apps/backend/internal/domain"
)

var ErrUnsupportedChannel = errors.New("unsupported notification channel")

type DeliveryReceipt struct {
	Provider   string
	ExternalID string
}

type EmailMessage struct {
	From    string
	To      string
	Subject string
	Text    string
}

type SMSMessage struct {
	From string
	To   string
	Text string
}

type EmailProvider interface {
	Send(context.Context, EmailMessage) (DeliveryReceipt, error)
}

type SMSProvider interface {
	Send(context.Context, SMSMessage) (DeliveryReceipt, error)
}

type Service struct {
	cfg           config.Config
	repo          db.Repository
	emailProvider EmailProvider
	smsProvider   SMSProvider
	now           func() time.Time
}

func NewService(cfg config.Config, repo db.Repository) *Service {
	return &Service{
		cfg:           cfg,
		repo:          repo,
		emailProvider: noopEmailProvider{},
		smsProvider:   noopSMSProvider{},
		now:           func() time.Time { return time.Now().UTC() },
	}
}

func (s *Service) DispatchDue(ctx context.Context, limit int) (domain.DispatchReminderJobsResponse, error) {
	if limit <= 0 {
		limit = 25
	}

	jobs, err := s.repo.ListDueReminderJobs(ctx, s.now(), limit)
	if err != nil {
		return domain.DispatchReminderJobsResponse{}, err
	}

	response := domain.DispatchReminderJobsResponse{}
	for _, job := range jobs {
		response.ProcessedCount++

		status := "sent"
		provider := "unknown"
		externalID := ""
		errorMessage := ""

		switch job.Channel {
		case "email":
			receipt, sendErr := s.emailProvider.Send(ctx, renderEmailMessage(s.cfg.EmailFrom, job))
			if sendErr != nil {
				status = "failed"
				errorMessage = sendErr.Error()
			} else {
				provider = receipt.Provider
				externalID = receipt.ExternalID
			}
		case "sms":
			receipt, sendErr := s.smsProvider.Send(ctx, renderSMSMessage(s.cfg.SMSFrom, job))
			if sendErr != nil {
				status = "failed"
				errorMessage = sendErr.Error()
			} else {
				provider = receipt.Provider
				externalID = receipt.ExternalID
			}
		default:
			status = "failed"
			errorMessage = ErrUnsupportedChannel.Error()
		}

		if provider == "unknown" {
			if job.Channel == "email" {
				provider = "noop-email"
			} else if job.Channel == "sms" {
				provider = "noop-sms"
			}
		}

		if err := s.repo.MarkReminderJobDispatched(ctx, job.ID, status, s.now()); err != nil {
			return domain.DispatchReminderJobsResponse{}, err
		}
		if err := s.repo.CreateNotificationDeliveryLog(ctx, db.NotificationDeliveryLogParams{
			TenantID:      job.TenantID,
			ReminderJobID: job.ID,
			Channel:       job.Channel,
			Provider:      provider,
			Recipient:     reminderRecipient(job),
			Status:        status,
			ExternalID:    externalID,
			ErrorMessage:  errorMessage,
		}); err != nil {
			return domain.DispatchReminderJobsResponse{}, err
		}

		if status == "sent" {
			response.SentCount++
		} else {
			response.FailedCount++
		}
	}

	return response, nil
}

func renderEmailMessage(from string, job db.ReminderJobRecord) EmailMessage {
	subject, body := renderReminderCopy(job)
	return EmailMessage{
		From:    from,
		To:      job.CustomerEmail,
		Subject: subject,
		Text:    body,
	}
}

func renderSMSMessage(from string, job db.ReminderJobRecord) SMSMessage {
	subject, body := renderReminderCopy(job)
	return SMSMessage{
		From: from,
		To:   job.CustomerEmail,
		Text: fmt.Sprintf("%s: %s", subject, body),
	}
}

func renderReminderCopy(job db.ReminderJobRecord) (string, string) {
	startLabel := localizedStartsAt(job)

	if job.Locale == "cs" {
		return "Pripominka rezervace Bookra", fmt.Sprintf(
			"Dobry den %s,\n\npripominame rezervaci %s u %s na %s.\n\nReference: %s\n",
			job.CustomerName,
			job.Reference,
			job.TenantName,
			startLabel,
			job.Reference,
		)
	}

	return "Bookra booking reminder", fmt.Sprintf(
		"Hello %s,\n\nthis is a reminder for booking %s with %s at %s.\n\nReference: %s\n",
		job.CustomerName,
		job.Reference,
		job.TenantName,
		startLabel,
		job.Reference,
	)
}

func localizedStartsAt(job db.ReminderJobRecord) string {
	location, err := time.LoadLocation(job.Timezone)
	if err != nil {
		location = time.UTC
	}
	localStartsAt := job.StartsAt.In(location)
	if job.Locale == "cs" {
		return localStartsAt.Format("02.01.2006 15:04")
	}
	return localStartsAt.Format("Jan 02, 2006 15:04")
}

func reminderRecipient(job db.ReminderJobRecord) string {
	if job.Channel == "email" {
		return job.CustomerEmail
	}
	return job.CustomerEmail
}

type noopEmailProvider struct{}

func (noopEmailProvider) Send(_ context.Context, message EmailMessage) (DeliveryReceipt, error) {
	if message.To == "" {
		return DeliveryReceipt{Provider: "noop-email"}, errors.New("missing email recipient")
	}
	return DeliveryReceipt{
		Provider:   "noop-email",
		ExternalID: fmt.Sprintf("noop-email-%d", time.Now().UnixNano()),
	}, nil
}

type noopSMSProvider struct{}

func (noopSMSProvider) Send(_ context.Context, message SMSMessage) (DeliveryReceipt, error) {
	if message.To == "" {
		return DeliveryReceipt{Provider: "noop-sms"}, errors.New("missing sms recipient")
	}
	return DeliveryReceipt{
		Provider:   "noop-sms",
		ExternalID: fmt.Sprintf("noop-sms-%d", time.Now().UnixNano()),
	}, nil
}