package emailtemplates

import (
	"Yimaru-Backend/internal/domain"
	"Yimaru-Backend/internal/ports"
	"context"
	"errors"
	"fmt"
	"strings"
	"sync"
	"time"

	"github.com/jackc/pgx/v5"
)

var (
	errSlugRequired  = errors.New("slug is required")
	errInvalidSlug   = errors.New("slug must start with a letter and contain only lowercase letters, numbers, and underscores")
	errInvalidStatus = fmt.Errorf("status must be one of %s, %s", domain.EmailTemplateStatusActive, domain.EmailTemplateStatusInactive)
)

const cacheTTL = 2 * time.Minute

type cacheEntry struct {
	template  domain.EmailTemplate
	expiresAt time.Time
}

type Service struct {
	store ports.EmailTemplateStore

	mu    sync.RWMutex
	cache map[string]cacheEntry
}

func NewService(store ports.EmailTemplateStore) *Service {
	return &Service{
		store: store,
		cache: make(map[string]cacheEntry),
	}
}

func (s *Service) CreateEmailTemplate(ctx context.Context, input domain.CreateEmailTemplateInput) (domain.EmailTemplate, error) {
	slug, err := normalizeSlug(input.Slug)
	if err != nil {
		return domain.EmailTemplate{}, err
	}

	input.Slug = slug
	input.Name = strings.TrimSpace(input.Name)
	input.Subject = strings.TrimSpace(input.Subject)
	input.BodyText = strings.TrimSpace(input.BodyText)
	input.BodyHTML = strings.TrimSpace(input.BodyHTML)
	input.Variables = normalizeVariables(input.Variables)

	if input.Name == "" {
		return domain.EmailTemplate{}, fmt.Errorf("name is required")
	}
	if input.Subject == "" {
		return domain.EmailTemplate{}, fmt.Errorf("subject is required")
	}
	if input.BodyText == "" {
		return domain.EmailTemplate{}, fmt.Errorf("body_text is required")
	}
	if input.BodyHTML == "" {
		return domain.EmailTemplate{}, fmt.Errorf("body_html is required")
	}

	status, err := normalizeStatus(input.Status)
	if err != nil {
		return domain.EmailTemplate{}, err
	}
	input.Status = &status

	if err := s.validateTemplateSyntax(input.Subject, input.BodyText, input.BodyHTML); err != nil {
		return domain.EmailTemplate{}, err
	}

	tmpl, err := s.store.CreateEmailTemplate(ctx, input)
	if err != nil {
		return domain.EmailTemplate{}, err
	}

	s.invalidateCache(tmpl.Slug)
	return tmpl, nil
}

func (s *Service) UpdateEmailTemplate(ctx context.Context, id int64, input domain.UpdateEmailTemplateInput) (domain.EmailTemplate, error) {
	if id <= 0 {
		return domain.EmailTemplate{}, fmt.Errorf("invalid email template id")
	}

	if input.Name != nil {
		trimmed := strings.TrimSpace(*input.Name)
		if trimmed == "" {
			return domain.EmailTemplate{}, fmt.Errorf("name cannot be empty")
		}
		input.Name = &trimmed
	}
	if input.Subject != nil {
		trimmed := strings.TrimSpace(*input.Subject)
		if trimmed == "" {
			return domain.EmailTemplate{}, fmt.Errorf("subject cannot be empty")
		}
		input.Subject = &trimmed
	}
	if input.BodyText != nil {
		trimmed := strings.TrimSpace(*input.BodyText)
		if trimmed == "" {
			return domain.EmailTemplate{}, fmt.Errorf("body_text cannot be empty")
		}
		input.BodyText = &trimmed
	}
	if input.BodyHTML != nil {
		trimmed := strings.TrimSpace(*input.BodyHTML)
		if trimmed == "" {
			return domain.EmailTemplate{}, fmt.Errorf("body_html cannot be empty")
		}
		input.BodyHTML = &trimmed
	}
	if input.Variables != nil {
		input.Variables = normalizeVariables(input.Variables)
	}
	if input.Status != nil {
		status, err := normalizeStatus(input.Status)
		if err != nil {
			return domain.EmailTemplate{}, err
		}
		input.Status = &status
	}

	current, err := s.store.GetEmailTemplateByID(ctx, id, true)
	if err != nil {
		return domain.EmailTemplate{}, err
	}

	subject := current.Subject
	if input.Subject != nil {
		subject = *input.Subject
	}
	bodyText := current.BodyText
	if input.BodyText != nil {
		bodyText = *input.BodyText
	}
	bodyHTML := current.BodyHTML
	if input.BodyHTML != nil {
		bodyHTML = *input.BodyHTML
	}

	if err := s.validateTemplateSyntax(subject, bodyText, bodyHTML); err != nil {
		return domain.EmailTemplate{}, err
	}

	tmpl, err := s.store.UpdateEmailTemplate(ctx, id, input)
	if err != nil {
		return domain.EmailTemplate{}, err
	}

	s.invalidateCache(tmpl.Slug)
	return tmpl, nil
}

func (s *Service) GetEmailTemplateByID(ctx context.Context, id int64, includeInactive bool) (domain.EmailTemplate, error) {
	if id <= 0 {
		return domain.EmailTemplate{}, fmt.Errorf("invalid email template id")
	}
	return s.store.GetEmailTemplateByID(ctx, id, includeInactive)
}

func (s *Service) GetEmailTemplateBySlug(ctx context.Context, slug string, includeInactive bool) (domain.EmailTemplate, error) {
	normalized, err := normalizeSlug(slug)
	if err != nil {
		return domain.EmailTemplate{}, err
	}
	return s.store.GetEmailTemplateBySlug(ctx, normalized, includeInactive)
}

func (s *Service) ListEmailTemplates(ctx context.Context, status *string, query *string, limit int32, offset int32) ([]domain.EmailTemplate, int64, error) {
	if status != nil {
		normalized, err := normalizeStatus(status)
		if err != nil {
			return nil, 0, err
		}
		status = &normalized
	}
	if query != nil {
		trimmed := strings.TrimSpace(*query)
		if trimmed == "" {
			query = nil
		} else {
			query = &trimmed
		}
	}
	if limit <= 0 {
		limit = 20
	}
	if limit > 200 {
		limit = 200
	}
	if offset < 0 {
		offset = 0
	}
	return s.store.ListEmailTemplates(ctx, status, query, limit, offset)
}

func (s *Service) DeleteEmailTemplate(ctx context.Context, id int64) error {
	if id <= 0 {
		return fmt.Errorf("invalid email template id")
	}

	tmpl, err := s.store.GetEmailTemplateByID(ctx, id, true)
	if err != nil {
		return err
	}
	if tmpl.IsSystem {
		return fmt.Errorf("system email templates cannot be deleted")
	}

	if err := s.store.DeleteEmailTemplate(ctx, id); err != nil {
		return err
	}

	s.invalidateCache(tmpl.Slug)
	return nil
}

func (s *Service) PreviewEmailTemplate(ctx context.Context, input domain.PreviewEmailTemplateInput) (domain.RenderedEmail, error) {
	slug, err := normalizeSlug(input.Slug)
	if err != nil {
		return domain.RenderedEmail{}, err
	}

	tmpl, err := s.resolveTemplate(ctx, slug, true)
	if err != nil {
		return domain.RenderedEmail{}, err
	}

	return renderTemplateFields(tmpl, input.Variables)
}

func (s *Service) Render(ctx context.Context, slug string, data map[string]any) (domain.RenderedEmail, error) {
	normalized, err := normalizeSlug(slug)
	if err != nil {
		return domain.RenderedEmail{}, err
	}

	tmpl, err := s.resolveTemplate(ctx, normalized, false)
	if err != nil {
		return domain.RenderedEmail{}, err
	}

	return renderTemplateFields(tmpl, data)
}

func (s *Service) resolveTemplate(ctx context.Context, slug string, includeInactive bool) (domain.EmailTemplate, error) {
	if !includeInactive {
		if tmpl, ok := s.getCached(slug); ok {
			return tmpl, nil
		}
	}

	tmpl, err := s.store.GetEmailTemplateBySlug(ctx, slug, includeInactive)
	if err == nil {
		if !includeInactive && tmpl.Status == domain.EmailTemplateStatusActive {
			s.setCached(slug, tmpl)
		}
		return tmpl, nil
	}
	if !errors.Is(err, pgx.ErrNoRows) {
		return domain.EmailTemplate{}, err
	}

	fallback, ok := defaultTemplate(slug)
	if !ok {
		return domain.EmailTemplate{}, fmt.Errorf("email template not found: %s", slug)
	}
	return fallback, nil
}

func (s *Service) validateTemplateSyntax(subject, bodyText, bodyHTML string) error {
	if _, err := newTextTemplate("validate-subject", subject); err != nil {
		return fmt.Errorf("invalid subject template: %w", err)
	}
	if _, err := newTextTemplate("validate-text", bodyText); err != nil {
		return fmt.Errorf("invalid body_text template: %w", err)
	}
	if _, err := newHTMLTemplate("validate-html", bodyHTML); err != nil {
		return fmt.Errorf("invalid body_html template: %w", err)
	}
	return nil
}

func (s *Service) getCached(slug string) (domain.EmailTemplate, bool) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	entry, ok := s.cache[slug]
	if !ok || time.Now().After(entry.expiresAt) {
		return domain.EmailTemplate{}, false
	}
	return entry.template, true
}

func (s *Service) setCached(slug string, tmpl domain.EmailTemplate) {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.cache[slug] = cacheEntry{
		template:  tmpl,
		expiresAt: time.Now().Add(cacheTTL),
	}
}

func (s *Service) invalidateCache(slug string) {
	s.mu.Lock()
	defer s.mu.Unlock()
	delete(s.cache, slug)
}