package service

import (
	"errors"
	"fmt"
	"log"
	"net/url"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/michael/flowreader/internal/domain"
)

// Feed service errors
var (
	ErrInvalidURL   = errors.New("invalid feed URL")
	ErrFeedExists   = errors.New("feed already exists")
	ErrFeedNotFound = errors.New("feed not found")
	ErrUnauthorized = errors.New("unauthorized access")
	ErrTooManyFeeds = errors.New("too many feeds in OPML file (max 500)")
)

// maxOPMLFeeds bounds a single OPML import.
const maxOPMLFeeds = 500

// validFeedURL accepts only absolute http(s) URLs.
func validFeedURL(raw string) (string, bool) {
	u, err := url.ParseRequestURI(raw)
	if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" || len(raw) > 2048 {
		return "", false
	}
	return u.String(), true
}

// FeedService handles feed-related business logic.
type FeedService struct {
	feedRepo domain.FeedRepository
}

// NewFeedService creates a new feed service.
func NewFeedService(feedRepo domain.FeedRepository) *FeedService {
	return &FeedService{feedRepo: feedRepo}
}

// AddFeedRequest contains the data needed to add a new feed.
type AddFeedRequest struct {
	URL    string    `json:"url"`
	UserID uuid.UUID `json:"-"`
}

// AddFeedResponse contains the created feed data.
type AddFeedResponse struct {
	ID        uuid.UUID `json:"id"`
	URL       string    `json:"url"`
	Title     string    `json:"title"`
	CreatedAt time.Time `json:"created_at"`
}

// AddFeed creates a new feed subscription.
func (s *FeedService) AddFeed(req AddFeedRequest) (*AddFeedResponse, error) {
	// Validate and normalize URL
	normalizedURL, ok := validFeedURL(strings.TrimSpace(req.URL))
	if !ok {
		return nil, ErrInvalidURL
	}

	// Check if feed already exists for this user
	existing, err := s.feedRepo.GetByURL(req.UserID, normalizedURL)
	if err != nil {
		return nil, fmt.Errorf("checking existing feed: %w", err)
	}
	if existing != nil {
		return nil, ErrFeedExists
	}

	// Create feed (title will be updated after first fetch)
	now := time.Now()
	feed := &domain.Feed{
		ID:        uuid.New(),
		UserID:    req.UserID,
		URL:       normalizedURL,
		Title:     normalizedURL, // Temporary title until fetched
		CreatedAt: now,
		UpdatedAt: now,
	}

	if err := s.feedRepo.Create(feed); err != nil {
		return nil, fmt.Errorf("creating feed: %w", err)
	}

	return &AddFeedResponse{
		ID:        feed.ID,
		URL:       feed.URL,
		Title:     feed.Title,
		CreatedAt: feed.CreatedAt,
	}, nil
}

// GetUserFeeds returns all feeds for a user.
func (s *FeedService) GetUserFeeds(userID uuid.UUID) ([]*domain.Feed, error) {
	feeds, err := s.feedRepo.GetByUserID(userID)
	if err != nil {
		return nil, fmt.Errorf("getting user feeds: %w", err)
	}
	return feeds, nil
}

// GetFeed returns a single feed by ID, verifying ownership.
func (s *FeedService) GetFeed(feedID, userID uuid.UUID) (*domain.Feed, error) {
	feed, err := s.feedRepo.GetByID(feedID)
	if err != nil {
		return nil, fmt.Errorf("getting feed: %w", err)
	}
	if feed == nil {
		return nil, ErrFeedNotFound
	}
	if feed.UserID != userID {
		return nil, ErrUnauthorized
	}
	return feed, nil
}

// DeleteFeed removes a feed subscription.
func (s *FeedService) DeleteFeed(feedID, userID uuid.UUID) error {
	feed, err := s.feedRepo.GetByID(feedID)
	if err != nil {
		return fmt.Errorf("getting feed: %w", err)
	}
	if feed == nil {
		return ErrFeedNotFound
	}
	if feed.UserID != userID {
		return ErrUnauthorized
	}

	if err := s.feedRepo.Delete(feedID); err != nil {
		return fmt.Errorf("deleting feed: %w", err)
	}

	return nil
}

// UpdateFeed updates a feed's title.
func (s *FeedService) UpdateFeed(feedID, userID uuid.UUID, title string) (*domain.Feed, error) {
	feed, err := s.feedRepo.GetByID(feedID)
	if err != nil {
		return nil, fmt.Errorf("getting feed: %w", err)
	}
	if feed == nil {
		return nil, ErrFeedNotFound
	}
	if feed.UserID != userID {
		return nil, ErrUnauthorized
	}

	feed.Title = title
	// UpdatedAt is handled by repo or we can set it here if we strictly follow domain logic, 
    // but repo.Update sets it to time.Now().

	if err := s.feedRepo.Update(feed); err != nil {
		return nil, fmt.Errorf("updating feed: %w", err)
	}

	return feed, nil
}

// ImportOPMLResult contains the result of an OPML import.
type ImportOPMLResult struct {
	Imported int      `json:"imported"`
	Skipped  int      `json:"skipped"`
	Errors   []string `json:"errors,omitempty"`
}

// ImportOPML imports feeds from an OPML file.
func (s *FeedService) ImportOPML(userID uuid.UUID, opmlFeeds []OPMLFeedInfo) (*ImportOPMLResult, error) {
	result := &ImportOPMLResult{}
	if len(opmlFeeds) > maxOPMLFeeds {
		return nil, ErrTooManyFeeds
	}

	for _, opmlFeed := range opmlFeeds {
		// Validate URL (http/https only)
		feedURL, ok := validFeedURL(strings.TrimSpace(opmlFeed.URL))
		if !ok {
			result.Errors = append(result.Errors, fmt.Sprintf("Invalid URL: %.200s", opmlFeed.URL))
			result.Skipped++
			continue
		}
		opmlFeed.URL = feedURL
		if _, ok := validFeedURL(opmlFeed.SiteURL); !ok {
			opmlFeed.SiteURL = ""
		}

		// Check if already exists
		existing, err := s.feedRepo.GetByURL(userID, opmlFeed.URL)
		if err != nil {
			log.Printf("OPML import: checking %s: %v", opmlFeed.URL, err)
			result.Errors = append(result.Errors, fmt.Sprintf("Could not import %.200s", opmlFeed.URL))
			result.Skipped++
			continue
		}
		if existing != nil {
			result.Skipped++
			continue
		}

		// Create feed with title from OPML
		now := time.Now()
		feed := &domain.Feed{
			ID:        uuid.New(),
			UserID:    userID,
			URL:       opmlFeed.URL,
			Title:     opmlFeed.Title,
			SiteURL:   opmlFeed.SiteURL,
			CreatedAt: now,
			UpdatedAt: now,
		}

		if feed.Title == "" {
			feed.Title = opmlFeed.URL
		}

		if err := s.feedRepo.Create(feed); err != nil {
			log.Printf("OPML import: creating %s: %v", opmlFeed.URL, err)
			result.Errors = append(result.Errors, fmt.Sprintf("Could not import %.200s", opmlFeed.URL))
			result.Skipped++
			continue
		}

		result.Imported++
	}

	return result, nil
}

// OPMLFeedInfo contains feed info from OPML parsing.
type OPMLFeedInfo struct {
	URL     string
	Title   string
	SiteURL string
}