package tender

import (
	"context"
	"encoding/json"
	"fmt"
	"strings"
	"time"

	"github.com/redis/go-redis/v9"
	"go.mongodb.org/mongo-driver/v2/bson"
	"golang.org/x/sync/errgroup"

	"tm/internal/company"
	"tm/pkg/response"
)

const (
	recommendedTendersPageCacheKeyPrefix = "ai:recommendations:page:"
	recommendationPageCacheReadTimeout   = 3 * time.Second
	recommendationPageCacheBuildTimeout  = 5 * time.Minute
	recommendationPageCacheConcurrency   = 8
)

type cachedRecommendedTendersPage struct {
	BuiltAt   int64            `json:"built_at"`
	CompanyID string           `json:"company_id"`
	Language  string           `json:"language"`
	Items     []TenderResponse `json:"items"`
}

func recommendedTendersPageCacheKey(companyID, language string) string {
	return recommendedTendersPageCacheKeyPrefix +
		strings.TrimSpace(companyID) + ":" +
		strings.ToLower(strings.TrimSpace(language))
}

// ScheduleRefreshRecommendedTendersPageCache rebuilds the page cache for the service default language.
func (s *tenderService) ScheduleRefreshRecommendedTendersPageCache(companyID string) {
	s.schedulePageCacheRefreshForLanguage(companyID, s.defaultLanguage)
}

// InvalidateRecommendedTendersPageCache drops the cached page for the service default language.
func (s *tenderService) InvalidateRecommendedTendersPageCache(companyID string) {
	companyID = strings.TrimSpace(companyID)
	if companyID == "" || s.redisClient == nil {
		return
	}

	ctx, cancel := context.WithTimeout(context.Background(), recommendationPageCacheReadTimeout)
	defer cancel()
	s.deleteRecommendedTendersPageCache(ctx, companyID, s.defaultLanguage)
}

func (s *tenderService) schedulePageCacheRefreshForLanguage(companyID, language string) {
	companyID = strings.TrimSpace(companyID)
	language = strings.ToLower(strings.TrimSpace(language))
	if companyID == "" || language == "" || s.redisClient == nil {
		return
	}

	go func() {
		ctx, cancel := context.WithTimeout(context.Background(), recommendationPageCacheBuildTimeout)
		defer cancel()

		if err := s.buildRecommendedTendersPageCache(ctx, companyID, language); err != nil {
			s.logger.Warn("Failed to refresh recommended tenders page cache", map[string]interface{}{
				"company_id": companyID,
				"language":   language,
				"error":      err.Error(),
			})
		}
	}()
}

func (s *tenderService) buildRecommendedTendersPageCache(ctx context.Context, companyID, language string) error {
	recommendations, err := s.companyService.GetAIRecommendations(ctx, companyID)
	if err != nil {
		return err
	}
	if len(recommendations) == 0 {
		s.deleteRecommendedTendersPageCache(ctx, companyID, language)
		return nil
	}

	items, err := s.buildAllRankedRecommendations(ctx, recommendations)
	if err != nil {
		return err
	}
	if len(items) == 0 {
		s.deleteRecommendedTendersPageCache(ctx, companyID, language)
		return nil
	}

	responses := s.buildRecommendedTenderResponsesParallel(ctx, items, language)
	page := cachedRecommendedTendersPage{
		BuiltAt:   time.Now().Unix(),
		CompanyID: companyID,
		Language:  language,
		Items:     responses,
	}

	encoded, err := json.Marshal(page)
	if err != nil {
		return fmt.Errorf("encode recommended tenders page cache: %w", err)
	}

	writeCtx, cancel := context.WithTimeout(ctx, recommendationPageCacheReadTimeout)
	defer cancel()

	if err := s.redisClient.Set(writeCtx, recommendedTendersPageCacheKey(companyID, language), string(encoded), s.pageCacheTTL); err != nil {
		return fmt.Errorf("store recommended tenders page cache: %w", err)
	}

	s.logger.Info("Recommended tenders page cache built", map[string]interface{}{
		"company_id": companyID,
		"language":   language,
		"count":      len(responses),
	})
	return nil
}

func (s *tenderService) getRecommendedTendersPageCache(ctx context.Context, companyID, language string) ([]TenderResponse, bool) {
	if s.redisClient == nil {
		return nil, false
	}

	readCtx, cancel := context.WithTimeout(ctx, recommendationPageCacheReadTimeout)
	defer cancel()

	raw, err := s.redisClient.Get(readCtx, recommendedTendersPageCacheKey(companyID, language))
	if err != nil {
		if err != redis.Nil {
			s.logger.Warn("Failed to read recommended tenders page cache", map[string]interface{}{
				"company_id": companyID,
				"language":   language,
				"error":      err.Error(),
			})
		}
		return nil, false
	}

	var page cachedRecommendedTendersPage
	if err := json.Unmarshal([]byte(raw), &page); err != nil {
		s.logger.Warn("Failed to decode recommended tenders page cache", map[string]interface{}{
			"company_id": companyID,
			"language":   language,
			"error":      err.Error(),
		})
		s.deleteRecommendedTendersPageCache(ctx, companyID, language)
		return nil, false
	}
	if len(page.Items) == 0 {
		return nil, false
	}

	return page.Items, true
}

func (s *tenderService) deleteRecommendedTendersPageCache(ctx context.Context, companyID, language string) {
	if s.redisClient == nil {
		return
	}
	_ = s.redisClient.Del(ctx, recommendedTendersPageCacheKey(companyID, language))
}

func (s *tenderService) buildAllRankedRecommendations(
	ctx context.Context,
	recommendations []company.RecommendedTenderResponse,
) ([]rankedRecommendedTender, error) {
	seenTenderIDs := make(map[string]struct{}, len(recommendations))
	out := make([]rankedRecommendedTender, 0, len(recommendations))

	for start := 0; start < len(recommendations); start += recommendationResolveBatchSize {
		end := start + recommendationResolveBatchSize
		if end > len(recommendations) {
			end = len(recommendations)
		}

		tenderByRef, err := s.resolveRecommendedTenders(ctx, recommendations[start:end])
		if err != nil {
			return nil, err
		}

		for _, rec := range recommendations[start:end] {
			tenderRef := strings.TrimSpace(rec.TenderID)
			tender, ok := tenderByRef[tenderRef]
			if !ok {
				continue
			}
			if markResolvedRecommendedTenderSeen(seenTenderIDs, tender, tenderRef) {
				continue
			}

			out = append(out, rankedRecommendedTender{
				tender:    tender,
				rank:      rec.Rank,
				analysis:  rec.Analysis,
				tenderRef: tenderRef,
			})
		}
	}

	return out, nil
}

func (s *tenderService) buildRecommendedTenderResponsesParallel(
	ctx context.Context,
	items []rankedRecommendedTender,
	language string,
) []TenderResponse {
	if len(items) == 0 {
		return nil
	}

	out := make([]TenderResponse, len(items))
	if len(items) == 1 {
		out[0] = s.buildRecommendedTenderResponse(
			ctx, items[0].tender, items[0].rank, items[0].analysis, items[0].tenderRef, language,
			newRecommendationTranslationCache(),
		)
		return out
	}

	translationCache := newRecommendationTranslationCache()
	group, groupCtx := errgroup.WithContext(ctx)
	group.SetLimit(recommendationPageCacheConcurrency)

	for i := range items {
		i := i
		item := items[i]
		group.Go(func() error {
			out[i] = s.buildRecommendedTenderResponse(
				groupCtx, item.tender, item.rank, item.analysis, item.tenderRef, language, translationCache,
			)
			return nil
		})
	}

	if err := group.Wait(); err != nil {
		s.logger.Warn("Parallel recommendation page cache build degraded to sequential", map[string]interface{}{
			"error": err.Error(),
			"count": len(items),
		})
		for i, item := range items {
			out[i] = s.buildRecommendedTenderResponse(
				ctx, item.tender, item.rank, item.analysis, item.tenderRef, language, translationCache,
			)
		}
	}

	return out
}

func (s *tenderService) recommendFromPageCache(
	ctx context.Context,
	companyID string,
	companyIDs []string,
	form *SearchForm,
	pagination *response.Pagination,
	lang string,
) (*SearchResponse, bool) {
	var cached []TenderResponse
	if len(companyIDs) > 0 {
		cached = s.mergeCachedRecommendationPages(ctx, companyIDs, lang)
	} else {
		items, ok := s.getRecommendedTendersPageCache(ctx, companyID, lang)
		if !ok {
			return nil, false
		}
		cached = items
	}
	if len(cached) == 0 {
		return nil, false
	}

	excluded, excludedByCompany, err := s.loadRecommendationExclusions(ctx, form, companyID, companyIDs)
	if err != nil {
		return nil, false
	}

	now := time.Now().Unix()
	filtered := filterCachedRecommendedTenders(cached, form, companyIDs, excluded, excludedByCompany, now)
	total := int64(len(filtered))

	start := pagination.Offset
	if start > len(filtered) {
		start = len(filtered)
	}
	end := start + pagination.Limit
	if end > len(filtered) {
		end = len(filtered)
	}

	return &SearchResponse{
		Tenders:  append([]TenderResponse(nil), filtered[start:end]...),
		Metadata: pagination.ListMeta(total, "", end < len(filtered), start),
	}, true
}

func (s *tenderService) mergeCachedRecommendationPages(ctx context.Context, companyIDs []string, lang string) []TenderResponse {
	normalized := normalizeRecommendationCompanyScope(companyIDs)
	if len(normalized) == 0 {
		return nil
	}

	lists := make([][]TenderResponse, 0, len(normalized))
	for _, companyID := range normalized {
		items, ok := s.getRecommendedTendersPageCache(ctx, companyID, lang)
		if !ok || len(items) == 0 {
			return nil
		}
		lists = append(lists, items)
	}

	merged := make([]TenderResponse, 0)
	for _, list := range lists {
		merged = append(merged, list...)
	}
	return dedupeCachedRecommendedTendersByID(merged)
}

func dedupeCachedRecommendedTendersByID(items []TenderResponse) []TenderResponse {
	seen := make(map[string]struct{}, len(items))
	out := make([]TenderResponse, 0, len(items))
	for _, item := range items {
		key := strings.TrimSpace(item.ID)
		if key == "" {
			key = strings.TrimSpace(item.ProcedureRef)
		}
		if key == "" {
			continue
		}
		if _, exists := seen[key]; exists {
			continue
		}
		seen[key] = struct{}{}
		out = append(out, item)
	}
	return out
}

func filterCachedRecommendedTenders(
	items []TenderResponse,
	form *SearchForm,
	companyIDs []string,
	excluded map[string]struct{},
	excludedByCompany map[string]map[string]struct{},
	now int64,
) []TenderResponse {
	if len(items) == 0 {
		return nil
	}

	out := make([]TenderResponse, 0, len(items))
	for _, item := range items {
		tender := tenderFromRecommendationResponse(item)
		tenderRef := strings.TrimSpace(item.ProcedureRef)

		if len(companyIDs) > 0 {
			if isRecommendedTenderExcludedForAllCompanies(tender, tenderRef, excludedByCompany, companyIDs) {
				continue
			}
		} else if isRecommendedTenderExcluded(tender, tenderRef, excluded) {
			continue
		}
		if form.OnlyActiveDeadlines && !tender.IsRecommendable(now) {
			continue
		}
		if len(form.Status) > 0 && !statusAllowed(tender.Status, form.Status) {
			continue
		}

		out = append(out, item)
	}
	return out
}

func tenderFromRecommendationResponse(item TenderResponse) Tender {
	var tender Tender
	if id, err := bson.ObjectIDFromHex(strings.TrimSpace(item.ID)); err == nil {
		tender.ID = id
	}
	tender.ContractFolderID = item.ContractFolderID
	tender.NoticePublicationID = item.NoticePublicationID
	tender.RelatedNoticePublicationIDs = append([]string(nil), item.RelatedNoticePublicationIDs...)
	tender.Status = item.Status
	tender.PublicationDate = item.PublicationDate
	tender.SubmissionDeadline = item.SubmissionDeadline
	tender.TenderDeadline = item.TenderDeadline
	return tender
}

// RecommendedTendersPageCacheKeyPrefix is shared with company invalidation logic.
const RecommendedTendersPageCacheKeyPrefix = recommendedTendersPageCacheKeyPrefix

// RecommendedTendersPageCacheKey builds the Redis key for a cached recommendation page.
func RecommendedTendersPageCacheKey(companyID, language string) string {
	return recommendedTendersPageCacheKey(companyID, language)
}