package tender

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

	goredis "github.com/redis/go-redis/v9"
	"tm/pkg/response"
)

const (
	searchListCacheTTL = 60 * time.Second
	// searchListCacheStaleTTL bounds how long the default unfiltered list may lag after
	// writes. Only isCacheableSearchList queries use this cache (~5 min max staleness).
	searchListCacheStaleTTL  = 5 * time.Minute
	searchListCacheKeyPrefix = "tender:search:list:"
)

type searchListCacheEntry struct {
	expiresAt  time.Time
	staleUntil time.Time
	value      *SearchResponse
}

type cachedSearchListPayload struct {
	Tenders  []TenderResponse `json:"tenders"`
	Metadata *response.Meta   `json:"metadata,omitempty"`
}

func searchResponseToCachePayload(resp *SearchResponse) *cachedSearchListPayload {
	if resp == nil {
		return nil
	}
	return &cachedSearchListPayload{
		Tenders:  resp.Tenders,
		Metadata: resp.Metadata,
	}
}

func cachePayloadToSearchResponse(payload *cachedSearchListPayload) *SearchResponse {
	if payload == nil {
		return nil
	}
	return &SearchResponse{
		Tenders:  payload.Tenders,
		Metadata: payload.Metadata,
	}
}

func isCacheableSearchList(form *SearchForm, pagination *response.Pagination) bool {
	if form == nil || pagination == nil {
		return false
	}
	if form.HasListFilters() {
		return false
	}
	if form.CompanyID != nil && strings.TrimSpace(*form.CompanyID) != "" {
		return false
	}
	if form.CustomerID != nil && strings.TrimSpace(*form.CustomerID) != "" {
		return false
	}
	if len(form.CompanyIDs) > 0 {
		return false
	}
	if pagination.Cursor != "" || pagination.IncludeTotal || pagination.Offset != 0 {
		return false
	}
	if pagination.Limit <= 0 || pagination.Limit > 20 {
		return false
	}

	sortBy := pagination.SortBy
	if sortBy == "" {
		sortBy = "created_at"
	}
	sortOrder := pagination.SortOrder
	if sortOrder == "" {
		sortOrder = "desc"
	}

	return sortBy == "created_at" && sortOrder == "desc"
}

func searchListCacheKey(pagination *response.Pagination, language string) string {
	return fmt.Sprintf("%d:%s", pagination.Limit, strings.ToLower(strings.TrimSpace(language)))
}

func (s *tenderService) cachedSearchList(ctx context.Context, form *SearchForm, pagination *response.Pagination, language string, load func(context.Context) (*SearchResponse, error)) (*SearchResponse, error) {
	if !isCacheableSearchList(form, pagination) {
		return load(ctx)
	}

	// Cached *SearchResponse values (including the Tenders slice) are shared across
	// concurrent callers via singleflight and stale hits; treat as read-only.
	cacheKey := searchListCacheKey(pagination, language)
	redisKey := searchListCacheKeyPrefix + cacheKey

	if cached, ok := s.getFreshSearchListCache(cacheKey); ok {
		return cached, nil
	}
	if stale, ok := s.getStaleSearchListCache(cacheKey); ok {
		go s.refreshSearchListCache(cacheKey, redisKey, load)
		return stale, nil
	}
	if cached, ok := s.getRedisSearchListCache(ctx, redisKey); ok {
		s.storeSearchListCache(cacheKey, cached)
		go s.refreshSearchListCache(cacheKey, redisKey, load)
		return cached, nil
	}

	out, err, _ := s.searchListCacheGroup.Do(cacheKey, func() (interface{}, error) {
		if cached, ok := s.getFreshSearchListCache(cacheKey); ok {
			return cached, nil
		}

		result, err := load(context.WithoutCancel(ctx))
		if err != nil {
			return nil, err
		}

		s.storeSearchListCache(cacheKey, result)
		s.storeRedisSearchListCache(context.Background(), redisKey, result)
		return result, nil
	})
	if err != nil {
		return nil, err
	}

	return out.(*SearchResponse), nil
}

func (s *tenderService) refreshSearchListCache(cacheKey, redisKey string, load func(context.Context) (*SearchResponse, error)) {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
	defer cancel()

	result, err := load(ctx)
	if err != nil {
		s.logger.Warn("Failed to refresh tender search list cache", map[string]interface{}{
			"cache_key": cacheKey,
			"error":     err.Error(),
		})
		return
	}

	s.storeSearchListCache(cacheKey, result)
	s.storeRedisSearchListCache(context.Background(), redisKey, result)
}

func (s *tenderService) getFreshSearchListCache(cacheKey string) (*SearchResponse, bool) {
	s.searchListCacheMu.Lock()
	defer s.searchListCacheMu.Unlock()

	entry, ok := s.searchListCache[cacheKey]
	if !ok || time.Now().After(entry.expiresAt) {
		return nil, false
	}
	return entry.value, true
}

func (s *tenderService) getStaleSearchListCache(cacheKey string) (*SearchResponse, bool) {
	s.searchListCacheMu.Lock()
	defer s.searchListCacheMu.Unlock()

	entry, ok := s.searchListCache[cacheKey]
	if !ok || time.Now().After(entry.staleUntil) {
		if ok {
			delete(s.searchListCache, cacheKey)
		}
		return nil, false
	}
	return entry.value, true
}

func (s *tenderService) storeSearchListCache(cacheKey string, value *SearchResponse) {
	now := time.Now()

	s.searchListCacheMu.Lock()
	defer s.searchListCacheMu.Unlock()

	s.searchListCache[cacheKey] = searchListCacheEntry{
		expiresAt:  now.Add(searchListCacheTTL),
		staleUntil: now.Add(searchListCacheTTL + searchListCacheStaleTTL),
		value:      value,
	}
}

func (s *tenderService) getRedisSearchListCache(ctx context.Context, redisKey string) (*SearchResponse, bool) {
	if s.redisClient == nil {
		return nil, false
	}

	raw, err := s.redisClient.Get(ctx, redisKey)
	if err != nil {
		if err != goredis.Nil {
			s.logger.Warn("Failed to read tender search list cache from Redis", map[string]interface{}{
				"cache_key": redisKey,
				"error":     err.Error(),
			})
		}
		return nil, false
	}

	var cached cachedSearchListPayload
	if err := json.Unmarshal([]byte(raw), &cached); err != nil {
		s.logger.Warn("Failed to decode tender search list cache from Redis", map[string]interface{}{
			"cache_key": redisKey,
			"error":     err.Error(),
		})
		_ = s.redisClient.Del(ctx, redisKey)
		return nil, false
	}

	return cachePayloadToSearchResponse(&cached), true
}

func (s *tenderService) storeRedisSearchListCache(ctx context.Context, redisKey string, value *SearchResponse) {
	if s.redisClient == nil || value == nil {
		return
	}

	encoded, err := json.Marshal(searchResponseToCachePayload(value))
	if err != nil {
		s.logger.Warn("Failed to encode tender search list cache for Redis", map[string]interface{}{
			"cache_key": redisKey,
			"error":     err.Error(),
		})
		return
	}

	if err := s.redisClient.Set(ctx, redisKey, string(encoded), searchListCacheTTL+searchListCacheStaleTTL); err != nil {
		s.logger.Warn("Failed to store tender search list cache in Redis", map[string]interface{}{
			"cache_key": redisKey,
			"error":     err.Error(),
		})
	}
}