package services

import (
	"context"
	"encoding/json"
	"fmt"
	"hash/fnv"
	"sync"
	"time"

	"github.com/redis/go-redis/v9"
	"github.com/rs/zerolog/log"

	"github.com/treytartt/honeydue-api/internal/config"
	"github.com/treytartt/honeydue-api/internal/i18n"
)

// CacheService provides Redis caching functionality
type CacheService struct {
	client *redis.Client
}

var (
	cacheInstance *CacheService
	cacheOnce     sync.Once
)

// NewCacheService creates a new cache service (thread-safe via sync.Once)
func NewCacheService(cfg *config.RedisConfig) (*CacheService, error) {
	var initErr error

	cacheOnce.Do(func() {
		opt, err := redis.ParseURL(cfg.URL)
		if err != nil {
			initErr = fmt.Errorf("failed to parse Redis URL: %w", err)
			return
		}

		if cfg.Password != "" {
			opt.Password = cfg.Password
		}
		if cfg.DB != 0 {
			opt.DB = cfg.DB
		}

		client := redis.NewClient(opt)

		// Test connection
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()

		if err := client.Ping(ctx).Err(); err != nil {
			initErr = fmt.Errorf("failed to connect to Redis: %w", err)
			// NOTE: Don't reassign `cacheOnce = sync.Once{}` here. Mutating the
			// Once from within its own Do() callback fatals with "unlock of
			// unlocked mutex" because Do is holding the inner lock while we
			// zero it. main.go handles the error (caching disabled, keep running);
			// a pod restart is the right "retry" path for a transient Redis
			// outage, not in-process.
			return
		}

		// S-14: Mask credentials in Redis URL before logging
		log.Info().
			Str("url", config.MaskURLCredentials(cfg.URL)).
			Int("db", opt.DB).
			Msg("Connected to Redis")

		cacheInstance = &CacheService{client: client}
	})

	if initErr != nil {
		return nil, initErr
	}

	return cacheInstance, nil
}

// GetCache returns the cache service instance
func GetCache() *CacheService {
	return cacheInstance
}

// Client returns the underlying Redis client
func (c *CacheService) Client() *redis.Client {
	return c.client
}

// Set stores a value with expiration
func (c *CacheService) Set(ctx context.Context, key string, value interface{}, expiration time.Duration) error {
	data, err := json.Marshal(value)
	if err != nil {
		return fmt.Errorf("failed to marshal value: %w", err)
	}

	return c.client.Set(ctx, key, data, expiration).Err()
}

// Get retrieves a value by key
func (c *CacheService) Get(ctx context.Context, key string, dest interface{}) error {
	data, err := c.client.Get(ctx, key).Bytes()
	if err != nil {
		return err
	}

	return json.Unmarshal(data, dest)
}

// GetString retrieves a string value by key
func (c *CacheService) GetString(ctx context.Context, key string) (string, error) {
	return c.client.Get(ctx, key).Result()
}

// SetString stores a string value with expiration
func (c *CacheService) SetString(ctx context.Context, key string, value string, expiration time.Duration) error {
	return c.client.Set(ctx, key, value, expiration).Err()
}

// Delete removes a key
func (c *CacheService) Delete(ctx context.Context, keys ...string) error {
	return c.client.Del(ctx, keys...).Err()
}

// Exists checks if a key exists
func (c *CacheService) Exists(ctx context.Context, keys ...string) (int64, error) {
	return c.client.Exists(ctx, keys...).Result()
}

// Close closes the Redis connection
func (c *CacheService) Close() error {
	if c.client != nil {
		return c.client.Close()
	}
	return nil
}

// Static data cache helpers
const (
	StaticDataKey = "static_data"
	StaticDataTTL = 1 * time.Hour
)

// CacheStaticData caches static lookup data
func (c *CacheService) CacheStaticData(ctx context.Context, data interface{}) error {
	return c.Set(ctx, StaticDataKey, data, StaticDataTTL)
}

// GetCachedStaticData retrieves cached static data
func (c *CacheService) GetCachedStaticData(ctx context.Context, dest interface{}) error {
	return c.Get(ctx, StaticDataKey, dest)
}

// InvalidateStaticData removes cached static data
func (c *CacheService) InvalidateStaticData(ctx context.Context) error {
	return c.Delete(ctx, StaticDataKey)
}

// Lookup data cache helpers - each lookup type gets its own key
const (
	LookupKeyPrefix         = "lookup:"
	LookupCategoriesKey     = LookupKeyPrefix + "categories"
	LookupPrioritiesKey     = LookupKeyPrefix + "priorities"
	LookupFrequenciesKey    = LookupKeyPrefix + "frequencies"
	LookupResidenceTypesKey = LookupKeyPrefix + "residence_types"
	LookupSpecialtiesKey    = LookupKeyPrefix + "specialties"
	LookupTaskTemplatesKey  = LookupKeyPrefix + "task_templates"
	LookupDataTTL           = 24 * time.Hour // Lookup data rarely changes
)

// CacheLookupData caches data for a specific lookup type
func (c *CacheService) CacheLookupData(ctx context.Context, key string, data interface{}) error {
	return c.Set(ctx, key, data, LookupDataTTL)
}

// GetCachedLookupData retrieves cached lookup data for a specific key
func (c *CacheService) GetCachedLookupData(ctx context.Context, key string, dest interface{}) error {
	return c.Get(ctx, key, dest)
}

// InvalidateLookupData removes cached data for a specific lookup type
func (c *CacheService) InvalidateLookupData(ctx context.Context, key string) error {
	return c.Delete(ctx, key)
}

// InvalidateAllLookups removes all cached lookup data
func (c *CacheService) InvalidateAllLookups(ctx context.Context) error {
	keys := []string{
		LookupCategoriesKey,
		LookupPrioritiesKey,
		LookupFrequenciesKey,
		LookupResidenceTypesKey,
		LookupSpecialtiesKey,
		LookupTaskTemplatesKey,
		StaticDataKey, // Also invalidate the combined static data
	}
	// Per-locale seeded-data + ETag keys.
	for _, lang := range i18n.SupportedLanguages {
		keys = append(keys, seededDataKey(lang), seededDataETagKey(lang))
	}
	return c.Delete(ctx, keys...)
}

// CacheCategories caches task categories
func (c *CacheService) CacheCategories(ctx context.Context, data interface{}) error {
	return c.CacheLookupData(ctx, LookupCategoriesKey, data)
}

// GetCachedCategories retrieves cached task categories
func (c *CacheService) GetCachedCategories(ctx context.Context, dest interface{}) error {
	return c.GetCachedLookupData(ctx, LookupCategoriesKey, dest)
}

// InvalidateCategories removes cached task categories
func (c *CacheService) InvalidateCategories(ctx context.Context) error {
	// Invalidate both specific key and combined static data
	return c.Delete(ctx, LookupCategoriesKey, StaticDataKey)
}

// CachePriorities caches task priorities
func (c *CacheService) CachePriorities(ctx context.Context, data interface{}) error {
	return c.CacheLookupData(ctx, LookupPrioritiesKey, data)
}

// GetCachedPriorities retrieves cached task priorities
func (c *CacheService) GetCachedPriorities(ctx context.Context, dest interface{}) error {
	return c.GetCachedLookupData(ctx, LookupPrioritiesKey, dest)
}

// InvalidatePriorities removes cached task priorities
func (c *CacheService) InvalidatePriorities(ctx context.Context) error {
	return c.Delete(ctx, LookupPrioritiesKey, StaticDataKey)
}

// CacheFrequencies caches task frequencies
func (c *CacheService) CacheFrequencies(ctx context.Context, data interface{}) error {
	return c.CacheLookupData(ctx, LookupFrequenciesKey, data)
}

// GetCachedFrequencies retrieves cached task frequencies
func (c *CacheService) GetCachedFrequencies(ctx context.Context, dest interface{}) error {
	return c.GetCachedLookupData(ctx, LookupFrequenciesKey, dest)
}

// InvalidateFrequencies removes cached task frequencies
func (c *CacheService) InvalidateFrequencies(ctx context.Context) error {
	return c.Delete(ctx, LookupFrequenciesKey, StaticDataKey)
}

// CacheResidenceTypes caches residence types
func (c *CacheService) CacheResidenceTypes(ctx context.Context, data interface{}) error {
	return c.CacheLookupData(ctx, LookupResidenceTypesKey, data)
}

// GetCachedResidenceTypes retrieves cached residence types
func (c *CacheService) GetCachedResidenceTypes(ctx context.Context, dest interface{}) error {
	return c.GetCachedLookupData(ctx, LookupResidenceTypesKey, dest)
}

// InvalidateResidenceTypes removes cached residence types
func (c *CacheService) InvalidateResidenceTypes(ctx context.Context) error {
	return c.Delete(ctx, LookupResidenceTypesKey, StaticDataKey)
}

// CacheSpecialties caches contractor specialties
func (c *CacheService) CacheSpecialties(ctx context.Context, data interface{}) error {
	return c.CacheLookupData(ctx, LookupSpecialtiesKey, data)
}

// GetCachedSpecialties retrieves cached contractor specialties
func (c *CacheService) GetCachedSpecialties(ctx context.Context, dest interface{}) error {
	return c.GetCachedLookupData(ctx, LookupSpecialtiesKey, dest)
}

// InvalidateSpecialties removes cached contractor specialties
func (c *CacheService) InvalidateSpecialties(ctx context.Context) error {
	return c.Delete(ctx, LookupSpecialtiesKey, StaticDataKey)
}

// CacheTaskTemplates caches task templates
func (c *CacheService) CacheTaskTemplates(ctx context.Context, data interface{}) error {
	return c.CacheLookupData(ctx, LookupTaskTemplatesKey, data)
}

// GetCachedTaskTemplates retrieves cached task templates
func (c *CacheService) GetCachedTaskTemplates(ctx context.Context, dest interface{}) error {
	return c.GetCachedLookupData(ctx, LookupTaskTemplatesKey, dest)
}

// InvalidateTaskTemplates removes cached task templates
func (c *CacheService) InvalidateTaskTemplates(ctx context.Context) error {
	return c.Delete(ctx, LookupTaskTemplatesKey, StaticDataKey)
}

// Unified seeded data cache helpers.
//
// The seeded-data payload is localized (lookup display_name + home-profile
// option labels), so the cache and ETag are namespaced per locale. Mixing
// locales under one key would let the first request poison every other
// language and make the ETag meaningless across locales.
const (
	seededDataPrefix = "seeded_data:"
	SeededDataTTL    = 24 * time.Hour
)

func seededDataKey(locale string) string     { return seededDataPrefix + locale }
func seededDataETagKey(locale string) string { return seededDataPrefix + locale + ":etag" }

// CacheSeededData caches the unified seeded data for a locale and generates an
// ETag. The locale is folded into the ETag so a client switching languages
// always re-fetches rather than getting a stale 304.
func (c *CacheService) CacheSeededData(ctx context.Context, locale string, data interface{}) (string, error) {
	jsonData, err := json.Marshal(data)
	if err != nil {
		return "", fmt.Errorf("failed to marshal seeded data: %w", err)
	}

	// FNV-64a ETag over locale + JSON (faster than MD5, non-cryptographic).
	h := fnv.New64a()
	h.Write([]byte(locale))
	h.Write([]byte{0})
	h.Write(jsonData)
	etag := fmt.Sprintf("\"%x\"", h.Sum64())

	if err := c.client.Set(ctx, seededDataKey(locale), jsonData, SeededDataTTL).Err(); err != nil {
		return "", fmt.Errorf("failed to cache seeded data: %w", err)
	}
	if err := c.client.Set(ctx, seededDataETagKey(locale), etag, SeededDataTTL).Err(); err != nil {
		return "", fmt.Errorf("failed to cache seeded data etag: %w", err)
	}
	return etag, nil
}

// GetCachedSeededData retrieves cached unified seeded data for a locale.
func (c *CacheService) GetCachedSeededData(ctx context.Context, locale string, dest interface{}) error {
	return c.Get(ctx, seededDataKey(locale), dest)
}

// GetSeededDataETag retrieves the cached ETag for a locale's seeded data.
func (c *CacheService) GetSeededDataETag(ctx context.Context, locale string) (string, error) {
	return c.GetString(ctx, seededDataETagKey(locale))
}

// InvalidateSeededData removes cached seeded data and ETags for every
// supported locale (lookup data is locale-independent at the source, so a
// change must clear all language variants).
func (c *CacheService) InvalidateSeededData(ctx context.Context) error {
	keys := make([]string, 0, len(i18n.SupportedLanguages)*2)
	for _, lang := range i18n.SupportedLanguages {
		keys = append(keys, seededDataKey(lang), seededDataETagKey(lang))
	}
	return c.Delete(ctx, keys...)
}

// === User → Residence-IDs cache ===
//
// Caches the set of residence IDs each user has access to. Hot read on
// every authenticated API call (auth + tasks + residences + contractors +
// documents all need it). Mutations on residences/share-codes invalidate
// only the affected user(s); see Invalidate*ResidenceIDsForUsers.

const (
	residenceIDsKeyPrefix = "residence_ids_user:"
	residenceIDsTTL       = 5 * time.Minute
)

// CacheResidenceIDsForUser stores the residence-ID list for a user with a
// 5-minute TTL. Membership rarely changes (only on share-code accept,
// remove-user, delete-residence) so a 5-minute window catches the vast
// majority of repeat reads while keeping staleness bounded.
func (c *CacheService) CacheResidenceIDsForUser(ctx context.Context, userID uint, ids []uint) error {
	if c == nil {
		return nil
	}
	key := fmt.Sprintf("%s%d", residenceIDsKeyPrefix, userID)
	data, err := json.Marshal(ids)
	if err != nil {
		return err
	}
	return c.client.Set(ctx, key, data, residenceIDsTTL).Err()
}

// GetCachedResidenceIDsForUser fetches the cached residence-ID list. Returns
// (nil, redis.Nil) when not cached so callers can distinguish from "user has
// zero residences" (empty slice) — though for practical purposes both result
// in an empty kanban response, so most callers can ignore the distinction.
func (c *CacheService) GetCachedResidenceIDsForUser(ctx context.Context, userID uint) ([]uint, error) {
	if c == nil {
		return nil, fmt.Errorf("cache not available")
	}
	key := fmt.Sprintf("%s%d", residenceIDsKeyPrefix, userID)
	var ids []uint
	if err := c.Get(ctx, key, &ids); err != nil {
		return nil, err
	}
	return ids, nil
}

// InvalidateResidenceIDsForUsers drops the cache for one or more users.
// Called from JoinWithCode (the joining user) and RemoveUser /
// DeleteResidence (every affected user). Cheap — single Redis DEL per user.
func (c *CacheService) InvalidateResidenceIDsForUsers(ctx context.Context, userIDs ...uint) error {
	if c == nil || len(userIDs) == 0 {
		return nil
	}
	keys := make([]string, len(userIDs))
	for i, id := range userIDs {
		keys[i] = fmt.Sprintf("%s%d", residenceIDsKeyPrefix, id)
	}
	return c.Delete(ctx, keys...)
}

// === SubscriptionSettings cache ===
//
// SubscriptionSettings is a 32-byte singleton row of admin-toggleable global
// flags (EnableLimitations, EnableMonitoring, TrialEnabled, TrialDurationDays).
// Read on every authed status check, every CreateResidence, and once per
// 30s by every monitoring goroutine. Cached forever-ish here; admin writes
// invalidate explicitly.
//
// 30-minute TTL is belt-and-suspenders against an admin update that somehow
// bypasses the invalidation path (e.g., a manual SQL UPDATE). The flag value
// converging within 30 min is fine for any real use case.

const (
	subscriptionSettingsKey = "subscription_settings:1"
	subscriptionSettingsTTL = 30 * time.Minute
)

// CacheSubscriptionSettings stores the singleton settings row. Caller passes
// any encodable value — typically *models.SubscriptionSettings. Best-effort.
func (c *CacheService) CacheSubscriptionSettings(ctx context.Context, settings interface{}) error {
	if c == nil {
		return nil
	}
	data, err := json.Marshal(settings)
	if err != nil {
		return err
	}
	return c.client.Set(ctx, subscriptionSettingsKey, data, subscriptionSettingsTTL).Err()
}

// GetCachedSubscriptionSettings unmarshals into the supplied destination.
// Returns redis.Nil on cache miss so callers can distinguish from genuine errors.
func (c *CacheService) GetCachedSubscriptionSettings(ctx context.Context, dest interface{}) error {
	if c == nil {
		return fmt.Errorf("cache not available")
	}
	return c.Get(ctx, subscriptionSettingsKey, dest)
}

// InvalidateSubscriptionSettings drops the singleton-settings cache. Called
// from admin handlers that update the row so the new values are visible
// immediately to all pods (instead of waiting for the 30-min TTL).
func (c *CacheService) InvalidateSubscriptionSettings(ctx context.Context) error {
	if c == nil {
		return nil
	}
	return c.Delete(ctx, subscriptionSettingsKey)
}

// === SubscriptionStatus cache (per-user) ===
//
// SubscriptionStatusResponse aggregates subscription tier, all tier limits, and
// per-user usage counts (residences/tasks/contractors/documents). The usage
// part requires 4+ COUNT queries against the transatlantic Neon Postgres at
// ~110ms RTT each — about a second of wall-clock per call before parallelism.
// Caching the assembled response collapses that to a single Redis GET (~5ms).
//
// TTL is short (5 min) so stale state self-heals if any mutation path forgets
// to invalidate. The primary correctness mechanism is explicit invalidation
// via InvalidateSubscriptionStatusForUsers — called from every CRUD on
// residences, tasks, contractors, documents, and subscription itself, fanning
// out to every user with access to the affected residence.

const (
	subscriptionStatusKeyPrefix = "sub_status:user:"
	subscriptionStatusTTL       = 5 * time.Minute
)

// CacheSubscriptionStatus stores the assembled SubscriptionStatusResponse for
// a user. Caller passes any encodable value to keep this package free of
// service-layer types; subscription_service.go marshals/unmarshals.
// Best-effort — Redis errors are returned but not fatal.
func (c *CacheService) CacheSubscriptionStatus(ctx context.Context, userID uint, status interface{}) error {
	if c == nil {
		return nil
	}
	key := fmt.Sprintf("%s%d", subscriptionStatusKeyPrefix, userID)
	data, err := json.Marshal(status)
	if err != nil {
		return err
	}
	return c.client.Set(ctx, key, data, subscriptionStatusTTL).Err()
}

// GetCachedSubscriptionStatus unmarshals the cached response into dest.
// Returns redis.Nil on cache miss so callers can distinguish from genuine errors.
func (c *CacheService) GetCachedSubscriptionStatus(ctx context.Context, userID uint, dest interface{}) error {
	if c == nil {
		return fmt.Errorf("cache not available")
	}
	key := fmt.Sprintf("%s%d", subscriptionStatusKeyPrefix, userID)
	return c.Get(ctx, key, dest)
}

// InvalidateSubscriptionStatusForUsers drops the cached status for one or more
// users. Used by every mutation that could change a user's usage counts —
// residence create/delete/share, task/contractor/document CRUD, subscription
// purchase/cancel/restore. Membership-changing residence ops fan out to every
// user with access to that residence.
func (c *CacheService) InvalidateSubscriptionStatusForUsers(ctx context.Context, userIDs ...uint) error {
	if c == nil || len(userIDs) == 0 {
		return nil
	}
	keys := make([]string, len(userIDs))
	for i, id := range userIDs {
		keys[i] = fmt.Sprintf("%s%d", subscriptionStatusKeyPrefix, id)
	}
	return c.Delete(ctx, keys...)
}