package workers

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

	"github.com/elastic/go-elasticsearch/v8/esapi"
	"github.com/google/uuid"
	"github.com/redis/go-redis/v9"
	"go.uber.org/zap"
	"gorm.io/gorm"

	vezaes "veza-backend-api/internal/elasticsearch"
)

// HardDeleteWorker performs final GDPR cleanup for users past recovery deadline (v0.10.8 F065).
// Runs periodically to irreversibly anonymize accounts that were soft-deleted 30+ days ago.
//
// The worker cleans three stores:
//   - PostgreSQL: anonymize users row, delete from user_profiles, user_sessions, user_settings,
//     user_follows, notifications, and null user_id in audit_logs.
//   - Redis (optional): all keys matching user:{id}:* using SCAN with a cursor — never KEYS,
//     which would block the server on large keyspaces.
//   - Elasticsearch (optional): the user doc from the users index, plus all track docs and
//     playlist docs authored by the user (collected from PG before anonymization, then removed
//     from ES via DeleteByQuery on the _id terms).
//
// Both Redis and Elasticsearch are optional. If either client is nil (feature disabled or
// unreachable at startup), the corresponding cleanup is skipped with a debug log and the
// worker continues. Transient Redis errors trigger a bounded retry loop; persistent errors
// are logged and the worker moves on to the next user (no silent panic).
type HardDeleteWorker struct {
	db          *gorm.DB
	redisClient *redis.Client
	esClient    *vezaes.Client
	logger      *zap.Logger
	interval    time.Duration
	stopChan    chan struct{}
	running     bool
}

// NewHardDeleteWorker creates a new hard delete worker with only the required PostgreSQL
// dependency. Use WithRedis and WithElasticsearch to enable the corresponding cleanups.
func NewHardDeleteWorker(db *gorm.DB, logger *zap.Logger, interval time.Duration) *HardDeleteWorker {
	if logger == nil {
		logger = zap.NewNop()
	}
	if interval <= 0 {
		interval = 24 * time.Hour
	}
	return &HardDeleteWorker{
		db:       db,
		logger:   logger,
		interval: interval,
		stopChan: make(chan struct{}),
		running:  false,
	}
}

// WithRedis enables Redis cache key cleanup for the user:{id}:* pattern.
// Pass nil to explicitly disable; pass a live *redis.Client to enable.
func (w *HardDeleteWorker) WithRedis(client *redis.Client) *HardDeleteWorker {
	w.redisClient = client
	return w
}

// WithElasticsearch enables Elasticsearch document cleanup. The veza wrapper is expected
// (it carries the index prefix via Config). Pass nil to explicitly disable.
func (w *HardDeleteWorker) WithElasticsearch(client *vezaes.Client) *HardDeleteWorker {
	w.esClient = client
	return w
}

// Start runs the worker periodically.
func (w *HardDeleteWorker) Start(ctx context.Context) {
	if w.running {
		w.logger.Warn("Hard delete worker is already running")
		return
	}
	w.running = true
	w.logger.Info("Starting hard delete worker",
		zap.Duration("interval", w.interval),
		zap.Bool("redis_enabled", w.redisClient != nil),
		zap.Bool("elasticsearch_enabled", w.esClient != nil),
	)

	go w.runOnce(ctx)

	ticker := time.NewTicker(w.interval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			w.logger.Info("Stopping hard delete worker")
			w.running = false
			return
		case <-w.stopChan:
			w.logger.Info("Stopping hard delete worker (stop requested)")
			w.running = false
			return
		case <-ticker.C:
			go w.runOnce(ctx)
		}
	}
}

// Stop stops the worker.
func (w *HardDeleteWorker) Stop() {
	if !w.running {
		return
	}
	close(w.stopChan)
}

// runOnce executes one pass of hard delete / final anonymization.
func (w *HardDeleteWorker) runOnce(ctx context.Context) {
	logger := w.logger.With(zap.String("worker", "hard_delete"))
	runCtx, cancel := context.WithTimeout(ctx, 30*time.Minute)
	defer cancel()

	var userIDs []uuid.UUID
	if err := w.db.WithContext(runCtx).Raw(`
		SELECT id FROM users
		WHERE deleted_at IS NOT NULL AND recovery_deadline IS NOT NULL AND recovery_deadline < NOW()
	`).Scan(&userIDs).Error; err != nil {
		logger.Error("Failed to query users for hard delete", zap.Error(err))
		return
	}

	if len(userIDs) == 0 {
		logger.Debug("No users eligible for hard delete")
		return
	}

	logger.Info("Processing hard delete", zap.Int("count", len(userIDs)))

	for _, id := range userIDs {
		// Collect ES doc IDs BEFORE PG anonymization, while creator/user relations
		// are still resolvable. The anonymization UPDATE does not cascade, so the
		// tracks and playlists rows still exist afterwards — we just need their IDs.
		trackIDs := w.collectTrackIDs(runCtx, logger, id)
		playlistIDs := w.collectPlaylistIDs(runCtx, logger, id)

		// Final anonymization pass (ORIGIN §19.3) — ensure no PII remains in users row.
		res := w.db.WithContext(runCtx).Exec(`
			UPDATE users SET
				password_hash = '',
				first_name = NULL,
				last_name = NULL,
				bio = '',
				location = '',
				avatar = '',
				banner_url = '',
				recovery_deadline = NULL,
				updated_at = NOW()
			WHERE id = ? AND deleted_at IS NOT NULL
		`, id)
		if res.Error != nil {
			logger.Error("Failed to anonymize user", zap.Error(res.Error), zap.String("user_id", id.String()))
			continue
		}
		// Delete user_profiles (may contain PII)
		w.db.WithContext(runCtx).Exec("DELETE FROM user_profiles WHERE user_id = ?", id)

		// SECURITY(HIGH-007): RGPD — clean additional PII-containing tables
		w.db.WithContext(runCtx).Exec("DELETE FROM user_sessions WHERE user_id = ?", id)
		w.db.WithContext(runCtx).Exec("DELETE FROM user_settings WHERE user_id = ?", id)
		w.db.WithContext(runCtx).Exec("DELETE FROM user_follows WHERE follower_id = ? OR following_id = ?", id, id)
		w.db.WithContext(runCtx).Exec("DELETE FROM notifications WHERE user_id = ? OR actor_id = ?", id, id)
		w.db.WithContext(runCtx).Exec("UPDATE audit_logs SET user_id = NULL, ip_address = NULL WHERE user_id = ?", id)

		// Redis cache cleanup — user:{id}:* keys.
		if deleted, rerr := w.cleanRedisKeys(runCtx, id); rerr != nil {
			logger.Error("Redis cleanup failed",
				zap.Error(rerr),
				zap.String("user_id", id.String()),
			)
			// Non-fatal: continue to ES so we still make partial progress.
		} else if deleted > 0 {
			logger.Info("Redis cleanup complete",
				zap.String("user_id", id.String()),
				zap.Int("deleted", deleted),
			)
		}

		// Elasticsearch doc cleanup — user + owned tracks + owned playlists.
		if eerr := w.cleanESDocs(runCtx, id, trackIDs, playlistIDs); eerr != nil {
			logger.Error("Elasticsearch cleanup failed",
				zap.Error(eerr),
				zap.String("user_id", id.String()),
			)
		}

		logger.Info("Hard delete completed",
			zap.String("user_id", id.String()),
			zap.Int("tracks_removed_from_es", len(trackIDs)),
			zap.Int("playlists_removed_from_es", len(playlistIDs)),
		)
	}
}

// collectTrackIDs returns the UUIDs of tracks whose creator_id is the given user.
// creator_id is the canonical ownership column; user_id is a denormalized legacy alias.
func (w *HardDeleteWorker) collectTrackIDs(ctx context.Context, logger *zap.Logger, userID uuid.UUID) []uuid.UUID {
	var ids []uuid.UUID
	if err := w.db.WithContext(ctx).Raw(
		`SELECT id FROM tracks WHERE creator_id = ?`, userID,
	).Scan(&ids).Error; err != nil {
		logger.Warn("Failed to collect track IDs for ES cleanup",
			zap.Error(err), zap.String("user_id", userID.String()))
		return nil
	}
	return ids
}

// collectPlaylistIDs returns the UUIDs of playlists owned by the user.
func (w *HardDeleteWorker) collectPlaylistIDs(ctx context.Context, logger *zap.Logger, userID uuid.UUID) []uuid.UUID {
	var ids []uuid.UUID
	if err := w.db.WithContext(ctx).Raw(
		`SELECT id FROM playlists WHERE user_id = ?`, userID,
	).Scan(&ids).Error; err != nil {
		logger.Warn("Failed to collect playlist IDs for ES cleanup",
			zap.Error(err), zap.String("user_id", userID.String()))
		return nil
	}
	return ids
}

// cleanRedisKeys removes all Redis keys matching user:{userID}:*.
//
// Uses SCAN with a cursor in a loop — NEVER KEYS, which would block the Redis server
// on keyspaces with millions of keys. COUNT hints at ~100 keys per round trip; Redis may
// return slightly fewer or more depending on internal bucket distribution.
//
// Transient Scan errors trigger up to 3 retries with exponential backoff. A persistent
// error returns immediately without panicking. DEL errors are logged but non-fatal —
// subsequent batches are still attempted so we don't leave the cache half-clean.
func (w *HardDeleteWorker) cleanRedisKeys(ctx context.Context, userID uuid.UUID) (int, error) {
	if w.redisClient == nil {
		w.logger.Debug("Redis cleanup skipped (no client)", zap.String("user_id", userID.String()))
		return 0, nil
	}

	const (
		batchSize  = 100
		maxRetries = 3
	)
	pattern := fmt.Sprintf("user:%s:*", userID.String())
	var cursor uint64
	totalDeleted := 0

	for {
		var (
			keys    []string
			scanErr error
		)
		retries := 0
		for {
			keys, cursor, scanErr = w.redisClient.Scan(ctx, cursor, pattern, batchSize).Result()
			if scanErr == nil {
				break
			}
			retries++
			w.logger.Warn("Redis SCAN failed, retrying",
				zap.Error(scanErr),
				zap.String("user_id", userID.String()),
				zap.String("pattern", pattern),
				zap.Int("retry", retries),
			)
			if retries >= maxRetries {
				return totalDeleted, fmt.Errorf("redis SCAN failed after %d retries: %w", maxRetries, scanErr)
			}
			select {
			case <-ctx.Done():
				return totalDeleted, ctx.Err()
			case <-time.After(time.Duration(retries) * 100 * time.Millisecond):
			}
		}

		if len(keys) > 0 {
			n, delErr := w.redisClient.Del(ctx, keys...).Result()
			if delErr != nil {
				w.logger.Error("Redis DEL failed for batch",
					zap.Error(delErr),
					zap.String("user_id", userID.String()),
					zap.Int("batch_size", len(keys)),
				)
				// Non-fatal: continue scanning so later batches still get cleaned.
			} else {
				totalDeleted += int(n)
			}
		}

		if cursor == 0 {
			break
		}
	}
	return totalDeleted, nil
}

// cleanESDocs removes user-bound documents from Elasticsearch.
//
//   - users index: delete the user doc by its document ID (the user UUID).
//   - tracks index: DeleteByQuery with a terms filter on _id for the collected track IDs.
//   - playlists index: DeleteByQuery with a terms filter on _id for the collected playlist IDs.
//
// Each index is handled independently: a failure on one does not prevent the others
// from being attempted. The first encountered error is returned so the caller can log it,
// but partial progress is still made.
func (w *HardDeleteWorker) cleanESDocs(
	ctx context.Context,
	userID uuid.UUID,
	trackIDs []uuid.UUID,
	playlistIDs []uuid.UUID,
) error {
	if w.esClient == nil {
		w.logger.Debug("Elasticsearch cleanup skipped (no client)", zap.String("user_id", userID.String()))
		return nil
	}

	prefix := w.esClient.Config.Index
	var firstErr error

	// 1. Users index — delete by document ID.
	usersIdx := esIndexNameFor(prefix, vezaes.IdxUsers)
	if err := w.esDeleteDoc(ctx, usersIdx, userID.String()); err != nil {
		w.logger.Error("ES user doc delete failed",
			zap.Error(err),
			zap.String("user_id", userID.String()),
			zap.String("index", usersIdx),
		)
		if firstErr == nil {
			firstErr = err
		}
	}

	// 2. Tracks index — batch delete by collected IDs.
	if len(trackIDs) > 0 {
		tracksIdx := esIndexNameFor(prefix, vezaes.IdxTracks)
		if err := w.esDeleteByIDs(ctx, tracksIdx, uuidsToStrings(trackIDs)); err != nil {
			w.logger.Error("ES tracks delete_by_query failed",
				zap.Error(err),
				zap.String("user_id", userID.String()),
				zap.String("index", tracksIdx),
				zap.Int("count", len(trackIDs)),
			)
			if firstErr == nil {
				firstErr = err
			}
		}
	}

	// 3. Playlists index — batch delete by collected IDs.
	if len(playlistIDs) > 0 {
		playlistsIdx := esIndexNameFor(prefix, vezaes.IdxPlaylists)
		if err := w.esDeleteByIDs(ctx, playlistsIdx, uuidsToStrings(playlistIDs)); err != nil {
			w.logger.Error("ES playlists delete_by_query failed",
				zap.Error(err),
				zap.String("user_id", userID.String()),
				zap.String("index", playlistsIdx),
				zap.Int("count", len(playlistIDs)),
			)
			if firstErr == nil {
				firstErr = err
			}
		}
	}

	return firstErr
}

// esDeleteDoc deletes a single document by ID. A 404 response is treated as success
// (the doc was already gone, which is the desired end state).
func (w *HardDeleteWorker) esDeleteDoc(ctx context.Context, index, docID string) error {
	req := esapi.DeleteRequest{
		Index:      index,
		DocumentID: docID,
		Refresh:    "true",
	}
	res, err := req.Do(ctx, w.esClient)
	if err != nil {
		return fmt.Errorf("es delete: %w", err)
	}
	defer res.Body.Close()
	if res.StatusCode == 404 {
		return nil
	}
	if res.IsError() {
		return fmt.Errorf("es delete status %d: %s", res.StatusCode, res.String())
	}
	return nil
}

// esDeleteByIDs runs a DeleteByQuery with a terms filter on _id. Safe for empty input
// (returns nil immediately).
func (w *HardDeleteWorker) esDeleteByIDs(ctx context.Context, index string, ids []string) error {
	if len(ids) == 0 {
		return nil
	}
	body := map[string]any{
		"query": map[string]any{
			"terms": map[string]any{
				"_id": ids,
			},
		},
	}
	buf, err := json.Marshal(body)
	if err != nil {
		return fmt.Errorf("marshal delete_by_query body: %w", err)
	}
	refresh := true
	req := esapi.DeleteByQueryRequest{
		Index:   []string{index},
		Body:    bytes.NewReader(buf),
		Refresh: &refresh,
	}
	res, err := req.Do(ctx, w.esClient)
	if err != nil {
		return fmt.Errorf("es delete_by_query: %w", err)
	}
	defer res.Body.Close()
	if res.IsError() {
		return fmt.Errorf("es delete_by_query status %d: %s", res.StatusCode, res.String())
	}
	return nil
}

// esIndexNameFor mirrors the internal/elasticsearch.indexName helper (private there).
func esIndexNameFor(prefix, name string) string {
	if prefix != "" {
		return prefix + "-" + name
	}
	return "veza-" + name
}

func uuidsToStrings(ids []uuid.UUID) []string {
	out := make([]string, len(ids))
	for i, id := range ids {
		out[i] = id.String()
	}
	return out
}