package worker

import (
	"context"
	"fmt"
	"log"
	"sort"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"

	"github.com/Silo-Server/silo-server/internal/cache"
	evt "github.com/Silo-Server/silo-server/internal/events"
)

// SessionSync represents the data needed to sync a playback session to the
// playback_sessions_sync table in PostgreSQL.
type SessionSync struct {
	SessionID            string
	UserID               int
	ProfileID            string
	MediaFileID          int
	RequestedMediaFileID int
	PlayMethod           string // current live transport method for admin session views
	ReportingNode        string
	ClientIP             string
	AudioTrackIndex      int
	TranscodeAudio       bool
	StreamBitrateKbps    int
	TranscodeNodeURL     string
	TargetResolution     string
	TargetVideoCodec     string
	TargetAudioCodec     string
	TargetBitrateKbps    int
	StartedAt            time.Time
	UpdatedAt            time.Time
	IsPaused             bool
	HasWebSocket         bool
}

// AggregateData represents the aggregate counts for a single user that are
// synced to the user_aggregates table in PostgreSQL.
type AggregateData struct {
	TotalWatched   int
	FavoritesCount int
	WatchlistCount int
	ActiveNode     string
}

// SessionSyncProvider returns the current set of active sessions to reconcile.
// This is typically a closure that reads from the SessionManager.
type SessionSyncProvider func() []SessionSync

// PreSyncHook is called before each reconciliation cycle. Implementations
// can use it to expire idle sessions from the in-memory manager so they are
// no longer included in the snapshot sent to the database.
type PreSyncHook func()

// Reconciler performs background reconciliation of user data from per-user
// SQLite databases into the central PostgreSQL instance.
type Reconciler struct {
	pool            *pgxpool.Pool
	nodeName        string
	sessionProvider SessionSyncProvider
	interval        time.Duration
	stop            chan struct{}
	EventBus        cache.EventBus
	EventsHub       *evt.Hub
	PreSync         PreSyncHook
}

// NewReconciler creates a new Reconciler with sensible defaults. The default
// reconciliation interval is 30 seconds. The sessionProvider may be nil if
// session sync is not needed (e.g. in tests).
func NewReconciler(pool *pgxpool.Pool, nodeName string, sp SessionSyncProvider) *Reconciler {
	return &Reconciler{
		pool:            pool,
		nodeName:        strings.TrimSpace(nodeName),
		sessionProvider: sp,
		interval:        15 * time.Second,
		stop:            make(chan struct{}),
	}
}

// ReconcileSessions upserts the given sessions into the playback_sessions_sync
// table. Each session is inserted or updated based on its session_id primary
// key, making the operation idempotent.
func (r *Reconciler) ReconcileSessions(ctx context.Context, sessions []SessionSync) error {
	if len(sessions) == 0 {
		return nil
	}

	grouped := make(map[string][]SessionSync)
	for _, session := range sessions {
		grouped[session.ReportingNode] = append(grouped[session.ReportingNode], session)
	}

	for reportingNode, nodeSessions := range grouped {
		if err := r.ReconcileNodeSessions(ctx, reportingNode, nodeSessions); err != nil {
			return err
		}
	}

	return nil
}

// ReconcileNodeSessions upserts the sessions currently active on one reporting
// node, then removes any stale rows for that same node that are no longer
// present in the provided snapshot.
func (r *Reconciler) ReconcileNodeSessions(ctx context.Context, reportingNode string, sessions []SessionSync) error {
	reportingNode = strings.TrimSpace(reportingNode)

	tx, err := r.pool.Begin(ctx)
	if err != nil {
		return fmt.Errorf("beginning transaction: %w", err)
	}
	defer func() { _ = tx.Rollback(ctx) }()

	currentSessions, err := loadNodeSessionsSnapshot(ctx, tx, reportingNode)
	if err != nil {
		return fmt.Errorf("loading existing sessions for node %s: %w", reportingNode, err)
	}
	normalizedIncoming := normalizeSessionSyncs(reportingNode, sessions)
	changed := !sessionSnapshotsEqual(currentSessions, normalizedIncoming)

	sessionIDs := make([]string, 0, len(sessions))
	for _, s := range sessions {
		sessionIDs = append(sessionIDs, s.SessionID)
		sessionNode := strings.TrimSpace(s.ReportingNode)
		if sessionNode == "" {
			sessionNode = reportingNode
		}
		_, err := tx.Exec(ctx, `
			INSERT INTO playback_sessions_sync
				(session_id, user_id, profile_id, media_file_id, requested_media_file_id, play_method,
				 reporting_node, started_at, updated_at, last_sync_at, client_ip,
				 audio_track_index, transcode_audio, stream_bitrate_kbps, transcode_node_url,
				 target_resolution, target_video_codec, target_audio_codec, target_bitrate_kbps,
				 is_paused, has_websocket)
			VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, NOW(), $10::inet, $11, $12, $13, $14, $15, $16, $17, $18, $19, $20)
			ON CONFLICT (session_id) DO UPDATE SET
				user_id             = EXCLUDED.user_id,
				profile_id          = EXCLUDED.profile_id,
				media_file_id       = EXCLUDED.media_file_id,
				requested_media_file_id = EXCLUDED.requested_media_file_id,
				play_method         = EXCLUDED.play_method,
				reporting_node      = EXCLUDED.reporting_node,
				started_at          = EXCLUDED.started_at,
				updated_at          = EXCLUDED.updated_at,
				client_ip           = EXCLUDED.client_ip,
				audio_track_index   = EXCLUDED.audio_track_index,
				transcode_audio     = EXCLUDED.transcode_audio,
				stream_bitrate_kbps = EXCLUDED.stream_bitrate_kbps,
				transcode_node_url  = EXCLUDED.transcode_node_url,
				target_resolution   = EXCLUDED.target_resolution,
				target_video_codec  = EXCLUDED.target_video_codec,
				target_audio_codec  = EXCLUDED.target_audio_codec,
				target_bitrate_kbps = EXCLUDED.target_bitrate_kbps,
				is_paused           = EXCLUDED.is_paused,
				has_websocket       = EXCLUDED.has_websocket,
				last_sync_at        = NOW()
		`, s.SessionID, s.UserID, s.ProfileID, s.MediaFileID, nullableInt(s.RequestedMediaFileID), s.PlayMethod,
			sessionNode, s.StartedAt, s.UpdatedAt, nullableIP(s.ClientIP), s.AudioTrackIndex,
			s.TranscodeAudio, nullableInt(s.StreamBitrateKbps), nullableString(s.TranscodeNodeURL),
			nullableString(s.TargetResolution), nullableString(s.TargetVideoCodec),
			nullableString(s.TargetAudioCodec), nullableInt(s.TargetBitrateKbps),
			s.IsPaused, s.HasWebSocket)
		if err != nil {
			return fmt.Errorf("upserting session %s: %w", s.SessionID, err)
		}
	}

	if len(sessionIDs) == 0 {
		if _, err := tx.Exec(ctx, `
			DELETE FROM playback_sessions_sync
			WHERE COALESCE(reporting_node, '') = $1
		`, reportingNode); err != nil {
			return fmt.Errorf("deleting empty snapshot for node %s: %w", reportingNode, err)
		}
	} else {
		if _, err := tx.Exec(ctx, `
			DELETE FROM playback_sessions_sync
			WHERE COALESCE(reporting_node, '') = $1
			  AND NOT (session_id = ANY($2))
		`, reportingNode, sessionIDs); err != nil {
			return fmt.Errorf("deleting missing sessions for node %s: %w", reportingNode, err)
		}
	}

	if err := tx.Commit(ctx); err != nil {
		return fmt.Errorf("committing transaction: %w", err)
	}
	if changed && r.EventsHub != nil {
		if err := r.EventsHub.PublishJSON(
			ctx,
			evt.ChannelSessions,
			"sessions.replaced",
			nil,
			evt.PublishOptions{AdminOnly: true},
		); err != nil {
			log.Printf("reconciler: failed to publish session event for node %s: %v", reportingNode, err)
		}
	} else if changed && r.EventBus != nil {
		if err := r.EventBus.Publish(ctx, cache.ChannelPlayback, cache.Event{
			Type:    cache.EventPlaybackSessionsChanged,
			Payload: reportingNode,
		}); err != nil {
			log.Printf("reconciler: failed to publish playback invalidation event for node %s: %v", reportingNode, err)
		}
	}

	return nil
}

func loadNodeSessionsSnapshot(ctx context.Context, tx pgx.Tx, reportingNode string) ([]SessionSync, error) {
	rows, err := tx.Query(ctx, `
		SELECT
			session_id,
			user_id,
			COALESCE(profile_id, ''),
			media_file_id,
			COALESCE(requested_media_file_id, media_file_id, 0),
			COALESCE(play_method, ''),
			COALESCE(reporting_node, ''),
			COALESCE(HOST(client_ip), ''),
			COALESCE(audio_track_index, 0),
			COALESCE(transcode_audio, FALSE),
			COALESCE(stream_bitrate_kbps, 0),
			COALESCE(transcode_node_url, ''),
			COALESCE(target_resolution, ''),
			COALESCE(target_video_codec, ''),
			COALESCE(target_audio_codec, ''),
			COALESCE(target_bitrate_kbps, 0),
			started_at,
			updated_at,
			COALESCE(is_paused, FALSE),
			COALESCE(has_websocket, FALSE)
		FROM playback_sessions_sync
		WHERE COALESCE(reporting_node, '') = $1
		ORDER BY session_id
	`, reportingNode)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var sessions []SessionSync
	for rows.Next() {
		var s SessionSync
		if err := rows.Scan(
			&s.SessionID,
			&s.UserID,
			&s.ProfileID,
			&s.MediaFileID,
			&s.RequestedMediaFileID,
			&s.PlayMethod,
			&s.ReportingNode,
			&s.ClientIP,
			&s.AudioTrackIndex,
			&s.TranscodeAudio,
			&s.StreamBitrateKbps,
			&s.TranscodeNodeURL,
			&s.TargetResolution,
			&s.TargetVideoCodec,
			&s.TargetAudioCodec,
			&s.TargetBitrateKbps,
			&s.StartedAt,
			&s.UpdatedAt,
			&s.IsPaused,
			&s.HasWebSocket,
		); err != nil {
			return nil, err
		}
		sessions = append(sessions, s)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return sessions, nil
}

func normalizeSessionSyncs(reportingNode string, sessions []SessionSync) []SessionSync {
	normalized := make([]SessionSync, len(sessions))
	for i, s := range sessions {
		cp := s
		if strings.TrimSpace(cp.ReportingNode) == "" {
			cp.ReportingNode = reportingNode
		}
		normalized[i] = cp
	}
	sort.Slice(normalized, func(i, j int) bool {
		return normalized[i].SessionID < normalized[j].SessionID
	})
	return normalized
}

func sessionSnapshotsEqual(left, right []SessionSync) bool {
	if len(left) != len(right) {
		return false
	}
	for i := range left {
		if left[i].SessionID != right[i].SessionID ||
			left[i].UserID != right[i].UserID ||
			left[i].ProfileID != right[i].ProfileID ||
			left[i].MediaFileID != right[i].MediaFileID ||
			left[i].RequestedMediaFileID != right[i].RequestedMediaFileID ||
			left[i].PlayMethod != right[i].PlayMethod ||
			left[i].ReportingNode != right[i].ReportingNode ||
			left[i].ClientIP != right[i].ClientIP ||
			left[i].AudioTrackIndex != right[i].AudioTrackIndex ||
			left[i].TranscodeAudio != right[i].TranscodeAudio ||
			left[i].StreamBitrateKbps != right[i].StreamBitrateKbps ||
			left[i].TranscodeNodeURL != right[i].TranscodeNodeURL ||
			left[i].TargetResolution != right[i].TargetResolution ||
			left[i].TargetVideoCodec != right[i].TargetVideoCodec ||
			left[i].TargetAudioCodec != right[i].TargetAudioCodec ||
			left[i].TargetBitrateKbps != right[i].TargetBitrateKbps ||
			!left[i].StartedAt.Equal(right[i].StartedAt) ||
			!left[i].UpdatedAt.Equal(right[i].UpdatedAt) ||
			left[i].IsPaused != right[i].IsPaused ||
			left[i].HasWebSocket != right[i].HasWebSocket {
			return false
		}
	}
	return true
}

func nullableIP(ip string) any {
	if strings.TrimSpace(ip) == "" {
		return nil
	}
	return ip
}

func nullableInt(value int) any {
	if value <= 0 {
		return nil
	}
	return value
}

func nullableString(value string) any {
	if strings.TrimSpace(value) == "" {
		return nil
	}
	return value
}

// ReconcileAggregates upserts the aggregate counts for a single user into the
// user_aggregates table. The operation is idempotent.
func (r *Reconciler) ReconcileAggregates(ctx context.Context, userID int, totals AggregateData) error {
	_, err := r.pool.Exec(ctx, `
		INSERT INTO user_aggregates
			(user_id, total_watched, favorites_count, watchlist_count, active_node, last_sync_at)
		VALUES ($1, $2, $3, $4, $5, NOW())
		ON CONFLICT (user_id) DO UPDATE SET
			total_watched   = EXCLUDED.total_watched,
			favorites_count = EXCLUDED.favorites_count,
			watchlist_count = EXCLUDED.watchlist_count,
			active_node     = EXCLUDED.active_node,
			last_sync_at    = NOW()
	`, userID, totals.TotalWatched, totals.FavoritesCount, totals.WatchlistCount, totals.ActiveNode)
	if err != nil {
		return fmt.Errorf("upserting aggregates for user %d: %w", userID, err)
	}

	return nil
}

// Start begins the background reconciliation loop. It runs until Stop is
// called. On each tick it syncs active playback sessions to PostgreSQL.
func (r *Reconciler) Start() {
	go func() {
		ticker := time.NewTicker(r.interval)
		defer ticker.Stop()

		for {
			select {
			case <-r.stop:
				return
			case <-ticker.C:
				r.tick()
			}
		}
	}()
}

// tick runs one reconciliation cycle.
func (r *Reconciler) tick() {
	if r.PreSync != nil {
		r.PreSync()
	}
	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
	defer cancel()
	if err := r.SyncNow(ctx); err != nil {
		log.Printf("reconciler: session sync error: %v", err)
	}
}

// SyncNow runs one immediate session reconciliation using the current local
// session snapshot. When nodeName is configured, an empty snapshot still
// clears any rows previously reported by that node.
func (r *Reconciler) SyncNow(ctx context.Context) error {
	if r.sessionProvider == nil {
		return nil
	}

	sessions := r.sessionProvider()
	if len(sessions) == 0 {
		if r.nodeName == "" {
			return nil
		}
		return r.ReconcileNodeSessions(ctx, r.nodeName, nil)
	}
	if r.nodeName != "" {
		for i := range sessions {
			if strings.TrimSpace(sessions[i].ReportingNode) == "" {
				sessions[i].ReportingNode = r.nodeName
			}
		}
	}
	return r.ReconcileSessions(ctx, sessions)
}

// Stop signals the reconciliation loop to stop.
func (r *Reconciler) Stop() {
	close(r.stop)
}