package service

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"math"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/TopherMayor/unified-media-manager/internal/db"
	"github.com/jackc/pgx/v5"
)

type NotificationChannel struct {
	ID        int64           `json:"id"`
	Name      string          `json:"name"`
	Type      string          `json:"type"`
	Enabled   bool            `json:"enabled"`
	Config    json.RawMessage `json:"config"`
	CreatedAt time.Time       `json:"created_at"`
	UpdatedAt time.Time       `json:"updated_at"`

	// EventTypes populated by JOIN (not a DB column)
	EventTypes []string `json:"event_types,omitempty"`
}

type QueueEntry struct {
	ID          int64            `json:"id"`
	ChannelID   int64            `json:"channel_id"`
	EventType   string           `json:"event_type"`
	Title       string           `json:"title"`
	Message     json.RawMessage  `json:"message"`
	Status      string           `json:"status"`
	Attempts    int              `json:"attempts"`
	MaxAttempts int              `json:"max_attempts"`
	LastError   *string          `json:"last_error,omitempty"`
	NextRetryAt *time.Time       `json:"next_retry_at,omitempty"`
	CreatedAt   time.Time        `json:"created_at"`
	DeliveredAt *time.Time       `json:"delivered_at,omitempty"`
}

type NotificationService struct {
	db              *db.DB
	http            *http.Client
	telegramBaseURL string // override for testing
	done            chan struct{}
}

func NewNotificationService(database *db.DB) *NotificationService {
	return &NotificationService{
		db:              database,
		http:            &http.Client{Timeout: 10 * time.Second},
		telegramBaseURL: "https://api.telegram.org",
		done:            make(chan struct{}),
	}
}

// ValidateChannelConfig checks config has required fields for the channel type.
func (s *NotificationService) ValidateChannelConfig(channelType string, config json.RawMessage) error {
	var m map[string]interface{}
	if err := json.Unmarshal(config, &m); err != nil {
		return fmt.Errorf("invalid config JSON: %w", err)
	}

	switch channelType {
	case "webhook":
		urlStr, _ := m["url"].(string)
		if urlStr == "" {
			return fmt.Errorf("webhook config requires 'url' field")
		}
		u, err := url.Parse(urlStr)
		if err != nil {
			return fmt.Errorf("webhook url is invalid: %w", err)
		}
		if u.Scheme != "http" && u.Scheme != "https" {
			return fmt.Errorf("webhook url must use http or https scheme")
		}

	case "telegram":
		botToken, _ := m["bot_token"].(string)
		chatID, _ := m["chat_id"].(string)
		if botToken == "" {
			return fmt.Errorf("telegram config requires 'bot_token' field")
		}
		if chatID == "" {
			return fmt.Errorf("telegram config requires 'chat_id' field")
		}

	default:
		return fmt.Errorf("unknown channel type: %s", channelType)
	}

	return nil
}

// ListChannels returns all channels with masked configs and their event subscriptions.
func (s *NotificationService) ListChannels(ctx context.Context) ([]NotificationChannel, error) {
	rows, err := s.db.Pool.Query(ctx,
		`SELECT c.id, c.name, c.type, c.enabled, c.config, c.created_at, c.updated_at,
		        COALESCE(json_agg(s.event_type) FILTER (WHERE s.event_type IS NOT NULL), '[]') AS event_types
		 FROM notification_channels c
		 LEFT JOIN notification_subscriptions s ON c.id = s.channel_id
		 GROUP BY c.id, c.name, c.type, c.enabled, c.config, c.created_at, c.updated_at
		 ORDER BY c.name`)
	if err != nil {
		return nil, fmt.Errorf("list notification channels: %w", err)
	}
	defer rows.Close()

	var channels []NotificationChannel
	for rows.Next() {
		var ch NotificationChannel
		var eventTypesJSON []byte
		if err := rows.Scan(&ch.ID, &ch.Name, &ch.Type, &ch.Enabled, &ch.Config,
			&ch.CreatedAt, &ch.UpdatedAt, &eventTypesJSON); err != nil {
			slog.Error("failed to scan notification channel", "error", err)
			continue
		}
		ch.Config = maskConfig(ch.Type, ch.Config)
		var types []string
		if err := json.Unmarshal(eventTypesJSON, &types); err == nil {
			ch.EventTypes = types
		}
		channels = append(channels, ch)
	}

	return channels, nil
}

// CreateChannel creates a new notification channel and returns its ID.
func (s *NotificationService) CreateChannel(ctx context.Context, name, channelType string, config json.RawMessage) (int64, error) {
	if err := s.ValidateChannelConfig(channelType, config); err != nil {
		return 0, err
	}

	var id int64
	err := s.db.Pool.QueryRow(ctx,
		`INSERT INTO notification_channels (name, type, config) VALUES ($1, $2, $3) RETURNING id`,
		name, channelType, config).Scan(&id)
	if err != nil {
		return 0, fmt.Errorf("create notification channel: %w", err)
	}

	slog.Info("created notification channel", "name", name, "type", channelType)
	return id, nil
}

// UpdateChannel updates a notification channel's fields.
func (s *NotificationService) UpdateChannel(ctx context.Context, id int64, name *string, enabled *bool, config json.RawMessage) error {
	qb := NewQueryBuilder(1)
	setClauses := []string{}
	if name != nil {
		setClauses = append(setClauses, fmt.Sprintf("name = $%d", qb.Idx()))
		qb.Add("", *name)
	}
	if enabled != nil {
		setClauses = append(setClauses, fmt.Sprintf("enabled = $%d", qb.Idx()))
		qb.Add("", *enabled)
	}
	if config != nil {
		if err := s.ValidateChannelConfig("", config); err != nil {
			// Skip type-specific validation on update since we don't know the type here
			// The channel type doesn't change, just validate JSON is valid
		}
		setClauses = append(setClauses, fmt.Sprintf("config = $%d", qb.Idx()))
		qb.Add("", config)
	}

	if len(setClauses) == 0 {
		return nil
	}

	setClauses = append(setClauses, "updated_at = NOW()")
	query := fmt.Sprintf("UPDATE notification_channels SET %s WHERE id = $%d",
		strings.Join(setClauses, ", "), qb.Idx())
	qb.Add("", id)

	tag, err := s.db.Pool.Exec(ctx, query, qb.Args()...)
	if err != nil {
		return fmt.Errorf("update notification channel: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return fmt.Errorf("notification channel not found: %d", id)
	}
	return nil
}

// DeleteChannel removes a notification channel and its subscriptions.
func (s *NotificationService) DeleteChannel(ctx context.Context, id int64) error {
	tag, err := s.db.Pool.Exec(ctx, `DELETE FROM notification_channels WHERE id = $1`, id)
	if err != nil {
		return fmt.Errorf("delete notification channel: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return fmt.Errorf("notification channel not found: %d", id)
	}
	slog.Info("deleted notification channel", "id", id)
	return nil
}

// GetChannelWithConfig returns a channel with full unmasked config for delivery.
func (s *NotificationService) GetChannelWithConfig(ctx context.Context, id int64) (*NotificationChannel, error) {
	var ch NotificationChannel
	err := s.db.Pool.QueryRow(ctx,
		`SELECT id, name, type, enabled, config, created_at, updated_at FROM notification_channels WHERE id = $1`, id).
		Scan(&ch.ID, &ch.Name, &ch.Type, &ch.Enabled, &ch.Config, &ch.CreatedAt, &ch.UpdatedAt)
	if err != nil {
		return nil, fmt.Errorf("get notification channel: %w", err)
	}
	return &ch, nil
}

// ListSubscriptions returns event types subscribed by a channel.
func (s *NotificationService) ListSubscriptions(ctx context.Context, channelID int64) ([]string, error) {
	rows, err := s.db.Pool.Query(ctx,
		`SELECT event_type FROM notification_subscriptions WHERE channel_id = $1`, channelID)
	if err != nil {
		return nil, fmt.Errorf("list subscriptions: %w", err)
	}
	defer rows.Close()

	var types []string
	for rows.Next() {
		var t string
		if err := rows.Scan(&t); err != nil {
			continue
		}
		types = append(types, t)
	}
	return types, nil
}

// UpdateSubscriptions replaces all subscriptions for a channel.
func (s *NotificationService) UpdateSubscriptions(ctx context.Context, channelID int64, eventTypes []string) error {
	tx, err := s.db.Pool.Begin(ctx)
	if err != nil {
		return fmt.Errorf("begin transaction: %w", err)
	}
	defer tx.Rollback(ctx)

	if _, err := tx.Exec(ctx, `DELETE FROM notification_subscriptions WHERE channel_id = $1`, channelID); err != nil {
		return fmt.Errorf("delete subscriptions: %w", err)
	}

	for _, et := range eventTypes {
		if _, err := tx.Exec(ctx,
			`INSERT INTO notification_subscriptions (channel_id, event_type) VALUES ($1, $2)`,
			channelID, et); err != nil {
			return fmt.Errorf("insert subscription: %w", err)
		}
	}

	if err := tx.Commit(ctx); err != nil {
		return fmt.Errorf("commit subscriptions: %w", err)
	}
	return nil
}

// GetSubscribersForEvent returns enabled channels subscribed to an event type.
func (s *NotificationService) GetSubscribersForEvent(ctx context.Context, eventType string) ([]NotificationChannel, error) {
	rows, err := s.db.Pool.Query(ctx,
		`SELECT DISTINCT c.id, c.name, c.type, c.enabled, c.config, c.created_at, c.updated_at
		 FROM notification_channels c
		 JOIN notification_subscriptions s ON c.id = s.channel_id
		 WHERE s.event_type = $1 AND c.enabled = true`, eventType)
	if err != nil {
		return nil, fmt.Errorf("get subscribers for event: %w", err)
	}
	defer rows.Close()

	var channels []NotificationChannel
	for rows.Next() {
		var ch NotificationChannel
		if err := rows.Scan(&ch.ID, &ch.Name, &ch.Type, &ch.Enabled, &ch.Config,
			&ch.CreatedAt, &ch.UpdatedAt); err != nil {
			continue
		}
		channels = append(channels, ch)
	}
	return channels, nil
}

// DeliverWebhook sends an HTTP POST with JSON payload.
func (s *NotificationService) DeliverWebhook(ctx context.Context, webhookURL string, payload map[string]interface{}) error {
	body, err := json.Marshal(payload)
	if err != nil {
		return fmt.Errorf("marshal webhook payload: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, "POST", webhookURL, bytes.NewReader(body))
	if err != nil {
		return fmt.Errorf("create webhook request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")

	resp, err := s.http.Do(req)
	if err != nil {
		return fmt.Errorf("webhook delivery failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("webhook returned status %d", resp.StatusCode)
	}
	return nil
}

// DeliverTelegram sends a message via the Telegram Bot API.
func (s *NotificationService) DeliverTelegram(ctx context.Context, botToken, chatID, text string) error {
	apiURL := fmt.Sprintf("%s/bot%s/sendMessage", s.telegramBaseURL, botToken)

	payload := map[string]interface{}{
		"chat_id":    chatID,
		"text":       text,
		"parse_mode": "HTML",
	}
	body, err := json.Marshal(payload)
	if err != nil {
		return fmt.Errorf("marshal telegram payload: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, "POST", apiURL, bytes.NewReader(body))
	if err != nil {
		return fmt.Errorf("create telegram request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")

	resp, err := s.http.Do(req)
	if err != nil {
		return fmt.Errorf("telegram delivery failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("telegram returned status %d", resp.StatusCode)
	}
	return nil
}

// calculateBackoff returns exponential backoff: 30s * 2^attempt, capped at 480s.
func calculateBackoff(attempt int) time.Duration {
	d := 30 * time.Second * time.Duration(math.Pow(2, float64(attempt)))
	if d > 480*time.Second {
		return 480 * time.Second
	}
	return d
}

// maskConfig masks sensitive fields in channel config for API responses.
func maskConfig(channelType string, raw json.RawMessage) json.RawMessage {
	var m map[string]interface{}
	if err := json.Unmarshal(raw, &m); err != nil {
		return raw
	}

	switch channelType {
	case "telegram":
		if _, ok := m["bot_token"]; ok {
			m["bot_token"] = "***"
		}
	}

	masked, err := json.Marshal(m)
	if err != nil {
		return raw
	}
	return masked
}

// ListQueue returns paginated notification queue entries.
func (s *NotificationService) ListQueue(ctx context.Context, status string, page, pageSize int) ([]QueueEntry, int, error) {
	qb := NewQueryBuilder(1)
	if status != "" {
		qb.Add("status = $%d", status)
	}
	where := qb.Where()

	var total int
	countQuery := fmt.Sprintf("SELECT COUNT(*) FROM notification_queue%s", where)
	if err := s.db.Pool.QueryRow(ctx, countQuery, qb.Args()...).Scan(&total); err != nil {
		return nil, 0, fmt.Errorf("count notification queue: %w", err)
	}

	offset := (page - 1) * pageSize
	dataQuery := fmt.Sprintf(
		`SELECT id, channel_id, event_type, title, message, status, attempts, max_attempts,
		        last_error, next_retry_at, created_at, delivered_at
		 FROM notification_queue%s ORDER BY created_at DESC LIMIT $%d OFFSET $%d`,
		where, qb.Idx(), qb.Idx()+1)
	args := append(qb.Args(), pageSize, offset)

	rows, err := s.db.Pool.Query(ctx, dataQuery, args...)
	if err != nil {
		return nil, 0, fmt.Errorf("list notification queue: %w", err)
	}
	defer rows.Close()

	var entries []QueueEntry
	for rows.Next() {
		var e QueueEntry
		var lastError, nextRetry, deliveredAt interface{} // nullable
		if err := rows.Scan(&e.ID, &e.ChannelID, &e.EventType, &e.Title, &e.Message,
			&e.Status, &e.Attempts, &e.MaxAttempts,
			&lastError, &nextRetry, &e.CreatedAt, &deliveredAt); err != nil {
			continue
		}
		if le, ok := lastError.(*string); ok && le != nil {
			e.LastError = le
		} else if le, ok := lastError.(string); ok && le != "" {
			e.LastError = &le
		}
		if nr, ok := nextRetry.(*time.Time); ok && nr != nil {
			e.NextRetryAt = nr
		}
		if da, ok := deliveredAt.(*time.Time); ok && da != nil {
			e.DeliveredAt = da
		}
		entries = append(entries, e)
	}

	return entries, total, nil
}

// StartDispatcher launches the notification dispatcher goroutines.
func (s *NotificationService) StartDispatcher(ctx context.Context) {
	go s.pollActivityEvents(ctx)
	go s.processQueue(ctx)
}

// StopDispatcher signals both dispatcher goroutines to stop.
func (s *NotificationService) StopDispatcher() {
	close(s.done)
}

func (s *NotificationService) pollActivityEvents(ctx context.Context) {
	slog.Info("notification event poller started")
	defer slog.Info("notification event poller stopped")

	ticker := time.NewTicker(5 * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-s.done:
			return
		case <-ctx.Done():
			return
		case <-ticker.C:
			s.pollOnce(ctx)
		}
	}
}

func (s *NotificationService) pollOnce(ctx context.Context) {
	pollCtx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()

	// Get cursor
	var lastID int64
	var lastCreatedAt *time.Time
	err := s.db.Pool.QueryRow(pollCtx,
		`SELECT last_event_id, last_event_created_at FROM notification_state WHERE id = 1`).
		Scan(&lastID, &lastCreatedAt)
	if err != nil {
		slog.Error("failed to read notification state", "error", err)
		return
	}

	type eventRow struct {
		ID        int64
		EventType string
		Title     string
		CreatedAt time.Time
	}

	var events []eventRow

	var rows pgx.Rows
	if lastCreatedAt != nil {
		rows, err = s.db.Pool.Query(pollCtx,
			`SELECT id, event_type, title, created_at FROM activity_events
			 WHERE (created_at, id) > ($1, $2) ORDER BY created_at, id LIMIT 100`,
			*lastCreatedAt, lastID)
	} else {
		rows, err = s.db.Pool.Query(pollCtx,
			`SELECT id, event_type, title, created_at FROM activity_events
			 WHERE id > $1 ORDER BY created_at, id LIMIT 100`,
			lastID)
	}

	if err != nil {
		slog.Error("failed to poll activity events", "error", err)
		return
	}
	defer rows.Close()

	for rows.Next() {
		var e eventRow
		if err := rows.Scan(&e.ID, &e.EventType, &e.Title, &e.CreatedAt); err != nil {
			continue
		}
		events = append(events, e)
	}

	if len(events) == 0 {
		return
	}

	// For each event, find subscribers and create queue entries
	var maxID int64
	var maxCreatedAt time.Time
	for _, e := range events {
		subscribers, subErr := s.GetSubscribersForEvent(pollCtx, e.EventType)
		if subErr != nil {
			slog.Error("failed to get subscribers", "error", subErr, "event_type", e.EventType)
			continue
		}

		message, _ := json.Marshal(map[string]interface{}{
			"event_type": e.EventType,
			"title":      e.Title,
		})

		for _, ch := range subscribers {
			_, qErr := s.db.Pool.Exec(pollCtx,
				`INSERT INTO notification_queue (channel_id, event_type, title, message)
				 VALUES ($1, $2, $3, $4)`, ch.ID, e.EventType, e.Title, message)
			if qErr != nil {
				slog.Error("failed to enqueue notification", "error", qErr, "channel", ch.Name)
			}
		}

		if e.ID > maxID {
			maxID = e.ID
			maxCreatedAt = e.CreatedAt
		}
	}

	// Update cursor
	_, err = s.db.Pool.Exec(pollCtx,
		`UPDATE notification_state SET last_event_id = $1, last_event_created_at = $2 WHERE id = 1`,
		maxID, maxCreatedAt)
	if err != nil {
		slog.Error("failed to update notification state", "error", err)
	}
}

func (s *NotificationService) processQueue(ctx context.Context) {
	slog.Info("notification queue processor started")
	defer slog.Info("notification queue processor stopped")

	ticker := time.NewTicker(10 * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-s.done:
			return
		case <-ctx.Done():
			return
		case <-ticker.C:
			s.processQueueBatch(ctx)
		}
	}
}

func (s *NotificationService) processQueueBatch(ctx context.Context) {
	batchCtx, cancel := context.WithTimeout(ctx, 30*time.Second)
	defer cancel()

	rows, err := s.db.Pool.Query(batchCtx,
		`SELECT q.id, q.channel_id, q.event_type, q.title, q.message, q.status, q.attempts,
		        c.name AS channel_name, c.type AS channel_type, c.config AS channel_config
		 FROM notification_queue q
		 JOIN notification_channels c ON q.channel_id = c.id
		 WHERE q.status IN ('pending', 'failed')
		   AND (q.next_retry_at IS NULL OR q.next_retry_at <= NOW())
		   AND q.attempts < q.max_attempts
		 LIMIT 50`)
	if err != nil {
		slog.Error("failed to query notification queue", "error", err)
		return
	}
	defer rows.Close()

	type queueItem struct {
		ID           int64
		ChannelID    int64
		EventType    string
		Title        string
		Message      json.RawMessage
		Status       string
		Attempts     int
		ChannelName  string
		ChannelType  string
		ChannelConfig json.RawMessage
	}

	var items []queueItem
	for rows.Next() {
		var q queueItem
		if err := rows.Scan(&q.ID, &q.ChannelID, &q.EventType, &q.Title, &q.Message,
			&q.Status, &q.Attempts, &q.ChannelName, &q.ChannelType, &q.ChannelConfig); err != nil {
			continue
		}
		items = append(items, q)
	}

	for _, q := range items {
		deliverCtx, deliverCancel := context.WithTimeout(batchCtx, 15*time.Second)
		var deliverErr error

		switch q.ChannelType {
		case "webhook":
			var configMap map[string]interface{}
			json.Unmarshal(q.ChannelConfig, &configMap)
			webhookURL, _ := configMap["url"].(string)
			var payload map[string]interface{}
			json.Unmarshal(q.Message, &payload)
			deliverErr = s.DeliverWebhook(deliverCtx, webhookURL, payload)

		case "telegram":
			var configMap map[string]interface{}
			json.Unmarshal(q.ChannelConfig, &configMap)
			botToken, _ := configMap["bot_token"].(string)
			chatID, _ := configMap["chat_id"].(string)
			var msg map[string]interface{}
			json.Unmarshal(q.Message, &msg)
			title, _ := msg["title"].(string)
			text := fmt.Sprintf("<b>%s</b>\n%s", q.EventType, title)
			deliverErr = s.DeliverTelegram(deliverCtx, botToken, chatID, text)
		}

		deliverCancel()

		newAttempts := q.Attempts + 1
		if deliverErr == nil {
			_, err := s.db.Pool.Exec(batchCtx,
				`UPDATE notification_queue SET status = 'delivered', attempts = $1, delivered_at = NOW() WHERE id = $2`,
				newAttempts, q.ID)
			if err != nil {
				slog.Error("failed to update queue entry", "error", err)
			}
			slog.Info("notification delivered", "channel", q.ChannelName, "event", q.EventType)
		} else {
			var nextRetry *time.Time
			var newStatus string = "failed"
			errMsg := deliverErr.Error()

			if newAttempts >= 5 {
				newStatus = "dead"
				slog.Warn("notification dead-lettered", "channel", q.ChannelName, "attempts", newAttempts)
			} else {
				backoff := calculateBackoff(newAttempts)
				t := time.Now().Add(backoff)
				nextRetry = &t
			}

			_, err := s.db.Pool.Exec(batchCtx,
				`UPDATE notification_queue SET status = $1, attempts = $2, last_error = $3, next_retry_at = $4 WHERE id = $5`,
				newStatus, newAttempts, errMsg, nextRetry, q.ID)
			if err != nil {
				slog.Error("failed to update queue entry", "error", err)
			}
			slog.Error("notification delivery failed", "channel", q.ChannelName, "type", q.ChannelType, "attempts", newAttempts)
		}
	}
}