// backend/user_sessions.go

package main

import (
	"context"
	"encoding/json"
	"net"
	"net/http"
	"strings"
	"time"

	"github.com/golang-jwt/jwt/v5"
)

type userSessionResponse struct {
	ID              string    `json:"id"`
	Browser         string    `json:"browser"`
	OperatingSystem string    `json:"operatingSystem"`
	DeviceType      string    `json:"deviceType"`
	UserAgent       string    `json:"userAgent"`
	IPAddress       string    `json:"ipAddress"`
	CreatedAt       time.Time `json:"createdAt"`
	LastSeenAt      time.Time `json:"lastSeenAt"`
	Current         bool      `json:"current"`
}

func (s *Server) createUserSession(
	ctx context.Context,
	userID string,
	input ClientSessionInfoRequest,
	r *http.Request,
) (string, error) {
	browser := strings.TrimSpace(input.Browser)
	operatingSystem := strings.TrimSpace(input.OperatingSystem)
	deviceType := strings.TrimSpace(input.DeviceType)
	userAgent := r.UserAgent()
	ipAddress := getRequestIP(r)

	if browser == "" {
		browser = detectBrowserFromUserAgent(userAgent)
	}

	if operatingSystem == "" {
		operatingSystem = detectOperatingSystemFromUserAgent(userAgent)
	}

	if deviceType == "" {
		deviceType = detectDeviceTypeFromUserAgent(userAgent)
	}

	var sessionID string

	err := s.db.QueryRow(
		ctx,
		`
		INSERT INTO user_sessions (
			user_id,
			browser,
			operating_system,
			device_type,
			user_agent,
			ip_address
		)
		VALUES ($1, $2, $3, $4, $5, $6)
		RETURNING id
		`,
		userID,
		browser,
		operatingSystem,
		deviceType,
		userAgent,
		ipAddress,
	).Scan(&sessionID)
	if err != nil {
		s.logUserEvent(ctx, UserLogEntry{
			UserID:   userID,
			Request:  r,
			Level:    UserLogLevelError,
			Category: "session",
			Action:   "create_session",
			Message:  "Sitzung konnte nicht erstellt werden",
			Error:    err,
			Details: LogFields{
				"browser":         browser,
				"operatingSystem": operatingSystem,
				"deviceType":      deviceType,
				"ipAddress":       ipAddress,
			},
		})

		return "", err
	}

	s.logUserEvent(ctx, UserLogEntry{
		UserID:   userID,
		Request:  r,
		Level:    UserLogLevelInfo,
		Category: "session",
		Action:   "create_session",
		Message:  "Neue Sitzung wurde erstellt",
		Details: LogFields{
			"sessionId":       sessionID,
			"browser":         browser,
			"operatingSystem": operatingSystem,
			"deviceType":      deviceType,
			"ipAddress":       ipAddress,
		},
	})

	return sessionID, nil
}

func (s *Server) isUserSessionActive(
	ctx context.Context,
	userID string,
	sessionID string,
) (bool, error) {
	var exists bool

	err := s.db.QueryRow(
		ctx,
		`
		SELECT EXISTS(
			SELECT 1
			FROM user_sessions
			WHERE id = $1
			  AND user_id = $2
			  AND revoked_at IS NULL
		)
		`,
		sessionID,
		userID,
	).Scan(&exists)

	return exists, err
}

func (s *Server) touchUserSession(
	ctx context.Context,
	userID string,
	sessionID string,
) error {
	_, err := s.db.Exec(
		ctx,
		`
		UPDATE user_sessions
		SET last_seen_at = now()
		WHERE id = $1
		  AND user_id = $2
		  AND revoked_at IS NULL
		`,
		sessionID,
		userID,
	)

	return err
}

func (s *Server) handleListUserSessions(w http.ResponseWriter, r *http.Request) {
	userID, ok := s.currentUserIDFromRequest(r)
	if !ok {
		s.logRequestWarning(
			r,
			"session",
			"list_sessions",
			"Sitzungen konnten nicht geladen werden: nicht angemeldet",
			nil,
			nil,
		)

		writeSettingsError(w, http.StatusUnauthorized, "Nicht angemeldet")
		return
	}

	currentSessionID, _ := s.currentSessionIDFromRequest(r)

	rows, err := s.db.Query(
		r.Context(),
		`
		SELECT
			id,
			browser,
			operating_system,
			device_type,
			user_agent,
			ip_address,
			created_at,
			last_seen_at
		FROM user_sessions
		WHERE user_id = $1
		  AND revoked_at IS NULL
		ORDER BY
			CASE WHEN id = $2 THEN 0 ELSE 1 END,
			last_seen_at DESC
		`,
		userID,
		currentSessionID,
	)
	if err != nil {
		s.logAndWriteSettingsError(
			w,
			r,
			http.StatusInternalServerError,
			"session",
			"list_sessions",
			"Sitzungen konnten nicht geladen werden",
			err,
			LogFields{
				"userId":           userID,
				"currentSessionId": currentSessionID,
			},
		)
		return
	}
	defer rows.Close()

	sessions := []userSessionResponse{}

	for rows.Next() {
		var session userSessionResponse

		if err := rows.Scan(
			&session.ID,
			&session.Browser,
			&session.OperatingSystem,
			&session.DeviceType,
			&session.UserAgent,
			&session.IPAddress,
			&session.CreatedAt,
			&session.LastSeenAt,
		); err != nil {
			s.logAndWriteSettingsError(
				w,
				r,
				http.StatusInternalServerError,
				"session",
				"scan_sessions",
				"Sitzungen konnten nicht gelesen werden",
				err,
				LogFields{
					"userId": userID,
				},
			)
			return
		}

		session.Current = session.ID == currentSessionID
		sessions = append(sessions, session)
	}

	if err := rows.Err(); err != nil {
		s.logAndWriteSettingsError(
			w,
			r,
			http.StatusInternalServerError,
			"session",
			"read_sessions",
			"Sitzungen konnten nicht gelesen werden",
			err,
			LogFields{
				"userId": userID,
			},
		)
		return
	}

	s.logRequestInfo(
		r,
		"session",
		"list_sessions",
		"Sitzungen wurden geladen",
		LogFields{
			"userId":       userID,
			"sessionCount": len(sessions),
		},
	)

	writeSettingsJSON(w, http.StatusOK, map[string]any{
		"sessions": sessions,
	})
}

func (s *Server) handleRevokeUserSession(w http.ResponseWriter, r *http.Request) {
	userID, ok := s.currentUserIDFromRequest(r)
	if !ok {
		s.logRequestWarning(
			r,
			"session",
			"revoke_session",
			"Sitzung konnte nicht abgemeldet werden: nicht angemeldet",
			nil,
			nil,
		)

		writeSettingsError(w, http.StatusUnauthorized, "Nicht angemeldet")
		return
	}

	sessionID := strings.TrimSpace(r.PathValue("id"))
	currentSessionID, _ := s.currentSessionIDFromRequest(r)

	if sessionID == "" {
		s.logRequestWarning(
			r,
			"session",
			"revoke_session",
			"Sitzung konnte nicht abgemeldet werden: Sitzung fehlt",
			nil,
			LogFields{
				"userId": userID,
			},
		)

		writeSettingsError(w, http.StatusBadRequest, "Sitzung fehlt")
		return
	}

	if sessionID == currentSessionID {
		s.logRequestWarning(
			r,
			"session",
			"revoke_session",
			"Aktuelle Sitzung kann hier nicht abgemeldet werden",
			nil,
			LogFields{
				"userId":           userID,
				"sessionId":        sessionID,
				"currentSessionId": currentSessionID,
			},
		)

		writeSettingsError(w, http.StatusBadRequest, "Die aktuelle Sitzung kann hier nicht abgemeldet werden")
		return
	}

	commandTag, err := s.db.Exec(
		r.Context(),
		`
		UPDATE user_sessions
		SET revoked_at = now()
		WHERE id = $1
		  AND user_id = $2
		  AND revoked_at IS NULL
		`,
		sessionID,
		userID,
	)
	if err != nil {
		s.logAndWriteSettingsError(
			w,
			r,
			http.StatusInternalServerError,
			"session",
			"revoke_session",
			"Sitzung konnte nicht abgemeldet werden",
			err,
			LogFields{
				"userId":    userID,
				"sessionId": sessionID,
			},
		)
		return
	}

	if commandTag.RowsAffected() == 0 {
		s.logRequestWarning(
			r,
			"session",
			"revoke_session",
			"Sitzung wurde nicht gefunden",
			nil,
			LogFields{
				"userId":    userID,
				"sessionId": sessionID,
			},
		)

		writeSettingsError(w, http.StatusNotFound, "Sitzung wurde nicht gefunden")
		return
	}

	s.logRequestInfo(
		r,
		"session",
		"revoke_session",
		"Sitzung wurde abgemeldet",
		LogFields{
			"userId":    userID,
			"sessionId": sessionID,
		},
	)

	writeSettingsJSON(w, http.StatusOK, map[string]any{
		"message": "Sitzung wurde abgemeldet",
	})
}

func (s *Server) currentSessionIDFromRequest(r *http.Request) (string, bool) {
	sessionID, ok := r.Context().Value(sessionContextKey).(string)

	return sessionID, ok && sessionID != ""
}

func (s *Server) currentSessionIDFromCookie(r *http.Request) (string, bool) {
	cookie, err := r.Cookie("session")
	if err != nil {
		return "", false
	}

	claims := &Claims{}

	token, err := jwt.ParseWithClaims(cookie.Value, claims, func(token *jwt.Token) (any, error) {
		return s.jwtSecret, nil
	})
	if err != nil || !token.Valid || claims.SessionID == "" {
		return "", false
	}

	return claims.SessionID, true
}

func getRequestIP(r *http.Request) string {
	forwardedFor := r.Header.Get("X-Forwarded-For")
	if forwardedFor != "" {
		parts := strings.Split(forwardedFor, ",")
		return strings.TrimSpace(parts[0])
	}

	realIP := r.Header.Get("X-Real-IP")
	if realIP != "" {
		return strings.TrimSpace(realIP)
	}

	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err == nil {
		return host
	}

	return r.RemoteAddr
}

func detectBrowserFromUserAgent(userAgent string) string {
	switch {
	case strings.Contains(userAgent, "Edg/"):
		return "Microsoft Edge"
	case strings.Contains(userAgent, "Chrome/") && !strings.Contains(userAgent, "Edg/"):
		return "Google Chrome"
	case strings.Contains(userAgent, "Firefox/"):
		return "Mozilla Firefox"
	case strings.Contains(userAgent, "Safari/") && !strings.Contains(userAgent, "Chrome/"):
		return "Safari"
	default:
		return "Unbekannter Browser"
	}
}

func detectOperatingSystemFromUserAgent(userAgent string) string {
	switch {
	case strings.Contains(userAgent, "Windows"):
		return "Windows"
	case strings.Contains(userAgent, "Mac OS X"):
		return "macOS"
	case strings.Contains(userAgent, "iPhone") || strings.Contains(userAgent, "iPad"):
		return "iOS"
	case strings.Contains(userAgent, "Android"):
		return "Android"
	case strings.Contains(userAgent, "Linux"):
		return "Linux"
	default:
		return "Unbekanntes Betriebssystem"
	}
}

func detectDeviceTypeFromUserAgent(userAgent string) string {
	switch {
	case strings.Contains(userAgent, "iPhone") ||
		(strings.Contains(userAgent, "Android") && strings.Contains(userAgent, "Mobile")):
		return "Smartphone"
	case strings.Contains(userAgent, "iPad") || strings.Contains(userAgent, "Tablet"):
		return "Tablet"
	default:
		return "Desktop"
	}
}

func writeSessionJSON(w http.ResponseWriter, status int, payload any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)

	_ = json.NewEncoder(w).Encode(payload)
}