package main

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

const presenceStatusSQL = `
	CASE
		WHEN presence_mode = 'offline'
			OR last_seen_at IS NULL
			OR last_seen_at < now() - INTERVAL '2 minutes'
			THEN 'offline'
		WHEN presence_mode = 'away'
			OR last_active_at IS NULL
			OR last_active_at < now() - make_interval(mins => away_after_minutes)
			THEN 'away'
		ELSE 'online'
	END
`

type presenceHeartbeatRequest struct {
	Active bool `json:"active"`
}

type presenceSettingsRequest struct {
	Mode             string `json:"mode"`
	AwayAfterMinutes int    `json:"awayAfterMinutes"`
	ShowLastSeen     bool   `json:"showLastSeen"`
}

type presenceStatusRequest struct {
	Mode string `json:"mode"`
}

func normalizePresenceMode(value string) string {
	switch strings.ToLower(strings.TrimSpace(value)) {
	case "away":
		return "away"
	case "offline":
		return "offline"
	default:
		return "online"
	}
}

func (s *Server) startPresenceMonitor(ctx context.Context) {
	s.refreshPresenceStatuses(ctx, false)

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

		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker.C:
				s.refreshPresenceStatuses(ctx, true)
			}
		}
	}()
}

func (s *Server) refreshPresenceStatuses(ctx context.Context, publish bool) {
	rows, err := s.db.Query(
		ctx,
		`
		SELECT id::TEXT, `+presenceStatusSQL+`
		FROM users
		`,
	)
	if err != nil {
		return
	}
	defer rows.Close()

	currentStatuses := map[string]string{}
	changedUserIDs := []string{}

	for rows.Next() {
		var userID string
		var status string
		if err := rows.Scan(&userID, &status); err != nil {
			return
		}

		currentStatuses[userID] = status

		s.presenceMu.Lock()
		previousStatus, known := s.presenceStatus[userID]
		s.presenceMu.Unlock()

		if publish && known && previousStatus != status {
			changedUserIDs = append(changedUserIDs, userID)
		}
	}

	if rows.Err() != nil {
		return
	}

	s.presenceMu.Lock()
	s.presenceStatus = currentStatuses
	s.presenceMu.Unlock()

	for _, userID := range changedUserIDs {
		user, err := s.getUserByID(ctx, userID)
		if err == nil {
			s.publishUserProfileEvent("user.presence", user)
		}
	}
}

func (s *Server) publishPresenceIfChanged(user User) {
	s.presenceMu.Lock()
	previousStatus, known := s.presenceStatus[user.ID]
	s.presenceStatus[user.ID] = user.PresenceStatus
	s.presenceMu.Unlock()

	if !known || previousStatus != user.PresenceStatus {
		s.publishUserProfileEvent("user.presence", user)
	}
}

func (s *Server) handlePresence(w http.ResponseWriter, r *http.Request) {
	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	var input presenceHeartbeatRequest
	if r.Body != nil {
		_ = json.NewDecoder(r.Body).Decode(&input)
	}

	_, err := s.db.Exec(
		r.Context(),
		`
		UPDATE users
		SET
			last_seen_at = now(),
			last_active_at = CASE
				WHEN $2 AND presence_mode = 'online' THEN now()
				ELSE last_active_at
			END
		WHERE id = $1
		`,
		user.ID,
		input.Active,
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Präsenz konnte nicht aktualisiert werden")
		return
	}

	updatedUser, err := s.getUserByID(r.Context(), user.ID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Präsenz konnte nicht geladen werden")
		return
	}

	s.publishPresenceIfChanged(updatedUser)

	writeJSON(w, http.StatusOK, map[string]any{
		"presenceStatus": updatedUser.PresenceStatus,
		"lastSeenAt":     updatedUser.LastSeenAt,
	})
}

func (s *Server) handleGetPresenceSettings(w http.ResponseWriter, r *http.Request) {
	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"settings": map[string]any{
			"mode":             user.PresenceMode,
			"awayAfterMinutes": user.AwayAfterMinutes,
			"currentStatus":    user.PresenceStatus,
			"showLastSeen":     user.ShowLastSeen,
		},
	})
}

func (s *Server) handleUpdatePresenceSettings(w http.ResponseWriter, r *http.Request) {
	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	var input presenceSettingsRequest
	if err := readJSON(r, &input); err != nil {
		writeError(w, http.StatusBadRequest, "Ungültige Anfrage")
		return
	}

	mode := user.PresenceMode
	if strings.TrimSpace(input.Mode) != "" {
		mode = normalizePresenceMode(input.Mode)
	}
	if input.AwayAfterMinutes < 1 || input.AwayAfterMinutes > 120 {
		writeError(w, http.StatusBadRequest, "Automatische Abwesenheit muss zwischen 1 und 120 Minuten liegen")
		return
	}

	_, err := s.db.Exec(
		r.Context(),
		`
		UPDATE users
		SET
			presence_mode_updated_at = CASE
				WHEN presence_mode IS DISTINCT FROM $2 THEN now()
				ELSE presence_mode_updated_at
			END,
			presence_mode = $2,
			away_after_minutes = $3,
			show_last_seen = $4,
			last_active_at = CASE WHEN $2 = 'online' THEN now() ELSE last_active_at END,
			updated_at = now()
		WHERE id = $1
		`,
		user.ID,
		mode,
		input.AwayAfterMinutes,
		input.ShowLastSeen,
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Präsenzeinstellungen konnten nicht gespeichert werden")
		return
	}

	updatedUser, err := s.getUserByID(r.Context(), user.ID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Präsenzeinstellungen konnten nicht geladen werden")
		return
	}

	s.publishPresenceIfChanged(updatedUser)

	writeJSON(w, http.StatusOK, map[string]any{
		"settings": map[string]any{
			"mode":             updatedUser.PresenceMode,
			"awayAfterMinutes": updatedUser.AwayAfterMinutes,
			"currentStatus":    updatedUser.PresenceStatus,
			"showLastSeen":     updatedUser.ShowLastSeen,
		},
		"user": updatedUser,
	})
}

func (s *Server) handleUpdatePresenceStatus(w http.ResponseWriter, r *http.Request) {
	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	var input presenceStatusRequest
	if err := readJSON(r, &input); err != nil {
		writeError(w, http.StatusBadRequest, "Ungültige Anfrage")
		return
	}

	mode := strings.ToLower(strings.TrimSpace(input.Mode))
	if mode != "online" && mode != "away" && mode != "offline" {
		writeError(w, http.StatusBadRequest, "Ungültiger Status")
		return
	}

	_, err := s.db.Exec(
		r.Context(),
		`
		UPDATE users
		SET
			presence_mode_updated_at = CASE
				WHEN presence_mode IS DISTINCT FROM $2 THEN now()
				ELSE presence_mode_updated_at
			END,
			presence_mode = $2,
			last_active_at = CASE WHEN $2 = 'online' THEN now() ELSE last_active_at END,
			last_seen_at = now(),
			updated_at = now()
		WHERE id = $1
		`,
		user.ID,
		mode,
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Status konnte nicht gespeichert werden")
		return
	}

	updatedUser, err := s.getUserByID(r.Context(), user.ID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Status konnte nicht geladen werden")
		return
	}

	s.publishPresenceIfChanged(updatedUser)
	writeJSON(w, http.StatusOK, map[string]any{"user": updatedUser})
}