package main

import (
	"context"
	"fmt"
	"net/http"
	"strings"
	"time"

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

type AdminGroupChat struct {
	ID        string    `json:"id"`
	Name      string    `json:"name"`
	Image     string    `json:"image"`
	OwnerID   string    `json:"ownerId"`
	TeamID    string    `json:"teamId"`
	UserIDs   []string  `json:"userIds"`
	CreatedAt time.Time `json:"createdAt"`
	UpdatedAt time.Time `json:"updatedAt"`
}

type saveAdminGroupChatRequest struct {
	Name    string   `json:"name"`
	Image   string   `json:"image"`
	UserIDs []string `json:"userIds"`
}

func (s *Server) handleAdminListGroupChats(w http.ResponseWriter, r *http.Request) {
	rows, err := s.db.Query(
		r.Context(),
		`
		SELECT
			c.id::TEXT,
			c.name,
			c.channel_image,
			COALESCE(c.created_by::TEXT, ''),
			COALESCE(c.team_id::TEXT, ''),
			COALESCE(
				array_agg(cm.user_id::TEXT ORDER BY cm.created_at)
					FILTER (WHERE cm.user_id IS NOT NULL),
				'{}'::TEXT[]
			),
			c.created_at,
			c.updated_at
		FROM conversations c
		LEFT JOIN conversation_members cm ON cm.conversation_id = c.id
		WHERE c.type = 'group'
		GROUP BY c.id
		ORDER BY (c.team_id IS NOT NULL), lower(c.name), c.created_at
		`,
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchats konnten nicht geladen werden")
		return
	}
	defer rows.Close()

	groups := []AdminGroupChat{}
	for rows.Next() {
		var group AdminGroupChat
		if err := rows.Scan(
			&group.ID,
			&group.Name,
			&group.Image,
			&group.OwnerID,
			&group.TeamID,
			&group.UserIDs,
			&group.CreatedAt,
			&group.UpdatedAt,
		); err != nil {
			writeError(w, http.StatusInternalServerError, "Gruppenchats konnten nicht gelesen werden")
			return
		}
		groups = append(groups, group)
	}
	if err := rows.Err(); err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchats konnten nicht vollständig geladen werden")
		return
	}
	rows.Close()

	users, err := s.listAdminChannelUsers(r.Context())
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Benutzer konnten nicht geladen werden")
		return
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"groups": groups,
		"users":  users,
	})
}

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

	conversationID := strings.TrimSpace(r.PathValue("id"))
	if conversationID == "" {
		writeError(w, http.StatusBadRequest, "Gruppenchat-ID fehlt")
		return
	}

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

	input.Name = strings.TrimSpace(input.Name)
	input.Image = strings.TrimSpace(input.Image)
	input.UserIDs = cleanStringList(input.UserIDs)
	if input.Name == "" || len([]rune(input.Name)) > maxGroupNameLength {
		writeError(w, http.StatusBadRequest, "Gruppenname muss 1–80 Zeichen lang sein")
		return
	}
	if len(input.Image) > maxGroupImageBytes {
		writeError(w, http.StatusBadRequest, "Das Gruppenbild ist zu groß")
		return
	}

	tx, err := s.db.Begin(r.Context())
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht aktualisiert werden")
		return
	}
	defer tx.Rollback(r.Context())

	var currentName, currentImage, ownerID string
	if err := tx.QueryRow(
		r.Context(),
		`
		SELECT name, channel_image, COALESCE(created_by::TEXT, '')
		FROM conversations
		WHERE id = $1
		  AND type = 'group'
		  AND team_id IS NULL
		FOR UPDATE
		`,
		conversationID,
	).Scan(&currentName, &currentImage, &ownerID); err != nil {
		if err == pgx.ErrNoRows {
			writeError(w, http.StatusNotFound, "Gruppenchat wurde nicht gefunden")
			return
		}
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht geladen werden")
		return
	}

	if ownerID != "" {
		input.UserIDs = cleanStringList(append(input.UserIDs, ownerID))
	}
	if len(input.UserIDs) == 0 {
		writeError(w, http.StatusBadRequest, "Mindestens ein Gruppenmitglied ist erforderlich")
		return
	}

	oldMemberIDs, err := adminGroupMemberIDs(r.Context(), tx, conversationID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenmitglieder konnten nicht geladen werden")
		return
	}

	if _, err := tx.Exec(
		r.Context(),
		`
		UPDATE conversations
		SET
			name = $2,
			channel_image = $3,
			updated_at = now()
		WHERE id = $1
		  AND type = 'group'
		  AND team_id IS NULL
		`,
		conversationID,
		input.Name,
		input.Image,
	); err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht aktualisiert werden")
		return
	}

	if _, err := tx.Exec(
		r.Context(),
		`
		DELETE FROM conversation_members
		WHERE conversation_id = $1
		  AND NOT (user_id::TEXT = ANY($2::TEXT[]))
		`,
		conversationID,
		input.UserIDs,
	); err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenmitglieder konnten nicht gespeichert werden")
		return
	}

	if _, err := tx.Exec(
		r.Context(),
		`
		INSERT INTO conversation_members (conversation_id, user_id)
		SELECT $1, id
		FROM users
		WHERE id::TEXT = ANY($2::TEXT[])
		ON CONFLICT (conversation_id, user_id) DO NOTHING
		`,
		conversationID,
		input.UserIDs,
	); err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenmitglieder konnten nicht gespeichert werden")
		return
	}

	newMemberIDs, err := adminGroupMemberIDs(r.Context(), tx, conversationID)
	if err != nil || len(newMemberIDs) == 0 {
		writeError(w, http.StatusBadRequest, "Mindestens ein gültiges Gruppenmitglied ist erforderlich")
		return
	}

	if err := tx.Commit(r.Context()); err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht gespeichert werden")
		return
	}

	changed := currentName != input.Name ||
		currentImage != input.Image ||
		!sameStringSet(oldMemberIDs, newMemberIDs)
	if changed {
		s.emitSystemMessage(
			r.Context(),
			conversationID,
			user.ID,
			"group_admin_updated",
			fmt.Sprintf("%s hat den Gruppenchat über die Administration aktualisiert.", conversationActorName(user)),
			nil,
		)
		s.publishConversationUpdate(r.Context(), conversationID)
	}

	newMembers := make(map[string]struct{}, len(newMemberIDs))
	for _, memberID := range newMemberIDs {
		newMembers[memberID] = struct{}{}
	}
	for _, memberID := range oldMemberIDs {
		if _, remains := newMembers[memberID]; remains {
			continue
		}
		chatSockets.publish(memberID, chatSocketEvent{
			Type:           "conversation.removed",
			ConversationID: conversationID,
		})
	}

	writeJSON(w, http.StatusOK, map[string]any{"id": conversationID})
}

func (s *Server) handleAdminDeleteGroupChat(w http.ResponseWriter, r *http.Request) {
	conversationID := strings.TrimSpace(r.PathValue("id"))
	if conversationID == "" {
		writeError(w, http.StatusBadRequest, "Gruppenchat-ID fehlt")
		return
	}

	memberIDs, err := s.chatConversationMemberIDs(r.Context(), conversationID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenmitglieder konnten nicht geladen werden")
		return
	}

	tx, err := s.db.Begin(r.Context())
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht gelöscht werden")
		return
	}
	defer tx.Rollback(r.Context())

	if _, err := tx.Exec(
		r.Context(),
		`DELETE FROM notifications WHERE entity_type = 'chat' AND entity_id = $1`,
		conversationID,
	); err != nil {
		writeError(w, http.StatusInternalServerError, "Chat-Benachrichtigungen konnten nicht gelöscht werden")
		return
	}

	commandTag, err := tx.Exec(
		r.Context(),
		`DELETE FROM conversations WHERE id = $1 AND type = 'group' AND team_id IS NULL`,
		conversationID,
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht gelöscht werden")
		return
	}
	if commandTag.RowsAffected() == 0 {
		writeError(w, http.StatusNotFound, "Gruppenchat wurde nicht gefunden")
		return
	}

	if err := tx.Commit(r.Context()); err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht gelöscht werden")
		return
	}

	for _, memberID := range memberIDs {
		chatSockets.publish(memberID, chatSocketEvent{
			Type:           "conversation.removed",
			ConversationID: conversationID,
		})
	}

	writeJSON(w, http.StatusOK, map[string]bool{"ok": true})
}

// handleAdminEmptyGroupChat löscht den gesamten Nachrichtenverlauf eines
// Gruppenchats (inkl. Anhänge über ON DELETE CASCADE), behält den Chat aber.
// Für Team-Gruppenchats ist dies die einzige zulässige Admin-Aktion.
func (s *Server) handleAdminEmptyGroupChat(w http.ResponseWriter, r *http.Request) {
	conversationID := strings.TrimSpace(r.PathValue("id"))
	if conversationID == "" {
		writeError(w, http.StatusBadRequest, "Gruppenchat-ID fehlt")
		return
	}

	tx, err := s.db.Begin(r.Context())
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht geleert werden")
		return
	}
	defer tx.Rollback(r.Context())

	var exists bool
	if err := tx.QueryRow(
		r.Context(),
		`SELECT true FROM conversations WHERE id = $1 AND type = 'group'`,
		conversationID,
	).Scan(&exists); err != nil {
		if err == pgx.ErrNoRows {
			writeError(w, http.StatusNotFound, "Gruppenchat wurde nicht gefunden")
			return
		}
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht geladen werden")
		return
	}

	if _, err := tx.Exec(
		r.Context(),
		`DELETE FROM notifications WHERE entity_type = 'chat' AND entity_id = $1`,
		conversationID,
	); err != nil {
		writeError(w, http.StatusInternalServerError, "Chat-Benachrichtigungen konnten nicht gelöscht werden")
		return
	}

	if _, err := tx.Exec(
		r.Context(),
		`DELETE FROM messages WHERE conversation_id = $1`,
		conversationID,
	); err != nil {
		writeError(w, http.StatusInternalServerError, "Nachrichten konnten nicht gelöscht werden")
		return
	}

	if _, err := tx.Exec(
		r.Context(),
		`UPDATE conversations SET last_message_at = NULL, updated_at = now() WHERE id = $1`,
		conversationID,
	); err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht aktualisiert werden")
		return
	}

	if err := tx.Commit(r.Context()); err != nil {
		writeError(w, http.StatusInternalServerError, "Gruppenchat konnte nicht geleert werden")
		return
	}

	s.publishChatMessagesReload(r.Context(), conversationID)
	s.publishConversationUpdate(r.Context(), conversationID)

	writeJSON(w, http.StatusOK, map[string]bool{"ok": true})
}

func adminGroupMemberIDs(ctx context.Context, tx pgx.Tx, conversationID string) ([]string, error) {
	rows, err := tx.Query(
		ctx,
		`
		SELECT user_id::TEXT
		FROM conversation_members
		WHERE conversation_id = $1
		ORDER BY created_at, user_id
		`,
		conversationID,
	)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

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

func sameStringSet(left []string, right []string) bool {
	if len(left) != len(right) {
		return false
	}

	values := make(map[string]struct{}, len(left))
	for _, value := range left {
		values[value] = struct{}{}
	}
	for _, value := range right {
		if _, exists := values[value]; !exists {
			return false
		}
	}
	return true
}