/*
 * This file is part of nftables-http-api.
 * Copyright (C) 2024 Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>
 *
 *  The nftables-http-api program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
 */

package main

import (
	"bytes"
	"errors"
	"github.com/google/nftables"
	"log"
	"net"
)

type nftError struct {
	Message string
}

func (nfterr nftError) Error() string {
	return nfterr.Message
}

func handleNft(task string, givenSet string, givenAddress string) (any, error) {
	nft, err := nftables.New()
	if err != nil {
		log.Println("handleNft():", err)
		return "", err
	}

	set, err := getNftSet(nft, givenSet)
	if err != nil {
		return nil, err
	}

	var element []nftables.SetElement

	if task != "get" {
		address, _ := parseIPAddress(givenAddress)
		if address == nil {
			return nil, errors.New("invalid address")
		}

		element = []nftables.SetElement{
			{
				Key: []byte(address),
			},
		}
	}

	var retmsg string

	switch task {
	case "get":
		nftResult, err := getNftSetElements(nft, set)
		if err != nil {
			return nil, err
		}
		return nftResult, nil

	case "add":
		contains, err := containsNftSetElement(nft, set, element)
		if err != nil {
			return nil, err
		}
		if contains {
			return "already", nil
		} else {
			err := nft.SetAddElements(set, element)
			if err != nil {
				log.Println("handleNft() add failure:", err)
				return nil, err
			}
			retmsg = "added"
		}
	}

	fErr := nft.Flush()
	if fErr != nil {
		log.Println("nftablesHandler: failed to save changes: %w", fErr)
		return nil, fErr
	}

	return retmsg, nil
}

func getNftTable(nft *nftables.Conn) (*nftables.Table, error) {
	targetTable := "filter" // TODO: make table configurable or smarter

	foundTables, err := nft.ListTables()
	if err != nil {
		log.Printf("getNftTable(): %s", err)
		return nil, err
	}

	exists := false
	var table *nftables.Table
	for _, foundTable := range foundTables {
		if foundTable.Name == targetTable {
			exists = true
			table = foundTable
			break
		}
	}

	if !exists {
		log.Printf("Table %s does not exist, cannot proceed", targetTable)
		return nil, nftError{Message: "Table does not exist"}
	}

	return table, nil
}

func getNftSet(nft *nftables.Conn, setName string) (*nftables.Set, error) {
	foundTable, err := getNftTable(nft)
	if err != nil {
		return nil, err
	}
	foundSet, err := nft.GetSetByName(foundTable, setName)
	if err != nil || foundSet == nil {
		log.Printf("Set lookup for %s failed: %s", setName, err)
		return nil, err
	}
	log.Printf("Found set %s", foundSet.Name)

	return foundSet, nil
}

func getNftSetElements(nft *nftables.Conn, set *nftables.Set) ([]string, error) {
	setElements, err := nft.GetSetElements(set)
	if err != nil {
		return nil, err
	}

	var returnElements []string

	for i, element := range setElements {
		ip := net.IP(element.Key)
		log.Printf("Element %d: %s", i, ip)
		returnElements = append(returnElements, ip.String())
	}

	return returnElements, nil
}

func containsNftSetElement(nft *nftables.Conn, set *nftables.Set, element []nftables.SetElement) (bool, error) {

	existingElements, err := nft.GetSetElements(set)
	if err != nil {
		return false, err
	}

	for _, existingElement := range existingElements {
		if bytes.Equal(existingElement.Key, element[0].Key) {
			log.Printf("Existing element found %v", existingElement.Key)
			return true, nil
		}
	}

	return false, nil
}