package parser

import (
	"bufio"
	"bytes"
	"errors"
	"io"
	"net/netip"
	"strings"

	"github.com/miekg/dns"
)

var ErrNoParser = errors.New("no suitable parser could be found")

type Parser interface {
	CanHandle(line string) bool
}

type DomainsParser interface {
	Parser
	ParseDomains(io.Reader) (domains []string, ignored int, err error)
}

type NetworksParser interface {
	Parser
	ParseNetworks(io.Reader) (prefixes []netip.Prefix, ignored int, err error)
}

var (
	domainsParsers  []DomainsParser
	networksParsers []NetworksParser
)

func RegisterDomainsParser(parser DomainsParser) {
	domainsParsers = append(domainsParsers, parser)
}

func RegisterNetworksParser(parser NetworksParser) {
	networksParsers = append(networksParsers, parser)
}

func ParseDomains(r io.Reader) (domains []string, ignored int, err error) {
	var (
		buffer  = new(bytes.Buffer)
		scanner = bufio.NewScanner(io.TeeReader(r, buffer))
		line    string
		parser  DomainsParser
	)
	for scanner.Scan() {
		line = strings.TrimSpace(scanner.Text())
		if isComment(line) {
			continue
		}
		for _, parser = range domainsParsers {
			if parser.CanHandle(line) {
				// log.Printf("using parser %T", parser)
				return parser.ParseDomains(io.MultiReader(buffer, r))
			}
		}
		break
	}
	return nil, 0, ErrNoParser
}

func ParseNetworks(r io.Reader) (prefixes []netip.Prefix, ignored int, err error) {
	var (
		buffer  = new(bytes.Buffer)
		scanner = bufio.NewScanner(io.TeeReader(r, buffer))
		line    string
		parser  NetworksParser
	)
	for scanner.Scan() {
		line = strings.TrimSpace(scanner.Text())
		if isComment(line) {
			continue
		}
		for _, parser = range networksParsers {
			if parser.CanHandle(line) {
				// log.Printf("using parser %T", parser)
				return parser.ParseNetworks(io.MultiReader(buffer, r))
			}
		}
		break
	}
	return nil, 0, ErrNoParser
}

func isComment(line string) bool {
	return line == "" || line[0] == '#' || line[0] == '!'
}

func isDomainName(s string) bool {
	n, ok := dns.IsDomainName(s)
	return n >= 2 && ok
}

func isIP(s string) bool {
	_, err := netip.ParseAddr(s)
	return err == nil
}

func isPrefix(s string) bool {
	_, err := netip.ParsePrefix(s)
	return err == nil
}

func addrToPrefix(addr netip.Addr) netip.Prefix {
	switch {
	case addr.Is4():
		prefix, _ := addr.Prefix(32)
		return prefix
	case addr.Is4In6():
		prefix, _ := addr.Unmap().Prefix(32)
		return prefix
	case addr.Is6():
		prefix, _ := addr.Prefix(128)
		return prefix
	default:
		return netip.Prefix{}
	}
}