package parser

import (
	"bufio"
	"bytes"
	"errors"
	"io"
	"log"
	"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)
}

var domainsParsers []DomainsParser

func RegisterDomainsParser(parser DomainsParser) {
	domainsParsers = append(domainsParsers, 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 isComment(line string) bool {
	return line == "" || line[0] == '#' || line[0] == '!'
}

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

func unique(strings []string) []string {
	if strings == nil {
		return nil
	}
	v := make(map[string]struct{})
	for _, s := range strings {
		v[s] = struct{}{}
	}
	o := make([]string, 0, len(v))
	for k := range v {
		o = append(o, k)
	}
	return o
}