package main

import (
	"bufio"
	"context"
	"log"
	"net"
	"os"
	"sort"
	"strings"
	"sync/atomic"
	"time"

	"github.com/miekg/dns"
)

// -------- Blacklist helpers (独立文件) --------

// 将输入域名规范化为 canonical FQDN（去空格、去 *. 前缀、统一大小写/尾点）
func canonicalFQDN(s string) string {
	s = strings.TrimSpace(s)
	if s == "" {
		return ""
	}
	s = strings.TrimPrefix(s, "*.")
	return dns.CanonicalName(s)
}

func uniqueStrings(in []string) []string {
	seen := make(map[string]struct{}, len(in))
	out := make([]string, 0, len(in))
	for _, s := range in {
		if s == "" {
			continue
		}
		if _, ok := seen[s]; ok {
			continue
		}
		seen[s] = struct{}{}
		out = append(out, s)
	}
	return out
}

// 支持 # / ; 注释；每行一个域名；支持以 "*.example.com" 书写
func loadBlacklistFile(path string) ([]string, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	sc := bufio.NewScanner(f)
	var rules []string
	for sc.Scan() {
		line := strings.TrimSpace(sc.Text())
		if line == "" {
			continue
		}
		// 行首注释
		if strings.HasPrefix(line, "//") || strings.HasPrefix(line, "#") || strings.HasPrefix(line, ";") {
			continue
		}
		// 行内注释：先 // 再 # ;
		if i := strings.Index(line, "//"); i >= 0 {
			line = strings.TrimSpace(line[:i])
		}
		if i := strings.IndexAny(line, "#;"); i >= 0 {
			line = strings.TrimSpace(line[:i])
		}
		if line == "" {
			continue
		}
		// hosts 风格：第一个字段是 IP，则其余每个字段视为域名
		fields := strings.Fields(line)
		if len(fields) == 0 {
			continue
		}
		start := 0
		if net.ParseIP(fields[0]) != nil {
			start = 1
		}
		for _, tok := range fields[start:] {
			if r := canonicalFQDN(tok); r != "" {
				rules = append(rules, r)
			}
		}
	}
	if err := sc.Err(); err != nil {
		return nil, err
	}
	return uniqueStrings(rules), nil
}

// 自动重载黑名单
func startBlacklistReloader(ctx context.Context, path string, interval time.Duration, holder *atomic.Pointer[suffixMatcher]) {
	if path == "" {
		return
	}
	go func() {
		var lastMod time.Time
		ticker := time.NewTicker(interval)
		defer ticker.Stop()
		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker.C:
				fi, err := os.Stat(path)
				if err != nil {
					log.Printf("[blacklist] reload check failed: %v", err)
					continue
				}
				modTime := fi.ModTime()
				if modTime.After(lastMod) {
					rules, err := loadBlacklistFile(path)
					if err != nil {
						log.Printf("[blacklist] reload failed: %v", err)
						continue
					}
					holder.Store(newSuffixMatcher(rules))
					lastMod = modTime
					log.Printf("[blacklist] reloaded %d rules (modified %s)", len(rules), modTime.Format(time.RFC3339))
				}
			}
		}
	}()
}

// 后缀匹配器：rules 已 canonical，按长度降序排列（更精确的规则优先）
type suffixMatcher struct {
	rules []string
}

func newSuffixMatcher(rules []string) *suffixMatcher {
	rs := uniqueStrings(rules)
	sort.Slice(rs, func(i, j int) bool { return len(rs[i]) > len(rs[j]) })
	return &suffixMatcher{rules: rs}
}

// 命中则返回匹配的规则
func (m *suffixMatcher) match(name string) (string, bool) {
	if m == nil || len(m.rules) == 0 {
		return "", false
	}
	name = dns.CanonicalName(name)
	for _, r := range m.rules {
		if name == r || strings.HasSuffix(name, "."+r) {
			return r, true
		}
	}
	return "", false
}

// 解析 RCODE 文本到常量
func parseRcode(s string) int {
	switch strings.ToUpper(strings.TrimSpace(s)) {
	case "REFUSED", "":
		return dns.RcodeRefused
	case "NXDOMAIN":
		return dns.RcodeNameError
	case "SERVFAIL":
		return dns.RcodeServerFailure
	default:
		log.Printf("[blacklist] unknown rcode %q, fallback REFUSED", s)
		return dns.RcodeRefused
	}
}

// 构造“伪上游”阻断响应；带 EDE=Blocked(15) 说明命中规则
func makeBlockedUpstream(rcode int, rule string) *dns.Msg {
	m := new(dns.Msg)
	m.RecursionAvailable = true
	m.AuthenticatedData = false
	m.Rcode = rcode
	opt := &dns.OPT{}
	opt.Hdr.Name = "."
	opt.Hdr.Rrtype = dns.TypeOPT
	ede := &dns.EDNS0_EDE{InfoCode: 15, ExtraText: "blocked by policy: " + rule}
	opt.Option = append(opt.Option, ede)
	m.Extra = append(m.Extra, opt)
	return m
}

func initBlacklist(ctx context.Context, listStr, filePath, rcodeStr string) (*atomic.Pointer[suffixMatcher], int) {
	var rules []string
	if v := strings.TrimSpace(listStr); v != "" {
		for _, s := range strings.Split(v, ",") {
			if r := canonicalFQDN(s); r != "" {
				rules = append(rules, r)
			}
		}
	}
	if filePath != "" {
		if fs, err := loadBlacklistFile(filePath); err != nil {
			log.Printf("[blacklist] load file error: %v", err)
		} else {
			rules = append(rules, fs...)
		}
	}
	var holder atomic.Pointer[suffixMatcher]
	holder.Store(newSuffixMatcher(rules))
	blRcode := parseRcode(rcodeStr)
	if filePath != "" {
		startBlacklistReloader(ctx, filePath, 30*time.Second, &holder)
	}
	log.Printf("[blacklist] loaded %d rules (file=%v, rcode=%s)", len(holder.Load().rules), filePath != "", strings.ToUpper(rcodeStr))
	return &holder, blRcode
}