// Package match finds the address in a log line: patterns are regular
// expressions (Go's, RE2) with one <IP>, which matches an IPv4 or IPv6
// address (bracketed, IPv4-mapped, with a zone). The address is checked
// with netip, so what only looks like one (a time, 12:34:56) never is.
package match

import (
	"fmt"
	"net/netip"
	"regexp"
	"strings"
)

// Placeholder is where a pattern's address is.
const Placeholder = "<IP>"

// ipRe matches an address: IPv4, or IPv6 (which may end in IPv4,
// ::ffff:203.0.113.9), bracketed or not, with an optional zone.
const ipRe = `\[?(?P<ip>[0-9]{1,3}(?:\.[0-9]{1,3}){3}|[0-9A-Fa-f]{0,4}(?::[0-9A-Fa-f]{0,4}){1,7}(?:[0-9]{1,3}(?:\.[0-9]{1,3}){3})?(?:%[0-9A-Za-z_.-]+)?)\]?`

// Matcher holds a watch's patterns.
type Matcher struct {
	match  []*regexp.Regexp
	ignore []*regexp.Regexp
}

// Compile makes a Matcher. Each match pattern must hold <IP> exactly
// once; ignore patterns are plain regular expressions.
func Compile(match, ignore []string) (*Matcher, error) {
	m := &Matcher{}
	for _, p := range match {
		if n := strings.Count(p, Placeholder); n != 1 {
			return nil, fmt.Errorf("pattern %q has %d %s; it needs exactly one, where the address is", p, n, Placeholder)
		}
		re, err := regexp.Compile(strings.Replace(p, Placeholder, ipRe, 1))
		if err != nil {
			return nil, fmt.Errorf("pattern %q: %v", p, err)
		}
		m.match = append(m.match, re)
	}
	for _, p := range ignore {
		re, err := regexp.Compile(p)
		if err != nil {
			return nil, fmt.Errorf("ignore pattern %q: %v", p, err)
		}
		m.ignore = append(m.ignore, re)
	}
	return m, nil
}

// Match returns the address of the first pattern a line matches, unless
// an ignore pattern matches it too.
func (m *Matcher) Match(line string) (netip.Addr, bool) {
	for _, re := range m.match {
		sub := re.FindStringSubmatch(line)
		if sub == nil {
			continue
		}
		text := sub[re.SubexpIndex("ip")]
		if i := strings.IndexByte(text, '%'); i >= 0 {
			text = text[:i]
		}
		a, err := netip.ParseAddr(text)
		if err != nil {
			continue
		}
		for _, ig := range m.ignore {
			if ig.MatchString(line) {
				return netip.Addr{}, false
			}
		}
		return a.Unmap(), true
	}
	return netip.Addr{}, false
}

// Group is the prefix an address is counted and banned by: an IPv4
// address alone, an IPv6 address by its /v6 (64: what one customer
// usually has).
func Group(a netip.Addr, v6 int) netip.Prefix {
	if a.Is4() || v6 <= 0 || v6 > 128 {
		if a.Is4() {
			return netip.PrefixFrom(a, 32)
		}
		v6 = 128
	}
	p, _ := a.Prefix(v6)
	return p
}