package main

import (
	"fmt"
	"net"
	"strings"
)

// LogRecord holds the four dimensions extracted from a single nginx log line.
type LogRecord struct {
	Website      string
	ClientPrefix string
	URI          string
	Status       string
}

// ParseLine parses a tab-separated logtail log line:
//
//	$host \t $remote_addr \t $msec \t $request_method \t $request_uri \t $status \t $body_bytes_sent \t $request_time
//
// Returns false for lines with fewer than 8 fields.
func ParseLine(line string, v4bits, v6bits int) (LogRecord, bool) {
	// SplitN caps allocations; we need exactly 8 fields.
	fields := strings.SplitN(line, "\t", 8)
	if len(fields) < 8 {
		return LogRecord{}, false
	}

	uri := fields[4]
	if i := strings.IndexByte(uri, '?'); i >= 0 {
		uri = uri[:i]
	}

	prefix, ok := truncateIP(fields[1], v4bits, v6bits)
	if !ok {
		return LogRecord{}, false
	}

	return LogRecord{
		Website:      fields[0],
		ClientPrefix: prefix,
		URI:          uri,
		Status:       fields[5],
	}, true
}

// truncateIP masks addr to the given prefix length depending on IP version.
// Returns the CIDR string (e.g. "1.2.3.0/24") and true on success.
func truncateIP(addr string, v4bits, v6bits int) (string, bool) {
	ip := net.ParseIP(addr)
	if ip == nil {
		return "", false
	}

	var bits int
	if ip.To4() != nil {
		ip = ip.To4()
		bits = v4bits
	} else {
		ip = ip.To16()
		bits = v6bits
	}

	mask := net.CIDRMask(bits, len(ip)*8)
	masked := make(net.IP, len(ip))
	for i := range ip {
		masked[i] = ip[i] & mask[i]
	}

	return fmt.Sprintf("%s/%d", masked.String(), bits), true
}