package dnsrecord

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

	"github.com/go-playground/validator/v10"

	"pdns_admin/internal/pdns"
)

var (
	txtValuePattern = regexp.MustCompile(`^"([^"\\]|\\.)*"( "([^"\\]|\\.)*")*$`)
	caaTagPattern   = regexp.MustCompile(`^[A-Za-z][A-Za-z0-9-]*$`)
)

type Validator struct {
	validate *validator.Validate
}

func NewValidator() (*Validator, error) {
	v := validator.New()
	if err := v.RegisterValidation("dns_fqdn", func(fl validator.FieldLevel) bool {
		return IsFQDN(fl.Field().String())
	}); err != nil {
		return nil, err
	}

	return &Validator{validate: v}, nil
}

func SupportedTypes() []string {
	return []string{"A", "AAAA", "CAA", "CNAME", "MX", "NS", "SOA", "SRV", "TXT"}
}

func (v *Validator) ValidateRRSet(name, recordType string, ttl uint64, contents []string) (pdns.RRSet, error) {
	name = EnsureTrailingDot(name)
	recordType = strings.ToUpper(strings.TrimSpace(recordType))

	if ttl == 0 || ttl > 1<<32-1 {
		return pdns.RRSet{}, fmt.Errorf("ttl must be between 1 and 4294967295")
	}
	if err := v.validate.Var(name, "required,dns_fqdn"); err != nil {
		return pdns.RRSet{}, fmt.Errorf("record name must be a fully qualified domain name")
	}
	if !supported(recordType) {
		return pdns.RRSet{}, fmt.Errorf("unsupported record type %q", recordType)
	}

	records := make([]pdns.Record, 0, len(contents))
	for _, content := range contents {
		content = strings.TrimSpace(content)
		if content == "" {
			continue
		}
		if err := validateContent(recordType, content); err != nil {
			return pdns.RRSet{}, err
		}
		records = append(records, pdns.Record{Content: content})
	}
	if len(records) == 0 {
		return pdns.RRSet{}, fmt.Errorf("at least one record value is required")
	}

	return pdns.RRSet{
		Name:    name,
		Type:    recordType,
		TTL:     uint32(ttl),
		Records: records,
	}, nil
}

func EnsureTrailingDot(value string) string {
	value = strings.TrimSpace(value)
	if value == "" || strings.HasSuffix(value, ".") {
		return value
	}
	return value + "."
}

func IsFQDN(value string) bool {
	value = strings.TrimSpace(value)
	if value == "." || value == "" || !strings.HasSuffix(value, ".") || len(value) > 253 {
		return false
	}

	labels := strings.Split(strings.TrimSuffix(value, "."), ".")
	for i, label := range labels {
		if label == "" || len(label) > 63 {
			return false
		}
		if label == "*" && i == 0 {
			continue
		}
		if strings.HasPrefix(label, "-") || strings.HasSuffix(label, "-") {
			return false
		}
		for _, r := range label {
			if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '-' {
				continue
			}
			return false
		}
	}
	return true
}

func validateContent(recordType, content string) error {
	switch recordType {
	case "A":
		addr, err := netip.ParseAddr(content)
		if err != nil || !addr.Is4() {
			return fmt.Errorf("A record content must be an IPv4 address")
		}
	case "AAAA":
		addr, err := netip.ParseAddr(content)
		if err != nil || !addr.Is6() {
			return fmt.Errorf("AAAA record content must be an IPv6 address")
		}
	case "CAA":
		return validateCAA(content)
	case "CNAME", "NS":
		if !IsFQDN(content) {
			return fmt.Errorf("%s record content must be a fully qualified domain name", recordType)
		}
	case "MX":
		return validateMX(content)
	case "SOA":
		return validateSOA(content)
	case "SRV":
		return validateSRV(content)
	case "TXT":
		if !txtValuePattern.MatchString(content) {
			return fmt.Errorf("TXT record content must be one or more quoted strings")
		}
	}
	return nil
}

func validateMX(content string) error {
	fields := strings.Fields(content)
	if len(fields) != 2 {
		return fmt.Errorf("MX record content must be: priority target")
	}
	if _, err := parseUint(fields[0], 16); err != nil {
		return fmt.Errorf("MX priority must be between 0 and 65535")
	}
	if !IsFQDN(fields[1]) {
		return fmt.Errorf("MX target must be a fully qualified domain name")
	}
	return nil
}

func validateSRV(content string) error {
	fields := strings.Fields(content)
	if len(fields) != 4 {
		return fmt.Errorf("SRV record content must be: priority weight port target")
	}
	for i, label := range []string{"priority", "weight", "port"} {
		if _, err := parseUint(fields[i], 16); err != nil {
			return fmt.Errorf("SRV %s must be between 0 and 65535", label)
		}
	}
	target := strings.TrimSpace(fields[3])
	if target != "." && !IsFQDN(target) {
		return fmt.Errorf("SRV target must be a fully qualified domain name or .")
	}
	return nil
}

func validateSOA(content string) error {
	fields := strings.Fields(content)
	if len(fields) != 7 {
		return fmt.Errorf("SOA record content must be: primary hostmaster serial refresh retry expire minimum")
	}
	if !IsFQDN(fields[0]) {
		return fmt.Errorf("SOA primary nameserver must be a fully qualified domain name")
	}
	if !IsFQDN(fields[1]) {
		return fmt.Errorf("SOA hostmaster must be a fully qualified domain name")
	}
	for i, label := range []string{"serial", "refresh", "retry", "expire", "minimum"} {
		if _, err := parseUint(fields[i+2], 32); err != nil {
			return fmt.Errorf("SOA %s must be between 0 and 4294967295", label)
		}
	}
	return nil
}

func validateCAA(content string) error {
	fields := strings.Fields(content)
	if len(fields) < 3 {
		return fmt.Errorf("CAA record content must be: flags tag \"value\"")
	}
	flags, err := parseUint(fields[0], 8)
	if err != nil || flags > 255 {
		return fmt.Errorf("CAA flags must be between 0 and 255")
	}
	if !caaTagPattern.MatchString(fields[1]) {
		return fmt.Errorf("CAA tag must start with a letter and contain only letters, numbers, and hyphens")
	}
	value := strings.Join(fields[2:], " ")
	if !txtValuePattern.MatchString(value) {
		return fmt.Errorf("CAA value must be quoted")
	}
	return nil
}

func parseUint(value string, bits int) (uint64, error) {
	return strconv.ParseUint(value, 10, bits)
}

func supported(recordType string) bool {
	for _, candidate := range SupportedTypes() {
		if candidate == recordType {
			return true
		}
	}
	return false
}