package main

import (
	"encoding/base32"
	"fmt"
	"hash/fnv"
	"os"
	"sort"
	"strings"
	"time"

	"codeberg.org/miekg/dns"
)

// base32hex encoding, lowercase, no padding
var b32 = base32.NewEncoding("0123456789abcdefghijklmnopqrstuv").WithPadding(base32.NoPadding)

// Hardcoded SOA timing values
const (
	soaRefresh = 900
	soaRetry   = 600
	soaExpire  = 2147483646
	soaMinimum = 0
)

// hashZoneName computes the FNV-1a 32-bit hash of a normalized zone name
// and returns it as a lowercase base32hex string (no padding).
func hashZoneName(zone string) string {
	h := fnv.New32a()
	h.Write([]byte(zone))
	sum := h.Sum32()
	b := make([]byte, 4)
	b[0] = byte(sum >> 24)
	b[1] = byte(sum >> 16)
	b[2] = byte(sum >> 8)
	b[3] = byte(sum)
	return b32.EncodeToString(b)
}

// generateCatalogZone builds the zone file content for a single catalog.
func generateCatalogZone(catName string, cfg *Config, members []ZoneEntry, serial uint32) (string, error) {
	catCfg := cfg.Catalogs[catName]
	origin := catCfg.Zone

	var records []string

	// SOA
	soaStr := fmt.Sprintf("%s 0 IN SOA %s %s %d %d %d %d %d",
		origin, cfg.SOA.Mname, cfg.SOA.Rname, serial, soaRefresh, soaRetry, soaExpire, soaMinimum)
	soaRR, err := dns.New(soaStr)
	if err != nil {
		return "", fmt.Errorf("building SOA: %w", err)
	}
	records = append(records, soaRR.String())

	// NS
	nsStr := fmt.Sprintf("%s 0 IN NS invalid.", origin)
	nsRR, err := dns.New(nsStr)
	if err != nil {
		return "", fmt.Errorf("building NS: %w", err)
	}
	records = append(records, nsRR.String())

	// Version TXT
	verStr := fmt.Sprintf("version.%s 0 IN TXT \"2\"", origin)
	verRR, err := dns.New(verStr)
	if err != nil {
		return "", fmt.Errorf("building version TXT: %w", err)
	}
	records = append(records, verRR.String())

	// Sort members alphabetically by normalized zone name
	sorted := make([]ZoneEntry, len(members))
	copy(sorted, members)
	sort.Slice(sorted, func(i, j int) bool {
		return sorted[i].Zone < sorted[j].Zone
	})

	// Check for hash collisions
	hashToZone := make(map[string]string)
	for _, entry := range sorted {
		h := hashZoneName(entry.Zone)
		if existing, ok := hashToZone[h]; ok && existing != entry.Zone {
			return "", fmt.Errorf("error: %s:%d: hash collision between %s and %s in catalog %q",
				entry.File, entry.Line, existing, entry.Zone, catName)
		}
		hashToZone[h] = entry.Zone
	}

	// Member records
	for _, entry := range sorted {
		h := hashZoneName(entry.Zone)

		// PTR record
		ptrOwner := fmt.Sprintf("%s.zones.%s", h, origin)
		ptrStr := fmt.Sprintf("%s 0 IN PTR %s", ptrOwner, entry.Zone)
		ptrRR, err := dns.New(ptrStr)
		if err != nil {
			return "", fmt.Errorf("building PTR for %s: %w", entry.Zone, err)
		}
		records = append(records, ptrRR.String())

		// Group TXT (optional)
		if entry.Group != "" {
			groupOwner := fmt.Sprintf("group.%s.zones.%s", h, origin)
			groupStr := fmt.Sprintf("%s 0 IN TXT \"%s\"", groupOwner, entry.Group)
			groupRR, err := dns.New(groupStr)
			if err != nil {
				return "", fmt.Errorf("building group TXT for %s: %w", entry.Zone, err)
			}
			records = append(records, groupRR.String())
		}

		// COO PTR (optional)
		if entry.COO != "" {
			cooOwner := fmt.Sprintf("coo.%s.zones.%s", h, origin)
			cooStr := fmt.Sprintf("%s 0 IN PTR %s", cooOwner, entry.COO)
			cooRR, err := dns.New(cooStr)
			if err != nil {
				return "", fmt.Errorf("building coo PTR for %s: %w", entry.Zone, err)
			}
			records = append(records, cooRR.String())
		}
	}

	return strings.Join(records, "\n") + "\n", nil
}

// readExistingSerial reads an existing zone file and extracts the SOA serial.
// Returns 0, nil if the file doesn't exist.
func readExistingSerial(path string) (uint32, error) {
	f, err := os.Open(path)
	if os.IsNotExist(err) {
		return 0, nil
	}
	if err != nil {
		return 0, fmt.Errorf("reading existing zone %s: %w", path, err)
	}
	defer f.Close()

	zp := dns.NewZoneParser(f, "", path)
	for rr, ok := zp.Next(); ok; rr, ok = zp.Next() {
		if soa, ok := rr.(*dns.SOA); ok {
			return soa.Serial, nil
		}
	}
	if err := zp.Err(); err != nil {
		return 0, fmt.Errorf("parsing existing zone %s: %w", path, err)
	}

	return 0, nil
}

// readExistingContent reads the full content of an existing zone file.
// Returns empty string if file doesn't exist.
func readExistingContent(path string) (string, error) {
	data, err := os.ReadFile(path)
	if os.IsNotExist(err) {
		return "", nil
	}
	if err != nil {
		return "", err
	}
	return string(data), nil
}

// defaultSerial returns a serial for today with sequence 01: YYYYMMDD01.
func defaultSerial(now time.Time) uint32 {
	return uint32(now.Year())*1000000 +
		uint32(now.Month())*10000 +
		uint32(now.Day())*100 + 1
}

// bumpSerial increments a serial. If same date, bumps the sequence number.
// If different date, starts at YYYYMMDD01.
// Returns error if sequence reaches 99 and needs another bump.
func bumpSerial(old uint32, now time.Time) (uint32, error) {
	todayBase := uint32(now.Year())*1000000 +
		uint32(now.Month())*10000 +
		uint32(now.Day())*100

	if old >= todayBase && old < todayBase+100 {
		// Same date, bump sequence
		seq := old - todayBase
		if seq >= 99 {
			return 0, fmt.Errorf("serial overflow: already at %d, cannot bump further on the same date", old)
		}
		return old + 1, nil
	}

	// Different date or old serial doesn't follow our format
	return todayBase + 1, nil
}

// processCatalog handles generating and writing a single catalog zone file.
// Returns true if the file was written (changed), false if unchanged.
func processCatalog(catName string, cfg *Config, members []ZoneEntry, outputDir string, now time.Time) (bool, error) {
	catCfg := cfg.Catalogs[catName]
	outputPath := outputDir + "/" + catCfg.Zone + "zone"

	// Read existing serial
	oldSerial, err := readExistingSerial(outputPath)
	if err != nil {
		return false, err
	}

	// Use old serial or default
	serial := oldSerial
	if serial == 0 {
		serial = defaultSerial(now)
	}

	// Generate with current serial
	content, err := generateCatalogZone(catName, cfg, members, serial)
	if err != nil {
		return false, err
	}

	// Compare with existing file
	existing, err := readExistingContent(outputPath)
	if err != nil {
		return false, err
	}

	if content == existing {
		return false, nil
	}

	// Content changed — bump serial only if we had an existing file.
	// For new files, the default serial is already correct.
	if oldSerial != 0 {
		newSerial, err := bumpSerial(serial, now)
		if err != nil {
			return false, err
		}
		if newSerial != serial {
			content, err = generateCatalogZone(catName, cfg, members, newSerial)
			if err != nil {
				return false, err
			}
		}
	}

	if err := os.WriteFile(outputPath, []byte(content), 0o644); err != nil {
		return false, fmt.Errorf("writing zone file %s: %w", outputPath, err)
	}

	return true, nil
}