package bind

import (
	"context"
	"encoding/hex"
	"fmt"
	"strconv"
	"strings"
)

// JournalPath returns the BIND journal that accompanies a zone database file.
func JournalPath(zonePath string) string { return zonePath + ".jnl" }

// ZoneDiskState is what the primary pod's filesystem holds for one zone.
// A journal is only replayable onto a zone file whose SOA serial lies within
// [JournalBegin, JournalEnd]; outside that range BIND fails the load with
// "out of range" and the zone never comes up.
type ZoneDiskState struct {
	ZoneFile     bool
	ZoneSerial   int64
	ZoneSerialOK bool
	Journal      bool
	JournalBegin int64
	JournalEnd   int64
	JournalOK    bool
}

// SeedPlan is the decision taken before writing a skeleton zone file.
type SeedPlan struct {
	WriteSeed          bool
	Serial             int64
	QuarantineZoneFile bool
	QuarantineJournal  bool
	QuarantineSuffix   string
}

// PlanSeed decides how to make a zone loadable without discarding live data.
// Nothing is ever deleted: unusable files are renamed aside so they stay
// recoverable on the PVC.
func PlanSeed(st ZoneDiskState) SeedPlan {
	suffix := fmt.Sprintf(".orphaned-%d", highestSerial(st))

	if !st.ZoneFile {
		p := SeedPlan{WriteSeed: true, Serial: nextSerial(st), QuarantineSuffix: suffix}
		// A journal without its zone file can only refuse to replay.
		p.QuarantineJournal = st.Journal
		return p
	}

	if !st.Journal || !st.JournalOK || !st.ZoneSerialOK {
		return SeedPlan{}
	}

	switch {
	case serialLT(st.ZoneSerial, st.JournalBegin):
		// The file has regressed behind the journal: it is the skeleton a
		// previous reconcile clobbered it with. Keep both aside and reseed
		// above the journal so secondaries still see a serial increase.
		return SeedPlan{
			WriteSeed:          true,
			Serial:             nextSerial(st),
			QuarantineZoneFile: true,
			QuarantineJournal:  true,
			QuarantineSuffix:   suffix,
		}
	case serialLT(st.JournalEnd, st.ZoneSerial):
		return SeedPlan{QuarantineJournal: true, QuarantineSuffix: suffix}
	default:
		return SeedPlan{}
	}
}

func highestSerial(st ZoneDiskState) int64 {
	var h int64
	if st.ZoneFile && st.ZoneSerialOK {
		h = st.ZoneSerial
	}
	if st.Journal && st.JournalOK && serialLT(h, st.JournalEnd) {
		h = st.JournalEnd
	}
	return h
}

func nextSerial(st ZoneDiskState) int64 {
	next := int64(uint32(highestSerial(st)) + 1)
	if next == 0 {
		return 1
	}
	return next
}

// serialLT compares DNS serials in RFC 1982 sequence space.
func serialLT(a, b int64) bool {
	if a == b {
		return false
	}
	return uint32(b)-uint32(a) < 1<<31
}

// ParseZoneSerial extracts the SOA serial from the head of a zone file, in
// both the operator's seed layout and BIND's own multi-line dump layout.
func ParseZoneSerial(content string) (int64, bool) {
	var tokens []string
	for _, line := range strings.Split(content, "\n") {
		if i := strings.IndexByte(line, ';'); i >= 0 {
			line = line[:i]
		}
		line = strings.ReplaceAll(line, "(", " ( ")
		line = strings.ReplaceAll(line, ")", " ) ")
		tokens = append(tokens, strings.Fields(line)...)
	}
	for i, tok := range tokens {
		if !strings.EqualFold(tok, "SOA") {
			continue
		}
		rest := tokens[i+1:]
		if len(rest) < 3 {
			return 0, false
		}
		rest = rest[2:] // MNAME, RNAME
		if rest[0] == "(" {
			rest = rest[1:]
		}
		if len(rest) == 0 {
			return 0, false
		}
		serial, err := strconv.ParseUint(rest[0], 10, 32)
		if err != nil {
			return 0, false
		}
		return int64(serial), true
	}
	return 0, false
}

const journalMagic = ";BIND LOG V9"

// parseJournalHeader reads the begin and end serials from a BIND journal
// header: a 16-byte format magic followed by two {serial,offset} big-endian
// pairs.
func parseJournalHeader(b []byte) (begin, end int64, ok bool) {
	if len(b) < 28 || !strings.HasPrefix(string(b[:16]), journalMagic) {
		return 0, 0, false
	}
	return int64(beUint32(b[16:20])), int64(beUint32(b[24:28])), true
}

func beUint32(b []byte) uint32 {
	return uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])
}

// zoneStateProbe reads only the head of the zone file: the SOA is the first
// record in both layouts the operator has to read.
func zoneStateProbe(path string) string {
	jnl := JournalPath(path)
	return strings.Join([]string{
		fmt.Sprintf("if [ -f '%s' ]; then printf 'zonefile=1\\nhead<<\\n'; head -c 4096 '%s'; printf '\\n>>head\\n'; else printf 'zonefile=0\\n'; fi", path, path),
		fmt.Sprintf("if [ -f '%s' ]; then printf 'journal=1\\njnl=%%s\\n' \"$(od -An -v -tx1 -N32 '%s' | tr -d ' \\n')\"; else printf 'journal=0\\n'; fi", jnl, jnl),
	}, "\n")
}

func parseZoneDiskState(out string) ZoneDiskState {
	var st ZoneDiskState
	var head []string
	inHead := false
	for _, line := range strings.Split(out, "\n") {
		switch {
		case inHead && line == ">>head":
			inHead = false
		case inHead:
			head = append(head, line)
		case line == "head<<":
			inHead = true
		case line == "zonefile=1":
			st.ZoneFile = true
		case line == "journal=1":
			st.Journal = true
		case strings.HasPrefix(line, "jnl="):
			if raw, err := hex.DecodeString(strings.TrimPrefix(line, "jnl=")); err == nil {
				st.JournalBegin, st.JournalEnd, st.JournalOK = parseJournalHeader(raw)
			}
		}
	}
	if st.ZoneFile {
		st.ZoneSerial, st.ZoneSerialOK = ParseZoneSerial(strings.Join(head, "\n"))
	}
	return st
}

// ZoneDiskState inspects the zone database file and journal on the pod.
func (e *Executor) ZoneDiskState(ctx context.Context, namespace, pod, path string) (ZoneDiskState, error) {
	out, err := e.Exec(ctx, namespace, pod, []string{"sh", "-c", zoneStateProbe(path)}, "")
	if err != nil {
		return ZoneDiskState{}, fmt.Errorf("inspect zone files %s: %w (out: %s)", path, err, out)
	}
	return parseZoneDiskState(out), nil
}

// Quarantine renames the files the plan marks unusable, leaving them on the
// PVC under a suffixed name.
func (e *Executor) Quarantine(ctx context.Context, namespace, pod, path string, plan SeedPlan) error {
	var cmds []string
	if plan.QuarantineZoneFile {
		cmds = append(cmds, moveAside(path, plan.QuarantineSuffix))
	}
	if plan.QuarantineJournal {
		cmds = append(cmds, moveAside(JournalPath(path), plan.QuarantineSuffix))
	}
	if len(cmds) == 0 {
		return nil
	}
	cmd := []string{"sh", "-c", strings.Join(cmds, "\n")}
	if out, err := e.Exec(ctx, namespace, pod, cmd, ""); err != nil {
		return fmt.Errorf("quarantine zone files %s: %w (out: %s)", path, err, out)
	}
	return nil
}

func moveAside(path, suffix string) string {
	return fmt.Sprintf("if [ -f '%s' ]; then mv -- '%s' '%s%s'; fi", path, path, path, suffix)
}