package nftupdate

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"net/netip"
	"os/exec"
	"sort"
	"strings"
	"time"

	"github.com/cenkalti/backoff/v4"
)

type ProgressCallback func(percent int, message string)

type CmdRunner func(timeout time.Duration, name string, args ...string) (stdout, stderr string, exitCode int, err error)

type Logger func(format string, args ...any)

func UpdateIPsSmart(ctx context.Context, ips []string, progressCb ProgressCallback, runCmd CmdRunner, logf Logger) error {
	return UpdateSetIPsSmart(ctx, "agvpn4", ips, progressCb, runCmd, logf)
}

func UpdateSetIPsSmart(ctx context.Context, setName string, ips []string, progressCb ProgressCallback, runCmd CmdRunner, logf Logger) error {
	setName = strings.TrimSpace(setName)
	if setName == "" {
		setName = "agvpn4"
	}
	if runCmd == nil {
		return fmt.Errorf("run command function is not configured")
	}

	if len(ips) == 0 {
		if progressCb != nil {
			progressCb(100, "nothing to update")
		}
		return nil
	}

	origCount := len(ips)
	ips = compressIPIntervals(ips)
	if len(ips) != origCount {
		log(logf, "compress(%s): %d -> %d IP elements (removed %d covered/duplicate entries)", setName, origCount, len(ips), origCount-len(ips))
	}

	if len(ips) == 0 {
		if progressCb != nil {
			progressCb(100, "nothing to update after compression")
		}
		return nil
	}

	log(logf, "nft UpdateSetIPsSmart(%s): start, ips=%d", setName, len(ips))

	if err := atomicUpdateWithProgress(ctx, setName, ips, progressCb, logf); err == nil {
		return nil
	} else {
		if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
			log(logf, "atomic update cancelled (%s): %v", setName, err)
			return err
		}
		log(logf, "atomic nft update failed (%s): %v; falling back to chunked mode", setName, err)
		if progressCb != nil {
			progressCb(0, "Falling back to non-atomic update")
		}
	}

	return chunkedUpdateWithFallback(ctx, setName, ips, progressCb, runCmd, logf)
}

func compressIPIntervals(ips []string) []string {
	seen := make(map[string]struct{})

	type prefixItem struct {
		p   netip.Prefix
		raw string
	}
	type addrItem struct {
		a   netip.Addr
		raw string
	}

	var prefixes []prefixItem
	var addrs []addrItem

	for _, s := range ips {
		s = strings.TrimSpace(s)
		if s == "" {
			continue
		}
		if _, ok := seen[s]; ok {
			continue
		}
		seen[s] = struct{}{}

		if strings.Contains(s, "/") {
			p, err := netip.ParsePrefix(s)
			if err != nil {
				continue
			}
			prefixes = append(prefixes, prefixItem{p: p, raw: s})
		} else {
			a, err := netip.ParseAddr(s)
			if err != nil {
				continue
			}
			addrs = append(addrs, addrItem{a: a, raw: s})
		}
	}

	sort.Slice(prefixes, func(i, j int) bool {
		ai := prefixes[i].p.Addr()
		aj := prefixes[j].p.Addr()
		if ai == aj {
			return prefixes[i].p.Bits() < prefixes[j].p.Bits()
		}
		return ai.Less(aj)
	})

	var keptPrefixes []prefixItem
	for _, pi := range prefixes {
		covered := false
		for _, kp := range keptPrefixes {
			if kp.p.Bits() <= pi.p.Bits() && kp.p.Contains(pi.p.Addr()) {
				covered = true
				break
			}
		}
		if !covered {
			keptPrefixes = append(keptPrefixes, pi)
		}
	}

	var keptAddrs []addrItem
	for _, ai := range addrs {
		inNet := false
		for _, kp := range keptPrefixes {
			if kp.p.Contains(ai.a) {
				inNet = true
				break
			}
		}
		if !inNet {
			keptAddrs = append(keptAddrs, ai)
		}
	}

	out := make([]string, 0, len(keptPrefixes)+len(keptAddrs))
	for _, ai := range keptAddrs {
		out = append(out, ai.raw)
	}
	for _, pi := range keptPrefixes {
		out = append(out, pi.raw)
	}

	return out
}

func atomicUpdateWithProgress(ctx context.Context, setName string, ips []string, progressCb ProgressCallback, logf Logger) error {
	if len(ips) == 0 {
		if progressCb != nil {
			progressCb(100, "nothing to update")
		}
		return nil
	}

	sort.Strings(ips)
	total := len(ips)
	chunkSize := 500

	bo := backoff.NewExponentialBackOff()
	bo.InitialInterval = 500 * time.Millisecond
	bo.MaxInterval = 10 * time.Second
	bo.MaxElapsedTime = 2 * time.Minute

	return backoff.Retry(func() error {
		select {
		case <-ctx.Done():
			if progressCb != nil {
				progressCb(0, "Cancelled by context")
			}
			return ctx.Err()
		default:
		}

		var script strings.Builder
		script.WriteString("flush set inet agvpn " + setName + "\n")

		processed := 0
		chunksTotal := (len(ips) + chunkSize - 1) / chunkSize

		for i := 0; i < len(ips); i += chunkSize {
			end := i + chunkSize
			if end > len(ips) {
				end = len(ips)
			}
			chunk := ips[i:end]

			script.WriteString("add element inet agvpn " + setName + " { ")
			script.WriteString(strings.Join(chunk, ", "))
			script.WriteString(" }\n")

			processed += len(chunk)
			if progressCb != nil {
				percent := processed * 100 / total
				progressCb(percent, fmt.Sprintf("Preparing chunk %d/%d (%d/%d IPs)", i/chunkSize+1, chunksTotal, processed, total))
			}
		}

		if progressCb != nil {
			progressCb(90, "Executing nft transaction...")
		}

		cmd := exec.CommandContext(ctx, "nft", "-f", "-")
		cmd.Stdin = strings.NewReader(script.String())

		var stdout, stderr bytes.Buffer
		cmd.Stdout = &stdout
		cmd.Stderr = &stderr

		err := cmd.Run()
		if err == nil {
			log(logf, "nft atomic transaction success (%s): %d IPs added", setName, len(ips))
			if progressCb != nil {
				progressCb(100, "Update complete")
			}
			return nil
		}

		errStr := stderr.String()
		log(logf, "nft atomic transaction failed (%s): err=%v, stderr=%q", setName, err, errStr)

		if strings.Contains(errStr, "too many elements") ||
			strings.Contains(errStr, "out of memory") ||
			strings.Contains(errStr, "interval overlaps") ||
			strings.Contains(errStr, "conflicting intervals") {

			newSize := chunkSize / 2
			if newSize < 100 {
				newSize = 100
			}
			if newSize == chunkSize {
				return backoff.Permanent(fmt.Errorf("atomic nft cannot shrink further: %w", err))
			}

			log(logf, "reducing atomic chunk size from %d to %d and retrying", chunkSize, newSize)
			chunkSize = newSize
			if progressCb != nil {
				progressCb(0, fmt.Sprintf("Retrying atomic with smaller chunks (%d IPs)", chunkSize))
			}
			return fmt.Errorf("retry atomic with smaller chunks")
		}

		return backoff.Permanent(fmt.Errorf("nft atomic transaction failed: %w", err))
	}, bo)
}

func chunkedUpdateWithFallback(ctx context.Context, setName string, ips []string, progressCb ProgressCallback, runCmd CmdRunner, logf Logger) error {
	if len(ips) == 0 {
		if progressCb != nil {
			progressCb(100, "nothing to update")
		}
		return nil
	}

	sort.Strings(ips)
	total := len(ips)
	chunkSize := 500

	_, stderr, _, err := runCmd(10*time.Second, "nft", "flush", "set", "inet", "agvpn", setName)
	if err != nil {
		return fmt.Errorf("flush set failed: %v (%s)", err, stderr)
	}

	processed := 0
	for i := 0; i < len(ips); i += chunkSize {
		select {
		case <-ctx.Done():
			if progressCb != nil {
				progressCb(0, "Cancelled during chunked update")
			}
			return ctx.Err()
		default:
		}

		end := i + chunkSize
		if end > len(ips) {
			end = len(ips)
		}
		chunk := ips[i:end]

		_, stderr, _, err := runCmd(15*time.Second, "nft", "add", "element", "inet", "agvpn", setName, "{ "+strings.Join(chunk, ", ")+" }")
		if err != nil {
			if strings.Contains(stderr, "interval overlaps") ||
				strings.Contains(stderr, "too many elements") ||
				strings.Contains(stderr, "out of memory") ||
				strings.Contains(stderr, "conflicting intervals") {

				log(logf, "chunk failed (%d IPs), fallback per-ip", len(chunk))
				if progressCb != nil {
					progressCb(processed*100/total, fmt.Sprintf("Chunk failed -> adding %d IPs one by one", len(chunk)))
				}

				for _, ip := range chunk {
					select {
					case <-ctx.Done():
						return ctx.Err()
					default:
					}
					_, _, _, _ = runCmd(5*time.Second, "nft", "add", "element", "inet", "agvpn", setName, "{ "+ip+" }")
				}
			} else {
				return fmt.Errorf("nft chunk add failed: %v (%s)", err, stderr)
			}
		}

		processed += len(chunk)
		if progressCb != nil {
			percent := processed * 100 / total
			progressCb(percent, fmt.Sprintf("Added %d/%d IPs", processed, total))
		}
	}

	if progressCb != nil {
		progressCb(100, "chunked update complete")
	}
	log(logf, "nft chunked update success (%s): %d IPs", setName, len(ips))
	return nil
}

func log(logf Logger, format string, args ...any) {
	if logf != nil {
		logf(format, args...)
	}
}