package wireguard

import (
	"bufio"
	"context"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"strconv"
	"strings"

	"git.netcell-it.de/projekte/edgeguard-native/internal/models"
	"git.netcell-it.de/projekte/edgeguard-native/internal/services/secrets"
)

// ImportResult summarises what an Import call did so the CLI can
// report it back to the operator.
type ImportResult struct {
	IfacesAdded  int      `json:"ifaces_added"`
	PeersAdded   int      `json:"peers_added"`
	Skipped      []string `json:"skipped,omitempty"` // ifaces already present, with reason
}

// Importer takes existing /etc/wireguard/*.conf files and translates
// them into wireguard_interfaces + wireguard_peers rows so the
// operator can keep their pre-EdgeGuard tunnels live across the
// migration. Heuristics:
//
//   - Iface name = filename without .conf (so wg0.conf → wg0)
//   - One [Interface] block becomes the wireguard_interfaces row
//   - [Peer] blocks with Endpoint+ no AllowedIPs/0.0.0.0/0 → mode=client
//     (rare — a wg conf usually has many peers in server mode)
//   - >1 [Peer] block → mode=server, peers go to the peer roster
//   - Single [Peer] with Endpoint set → mode=client (the peer is the
//     upstream we dial)
//
// Existing iface names in the DB are skipped (idempotent re-run).
type Importer struct {
	Ifaces *InterfacesRepo
	Peers  *PeersRepo
	Box    *secrets.Box
}

func NewImporter(ifaces *InterfacesRepo, peers *PeersRepo, box *secrets.Box) *Importer {
	return &Importer{Ifaces: ifaces, Peers: peers, Box: box}
}

func (im *Importer) ImportDir(ctx context.Context, dir string) (*ImportResult, error) {
	res := &ImportResult{}
	entries, err := os.ReadDir(dir)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return res, nil
		}
		return nil, err
	}
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".conf") {
			continue
		}
		path := filepath.Join(dir, e.Name())
		ifaceName := strings.TrimSuffix(e.Name(), ".conf")
		// Skip names that violate our regex — operator can rename
		// the file and re-run.
		if !validIfaceName(ifaceName) {
			res.Skipped = append(res.Skipped, ifaceName+" (invalid name)")
			continue
		}
		if err := im.importFile(ctx, ifaceName, path, res); err != nil {
			res.Skipped = append(res.Skipped, ifaceName+": "+err.Error())
		}
	}
	return res, nil
}

func (im *Importer) importFile(ctx context.Context, ifaceName, path string, res *ImportResult) error {
	// Skip if already present.
	all, err := im.Ifaces.List(ctx)
	if err != nil {
		return err
	}
	for _, x := range all {
		if x.Name == ifaceName {
			res.Skipped = append(res.Skipped, ifaceName+" (already in DB)")
			return nil
		}
	}

	parsed, err := parseWGConf(path)
	if err != nil {
		return err
	}
	if parsed.PrivateKey == "" {
		return errors.New("no PrivateKey in [Interface]")
	}
	if parsed.Address == "" {
		return errors.New("no Address in [Interface]")
	}

	// Mode heuristic: an [Interface] without ListenPort plus a single
	// [Peer] with Endpoint set is a client tunnel. Anything else
	// (multiple peers, ListenPort set, peers without Endpoint) we
	// treat as server.
	mode := "server"
	if parsed.ListenPort == 0 && len(parsed.Peers) == 1 && parsed.Peers[0].Endpoint != "" {
		mode = "client"
	}

	pub, err := PublicFromPrivate(parsed.PrivateKey)
	if err != nil {
		return fmt.Errorf("derive pubkey: %w", err)
	}
	encPriv, err := im.Box.Seal([]byte(parsed.PrivateKey))
	if err != nil {
		return fmt.Errorf("seal: %w", err)
	}

	ifc := models.WireguardInterface{
		Name:          ifaceName,
		Mode:          mode,
		AddressCIDR:   parsed.Address,
		PublicKey:     pub,
		PrivateKeyEnc: encPriv,
		Role:          "wan",
		Active:        true,
		MTU:           intPtrIfNonzero(parsed.MTU),
	}
	if mode == "server" {
		port := parsed.ListenPort
		if port == 0 {
			port = 51820
		}
		ifc.ListenPort = &port
	} else {
		// client mode → fold the single peer into the iface row.
		p := parsed.Peers[0]
		ep := p.Endpoint
		pk := p.PublicKey
		ifc.PeerEndpoint = &ep
		ifc.PeerPublicKey = &pk
		if p.AllowedIPs != "" {
			ai := p.AllowedIPs
			ifc.AllowedIPs = &ai
		}
		if p.Keepalive > 0 {
			k := p.Keepalive
			ifc.PersistentKeepalive = &k
		}
		if p.PSK != "" {
			pskEnc, err := im.Box.Seal([]byte(p.PSK))
			if err != nil {
				return fmt.Errorf("seal psk: %w", err)
			}
			ifc.PeerPSKEnc = pskEnc
		}
	}

	created, err := im.Ifaces.Create(ctx, ifc)
	if err != nil {
		return fmt.Errorf("insert iface: %w", err)
	}
	res.IfacesAdded++

	if mode == "server" {
		for i, p := range parsed.Peers {
			if p.PublicKey == "" {
				res.Skipped = append(res.Skipped, fmt.Sprintf("%s peer #%d (no PublicKey)", ifaceName, i))
				continue
			}
			peer := models.WireguardPeer{
				InterfaceID: created.ID,
				Name:        p.Name,
				PublicKey:   p.PublicKey,
				AllowedIPs:  p.AllowedIPs,
				Enabled:     true,
			}
			if peer.Name == "" {
				peer.Name = fmt.Sprintf("imported-%d", i+1)
			}
			if peer.AllowedIPs == "" {
				peer.AllowedIPs = "0.0.0.0/0"
			}
			if p.Keepalive > 0 {
				k := p.Keepalive
				peer.Keepalive = &k
			}
			if p.PSK != "" {
				pskEnc, err := im.Box.Seal([]byte(p.PSK))
				if err != nil {
					return fmt.Errorf("seal peer psk: %w", err)
				}
				peer.PSKEnc = pskEnc
			}
			if _, err := im.Peers.Create(ctx, peer); err != nil {
				res.Skipped = append(res.Skipped, fmt.Sprintf("%s peer %s: %v", ifaceName, peer.Name, err))
				continue
			}
			res.PeersAdded++
		}
	}
	return nil
}

// parsedConf is the intermediate shape of a parsed wg-quick file.
type parsedConf struct {
	Address    string
	ListenPort int
	PrivateKey string
	MTU        int
	Peers      []parsedPeer
}

type parsedPeer struct {
	Name       string
	PublicKey  string
	Endpoint   string
	AllowedIPs string
	Keepalive  int
	PSK        string
}

// parseWGConf is intentionally lenient — it accepts anything wg-quick
// would accept, ignores PostUp/PostDown/Table/SaveConfig since
// edgeguard owns runtime, and collapses comment lines starting with
// '#' into the next [Peer]'s Name (mirrors the wg-easy convention).
func parseWGConf(path string) (*parsedConf, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	var (
		out         parsedConf
		section     string
		currentPeer *parsedPeer
		nextName    string
	)

	flushPeer := func() {
		if currentPeer != nil {
			if currentPeer.Name == "" && nextName != "" {
				currentPeer.Name = nextName
			}
			out.Peers = append(out.Peers, *currentPeer)
			currentPeer = nil
			nextName = ""
		}
	}

	sc := bufio.NewScanner(f)
	for sc.Scan() {
		line := strings.TrimSpace(sc.Text())
		if line == "" {
			continue
		}
		if strings.HasPrefix(line, "#") {
			// Comment line; if the next thing we see is a [Peer],
			// use this as the peer's name.
			nextName = strings.TrimSpace(strings.TrimPrefix(line, "#"))
			continue
		}
		if strings.HasPrefix(line, "[") && strings.HasSuffix(line, "]") {
			flushPeer()
			section = strings.ToLower(strings.Trim(line, "[]"))
			if section == "peer" {
				currentPeer = &parsedPeer{}
			}
			continue
		}
		idx := strings.Index(line, "=")
		if idx < 0 {
			continue
		}
		key := strings.TrimSpace(strings.ToLower(line[:idx]))
		val := strings.TrimSpace(line[idx+1:])
		switch section {
		case "interface":
			switch key {
			case "address":
				out.Address = strings.Split(val, ",")[0] // first addr only
			case "listenport":
				if n, err := strconv.Atoi(val); err == nil {
					out.ListenPort = n
				}
			case "privatekey":
				out.PrivateKey = val
			case "mtu":
				if n, err := strconv.Atoi(val); err == nil {
					out.MTU = n
				}
			}
		case "peer":
			if currentPeer == nil {
				continue
			}
			switch key {
			case "publickey":
				currentPeer.PublicKey = val
			case "endpoint":
				currentPeer.Endpoint = val
			case "allowedips":
				currentPeer.AllowedIPs = val
			case "persistentkeepalive":
				if n, err := strconv.Atoi(val); err == nil {
					currentPeer.Keepalive = n
				}
			case "presharedkey":
				currentPeer.PSK = val
			}
		}
	}
	flushPeer()
	if err := sc.Err(); err != nil {
		return nil, err
	}
	return &out, nil
}

func validIfaceName(s string) bool {
	if len(s) < 2 || len(s) > 15 {
		return false
	}
	if !strings.HasPrefix(s, "wg") {
		return false
	}
	for _, r := range s[2:] {
		switch {
		case r >= 'a' && r <= 'z',
			r >= '0' && r <= '9',
			r == '-':
		default:
			return false
		}
	}
	return true
}

func intPtrIfNonzero(n int) *int {
	if n == 0 {
		return nil
	}
	return &n
}