package authenticator

import (
	"bytes"
	"context"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha1"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"io"
	"math/big"
	mrand "math/rand"
	"net/http"
	"strings"
	"time"

	"git.wxccs.org/iceking2nd/winauth-go/internal/global"
	"git.wxccs.org/iceking2nd/winauth-go/internal/httpc"
)

// Battle.Net mobile-service URLs by region. Matches the original C# table.
var battlenetURLs = map[string]string{
	"US": "http://mobile-service.blizzard.com",
	"EU": "http://mobile-service.blizzard.com",
	"KR": "http://mobile-service.blizzard.com",
	"CN": "http://mobile-service.battlenet.com.cn",
}

const (
	bnetEnrollPath          = "/enrollment/enroll2.htm"
	bnetSyncPath            = "/enrollment/time.htm"
	bnetRestorePath         = "/enrollment/initiatePaperRestore.htm"
	bnetRestoreValidatePath = "/enrollment/validatePaperRestore.htm"

	bnetCodeDigits   = 8
	bnetModelSize    = 16
	bnetModelChars   = " ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz01234567890"
	bnetEnrollRespSz = 45
	bnetSyncRespSz   = 8

	bnetEnrollModulus = "955e4bd989f3917d2f15544a7e0504eb9d7bb66b6f8a2fe470e453c779200e5e" +
		"3ad2e43a02d06c4adbd8d328f1a426b83658e88bfd949b2af4eaf30054673a14" +
		"19a250fa4cc1278d12855b5b25818d162c6e6ee2ab4a350d401d78f6ddb99711" +
		"e72626b48bd8b5b0b7f3acf9ea3c9e0005fee59e19136cdb7c83f2ab8b0a2a99"
	bnetEnrollExponent = "0101"
)

// BattleNetAuthenticator is the Go port of the C# BattleNetAuthenticator.
// It supports Enroll, Sync, Restore (paper restore), and the customary
// 8-digit TOTP code generation.
type BattleNetAuthenticator struct {
	Base
	Serial              string
	RestoreCodeVerified bool
}

// NewBattleNetAuthenticator returns an empty 8-digit Battle.Net authenticator.
func NewBattleNetAuthenticator() *BattleNetAuthenticator {
	b := &BattleNetAuthenticator{Base: NewBase()}
	b.CodeDigits = bnetCodeDigits
	return b
}

// Name returns the short logger tag for this type.
func (b *BattleNetAuthenticator) Name() string { return "battlenet" }

// Region returns the two-letter region prefix derived from the serial.
func (b *BattleNetAuthenticator) Region() string {
	if len(b.Serial) >= 2 {
		return strings.ToUpper(b.Serial[:2])
	}
	return ""
}

// CurrentCode returns the live 8-digit Battle.Net authenticator code.
func (b *BattleNetAuthenticator) CurrentCode() (string, error) {
	if b.SecretKey == nil {
		return "", fmt.Errorf("battlenet: no secret loaded")
	}
	return b.CalculateTOTP(), nil
}

// SecretData / SetSecretData persist both the secret and the serial number,
// matching the C# format "<basesecret>|<utf8-hex-serial>".
func (b *BattleNetAuthenticator) SecretData() string {
	return b.EncodeSecretData() + "|" + strings.ToUpper(hex.EncodeToString([]byte(b.Serial)))
}

func (b *BattleNetAuthenticator) SetSecretData(value string) error {
	if value == "" {
		b.SecretKey = nil
		b.Serial = ""
		return nil
	}
	parts := strings.Split(value, "|")
	if len(parts) == 1 {
		// legacy WinAuth2 form: 40 hex chars secret then UTF8-hex serial
		if len(value) < 40 {
			return fmt.Errorf("battlenet: secret data too short")
		}
		raw, err := hex.DecodeString(value[:40])
		if err != nil {
			return fmt.Errorf("battlenet: bad secret hex: %w", err)
		}
		b.SecretKey = raw
		serialBytes, err := hex.DecodeString(value[40:])
		if err == nil {
			b.Serial = string(serialBytes)
		}
		return nil
	}
	if err := b.DecodeSecretData(parts[0]); err != nil {
		return err
	}
	serialIdx := 1
	if len(parts) == 3 {
		// alpha 3.0.6 form: secret|script|serial
		serialIdx = 2
	}
	if len(parts) > serialIdx {
		raw, err := hex.DecodeString(parts[serialIdx])
		if err == nil {
			b.Serial = string(raw)
		}
	}
	return nil
}

// Enroll registers a brand-new Battle.Net authenticator with the Blizzard
// mobile service. Country is auto-detected via Wikimedia GEO IP; pass an
// explicit two-letter override to skip the lookup.
func (b *BattleNetAuthenticator) Enroll(ctx context.Context, countryOverride string) error {
	const fn = "internal.authenticator.BattleNetAuthenticator.Enroll"
	logger := global.Log.WithField("func", fn)

	country := strings.ToUpper(strings.TrimSpace(countryOverride))
	region := "US"
	if country == "" {
		c, r := lookupRegion(ctx)
		country, region = c, r
	} else {
		region = regionForCountry(country)
	}
	logger.WithField("country", country).WithField("region", region).Debug("region determined")

	otp := mustOneTimePad(20)
	payload := make([]byte, 38)
	copy(payload[0:20], otp)
	copy(payload[20:22], []byte(country))
	copy(payload[22:38], []byte(randomModel()))

	encrypted, err := rsaEncryptRaw(payload)
	if err != nil {
		return fmt.Errorf("battlenet: rsa encrypt failed: %w", err)
	}

	respBytes, err := bnetPostBinary(ctx, mobileURL(region)+bnetEnrollPath, encrypted)
	if err != nil {
		return err
	}
	if len(respBytes) != bnetEnrollRespSz {
		return fmt.Errorf("battlenet: enroll response size %d, want %d", len(respBytes), bnetEnrollRespSz)
	}

	serverMs := int64(binary.BigEndian.Uint64(respBytes[0:8]))
	b.ServerTimeDiff = serverMs - NowMillis()

	secret := make([]byte, 20)
	copy(secret, respBytes[25:45])
	for i := range secret {
		secret[i] ^= otp[i]
	}
	b.SecretKey = secret
	b.Serial = string(respBytes[8:25])
	logger.WithField("serial", b.Serial).Info("enrolled with Battle.Net mobile service")
	return nil
}

// Sync re-aligns ServerTimeDiff against the mobile service for our region.
func (b *BattleNetAuthenticator) Sync() error {
	const fn = "internal.authenticator.BattleNetAuthenticator.Sync"
	logger := global.Log.WithField("func", fn).WithField("region", b.Region())

	if b.SecretKey == nil {
		logger.Debug("skip sync: no secret loaded")
		return nil
	}

	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	url := mobileURL(b.Region()) + bnetSyncPath
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return err
	}
	resp, err := httpc.New().Do(req)
	if err != nil {
		logger.WithError(err).Warn("sync failed; using local clock")
		return nil
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return err
	}
	if len(body) != bnetSyncRespSz {
		return fmt.Errorf("battlenet: sync response size %d, want %d", len(body), bnetSyncRespSz)
	}
	serverMs := int64(binary.BigEndian.Uint64(body))
	b.ServerTimeDiff = serverMs - NowMillis()
	b.LastServerTime = NowMillis()
	logger.WithField("offset_ms", b.ServerTimeDiff).Debug("clock synced")
	return nil
}

// RestoreCode computes the 10-char Battle.Net restore code derived from
// the SHA1 of (serial || secretKey).
func (b *BattleNetAuthenticator) RestoreCode() string {
	if b.Serial == "" || b.SecretKey == nil {
		return ""
	}
	serial := strings.ReplaceAll(strings.ToUpper(b.Serial), "-", "")
	hash := sha1.Sum(append([]byte(serial), b.SecretKey...))
	out := make([]byte, 10)
	for i := 0; i < 10; i++ {
		out[i] = restoreByteToChar(hash[len(hash)-10+i])
	}
	return string(out)
}

// helpers ------------------------------------------------------------------

func mobileURL(region string) string {
	region = strings.ToUpper(region)
	if len(region) > 2 {
		region = region[:2]
	}
	if u, ok := battlenetURLs[region]; ok {
		return u
	}
	return battlenetURLs["US"]
}

func regionForCountry(country string) string {
	switch country {
	case "CN":
		return "CN"
	case "KR", "KP", "TW", "HK", "MO":
		return "KR"
	}
	euCountries := []string{
		"AL", "AD", "AM", "AT", "AZ", "BY", "BE", "BA", "BG", "HR",
		"CY", "CZ", "DK", "EE", "FI", "FR", "GE", "DE", "GR", "HU",
		"IS", "IE", "IT", "KV", "XK", "LV", "LI", "LT", "LU", "MK",
		"MT", "MD", "MC", "ME", "NL", "NO", "PL", "PT", "RO", "RU",
		"SM", "RS", "SK", "ES", "SE", "CH", "TR", "UA", "UK", "GB",
		"VA",
	}
	for _, c := range euCountries {
		if c == country {
			return "EU"
		}
	}
	return "US"
}

func lookupRegion(ctx context.Context) (country, region string) {
	const fn = "internal.authenticator.lookupRegion"
	logger := global.Log.WithField("func", fn)

	geoCtx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()
	req, _ := http.NewRequestWithContext(geoCtx, http.MethodGet, "http://geoiplookup.wikimedia.org", nil)
	resp, err := httpc.New().Do(req)
	if err != nil {
		logger.WithError(err).Debug("geoip lookup failed; defaulting to US")
		return "US", "US"
	}
	defer resp.Body.Close()
	body, _ := io.ReadAll(resp.Body)
	// Cheap regex-free parse for "country":"XX"
	const key = `"country":"`
	idx := strings.Index(string(body), key)
	if idx < 0 {
		return "US", "US"
	}
	rest := string(body)[idx+len(key):]
	end := strings.Index(rest, `"`)
	if end < 0 {
		return "US", "US"
	}
	country = strings.ToUpper(rest[:end])
	return country, regionForCountry(country)
}

func bnetPostBinary(ctx context.Context, url string, body []byte) ([]byte, error) {
	reqCtx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()
	req, err := http.NewRequestWithContext(reqCtx, http.MethodPost, url, bytes.NewReader(body))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/octet-stream")
	resp, err := httpc.New().Do(req)
	if err != nil {
		return nil, fmt.Errorf("battlenet: contact mobile service: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("battlenet: server returned %d %s", resp.StatusCode, resp.Status)
	}
	return io.ReadAll(resp.Body)
}

func rsaEncryptRaw(data []byte) ([]byte, error) {
	n, ok := new(big.Int).SetString(bnetEnrollModulus, 16)
	if !ok {
		return nil, fmt.Errorf("invalid RSA modulus")
	}
	e, ok := new(big.Int).SetString(bnetEnrollExponent, 16)
	if !ok {
		return nil, fmt.Errorf("invalid RSA exponent")
	}
	pub := &rsa.PublicKey{N: n, E: int(e.Int64())}

	// The original C# uses BouncyCastle's RsaEngine.ProcessBlock without
	// padding (raw RSA / "no padding"). We emulate that by padding the input
	// to modulus length with leading zeros and using big.Int exponentiation.
	keySize := (pub.N.BitLen() + 7) / 8
	if len(data) > keySize {
		return nil, fmt.Errorf("data too large for raw RSA")
	}
	m := new(big.Int).SetBytes(data)
	c := new(big.Int).Exp(m, big.NewInt(int64(pub.E)), pub.N)
	out := make([]byte, keySize)
	cBytes := c.Bytes()
	copy(out[keySize-len(cBytes):], cBytes)
	return out, nil
}

func mustOneTimePad(n int) []byte {
	out := make([]byte, n)
	if _, err := rand.Read(out); err != nil {
		panic(err)
	}
	return out
}

func randomModel() string {
	var seedBytes [8]byte
	_, _ = rand.Read(seedBytes[:])
	r := mrand.New(mrand.NewSource(int64(binary.LittleEndian.Uint64(seedBytes[:]))))
	out := make([]byte, bnetModelSize)
	for i := range out {
		out[i] = bnetModelChars[r.Intn(len(bnetModelChars))]
	}
	return string(out)
}

func restoreByteToChar(b byte) byte {
	// Mirror C# ConvertRestoreCodeByteToChar — but we only need the inverse
	// for code *display*. The original algorithm maps each byte to an alpha
	// or numeric, skipping I, L, O, S to avoid ambiguity. Below is a direct
	// translation of the C# code path that lives at the bottom of
	// BattleNetAuthenticator.cs (ConvertRestoreCodeByteToChar).
	v := int(b) & 0x1F // 5 bits
	switch {
	case v < 10:
		return byte('0' + v)
	}
	c := v - 10 + 'A'
	if c >= 'I' {
		c++
	}
	if c >= 'L' {
		c++
	}
	if c >= 'O' {
		c++
	}
	if c >= 'S' {
		c++
	}
	return byte(c)
}