package utils

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/hex"
	"errors"
	"os"
	"strings"
	"sync"
	"time"

	"github.com/golang-jwt/jwt/v5"
	"github.com/google/uuid"
	"golang.org/x/crypto/bcrypt"
)

// ── UID ───────────────────────────────────────────────────────────────────────

func NewUID() string {
	raw := strings.ReplaceAll(uuid.New().String(), "-", "")
	return "cos_" + raw[:16]
}

// ── Password ──────────────────────────────────────────────────────────────────

func HashPassword(pw string) (string, error) {
	b, err := bcrypt.GenerateFromPassword([]byte(pw), 12)
	return string(b), err
}

func CheckPassword(hash, pw string) bool {
	return bcrypt.CompareHashAndPassword([]byte(hash), []byte(pw)) == nil
}

// ── JWT ───────────────────────────────────────────────────────────────────────

const jwtTTL = 7 * 24 * time.Hour

type Claims struct {
	UID      string `json:"uid"`
	Email    string `json:"email"`
	Provider string `json:"provider"`
	jwt.RegisteredClaims
}

func SignJWT(uid, email, provider string) (string, error) {
	secret := os.Getenv("JWT_SECRET")
	if secret == "" {
		return "", errors.New("JWT_SECRET not set")
	}
	c := Claims{
		UID: uid, Email: email, Provider: provider,
		RegisteredClaims: jwt.RegisteredClaims{
			Subject:   uid,
			IssuedAt:  jwt.NewNumericDate(time.Now()),
			ExpiresAt: jwt.NewNumericDate(time.Now().Add(jwtTTL)),
		},
	}
	return jwt.NewWithClaims(jwt.SigningMethodHS256, c).SignedString([]byte(secret))
}

func VerifyJWT(tokenStr string) (*Claims, error) {
	secret := os.Getenv("JWT_SECRET")
	if secret == "" {
		return nil, errors.New("JWT_SECRET not set")
	}
	t, err := jwt.ParseWithClaims(tokenStr, &Claims{}, func(t *jwt.Token) (interface{}, error) {
		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, errors.New("unexpected signing method")
		}
		return []byte(secret), nil
	})
	if err != nil {
		return nil, err
	}
	c, ok := t.Claims.(*Claims)
	if !ok || !t.Valid {
		return nil, errors.New("invalid token")
	}
	return c, nil
}

// ── Constant-time key comparison ──────────────────────────────────────────────

// KeyMatch compares two API keys in constant time to prevent timing attacks.
func KeyMatch(a, b string) bool {
	if len(a) == 0 || len(b) == 0 {
		return false
	}
	return subtle.ConstantTimeCompare([]byte(a), []byte(b)) == 1
}

// ── Nonce store (auth pipe challenge) ─────────────────────────────────────────

const nonceTTL = 15 * time.Minute // full pipeline window

type nonceEntry struct{ exp time.Time }

var (
	nonceMu    sync.Mutex
	nonceStore = map[string]nonceEntry{}
)

func NewNonce() string {
	b := make([]byte, 24)
	_, _ = rand.Read(b)
	n := hex.EncodeToString(b)
	nonceMu.Lock()
	nonceStore[n] = nonceEntry{exp: time.Now().Add(nonceTTL)}
	nonceMu.Unlock()
	go sweepNonces()
	return n
}

func ClaimNonce(n string) bool {
	nonceMu.Lock()
	defer nonceMu.Unlock()
	e, ok := nonceStore[n]
	if !ok {
		return false
	}
	delete(nonceStore, n)
	return time.Now().Before(e.exp)
}

func sweepNonces() {
	nonceMu.Lock()
	defer nonceMu.Unlock()
	now := time.Now()
	for k, v := range nonceStore {
		if now.After(v.exp) {
			delete(nonceStore, k)
		}
	}
}