package bouncer

import (
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"strings"
	"time"

	"github.com/golang-jwt/jwt/v5"
)

// prvHash is sha1("Golem15\User\Models\User"), the lock-subject PHP jwt-auth
// stamps on every frontend user token. Backend tokens do not carry it.
const prvHash = "a867434cbc213adfbe78a02bed7082a6bd99c883"

const (
	// AudienceUser is the frontend jwt-guard audience.
	AudienceUser = "user"
	// AudienceBackend is the admin jwt-guard audience.
	AudienceBackend = "backend"
)

// ClaimAuthTime is the JWT claim holding the time of the sign-in that started
// the session (OIDC Core's auth_time, NumericDate seconds). Every direct mint
// is a sign-in and stamps it equal to iat; a refresh copies it unchanged, so
// a "fresh sign-in" check compares auth_time, never iat.
const ClaimAuthTime = "auth_time"

type registeredClaims struct {
	jwt.RegisteredClaims
	Prv      string           `json:"prv,omitempty"`
	AuthTime *jwt.NumericDate `json:"auth_time,omitempty"`
}

// Mint signs a frontend-audience HS256 token. iss is the minting endpoint URL.
// The returned jti is the token's own jti claim.
func Mint(secret, sub, issuerURL string, ttl time.Duration) (string, string, error) {
	return MintAudience(secret, sub, issuerURL, ttl, AudienceUser)
}

// MintAudience signs an HS256 token for audience. Frontend tokens keep the PHP
// prv lock-subject; backend tokens omit it. Every MintAudience call is a
// sign-in, so the token's auth_time (ClaimAuthTime) equals its iat.
func MintAudience(secret, sub, issuerURL string, ttl time.Duration, audience string) (string, string, error) {
	now := time.Now()
	return mintAudience(secret, sub, issuerURL, ttl, audience, now, now)
}

// mintAudience signs the token issued at now. authTime, when non-zero,
// becomes the auth_time claim; a zero authTime mints a token without one. A
// sign-in passes the same instant as now and authTime, so auth_time equals iat.
func mintAudience(secret, sub, issuerURL string, ttl time.Duration, audience string, now, authTime time.Time) (string, string, error) {
	if strings.TrimSpace(secret) == "" {
		return "", "", fmt.Errorf("bouncer: jwt secret is empty")
	}
	if strings.TrimSpace(audience) == "" {
		return "", "", fmt.Errorf("bouncer: jwt audience is empty")
	}
	jti, err := newJTI()
	if err != nil {
		return "", "", err
	}
	prv := ""
	if audience == AudienceUser {
		prv = prvHash
	}
	claims := registeredClaims{
		RegisteredClaims: jwt.RegisteredClaims{
			Issuer:    issuerURL,
			Subject:   sub,
			Audience:  jwt.ClaimStrings{audience},
			ExpiresAt: jwt.NewNumericDate(now.Add(ttl)),
			NotBefore: jwt.NewNumericDate(now),
			IssuedAt:  jwt.NewNumericDate(now),
			ID:        jti,
		},
		Prv: prv,
	}
	if !authTime.IsZero() {
		claims.AuthTime = jwt.NewNumericDate(authTime)
	}
	signed, err := jwt.NewWithClaims(jwt.SigningMethodHS256, claims).SignedString([]byte(secret))
	if err != nil {
		return "", "", err
	}
	return signed, jti, nil
}

func newJTI() (string, error) {
	buf := make([]byte, 16)
	if _, err := rand.Read(buf); err != nil {
		return "", err
	}
	return hex.EncodeToString(buf), nil
}