package security

import (
	"errors"
	"fmt"
	"time"

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

// Audience separates admin-space tokens from customer-space tokens so a
// token issued for one space can never be accepted by the other, even
// though both are signed with the same server secret.
type Audience string

const (
	AudienceAdmin    Audience = "admin"
	AudienceCustomer Audience = "customer"
)

// Claims are the JWT claims carried by access tokens issued by this platform.
type Claims struct {
	Role string `json:"role"`
	jwt.RegisteredClaims
}

// IssueAccessToken creates a signed, short-lived access token for the given
// user, role and audience (admin or customer space).
func IssueAccessToken(secret string, ttl time.Duration, userID uuid.UUID, role string, aud Audience) (string, error) {
	if role == "" {
		return "", fmt.Errorf("role must not be empty")
	}

	now := time.Now()
	claims := Claims{
		Role: role,
		RegisteredClaims: jwt.RegisteredClaims{
			Subject:   userID.String(),
			Audience:  jwt.ClaimStrings{string(aud)},
			IssuedAt:  jwt.NewNumericDate(now),
			NotBefore: jwt.NewNumericDate(now),
			ExpiresAt: jwt.NewNumericDate(now.Add(ttl)),
			ID:        uuid.NewString(),
		},
	}

	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	signed, err := token.SignedString([]byte(secret))
	if err != nil {
		return "", fmt.Errorf("sign token: %w", err)
	}
	return signed, nil
}

// ParseAccessToken verifies signature, algorithm and every claim explicitly:
// - signing method must be HMAC (rejects "alg":"none" and any asymmetric swap attempt)
// - exp/iat/nbf must be present and internally consistent (no expired/not-yet-valid tokens)
// - aud must match exactly the expected audience (admin token can never pass as a customer token, or vice versa)
// - sub must be present and a well-formed UUID (matches our user ID format)
// - role must be present and non-empty
// - jti must be present (reserved for future revocation lookups)
func ParseAccessToken(secret string, tokenString string, expectedAud Audience) (*Claims, error) {
	claims := &Claims{}

	token, err := jwt.ParseWithClaims(tokenString, claims, func(t *jwt.Token) (interface{}, error) {
		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("unexpected signing method: %v", t.Header["alg"])
		}
		return []byte(secret), nil
	}, jwt.WithValidMethods([]string{jwt.SigningMethodHS256.Name}))

	if err != nil {
		return nil, fmt.Errorf("parse token: %w", err)
	}
	if !token.Valid {
		return nil, errors.New("invalid token")
	}

	if claims.ExpiresAt == nil {
		return nil, errors.New("missing exp claim")
	}
	if claims.IssuedAt == nil {
		return nil, errors.New("missing iat claim")
	}
	if claims.ID == "" {
		return nil, errors.New("missing jti claim")
	}
	if claims.Subject == "" {
		return nil, errors.New("missing sub claim")
	}
	if _, err := uuid.Parse(claims.Subject); err != nil {
		return nil, fmt.Errorf("invalid sub claim: %w", err)
	}
	if claims.Role == "" {
		return nil, errors.New("missing role claim")
	}

	if len(claims.Audience) != 1 || claims.Audience[0] != string(expectedAud) {
		return nil, fmt.Errorf("token audience does not match expected space %q", expectedAud)
	}

	return claims, nil
}