// Copyright 2024 Patial Tech (Ankit Patial).
//
// This file is part of code.patial.tech/go/appcore, which is MIT licensed.
// See http://opensource.org/licenses/MIT

package jwt

import (
	"crypto/ecdsa"
	"crypto/ed25519"
	"errors"
	"fmt"
	"maps"
	"time"

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

// Sign using EdDSA
func Sign(key ed25519.PrivateKey, claims map[string]any, issuer string, d time.Duration) (string, error) {
	return SignEdDSA(key, claims, issuer, d)
}

func Parse(key ed25519.PrivateKey, tokenString string, issuer string) (jwt.MapClaims, error) {
	return ParseEdDSA(key, tokenString, issuer)
}

// SignEdDSA (Edwards-curve Digital Signature Algorithm, typically Ed25519) is an excellent,
// modern choice for JWT signing—arguably safer and more efficient than both HS256 and traditional RSA/ECDSA.
func SignEdDSA(key ed25519.PrivateKey, claims map[string]any, issuer string, d time.Duration) (string, error) {
	cl := jwt.MapClaims{
		"iss": issuer,
		"iat": jwt.NewNumericDate(time.Now().UTC()),
		"exp": jwt.NewNumericDate(time.Now().Add(d)),
	}
	maps.Copy(cl, claims)

	t := jwt.NewWithClaims(jwt.SigningMethodEdDSA, cl)
	return t.SignedString(key)
}

func ParseEdDSA(key ed25519.PrivateKey, tokenString string, issuer string) (jwt.MapClaims, error) {
	token, err := jwt.Parse(
		tokenString,
		func(token *jwt.Token) (any, error) {
			return key.Public(), nil
		},
		jwt.WithValidMethods([]string{jwt.SigningMethodEdDSA.Alg()}),
		jwt.WithIssuer(issuer),
		jwt.WithIssuedAt(),
		jwt.WithExpirationRequired(),
	)
	if err != nil {
		return nil, fmt.Errorf("failed to parse JWT token: %w", err)
	}

	if claims, ok := token.Claims.(jwt.MapClaims); ok {
		return claims, nil
	}
	return nil, errors.New("no claims found in token")
}

func SignHS256(secret []byte, claims map[string]any, issuer string, d time.Duration) (string, error) {
	cl := jwt.MapClaims{
		"iss": issuer,
		"iat": jwt.NewNumericDate(time.Now().UTC()),
		"exp": jwt.NewNumericDate(time.Now().Add(d)),
	}
	maps.Copy(cl, claims)

	t := jwt.NewWithClaims(jwt.SigningMethodHS256, cl)
	return t.SignedString(secret)
}

func ParseHS256(secret []byte, tokenString string, issuer string) (jwt.MapClaims, error) {
	token, err := jwt.Parse(
		tokenString,
		func(token *jwt.Token) (any, error) {
			if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
				return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
			}
			return secret, nil
		},
		jwt.WithValidMethods([]string{jwt.SigningMethodHS256.Alg()}),
		jwt.WithIssuer(issuer),
		jwt.WithIssuedAt(),
		jwt.WithExpirationRequired(),
	)
	if err != nil {
		return nil, fmt.Errorf("failed to parse JWT token: %w", err)
	}

	if claims, ok := token.Claims.(jwt.MapClaims); ok {
		return claims, nil
	}
	return nil, errors.New("no claims found in token")
}

// SignES256 signs a JWT using ES256 (ECDSA P-256) algorithm.
// This is required for Apple Sign In which mandates ES256.
// Pass empty string for issuer, audience, or subject to omit them from the token.
func SignES256(
	key *ecdsa.PrivateKey, issuer, audience, subject string, d time.Duration, claims map[string]any,
) (string, error) {
	cl := jwt.MapClaims{
		"iat": jwt.NewNumericDate(time.Now().UTC()),
		"exp": jwt.NewNumericDate(time.Now().Add(d)),
	}

	if issuer != "" {
		cl["iss"] = issuer
	}

	if audience != "" {
		cl["aud"] = audience
	}

	if subject != "" {
		cl["sub"] = subject
	}

	maps.Copy(cl, claims)

	t := jwt.NewWithClaims(jwt.SigningMethodES256, cl)
	return t.SignedString(key)
}

// ParseES256 parses and validates a JWT signed with ES256 (ECDSA P-256) algorithm.
// This is required for Apple Sign In which mandates ES256.
// issuer and audience are typically validated, while subject is optional (pass empty string to skip).
func ParseES256(key *ecdsa.PublicKey, tokenString, issuer, audience string) (jwt.MapClaims, error) {
	opts := []jwt.ParserOption{
		jwt.WithValidMethods([]string{jwt.SigningMethodES256.Alg()}),
		jwt.WithIssuedAt(),
		jwt.WithExpirationRequired(),
	}

	if issuer != "" {
		opts = append(opts, jwt.WithIssuer(issuer))
	}
	if audience != "" {
		opts = append(opts, jwt.WithAudience(audience))
	}

	token, err := jwt.Parse(
		tokenString,
		func(token *jwt.Token) (any, error) {
			if _, ok := token.Method.(*jwt.SigningMethodECDSA); !ok {
				return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
			}
			return key, nil
		},
		opts...,
	)
	if err != nil {
		return nil, fmt.Errorf("failed to parse JWT token: %w", err)
	}

	if claims, ok := token.Claims.(jwt.MapClaims); ok {
		return claims, nil
	}
	return nil, errors.New("no claims found in token")
}