/*
 * Copyright (C) 2008-2019, Juick
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package com.github.scribejava.apis;

import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.security.Key;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.spec.EncodedKeySpec;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.time.Instant;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.util.Base64;
import java.util.Date;

public class AppleClientSecretGenerator {
    private final String subject;
    private final String teamId;
    private final String keyId;

    private final Key signingKey;

    private final byte[] pemData;

    public AppleClientSecretGenerator(final String subject, final String teamId, final String keyId, final byte[] pemData)
            throws NoSuchAlgorithmException, InvalidKeySpecException {
        this.subject = subject;
        this.keyId = keyId;
        this.teamId = teamId;

        this.pemData = pemData;
        String p8encodedData = new String(getPemData(), StandardCharsets.UTF_8)
                .replace(
                        "-----BEGIN PRIVATE KEY-----\n", "")
                .replace("\n", "")
                .replace("-----END PRIVATE KEY-----", "");
        KeyFactory kf = KeyFactory.getInstance("EC");
        EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(Base64.getDecoder().decode(p8encodedData));
        signingKey = kf.generatePrivate(keySpec);
    }

    public String getClientSecret() {
        Instant now = Instant.now();
        return Jwts.builder()
                .setHeaderParam("kid", keyId)
                .setIssuer(teamId)
                .setAudience("https://appleid.apple.com")
                .setIssuedAt(Date.from(now))
                .setSubject(subject)
                .setExpiration(Date.from(ZonedDateTime.ofInstant(now, ZoneId.of("UTC")).plusMonths(1).toInstant()))
                .signWith(signingKey, SignatureAlgorithm.ES256)
                .compact();
    }

    public String getTeamId() {
        return teamId;
    }

    public String getKeyId() {
        return keyId;
    }

    public String getApplicationId() {
        return subject;
    }

    public byte[] getPemData() {
        return pemData;
    }
}