Flow 7 -- AES-256 Compact-JWE Encrypt / Decrypt (Non-Streaming)

/*
 * Copyright 2025 ANKATech Solutions Inc
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * SPDX-License-Identifier: Apache-2.0
 */
package co.ankatech.ankasecure.sdk.examples;

import co.ankatech.ankasecure.sdk.AuthenticatedSdk;
import co.ankatech.ankasecure.sdk.model.DecryptResultMetadata;
import co.ankatech.ankasecure.sdk.model.EncryptResult;
import co.ankatech.ankasecure.sdk.model.GenerateKeySpec;
import co.ankatech.ankasecure.sdk.util.FileIO;

import java.nio.file.Path;
import java.util.Properties;

import static co.ankatech.ankasecure.sdk.examples.ExampleUtil.*;

/**
 * Scenario 7 — AES-256 Compact JWE Helpers.
 *
 * <p>This scenario showcases the SDK's <strong>non-streaming</strong> helpers
 * for symmetric Compact&nbsp;JWE operations:</p>
 * <ol>
 *   <li>Generate an <code>AES-256</code> key (<code>kty="oct"</code>).</li>
 *   <li>Encrypt a plaintext file (helper stores a Compact&nbsp;JWE).</li>
 *   <li>Decrypt the ciphertext (helper resolves the key from the JWE header).</li>
 *   <li>Print metadata and validate integrity.</li>
 * </ol>
 *
 * <p><b>Implementation notes (Java&nbsp;21+):</b></p>
 * <ul>
 *   <li>All filesystem interactions use the {@link java.nio.file.Path} API.</li>
 *   <li>UTF-8 is enforced explicitly for deterministic encoding.</li>
 *   <li>Temporary artefacts reside under <kbd>temp_files/</kbd>.</li>
 * </ul>
 *
 * <p><b>Thread-safety:</b> this class is stateless and immutable.</p>
 *
 * @author ANKATech Solutions Inc.
 * @since 3.0.0
 * @see ExampleUtil
 * @see AuthenticatedSdk
 */
public final class ExampleScenario7 {

    /** No instantiation &mdash; this class only exposes {@link #main(String[])}. */
    private ExampleScenario7() { }

    /**
     * Runs the AES-256 compact JWE encrypt/decrypt scenario.
     *
     * <p>Loads CLI properties, authenticates against ANKASecure&copy;,
     * and delegates to the scenario logic. On any unrecoverable error
     * the JVM terminates via
     * {@link ExampleUtil#fatal(String, Throwable)}.</p>
     *
     * @param args command-line arguments (ignored)
     */
    public static void main(final String[] args) {

        System.out.println("===== SCENARIO 7 START =====");
        System.out.println("""
                Purpose :
                  * AES-256 Compact-JWE encrypt / decrypt helpers
                  * Non-streaming - full token handled in memory
                Steps   :
                  1) Generate AES-256 key
                  2) Create sample payload
                  3) Encrypt payload (compact JWE)
                  4) Decrypt ciphertext
                  5) Validate integrity
                --------------------------------------------------------------""");

        try {
            ensureTempDir(TEMP_DIR);

            Properties   props = loadProperties();
            AuthenticatedSdk sdk  = authenticate(props);

            runScenario(sdk);

        } catch (Exception ex) {
            fatal("Scenario 7 failed", ex);
        }

        System.out.println("===== SCENARIO 7 END =====");
    }

    /**
     * Executes the 4-step AES-256 compact JWE scenario.
     *
     * <ol>
     *   <li>Create sample plaintext file.</li>
     *   <li>Generate AES-256 symmetric key.</li>
     *   <li>Encrypt file (compact JWE).</li>
     *   <li>Decrypt and validate integrity.</li>
     * </ol>
     *
     * @param sdk an authenticated {@link AuthenticatedSdk} instance;
     *            must not be {@code null}
     * @throws Exception if any step fails
     */
    private static void runScenario(final AuthenticatedSdk sdk) throws Exception {

        /* 1 -- create sample plaintext -------------------------------------- */
        Path plain = TEMP_DIR.resolve("scenario7_plain.txt");
        FileIO.writeUtf8(plain,
                "Scenario-7 - AES-256 Compact-JWE encrypt / decrypt demo.");
        System.out.println("[1] Plaintext ready          -> " + plain.toAbsolutePath());

        /* 2 -- generate AES-256 key ----------------------------------------- */
        String kid = "sc7_aes256_" + System.currentTimeMillis();
        sdk.generateKey(new GenerateKeySpec()
                .setKid(kid)
                .setKty("oct")
                .setAlg("AES-GCM-256"));
        System.out.println("[2] Key generated            -> kid = " + kid);

        /* 3 -- encrypt file (compact JWE) ----------------------------------- */
        Path jweFile = TEMP_DIR.resolve("scenario7.jwe");
        EncryptResult encMeta = sdk.encryptFile(kid, plain, jweFile);
        System.out.println("[3] Ciphertext stored         -> " + jweFile.toAbsolutePath());
        printEncryptMeta(encMeta);

        /* 4 -- decrypt ------------------------------------------------------ */
        Path recovered = TEMP_DIR.resolve("scenario7_dec.txt");
        DecryptResultMetadata decMeta = sdk.decryptFile(jweFile, recovered);
        System.out.println("[4] Decrypted file            -> " + recovered.toAbsolutePath());
        printDecryptMeta(decMeta);

        /* 5 -- validation --------------------------------------------------- */
        boolean match = FileIO.readUtf8(plain)
                .equals(FileIO.readUtf8(recovered));
        System.out.println(match
                ? "[5] SUCCESS - plaintext matches."
                : "[5] FAILURE - plaintext mismatch.");
    }
}