using System.Text;
using ZB.MOM.WW.Secrets.Abstractions;
using ZB.MOM.WW.Secrets.Crypto;
using ZB.MOM.WW.Secrets.Tests.Fakes;

namespace ZB.MOM.WW.Secrets.Tests.Crypto;

public class AesGcmEnvelopeCipherTests
{
    [Fact]
    public void RoundTrips()
    {
        var provider = new FakeMasterKeyProvider("k1");
        var cipher = new AesGcmEnvelopeCipher(provider);
        var name = new SecretName("sql/foo");

        StoredSecret row = cipher.Encrypt(name, "hunter2", SecretContentType.Text);

        Assert.Equal("k1", row.KekId);
        // Ciphertext must not leak the plaintext in the clear.
        byte[] plaintextBytes = Encoding.UTF8.GetBytes("hunter2");
        Assert.False(Contains(row.Ciphertext, plaintextBytes));

        string decrypted = cipher.Decrypt(row);
        Assert.Equal("hunter2", decrypted);
    }

    [Fact]
    public void TamperedCiphertextThrows()
    {
        var provider = new FakeMasterKeyProvider("k1");
        var cipher = new AesGcmEnvelopeCipher(provider);
        var name = new SecretName("sql/foo");

        StoredSecret row = cipher.Encrypt(name, "hunter2", SecretContentType.Text);
        row.Ciphertext[0] ^= 0xFF;

        Assert.Throws<SecretDecryptionException>(() => cipher.Decrypt(row));
    }

    [Fact]
    public void AadBindingRejectsRenamedRow()
    {
        var provider = new FakeMasterKeyProvider("k1");
        var cipher = new AesGcmEnvelopeCipher(provider);

        StoredSecret row = cipher.Encrypt(new SecretName("sql/foo"), "hunter2", SecretContentType.Text);
        var renamed = row with { Name = new SecretName("sql/bar") };

        Assert.Throws<SecretDecryptionException>(() => cipher.Decrypt(renamed));
    }

    [Fact]
    public void WrongKekThrows()
    {
        // Both providers report KekId "k1" but hold different random key bytes.
        var providerA = new FakeMasterKeyProvider("k1");
        var providerB = new FakeMasterKeyProvider("k1");
        var cipherA = new AesGcmEnvelopeCipher(providerA);
        var cipherB = new AesGcmEnvelopeCipher(providerB);

        StoredSecret row = cipherA.Encrypt(new SecretName("sql/foo"), "hunter2", SecretContentType.Text);

        // Matching KekId string but wrong key material must still fail closed (unwrap tag mismatch).
        Assert.Throws<SecretDecryptionException>(() => cipherB.Decrypt(row));
    }

    [Fact]
    public void UnknownKekIdThrows()
    {
        var providerK1 = new FakeMasterKeyProvider("k1");
        var providerK2 = new FakeMasterKeyProvider("k2");
        var cipherK1 = new AesGcmEnvelopeCipher(providerK1);
        var cipherK2 = new AesGcmEnvelopeCipher(providerK2);

        StoredSecret row = cipherK1.Encrypt(new SecretName("sql/foo"), "hunter2", SecretContentType.Text);

        var ex = Assert.Throws<SecretDecryptionException>(() => cipherK2.Decrypt(row));
        Assert.Contains("unknown KEK", ex.Message, StringComparison.Ordinal);
    }

    private static bool Contains(byte[] haystack, byte[] needle)
    {
        if (needle.Length == 0 || haystack.Length < needle.Length)
        {
            return false;
        }

        for (int i = 0; i <= haystack.Length - needle.Length; i++)
        {
            bool match = true;
            for (int j = 0; j < needle.Length; j++)
            {
                if (haystack[i + j] != needle[j])
                {
                    match = false;
                    break;
                }
            }

            if (match)
            {
                return true;
            }
        }

        return false;
    }
}