"""Tests for i2p_crypto ElGamal — 2048-bit encryption/decryption."""

import pytest


class TestElGamalEngine:
    def test_encrypt_decrypt_roundtrip(self):
        from i2p_crypto.elgamal import ElGamalEngine
        pub, priv = ElGamalEngine.generate_keypair()
        data = b"Hello, ElGamal!"
        ct = ElGamalEngine.encrypt(data, pub)
        assert len(ct) == 514
        pt = ElGamalEngine.decrypt(ct, priv)
        assert pt == data

    def test_encrypt_decrypt_empty(self):
        from i2p_crypto.elgamal import ElGamalEngine
        pub, priv = ElGamalEngine.generate_keypair()
        ct = ElGamalEngine.encrypt(b"", pub)
        pt = ElGamalEngine.decrypt(ct, priv)
        assert pt == b""

    def test_encrypt_decrypt_max_size(self):
        from i2p_crypto.elgamal import ElGamalEngine, MAX_CLEARTEXT
        pub, priv = ElGamalEngine.generate_keypair()
        data = b"X" * MAX_CLEARTEXT
        ct = ElGamalEngine.encrypt(data, pub)
        pt = ElGamalEngine.decrypt(ct, priv)
        assert pt == data

    def test_reject_oversized_data(self):
        from i2p_crypto.elgamal import ElGamalEngine, MAX_CLEARTEXT
        pub, _ = ElGamalEngine.generate_keypair()
        with pytest.raises(ValueError):
            ElGamalEngine.encrypt(b"X" * (MAX_CLEARTEXT + 1), pub)

    def test_ciphertext_size(self):
        from i2p_crypto.elgamal import ElGamalEngine, CIPHERTEXT_SIZE
        pub, _ = ElGamalEngine.generate_keypair()
        ct = ElGamalEngine.encrypt(b"test", pub)
        assert len(ct) == CIPHERTEXT_SIZE

    def test_wrong_key_fails(self):
        from i2p_crypto.elgamal import ElGamalEngine
        pub1, priv1 = ElGamalEngine.generate_keypair()
        _, priv2 = ElGamalEngine.generate_keypair()
        ct = ElGamalEngine.encrypt(b"secret", pub1)
        pt = ElGamalEngine.decrypt(ct, priv2)
        assert pt is None  # Hash mismatch

    def test_corrupted_ciphertext_fails(self):
        from i2p_crypto.elgamal import ElGamalEngine
        pub, priv = ElGamalEngine.generate_keypair()
        ct = bytearray(ElGamalEngine.encrypt(b"test", pub))
        ct[100] ^= 0xFF
        pt = ElGamalEngine.decrypt(bytes(ct), priv)
        assert pt is None

    def test_wrong_size_ciphertext(self):
        from i2p_crypto.elgamal import ElGamalEngine
        _, priv = ElGamalEngine.generate_keypair()
        assert ElGamalEngine.decrypt(b"too short", priv) is None

    def test_randomized_ciphertext(self):
        """Same plaintext should produce different ciphertext each time."""
        from i2p_crypto.elgamal import ElGamalEngine
        pub, _ = ElGamalEngine.generate_keypair()
        ct1 = ElGamalEngine.encrypt(b"same", pub)
        ct2 = ElGamalEngine.encrypt(b"same", pub)
        assert ct1 != ct2

    def test_key_sizes(self):
        from i2p_crypto.elgamal import ElGamalEngine
        pub, priv = ElGamalEngine.generate_keypair()
        assert len(pub) == 256
        assert len(priv) == 256

    def test_various_data_sizes(self):
        from i2p_crypto.elgamal import ElGamalEngine
        pub, priv = ElGamalEngine.generate_keypair()
        for size in [1, 10, 50, 100, 200, 222]:
            data = bytes(range(size % 256)) * (size // 256 + 1)
            data = data[:size]
            ct = ElGamalEngine.encrypt(data, pub)
            pt = ElGamalEngine.decrypt(ct, priv)
            assert pt == data, f"Failed for size {size}"