import pytest

from app.rounds.draw import (
    draw_winner,
    header_hex_to_block_hash,
    header_meets_its_own_target,
    header_prev_hash,
)

# Real PLM mainnet block 477486: header from blockchain.block.header, hash
# cross-checked against the blockhash reported by blockchain.transaction.get for a
# tx confirmed in that block.
_REAL_HEADER_HEX = (
    "0020ed30fbc39ee45200d10214f5107c5f36e7bf753032fd1d3279810c170000000000"
    "009a4ea723f732be4c538f3a2490837dd6560103d73ece606aa7d578a66700447b28875"
    "e6a47a61b1ad8012582"
)


def test_header_hex_to_block_hash_matches_known_mainnet_block():
    known_block_hash = "00000000000008788b55ade13b74d54ceffda9e54315b802411be1ca65064e86"
    assert header_hex_to_block_hash(_REAL_HEADER_HEX) == known_block_hash


def test_header_meets_its_own_target_accepts_a_real_mined_header():
    """B-28: a genuinely mined mainnet header must pass its own self-consistency
    check — this isn't just a synthetic-header property."""
    assert header_meets_its_own_target(_REAL_HEADER_HEX) is True


def test_header_meets_its_own_target_rejects_a_tampered_header():
    """Flipping a single nonce bit changes the hash completely (avalanche effect)
    without changing the claimed difficulty, so a tampered-but-otherwise-real
    header should almost certainly fail — this is what would catch a
    hostile/MITM'd server replaying a real header with a doctored field."""
    tampered = bytearray(bytes.fromhex(_REAL_HEADER_HEX))
    tampered[-1] ^= 0xFF  # flip the last byte of the nonce
    assert header_meets_its_own_target(tampered.hex()) is False


def test_header_meets_its_own_target_rejects_wrong_length():
    assert header_meets_its_own_target("aa" * 10) is False


def test_header_prev_hash_matches_the_known_previous_block():
    # Block 477486's predecessor, 477485 — independently known from the same chain.
    assert header_prev_hash(_REAL_HEADER_HEX) == "000000000000170c8179321dfd323075bfe7365f7c10f51402d10052e49ec3fb"


def test_draw_winner_is_deterministic_and_within_range():
    participants = ["addrA", "addrB", "addrC"]
    block_hash = "00" * 31 + "05"  # seed = 5, index = 5 % 3 = 2
    assert draw_winner(participants, block_hash) == "addrC"


def test_draw_winner_single_participant_always_wins():
    block_hash = "ff" * 32
    assert draw_winner(["only"], block_hash) == "only"


def test_draw_winner_raises_on_empty_participants():
    with pytest.raises(ValueError):
        draw_winner([], "00" * 32)