plm-lottery/tests/unit/test_draw.py

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"


# --- B-73 (RND-14, RND-17, RND-34): the commit-reveal draw -------------------------------

_SEED = "11" * 32
_BLOCK = "00" * 28 + "deadbeef"
_LIST_HASH = "22" * 32


def test_draw_seed_is_the_sha256_of_the_three_32_byte_values_read_big_endian():
    """RND-17: the algorithm, written out here independently of the code under test."""
    import hashlib

    from app.rounds.draw import draw_seed

    expected = int.from_bytes(
        hashlib.sha256(bytes.fromhex(_SEED) + bytes.fromhex(_BLOCK) + bytes.fromhex(_LIST_HASH)).digest(), "big"
    )
    assert draw_seed(_SEED, _BLOCK, _LIST_HASH) == expected


def test_draw_seed_depends_on_all_three_inputs():
    from app.rounds.draw import draw_seed

    base = draw_seed(_SEED, _BLOCK, _LIST_HASH)
    assert draw_seed("12" * 32, _BLOCK, _LIST_HASH) != base  # without the secret nobody can predict it
    assert draw_seed(_SEED, "00" * 28 + "deadbeee", _LIST_HASH) != base
    assert draw_seed(_SEED, _BLOCK, "23" * 32) != base  # nor can the list change after the block


def test_draw_winner_is_deterministic_and_within_range():
    from app.rounds.draw import draw_index, draw_seed

    participants = ["addrA", "addrB", "addrC"]
    winner = draw_winner(participants, _SEED, _BLOCK, _LIST_HASH)
    assert winner == participants[draw_seed(_SEED, _BLOCK, _LIST_HASH) % 3]
    assert winner == draw_winner(participants, _SEED, _BLOCK, _LIST_HASH)
    assert 0 <= draw_index(draw_seed(_SEED, _BLOCK, _LIST_HASH), 3) < 3


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


def test_draw_winner_raises_on_empty_participants():
    with pytest.raises(ValueError):
        draw_winner([], _SEED, _BLOCK, _LIST_HASH)


def test_equal_odds_every_position_can_win():
    """RND-17: one position per participant, whatever the amount — the index is uniform
    over 0..n-1 (checked over many seeds, not exactly)."""
    from collections import Counter

    from app.rounds.draw import draw_index, draw_seed

    wins = Counter(draw_index(draw_seed(f"{i:064x}", _BLOCK, _LIST_HASH), 4) for i in range(2000))
    assert set(wins) == {0, 1, 2, 3}
    assert min(wins.values()) > 400  # about 500 each


def test_server_seed_commitment_is_sha256_of_the_32_bytes():
    import hashlib

    from app.rounds.draw import server_seed_commitment

    assert server_seed_commitment(_SEED) == hashlib.sha256(bytes.fromhex(_SEED)).hexdigest()


def test_new_server_seeds_are_32_random_bytes_in_hex():
    from app.rounds.draw import new_server_seed

    seeds = {new_server_seed() for _ in range(20)}
    assert len(seeds) == 20
    assert all(len(seed) == 64 and bytes.fromhex(seed) for seed in seeds)


def test_participants_hash_encodes_one_txid_vout_address_line_per_participant():
    """RND-14: sha256 of `txid:vout:address\n` lines in draw_position order, UTF-8."""
    import hashlib

    from app.rounds.draw import participants_hash

    rows = [("aa" * 32, 0, "plm1qfirst"), ("bb" * 32, 1, "plm1qsecond")]
    text = f"{'aa' * 32}:0:plm1qfirst\n{'bb' * 32}:1:plm1qsecond\n"
    assert participants_hash(rows) == hashlib.sha256(text.encode("utf-8")).hexdigest()
    assert participants_hash(list(reversed(rows))) != participants_hash(rows)  # the order is part of it


# --- B-74 (ELC-11): the claimed target must not be easier than the powLimit ------------


def test_pow_limit_is_the_mainnet_constant():
    """B-74, ELC-11: PLM mainnet's `consensus.powLimit`, 00000000ffff…ffff."""
    from app.rounds import draw

    assert draw.MAINNET_POW_LIMIT == int("00000000" + "ff" * 28, 16)
    assert draw.MAINNET_POW_LIMIT == (1 << 224) - 1


def test_a_header_below_the_pow_limit_is_rejected_even_if_it_meets_its_own_target(monkeypatch):
    """B-74, ELC-11: a header whose hash satisfies the target *it declares* (bits =
    0x207fffff, a target of about 2^255) used to pass — and whoever fabricates a header
    picks its bits, so a random header passed with probability 1/2. With the mainnet
    powLimit in force it is rejected however its hash falls."""
    import struct

    from app.rounds import draw

    def build(nonce: int) -> str:
        return (
            struct.pack("<I", 1) + bytes(32) + bytes(32) + struct.pack("<II", 0, 0x207FFFFF) + struct.pack("<I", nonce)
        ).hex()

    # Mined at the trivial target, so it satisfies its own claim ...
    header = next(h for h in map(build, range(1000)) if header_meets_its_own_target(h))  # regtest limit (conftest)
    # ... and is nonetheless refused once the real limit is back.
    monkeypatch.setattr(draw, "POW_LIMIT", draw.MAINNET_POW_LIMIT)
    assert header_meets_its_own_target(header) is False


def test_a_real_mainnet_header_passes_with_the_mainnet_pow_limit(monkeypatch):
    from app.rounds import draw

    monkeypatch.setattr(draw, "POW_LIMIT", draw.MAINNET_POW_LIMIT)
    assert header_meets_its_own_target(_REAL_HEADER_HEX) is True