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"


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)


# --- 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