"""Do not collapse a directed dispositor cycle into an arbitrary terminal."""
import ast
from pathlib import Path


def resolver():
    # Isolate the pure function without importing the large CLI and adapters.
    source = Path(__file__).parents[1] / 'scripts/jyotish_engine.py'
    tree = ast.parse(source.read_text())
    node = next(n for n in tree.body if isinstance(n, ast.FunctionDef)
                and n.name == 'final_dispositor_from_chain')
    namespace = {}
    exec(compile(ast.Module(body=[node], type_ignores=[]), str(source), 'exec'), namespace)
    return namespace[node.name]


def chain(*names):
    return [{'planet':a,'dispositor':b} for a,b in zip(names,names[1:])]


def test_cycle_rotation_and_leading_planet():
    f = resolver()
    expected = 'Cycle: Jupiter -> Mercury -> Jupiter'
    assert f(chain('Mercury','Jupiter','Mercury')) == expected
    assert f(chain('Jupiter','Mercury','Jupiter')) == expected
    assert f(chain('Venus','Jupiter','Mercury','Jupiter')) == expected


def test_terminal_and_incomplete_are_distinct():
    f = resolver()
    assert f(chain('Sun','Mars','Saturn','Saturn')) == 'Saturn'
    assert f(chain('Sun','Mars')) is None
    assert f([]) is None
    assert f(chain('Sun','Mars') + chain('Venus','Venus')) is None


def test_three_body_cycle_preserves_direction():
    assert resolver()(chain('Sun','Mars','Moon','Sun')) == 'Cycle: Mars -> Moon -> Sun -> Mars'