import pytest
from rdkit import Chem
from src.splicing.engine import splice_molecule

def test_splice_benzene_methyl():
    """
    Test splicing a benzene scaffold (isotope 1) with a methyl fragment.
    Scaffold: c1ccccc1[1*] (Phenyl radical-ish dummy)
    Fragment: C* (Methyl radical-ish dummy)
    Result: Cc1ccccc1 (Toluene)
    """
    scaffold = Chem.MolFromSmiles("c1ccccc1[1*]")
    fragment = Chem.MolFromSmiles("C*")
    
    assert scaffold is not None
    assert fragment is not None
    
    product = splice_molecule(scaffold, fragment, position=1)
    
    # Expected result: Toluene
    expected_smiles = "Cc1ccccc1"
    expected_mol = Chem.MolFromSmiles(expected_smiles)
    expected_canonical = Chem.MolToSmiles(expected_mol, isomericSmiles=True)
    
    product_canonical = Chem.MolToSmiles(product, isomericSmiles=True)
    
    assert product_canonical == expected_canonical

def test_splice_missing_isotope():
    """Test that error is raised if the requested position is not found on scaffold."""
    scaffold = Chem.MolFromSmiles("c1ccccc1[2*]") # Isotope 2
    fragment = Chem.MolFromSmiles("C*")
    
    with pytest.raises(ValueError, match="Scaffold dummy atom with isotope 1 not found"):
        splice_molecule(scaffold, fragment, position=1)

def test_splice_no_fragment_dummy():
    """Test that error is raised if fragment has no dummy atom."""
    scaffold = Chem.MolFromSmiles("c1ccccc1[1*]")
    fragment = Chem.MolFromSmiles("C") # Methane, no dummy
    
    with pytest.raises(ValueError, match="Fragment does not contain a dummy atom"):
        splice_molecule(scaffold, fragment, position=1)

def test_complex_splicing():
    """
    Test splicing with more complex structures.
    Scaffold: Pyridine derivative n1cccc1CC[1*]
    Fragment: Cyclopropane C1CC1*
    Result: n1cccc1CCC1CC1
    """
    scaffold = Chem.MolFromSmiles("n1cccc1CC[1*]")
    fragment = Chem.MolFromSmiles("*C1CC1")
    
    product = splice_molecule(scaffold, fragment, position=1)
    
    expected = Chem.MolFromSmiles("n1cccc1CCC1CC1")
    
    assert Chem.MolToSmiles(product) == Chem.MolToSmiles(expected)

def test_scaffold_with_multiple_different_dummies():
    """
    Test splicing when scaffold has multiple dummies with different isotopes.
    Scaffold: [1*]c1ccccc1[2*]
    Fragment: C*
    Target: Splicing at 1 should leave [2*] intact.
    """
    scaffold = Chem.MolFromSmiles("[1*]c1ccccc1[2*]")
    fragment = Chem.MolFromSmiles("C*")
    
    # Splice at 1
    product = splice_molecule(scaffold, fragment, position=1)
    
    # Expected: Cc1ccccc1[2*]
    expected = Chem.MolFromSmiles("Cc1ccccc1[2*]")
    
    assert Chem.MolToSmiles(product) == Chem.MolToSmiles(expected)