use query_engine::chase::materialize;
use query_engine::chase::rule::RuleBuilder;
use query_engine::frontend::Session;
use query_engine::{Atom, Instance, Term, chase};

#[test]
fn existential_trigger_stays_inactive_when_head_is_already_satisfied() {
    let instance: Instance = vec![
        Atom::new("Person", vec![Term::constant("alice")]),
        Atom::new(
            "HasSSN",
            vec![Term::constant("alice"), Term::constant("known")],
        ),
    ]
    .into_iter()
    .collect();

    let rule = RuleBuilder::new()
        .when("Person", vec![Term::var("X")])
        .then("HasSSN", vec![Term::var("X"), Term::var("Y")])
        .build();

    let result = chase(instance, &[rule]);

    assert!(result.terminated);
    assert_eq!(result.steps, 0);
    assert_eq!(result.instance.facts_for_predicate("HasSSN").len(), 1);
}

#[test]
fn fresh_nulls_skip_existing_input_null_ids() {
    let instance: Instance = vec![
        Atom::new("Seed", vec![Term::null(0)]),
        Atom::new("Person", vec![Term::constant("alice")]),
    ]
    .into_iter()
    .collect();

    let rule = RuleBuilder::new()
        .when("Person", vec![Term::var("X")])
        .then("HasSSN", vec![Term::var("X"), Term::var("Y")])
        .build();

    let result = chase(instance, &[rule]);

    assert!(result.terminated);
    assert_eq!(result.instance.facts_for_predicate("HasSSN").len(), 1);

    let fact = result.instance.facts_for_predicate("HasSSN")[0];
    assert!(matches!(fact.terms[1], Term::Null(id) if id > 0));
}

#[test]
fn frontend_materialization_respects_existing_existential_witnesses() {
    let mut session = Session::new();
    let output = session
        .execute_script(
            "fact Person(alice).\n\
             fact HasSSN(alice, known).\n\
             rule Person(?X) -> HasSSN(?X, ?Y).\n\
             run.\n\
             query HasSSN(alice, ?Y)?",
        )
        .unwrap();

    assert!(output.contains("1 row(s)"));
    assert!(output.contains("?Y = known"));
    assert!(!output.contains("⊥"));
}

#[test]
fn frontend_materialization_starts_after_existing_null_ids() {
    let instance: Instance = vec![
        Atom::new("Seed", vec![Term::null(7)]),
        Atom::new("Employee", vec![Term::constant("alice")]),
    ]
    .into_iter()
    .collect();

    let rule = RuleBuilder::new()
        .when("Employee", vec![Term::var("X")])
        .then("WorksIn", vec![Term::var("X"), Term::var("Dept")])
        .build();

    let state = materialize(instance, &[rule]);

    assert!(state.result.terminated);
    assert_eq!(
        state.result.instance.facts_for_predicate("WorksIn").len(),
        1
    );

    let fact = state.result.instance.facts_for_predicate("WorksIn")[0];
    assert!(matches!(fact.terms[1], Term::Null(id) if id > 7));
}