//! Configuring a competitor before anything is observed about them.
//!
//! The configuration a competitor needs is usually a property of the domain —
//! "every layout is static" — not of whichever event happens to mention them
//! first. Stating it per-event meant every ingestion path had to remember it,
//! and two of the four paths could not state it at all.

use smallvec::smallvec;
use trueskill_tt::{
    ConstantDrift, ConvergenceOptions, Event, Gaussian, History, InferenceError, Member, Outcome,
    Team,
};

type H = History<i64, ConstantDrift, trueskill_tt::NullObserver, &'static str>;

const PINNED: Gaussian = Gaussian::from_ms(2.0, 0.5);

fn history() -> H {
    History::builder()
        .mu(0.0)
        .sigma(6.0)
        .beta(1.0)
        .score_sigma(2.0)
        .drift(ConstantDrift(0.5))
        .convergence(ConvergenceOptions {
            max_iter: 20_000,
            epsilon: 1e-13,
            alpha: 1.0,
        })
        .build()
}

fn duel(
    a: &'static str,
    b: &'static str,
    t: i64,
    m: Option<Member<&'static str>>,
) -> Event<i64, &'static str> {
    Event {
        time: t,
        teams: smallvec![
            Team::with_members([Member::new(a)]),
            Team::with_members([m.unwrap_or_else(|| Member::new(b))]),
        ],
        outcome: Outcome::scores([5.0, 2.0]),
    }
}

fn skills(h: &H) -> Vec<(&'static str, Gaussian)> {
    ["player", "layout"]
        .into_iter()
        .map(|k| (k, h.current_skill(&k).unwrap()))
        .collect()
}

/// The headline contract.
#[test]
fn registering_matches_configuring_on_the_first_event() {
    let configured = {
        let mut h = history();
        h.add_events(vec![
            duel(
                "player",
                "layout",
                1,
                Some(
                    Member::new("layout")
                        .with_drift_scale(0.0)
                        .with_prior(PINNED),
                ),
            ),
            duel("player", "layout", 2, None),
        ])
        .unwrap();
        let _ = h.converge().unwrap();
        h
    };

    let registered = {
        let mut h = history();
        h.register(
            Member::new("layout")
                .with_drift_scale(0.0)
                .with_prior(PINNED),
        )
        .unwrap();
        h.add_events(vec![
            duel("player", "layout", 1, None),
            duel("player", "layout", 2, None),
        ])
        .unwrap();
        let _ = h.converge().unwrap();
        h
    };

    for ((k, a), (_, b)) in skills(&configured).into_iter().zip(skills(&registered)) {
        assert_eq!(a.pi(), b.pi(), "{k} pi");
        assert_eq!(a.tau(), b.tau(), "{k} tau");
    }
}

/// The case `EventBuilder` and the typed path cannot reach: a competitor whose
/// first appearance arrives through the two-argument convenience route.
#[test]
fn registration_reaches_a_competitor_first_seen_through_record_winner() {
    let mut h = history();
    h.register(
        Member::new("layout")
            .with_drift_scale(0.0)
            .with_prior(PINNED),
    )
    .unwrap();
    h.record_winner(&"player", &"layout", 1).unwrap();
    h.record_winner(&"player", &"layout", 2).unwrap();
    let _ = h.converge().unwrap();

    let rating = h.rating(&"layout").unwrap();
    assert_eq!(rating.drift_scale(), 0.0);
    assert_eq!(rating.prior().mu(), PINNED.mu());

    // Pinned means pinned: no drift across the two slices.
    let curve = h.learning_curve(&"layout");
    assert!(curve.len() >= 2);
    let widest = curve
        .iter()
        .map(|(_, g)| g.sigma())
        .fold(f64::MIN, f64::max);
    let narrowest = curve
        .iter()
        .map(|(_, g)| g.sigma())
        .fold(f64::MAX, f64::min);
    assert!(
        (widest - narrowest) / widest < 1e-9,
        "{narrowest} .. {widest}"
    );
}

#[test]
fn registering_a_known_competitor_is_an_error() {
    let mut h = history();
    h.record_winner(&"player", &"layout", 1).unwrap();
    let err = h.register(Member::new("layout")).unwrap_err();
    assert!(
        matches!(err, InferenceError::AlreadyRegistered { .. }),
        "{err:?}"
    );
}

#[test]
fn registering_twice_is_an_error() {
    let mut h = history();
    h.register(Member::new("layout").with_drift_scale(0.0))
        .unwrap();
    let err = h
        .register(Member::new("layout").with_drift_scale(1.0))
        .unwrap_err();
    assert!(
        matches!(err, InferenceError::AlreadyRegistered { .. }),
        "{err:?}"
    );
    // The first registration stands.
    assert_eq!(h.rating(&"layout").unwrap().drift_scale(), 0.0);
}

/// `weight` is per-event and meaningless here, so it is rejected rather than
/// dropped — dropping it silently is the defect class this whole area keeps
/// producing.
#[test]
fn a_weight_on_a_registration_is_rejected() {
    let mut h = history();
    let err = h
        .register(Member::new("layout").with_weight(0.5))
        .unwrap_err();
    assert!(
        matches!(err, InferenceError::InvalidParameter { name: "weight", .. }),
        "{err:?}"
    );
}

#[test]
fn an_invalid_drift_scale_on_a_registration_is_rejected() {
    for bad in [-1.0, f64::NAN, f64::INFINITY] {
        let mut h = history();
        let err = h
            .register(Member::new("layout").with_drift_scale(bad))
            .unwrap_err();
        assert!(
            matches!(
                err,
                InferenceError::InvalidParameter {
                    name: "drift_scale",
                    ..
                }
            ),
            "{bad}: {err:?}"
        );
    }
}

/// Registration makes the fit independent of the order events arrive in,
/// which is what the per-event shape could not guarantee.
#[test]
fn registration_makes_the_fit_order_independent() {
    let build = |reversed: bool| {
        let mut h = history();
        h.register(
            Member::new("layout")
                .with_drift_scale(0.0)
                .with_prior(PINNED),
        )
        .unwrap();
        let mut events = vec![
            duel("player", "layout", 1, None),
            duel("player", "layout", 2, None),
            duel("player", "layout", 3, None),
        ];
        if reversed {
            events.reverse();
        }
        h.add_events(events).unwrap();
        let _ = h.converge().unwrap();
        h
    };

    let forward = build(false);
    let backward = build(true);
    for ((k, a), (_, b)) in skills(&forward).into_iter().zip(skills(&backward)) {
        assert_eq!(a.pi(), b.pi(), "{k} pi");
        assert_eq!(a.tau(), b.tau(), "{k} tau");
    }
}

/// `rating` is the read-back that made a configuration mistake detectable from
/// outside the crate at all. Every other accessor reports what inference
/// inferred; this reports what it was told.
#[test]
fn rating_reads_back_what_was_stored() {
    let mut h = history();
    assert!(h.rating(&"nobody").is_none());

    h.register(
        Member::new("layout")
            .with_drift_scale(0.25)
            .with_prior(PINNED),
    )
    .unwrap();
    let r = h.rating(&"layout").unwrap();
    assert_eq!(r.drift_scale(), 0.25);
    assert_eq!(r.prior().pi(), PINNED.pi());
    assert_eq!(r.prior().tau(), PINNED.tau());

    // A competitor created by an event reports the history defaults.
    h.record_winner(&"player", &"layout", 1).unwrap();
    assert_eq!(h.rating(&"player").unwrap().drift_scale(), 1.0);
}

/// The decision this issue turned on: two different values for one competitor
/// are an error whether they arrive in one batch or two.
///
/// Last-write-wins across batches cut against the invariant
/// `tests/ingestion_equivalence.rs` protects — the same contradictory events
/// errored when batched and succeeded, order-dependently, one at a time.
mod conflicting_configuration {
    use super::*;

    fn seed(scale: f64) -> Event<i64, &'static str> {
        duel(
            "player",
            "layout",
            1,
            Some(Member::new("layout").with_drift_scale(scale)),
        )
    }

    #[test]
    fn within_one_batch_is_an_error() {
        let mut h = history();
        let err = h.add_events(vec![seed(0.0), seed(1.0)]).unwrap_err();
        assert!(
            matches!(
                err,
                InferenceError::ConflictingCompetitorConfig {
                    field: "drift_scale",
                    ..
                }
            ),
            "{err:?}"
        );
    }

    #[test]
    fn across_two_batches_is_also_an_error() {
        let mut h = history();
        h.add_events(vec![seed(0.0)]).unwrap();
        let err = h.add_events(vec![seed(1.0)]).unwrap_err();
        assert!(
            matches!(
                err,
                InferenceError::ConflictingCompetitorConfig {
                    field: "drift_scale",
                    ..
                }
            ),
            "{err:?}"
        );
        // Rejected before anything mutates: the first declaration stands.
        assert_eq!(h.rating(&"layout").unwrap().drift_scale(), 0.0);
    }

    /// Repeating the *same* value stays inert, which is the expected shape
    /// when the configuration is a property of the domain.
    #[test]
    fn repeating_the_same_value_is_inert() {
        let mut h = history();
        h.add_events(vec![seed(0.0)]).unwrap();
        h.add_events(vec![seed(0.0)]).unwrap();
        assert_eq!(h.rating(&"layout").unwrap().drift_scale(), 0.0);
    }

    /// A registration and a later event that agree are fine; one that
    /// disagrees is the same error.
    #[test]
    fn a_registration_conflicts_with_a_later_event() {
        let mut h = history();
        h.register(Member::new("layout").with_drift_scale(0.0))
            .unwrap();
        h.add_events(vec![seed(0.0)]).unwrap();

        let mut h2 = history();
        h2.register(Member::new("layout").with_drift_scale(0.0))
            .unwrap();
        let err = h2.add_events(vec![seed(1.0)]).unwrap_err();
        assert!(
            matches!(err, InferenceError::ConflictingCompetitorConfig { .. }),
            "{err:?}"
        );
    }
}