//! `Gt` — a stateless `f64 × f64 -> bool` comparator: `out = (a > b)`, STRICT
//! greater-than.
//!
//! The first **bool-emitting f64 comparator** in `aura-std` (the `f64` cousin of
//! `EqConst`'s `i64 -> bool` gate). Its purpose in the session-breakout strategy
//! is `breakout = close15 > prevHigh15`: a fresh 15m close strictly above the
//! prior bar's high. **Strict `>` is load-bearing** — a close exactly *equal* to
//! the previous high is **not** a breakout, so `a == b` emits `false`.
//!
//! The **operator is topology** — `Gt` is a concrete node type, not an op
//! selected by a swept param. The relational siblings (`Lt`, `Ge`, `Le`, `Eq`)
//! would each be their own node type, never a param. Two `f64` inputs
//! (`Firing::Any`), one `bool` output, allocation-free on the hot path (the
//! single-cell output buffer is sized once at construction, C7).

use aura_core::{Cell, Ctx, FieldSpec, Firing, Node, NodeSchema, PortSpec, PrimitiveBuilder, ScalarKind};

/// Stateless `f64 × f64 -> bool` strict comparator: emits `a > b` each cycle.
/// Emits `None` until **both** inputs have a value (warm-up gate, C8).
pub struct Gt {
    out: [Cell; 1],
}

impl Gt {
    /// Build a `Gt` node.
    pub fn new() -> Self {
        Self { out: [Cell::from_bool(false)] }
    }

    /// The param-generic recipe for a blueprint primitive: paramless, builds
    /// through `Gt::new`.
    pub fn builder() -> PrimitiveBuilder {
        PrimitiveBuilder::new(
            "Gt",
            NodeSchema {
                inputs: vec![
                    PortSpec { kind: ScalarKind::F64, firing: Firing::Any, name: "a".into() },
                    PortSpec { kind: ScalarKind::F64, firing: Firing::Any, name: "b".into() },
                ],
                output: vec![FieldSpec { name: "value".into(), kind: ScalarKind::Bool }],
                params: vec![],
            },
            |_| Box::new(Gt::new()),
        )
    }
}

impl Default for Gt {
    fn default() -> Self {
        Self::new()
    }
}

impl Node for Gt {
    fn lookbacks(&self) -> Vec<usize> {
        vec![1, 1]
    }

    fn eval(&mut self, ctx: Ctx<'_>) -> Option<&[Cell]> {
        let a = ctx.f64_in(0);
        let b = ctx.f64_in(1);
        if a.is_empty() || b.is_empty() {
            return None; // not yet warmed up — both legs required (C8 filter)
        }
        self.out[0] = Cell::from_bool(a[0] > b[0]); // STRICT: a == b -> false
        Some(&self.out)
    }

    fn label(&self) -> String {
        "Gt".to_string()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use aura_core::{AnyColumn, Scalar, Timestamp};

    #[test]
    fn gt_is_strict_greater_than_once_both_inputs_present() {
        // The core property: out == (a > b), STRICT. Three regions are covered,
        // and the a==b case is the load-bearing one — a close exactly equal to
        // the previous high is NOT a breakout, so equality emits `false`.
        let mut node = Gt::new();
        let mut inputs = vec![
            AnyColumn::with_capacity(ScalarKind::F64, 1),
            AnyColumn::with_capacity(ScalarKind::F64, 1),
        ];

        let a_feed = [1.0_f64, 5.0, 3.0];
        let b_feed = [2.0_f64, 2.0, 3.0];
        //            a<b      a>b   a==b
        let expect = [Some(false), Some(true), Some(false)];

        for ((av, bv), want) in a_feed.iter().zip(b_feed.iter()).zip(expect) {
            inputs[0].push(Scalar::f64(*av)).unwrap();
            inputs[1].push(Scalar::f64(*bv)).unwrap();
            let got = node.eval(Ctx::new(&inputs, Timestamp(0)));
            assert_eq!(got, Some([Cell::from_bool(want.unwrap())].as_slice()));
        }
    }

    #[test]
    fn gt_is_none_until_both_inputs_present() {
        // Both-inputs warm-up gate (C8), like `Sub`: only one leg present -> None.
        let mut node = Gt::new();
        let mut inputs = vec![
            AnyColumn::with_capacity(ScalarKind::F64, 1),
            AnyColumn::with_capacity(ScalarKind::F64, 1),
        ];

        // only input 0 present -> None
        inputs[0].push(Scalar::f64(10.0)).unwrap();
        assert_eq!(node.eval(Ctx::new(&inputs, Timestamp(0))), None);

        // both present -> a strict-gt bool (10.0 > 4.0 == true)
        inputs[1].push(Scalar::f64(4.0)).unwrap();
        assert_eq!(node.eval(Ctx::new(&inputs, Timestamp(0))), Some([Cell::from_bool(true)].as_slice()));
    }

    #[test]
    fn input_slots_are_named_a_b() {
        let g = Gt::builder();
        let names: Vec<&str> = g.schema().inputs.iter().map(|p| p.name.as_str()).collect();
        assert_eq!(names, ["a", "b"]);
    }
}
