//! `Abs` — one-input f64 absolute value. Turns a signed delta (e.g. the
//! negative-side split of a price change) into a positive magnitude, e.g.
//! RSI-class signals' `loss = Abs(Min(delta, 0))`. Emits `None` until its
//! input has a value.

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

/// One-input f64 absolute value, `value.abs()`. Emits `None` until its input
/// has a value (warm-up filter, C8).
pub struct Abs {
    out: [Cell; 1],
}

impl Abs {
    pub fn new() -> Self {
        Self { out: [Cell::from_f64(0.0)] }
    }

    pub fn builder() -> PrimitiveBuilder {
        PrimitiveBuilder::new(
            "Abs",
            NodeSchema {
                inputs: vec![PortSpec { kind: ScalarKind::F64, firing: Firing::Any, name: "value".into() }],
                output: vec![FieldSpec { name: "value".into(), kind: ScalarKind::F64 }],
                params: vec![],
            },
            |_| Box::new(Abs::new()),
        )
    }
}

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

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

    fn eval(&mut self, ctx: Ctx<'_>) -> Option<&[Cell]> {
        let w = ctx.f64_in(0);
        if w.is_empty() {
            return None;
        }
        self.out[0] = Cell::from_f64(w[0].abs());
        Some(&self.out)
    }

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

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

    #[test]
    fn abs_of_negative_and_positive_is_the_magnitude() {
        let mut a = Abs::new();
        let mut inputs = vec![AnyColumn::with_capacity(ScalarKind::F64, 1)];
        inputs[0].push(Scalar::f64(-3.0)).unwrap();
        assert_eq!(a.eval(Ctx::new(&inputs, Timestamp(0))), Some([Cell::from_f64(3.0)].as_slice()));
        inputs[0].push(Scalar::f64(3.0)).unwrap();
        assert_eq!(a.eval(Ctx::new(&inputs, Timestamp(0))), Some([Cell::from_f64(3.0)].as_slice()));
    }

    #[test]
    fn abs_is_none_until_input_present() {
        let mut a = Abs::new();
        let inputs = vec![AnyColumn::with_capacity(ScalarKind::F64, 1)];
        assert_eq!(a.eval(Ctx::new(&inputs, Timestamp(0))), None);
    }
}
