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//! Absolute Breadth Index — the magnitude of net advancing-minus-declining issues.
use crate::cross_section::CrossSection;
use crate::traits::Indicator;
/// Absolute Breadth Index (ABI) — the absolute value of net advancing issues,
/// `|advancers - decliners|`.
///
/// The ABI ignores the *direction* of breadth and measures only its *magnitude*:
/// a high reading means the universe moved decisively one way or the other (high
/// internal activity / volatility), while a low reading means advances and
/// declines were nearly balanced (a quiet, directionless market). It is sometimes
/// called a "market thermometer" because elevated readings often cluster around
/// turning points.
///
/// `Input = CrossSection`, `Output = f64`, `warmup_period == 1`.
///
/// # Example
///
/// ```
/// use wickra_core::{AbsoluteBreadthIndex, CrossSection, Indicator, Member};
///
/// let mut abi = AbsoluteBreadthIndex::new();
/// // 2 advancers, 5 decliners -> |2 - 5| = 3.
/// let tick = CrossSection::new(
/// vec![
/// Member::new(1.0, 10.0, false, false),
/// Member::new(1.0, 10.0, false, false),
/// Member::new(-1.0, 10.0, false, false),
/// Member::new(-1.0, 10.0, false, false),
/// Member::new(-1.0, 10.0, false, false),
/// Member::new(-1.0, 10.0, false, false),
/// Member::new(-1.0, 10.0, false, false),
/// ],
/// 0,
/// )
/// .unwrap();
/// assert_eq!(abi.update(tick), Some(3.0));
/// ```
#[derive(Debug, Clone, Default)]
pub struct AbsoluteBreadthIndex {
has_emitted: bool,
}
impl AbsoluteBreadthIndex {
/// Construct a new Absolute Breadth Index indicator.
#[must_use]
pub const fn new() -> Self {
Self { has_emitted: false }
}
}
impl Indicator for AbsoluteBreadthIndex {
type Input = CrossSection;
type Output = f64;
fn update(&mut self, section: CrossSection) -> Option<f64> {
let net = section.advancers() as f64 - section.decliners() as f64;
self.has_emitted = true;
Some(net.abs())
}
fn reset(&mut self) {
self.has_emitted = false;
}
fn warmup_period(&self) -> usize {
1
}
fn is_ready(&self) -> bool {
self.has_emitted
}
fn name(&self) -> &'static str {
"AbsoluteBreadthIndex"
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::cross_section::Member;
use crate::traits::BatchExt;
fn section(up: usize, down: usize) -> CrossSection {
let mut members = Vec::new();
for _ in 0..up {
members.push(Member::new(1.0, 10.0, false, false));
}
for _ in 0..down {
members.push(Member::new(-1.0, 10.0, false, false));
}
members.push(Member::new(0.0, 10.0, false, false));
CrossSection::new(members, 0).unwrap()
}
#[test]
fn accessors_and_metadata() {
let abi = AbsoluteBreadthIndex::new();
assert_eq!(abi.name(), "AbsoluteBreadthIndex");
assert_eq!(abi.warmup_period(), 1);
assert!(!abi.is_ready());
}
#[test]
fn magnitude_ignores_direction() {
let mut abi = AbsoluteBreadthIndex::new();
assert_eq!(abi.update(section(2, 5)), Some(3.0));
// Same magnitude with the direction reversed.
let mut abi2 = AbsoluteBreadthIndex::new();
assert_eq!(abi2.update(section(5, 2)), Some(3.0));
}
#[test]
fn balanced_universe_yields_zero() {
let mut abi = AbsoluteBreadthIndex::new();
assert_eq!(abi.update(section(3, 3)), Some(0.0));
assert!(abi.is_ready());
}
#[test]
fn reset_clears_state() {
let mut abi = AbsoluteBreadthIndex::new();
abi.update(section(2, 5));
assert!(abi.is_ready());
abi.reset();
assert!(!abi.is_ready());
}
#[test]
fn batch_equals_streaming() {
let sections = vec![section(2, 5), section(5, 2), section(3, 3)];
let mut a = AbsoluteBreadthIndex::new();
let mut b = AbsoluteBreadthIndex::new();
assert_eq!(
a.batch(§ions),
sections
.iter()
.map(|s| b.update(s.clone()))
.collect::<Vec<_>>()
);
}
}