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//! Williams Accumulation/Distribution.
use crate::ohlcv::Candle;
use crate::traits::Indicator;
/// Larry Williams' Accumulation/Distribution — a cumulative volume-less price
/// flow that classifies each bar as accumulation or distribution based on its
/// close relative to the previous close, then sums the directional component.
///
/// Williams' definition (1972) uses a *true* high/low that includes the prior
/// close as an anchor — the same idea that motivates true range:
///
/// ```text
/// TR_h_t = max(close_{t−1}, high_t)
/// TR_l_t = min(close_{t−1}, low_t)
/// AD_t = AD_{t−1} + (close_t − TR_l_t) if close_t > close_{t−1} (accumulation)
/// AD_t = AD_{t−1} + (close_t − TR_h_t) if close_t < close_{t−1} (distribution)
/// AD_t = AD_{t−1} if close_t == close_{t−1} (no change)
/// ```
///
/// Unlike Chaikin's Accumulation/Distribution Line, the Williams A/D ignores
/// volume entirely — Williams argued that the relative position of the close
/// already encodes the day's "true" buying or selling pressure. The series is
/// unbounded and used primarily for divergence analysis. The first candle only
/// seeds the previous close; the first emission lands at bar 2.
///
/// # Example
///
/// ```
/// use wickra_core::{Candle, Indicator, AdOscillator};
///
/// let mut indicator = AdOscillator::new();
/// let mut last = None;
/// for i in 0..80 {
/// let base = 100.0 + f64::from(i);
/// let candle =
/// Candle::new(base, base + 2.0, base - 2.0, base + 1.0, 10.0, i64::from(i)).unwrap();
/// last = indicator.update(candle);
/// }
/// assert!(last.is_some());
/// ```
#[derive(Debug, Clone, Default)]
pub struct AdOscillator {
prev_close: Option<f64>,
total: f64,
has_emitted: bool,
}
impl AdOscillator {
/// Construct a new Williams A/D starting at zero.
pub const fn new() -> Self {
Self {
prev_close: None,
total: 0.0,
has_emitted: false,
}
}
/// Current cumulative value if at least one emission has happened.
pub const fn value(&self) -> Option<f64> {
if self.has_emitted {
Some(self.total)
} else {
None
}
}
}
impl Indicator for AdOscillator {
type Input = Candle;
type Output = f64;
fn update(&mut self, candle: Candle) -> Option<f64> {
let Some(prev) = self.prev_close else {
// The first bar only establishes the previous close anchor.
self.prev_close = Some(candle.close);
return None;
};
let delta = if candle.close > prev {
// Accumulation: distance from the true low.
let tr_l = prev.min(candle.low);
candle.close - tr_l
} else if candle.close < prev {
// Distribution: distance from the true high (negative).
let tr_h = prev.max(candle.high);
candle.close - tr_h
} else {
// Unchanged close contributes nothing.
0.0
};
self.total += delta;
self.prev_close = Some(candle.close);
self.has_emitted = true;
Some(self.total)
}
fn reset(&mut self) {
self.prev_close = None;
self.total = 0.0;
self.has_emitted = false;
}
fn warmup_period(&self) -> usize {
// One seed bar; the second bar is the first emission.
2
}
fn is_ready(&self) -> bool {
self.has_emitted
}
fn name(&self) -> &'static str {
"WilliamsAD"
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::traits::BatchExt;
use approx::assert_relative_eq;
fn c(open: f64, high: f64, low: f64, close: f64, ts: i64) -> Candle {
Candle::new(open, high, low, close, 100.0, ts).unwrap()
}
#[test]
fn accessors_and_metadata() {
let ad = AdOscillator::new();
assert_eq!(ad.name(), "WilliamsAD");
assert_eq!(ad.warmup_period(), 2);
assert_eq!(ad.value(), None);
}
#[test]
fn value_returns_total_after_first_emission() {
let mut ad = AdOscillator::new();
ad.update(c(10.0, 11.0, 9.0, 10.0, 0));
let v = ad.update(c(11.0, 13.0, 8.0, 12.0, 1)).unwrap();
assert_relative_eq!(ad.value().unwrap(), v, epsilon = 1e-12);
}
#[test]
fn first_bar_only_seeds() {
let mut ad = AdOscillator::new();
assert_eq!(ad.update(c(10.0, 11.0, 9.0, 10.0, 0)), None);
assert!(!ad.is_ready());
}
#[test]
fn accumulation_adds_distance_from_true_low() {
// prev close = 10, today low = 8, today close = 12 (up day).
// TR_l = min(10, 8) = 8, delta = 12 - 8 = 4. AD = 0 + 4 = 4.
let mut ad = AdOscillator::new();
ad.update(c(10.0, 11.0, 9.0, 10.0, 0));
let v = ad.update(c(11.0, 13.0, 8.0, 12.0, 1)).unwrap();
assert_relative_eq!(v, 4.0, epsilon = 1e-12);
}
#[test]
fn distribution_adds_distance_from_true_high() {
// prev close = 10, today high = 11, today close = 7 (down day).
// TR_h = max(10, 11) = 11, delta = 7 - 11 = -4. AD = -4.
let mut ad = AdOscillator::new();
ad.update(c(10.0, 11.0, 9.0, 10.0, 0));
let v = ad.update(c(10.0, 11.0, 7.0, 7.0, 1)).unwrap();
assert_relative_eq!(v, -4.0, epsilon = 1e-12);
}
#[test]
fn unchanged_close_keeps_total() {
// close equals prev close -> no contribution.
let mut ad = AdOscillator::new();
ad.update(c(10.0, 11.0, 9.0, 10.0, 0));
let v = ad.update(c(10.0, 12.0, 8.0, 10.0, 1)).unwrap();
assert_relative_eq!(v, 0.0, epsilon = 1e-12);
}
#[test]
fn constant_series_yields_zero() {
// Every close equals the previous -> AD stays at zero forever.
let candles: Vec<Candle> = (0..40).map(|i| c(10.0, 11.0, 9.0, 10.0, i)).collect();
let mut ad = AdOscillator::new();
for v in ad.batch(&candles).into_iter().flatten() {
assert_relative_eq!(v, 0.0, epsilon = 1e-12);
}
}
#[test]
fn batch_equals_streaming() {
let candles: Vec<Candle> = (0..80i64)
.map(|i| {
let f = i as f64;
let mid = 100.0 + (f * 0.3).sin() * 5.0;
c(mid, mid + 2.0, mid - 2.0, mid + 0.5, i)
})
.collect();
let mut a = AdOscillator::new();
let mut b = AdOscillator::new();
assert_eq!(
a.batch(&candles),
candles.iter().map(|x| b.update(*x)).collect::<Vec<_>>()
);
}
#[test]
fn reset_clears_state() {
let mut ad = AdOscillator::new();
ad.batch(&[
c(10.0, 11.0, 9.0, 10.0, 0),
c(10.0, 12.0, 9.0, 11.0, 1),
c(11.0, 13.0, 10.0, 12.0, 2),
]);
assert!(ad.is_ready());
ad.reset();
assert!(!ad.is_ready());
assert_eq!(ad.value(), None);
assert_eq!(ad.update(c(10.0, 11.0, 9.0, 10.0, 3)), None);
}
}