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//! Flag / Pennant continuation chart pattern.
use crate::indicators::pattern_swing::{SwingTracker, SWING_THRESHOLD};
use crate::ohlcv::Candle;
use crate::traits::Indicator;
/// Maximum size of the consolidation swing relative to the pole for a
/// flag/pennant to qualify — the pullback must retrace less than half the pole.
const MAX_RETRACE_FRACTION: f64 = 0.5;
/// Flag / Pennant — a brief consolidation against a sharp prior move (the
/// "pole"), resolving in the pole's direction.
///
/// Built on confirmed swing pivots (`SWING_THRESHOLD` = 5%); evaluated from the
/// last three pivots `pole_start → pole_end → consolidation`:
///
/// ```text
/// pole = |pole_end − pole_start| (the sharp impulse)
/// pullback = |consolidation − pole_end| (the shallow counter-move)
/// qualifies when pullback < 0.5 · pole
/// bull flag : pole_end is a swing high → +1 (up-pole, continuation up)
/// bear flag : pole_end is a swing low → -1 (down-pole, continuation down)
/// ```
///
/// The detector fires on the bar that confirms the consolidation pivot (the flag
/// is complete; the breakout is expected to follow). Output is `+1.0` / `-1.0` /
/// `0.0`; never `None`.
#[derive(Debug, Clone)]
pub struct FlagPennant {
swing: SwingTracker,
has_emitted: bool,
}
impl FlagPennant {
/// Construct a new Flag / Pennant detector.
pub const fn new() -> Self {
Self {
swing: SwingTracker::new(SWING_THRESHOLD, 3),
has_emitted: false,
}
}
}
impl Default for FlagPennant {
fn default() -> Self {
Self::new()
}
}
impl Indicator for FlagPennant {
type Input = Candle;
type Output = f64;
#[inline]
fn update(&mut self, candle: Candle) -> Option<f64> {
let advanced = self.swing.update(candle);
let pivots = self.swing.pivots();
// Too few pivots to form the shape at all: the indicator cannot
// judge yet, which is what `None` means.
if pivots.len() < 3 {
return None;
}
self.has_emitted = true;
// Armed, but this bar did not close a new pivot, so there is
// nothing new to match against.
if !advanced {
return Some(0.0);
}
let n = pivots.len();
let pole_start = pivots[n - 3];
let pole_end = pivots[n - 2];
let consolidation = pivots[n - 1];
let pole = (pole_end.price - pole_start.price).abs();
let pullback = (consolidation.price - pole_end.price).abs();
if pole > 0.0 && pullback < MAX_RETRACE_FRACTION * pole {
// pole_end a high → up-pole → bull flag; a low → bear flag.
return Some(if pole_end.direction > 0.0 { 1.0 } else { -1.0 });
}
Some(0.0)
}
fn reset(&mut self) {
self.swing.reset();
self.has_emitted = false;
}
#[inline]
fn warmup_period(&self) -> usize {
// Three confirmed pivots; the earliest confirmation of the third is bar 4.
4
}
#[inline]
fn is_ready(&self) -> bool {
self.has_emitted
}
#[inline]
fn name(&self) -> &'static str {
"FlagPennant"
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::indicators::pattern_swing::candles_for_pivots;
use crate::traits::BatchExt;
fn run(pivots: &[f64]) -> Vec<f64> {
let mut indicator = FlagPennant::new();
candles_for_pivots(pivots)
.into_iter()
.filter_map(|c| indicator.update(c))
.collect()
}
#[test]
fn accessors_and_metadata() {
let indicator = FlagPennant::new();
assert_eq!(indicator.name(), "FlagPennant");
assert_eq!(indicator.warmup_period(), 4);
assert!(!indicator.is_ready());
assert!(!FlagPennant::default().is_ready());
}
#[test]
fn bull_flag_is_plus_one() {
// Up-pole 100 → 140 (40), shallow pullback to 130 (10 < 20) → bull flag.
let out = run(&[150.0, 100.0, 140.0, 130.0]);
assert_eq!(*out.last().unwrap(), 1.0);
}
#[test]
fn bear_flag_is_minus_one() {
// Down-pole 140 → 100 (40), shallow pullback to 110 (10 < 20) → bear flag.
let out = run(&[140.0, 100.0, 110.0]);
assert_eq!(*out.last().unwrap(), -1.0);
}
#[test]
fn deep_pullback_is_not_a_flag() {
// Pole 100 → 140 (40) but pullback to 104 (36 > 20) → not a flag.
let out = run(&[150.0, 100.0, 140.0, 104.0]);
assert_eq!(*out.last().unwrap(), 0.0);
}
#[test]
fn reset_clears_state() {
let mut indicator = FlagPennant::new();
for c in candles_for_pivots(&[150.0, 100.0, 140.0]) {
let _ = indicator.update(c);
}
indicator.reset();
assert!(!indicator.is_ready());
let c = Candle::new(99.5, 100.0, 99.5, 99.5, 1.0, 0).unwrap();
assert_eq!(indicator.update(c), None);
}
#[test]
fn batch_equals_streaming() {
let candles = candles_for_pivots(&[150.0, 100.0, 140.0, 130.0]);
let mut a = FlagPennant::new();
let mut b = FlagPennant::new();
assert_eq!(
a.batch(&candles),
candles.iter().map(|x| b.update(*x)).collect::<Vec<_>>()
);
}
}