//! Catchment rain series (`src/ml/rain.py`: `catchment_mean`).

use chrono::NaiveDateTime;
use std::collections::BTreeMap;

/// Hourly catchment-average precipitation (mm); NaN = no value.
pub type RainSeries = BTreeMap<NaiveDateTime, f64>;

/// pandas `mean(axis=1)` over the catchment points: the points that have a
/// value, summed in column order, divided by their count.
pub fn catchment_mean(points: &[Option<f64>]) -> Option<f64> {
    let mut sum = 0.0;
    let mut n = 0usize;
    for v in points.iter().flatten() {
        sum += *v;
        n += 1;
    }
    (n > 0).then(|| sum / n as f64)
}

/// The series on the given hours (`Series.reindex`), NaN where absent.
pub fn reindex(rain: &RainSeries, times: &[NaiveDateTime]) -> Vec<f64> {
    times
        .iter()
        .map(|t| rain.get(t).copied().unwrap_or(f64::NAN))
        .collect()
}