use super::funejson::Value;
use super::math_round_float::round_float;

/// Population or sample standard deviation, two-pass.
///
/// The one-pass "mean of squares minus square of mean" shortcut cancels
/// catastrophically on large, close values; two passes do not.
///
/// # Panics
/// Panics on a non-finite value, an unknown kind, decimals outside 0..=12, an
/// empty list, or a sample of fewer than two values.
pub fn standard_deviation(values: &[f64], kind: &str, decimals: i64) -> f64 {
    for v in values {
        if !v.is_finite() {
            panic!("values must be finite numbers, received {}", v);
        }
    }
    if kind != "population" && kind != "sample" {
        panic!("unknown standard deviation kind \"{}\"", kind);
    }
    // Checked up front as well as in round_float (same wording), so a bad
    // decimals is reported before an empty list, as in 1.x.
    if !(0..=12).contains(&decimals) {
        panic!("decimals must be a whole number from 0 to 12, received {}", decimals);
    }
    let n = values.len();
    if n == 0 {
        panic!("values must not be empty");
    }
    if kind == "sample" && n < 2 {
        panic!("sample standard deviation needs at least 2 values");
    }

    let mut sum = 0.0;
    for v in values {
        sum += *v;
    }
    let mean = sum / n as f64;
    let mut squares = 0.0;
    for v in values {
        let d = *v - mean;
        squares += d * d;
    }
    let divisor = if kind == "sample" { n - 1 } else { n } as f64;
    // math.round-float rounds on the exact value of the double: 2.675 gives 2.67.
    round_float((squares / divisor).sqrt(), decimals)
}

pub fn fune_vector(args: &[Value]) -> Value {
    // Refuse what the typed signature cannot hold, with the wording TypeScript
    // and Python use, rather than let the conversion below quietly change it.
    for v in args[0].as_arr() {
        if !matches!(v, Value::Int(_) | Value::Float(_)) {
            panic!("values must be finite numbers, received {:?}", v);
        }
    }
    let values: Vec<f64> = args[0].as_arr().iter().map(|v| v.as_f64()).collect();
    Value::Float(standard_deviation(&values, args[1].as_str(), args[2].as_i64()))
}