agri.stocking-rate

Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.

use super::agri_stocking_rate_data::{LivestockUnitCoefficient, LIVESTOCK_UNITS};  ← this capability’s own data, compiled from data/livestock-units.json into the same file by fune build
use super::funejson::Value;  ← the fune runtime: the JSON value the test vectors use; fune build keeps it only where a signature takes one
use super::math_round_div::round_div;  ← from math.round-div ^1.0.0 · built alongside by fune
use super::math_round_float::round_float;  ← from math.round-float ^1.0.0 · built alongside by fune

const MAX_COUNT: i64 = 10_000_000;

/// Livestock units and the stocking rate per hectare.
///
/// Coefficients are held in thousandths of a livestock unit, so a herd's total
/// is an exact integer and only the rate per hectare is rounded. Adding float
/// coefficients drifts: 3 x 0.7 is 2.0999999999999996, which puts 3 yearlings
/// on 12 ha at 0.17 LU/ha instead of 0.18 (0.175 rounded half up).
///
/// # Panics
/// Panics on an unknown scheme or category, a count out of range, or an area
/// that is not positive.
pub fn stocking_rate(scheme: &str, animals: &[LivestockCount], area_hectares: f64) -> StockingRate {
    let table: Vec<&LivestockUnitCoefficient> = LIVESTOCK_UNITS.iter().filter(|r| r.scheme == scheme).collect();
    if table.is_empty() {
        panic!("unknown scheme \"{}\": use eurostat or uk-countryside-stewardship", scheme);
    }
    if !area_hectares.is_finite() || area_hectares <= 0.0 || area_hectares > 1_000_000.0 {
        panic!("areaHectares must be a finite number greater than 0 and at most 1000000, received {}", area_hectares);
    }
    let area = (round_float(area_hectares, 4) * 10000.0).round() as i64;
    if area < 1 {
        panic!("areaHectares must be at least 0.0001 hectares, received {}", area_hectares);
    }

    let mut total: i64 = 0;
    let mut lines: Vec<LivestockUnitLine> = Vec::with_capacity(animals.len());
    for (i, animal) in animals.iter().enumerate() {
        let row = match table.iter().find(|r| r.category == animal.category) {
            Some(r) => r,
            None => panic!("unknown category \"{}\" in scheme {}", animal.category, scheme),
        };
        if animal.count < 0 || animal.count > MAX_COUNT {
            panic!("animal {}: count must be a whole number from 0 to 10000000, received {}", i + 1, animal.count);
        }
        let thousandths = animal.count * row.thousandths;
        total += thousandths;
        lines.push(LivestockUnitLine {
            category: animal.category.clone(),
            count: animal.count,
            coefficient: row.thousandths as f64 / 1000.0,
            livestock_units: thousandths as f64 / 1000.0,
        });
    }
    // LU/ha in hundredths = (total / 1000) / (area / 10000) x 100.
    StockingRate {
        livestock_units: total as f64 / 1000.0,
        units_per_hectare: round_div(total * 1000, area, "half-up") as f64 / 100.0,
        lines,
    }
}

pub fn stocking_rate_to_value(s: &StockingRate) -> Value {
    let lines = s
        .lines
        .iter()
        .map(|l| {
            Value::obj(vec![
                ("category", Value::str(&l.category)),
                ("count", Value::Int(l.count)),
                ("coefficient", Value::Float(l.coefficient)),
                ("livestockUnits", Value::Float(l.livestock_units)),
            ])
        })
        .collect();
    Value::obj(vec![
        ("livestockUnits", Value::Float(s.livestock_units)),
        ("unitsPerHectare", Value::Float(s.units_per_hectare)),
        ("lines", Value::Arr(lines)),
    ])
}

pub fn fune_vector(args: &[Value]) -> Value {
    let animals: Vec<LivestockCount> = args[1]
        .as_arr()
        .iter()
        .enumerate()
        .map(|(i, v)| {
            let count = match v.get("count") {
                Value::Int(n) => *n,
                other => panic!("animal {}: count must be a whole number from 0 to 10000000, received {:?}", i + 1, other),
            };
            LivestockCount {
                category: v.get("category").as_str().to_string(),
                count,
            }
        })
        .collect();
    stocking_rate_to_value(&stocking_rate(args[0].as_str(), &animals, args[2].as_f64()))
}