use crate::units::{Metric, MetricQuantity};

pub fn format(quantity: MetricQuantity) -> String {
	let SiUnit(multiplier, unit) = si_unit(quantity);
	let amount = quantity.amount / multiplier;

	format!("{amount} {unit}")
}

#[derive(Debug, PartialEq)]
struct SiUnit(f64, &'static str);

fn si_unit(quantity: MetricQuantity) -> SiUnit {
	let absolute = quantity.amount.abs();

	match quantity.unit {
		Metric::Metre => {
			if absolute >= 1000.0 {
				return SiUnit(1000.0, "km");
			} else if absolute >= 1.0 {
				return SiUnit(1.0, "m");
			} else if absolute >= 0.01 {
				return SiUnit(0.01, "cm");
			} else {
				return SiUnit(0.001, "mm");
			}
		}
		Metric::Gram => {
			if absolute >= 1000.0 {
				return SiUnit(1000.0, "kg");
			} else {
				return SiUnit(1.0, "g");
			}
		}
	}
}

#[cfg(test)]
mod test {
	use super::*;

	#[test]
	fn quantities() {
		assert_eq!("0.1 mm", &format(MetricQuantity {
			amount: 0.000_1,
			unit: Metric::Metre,
		}));
		assert_eq!("-1 m", &format(MetricQuantity {
			amount: -1.0,
			unit: Metric::Metre,
		}));
		assert_eq!("1.5 m", &format(MetricQuantity {
			amount: 1.5,
			unit: Metric::Metre,
		}));
		assert_eq!("1000 km", &format(MetricQuantity {
			amount: 1_000_000.0,
			unit: Metric::Metre,
		}));

		assert_eq!("-5 g", &format(MetricQuantity {
			amount: -5.0,
			unit: Metric::Gram,
		}));
		assert_eq!("3.2 kg", &format(MetricQuantity {
			amount: 3_200.0,
			unit: Metric::Gram,
		}));
	}

	#[test]
	fn units() {
		assert_eq!(SiUnit(0.001, "mm"), si_unit(MetricQuantity {
			amount: 0.0001,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(0.001, "mm"), si_unit(MetricQuantity {
			amount: 0.001,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(0.01, "cm"), si_unit(MetricQuantity {
			amount: 0.01,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(0.01, "cm"), si_unit(MetricQuantity {
			amount: 0.1,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(1.0, "m"), si_unit(MetricQuantity {
			amount: 1.0,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(1.0, "m"), si_unit(MetricQuantity {
			amount: 10.0,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(1.0, "m"), si_unit(MetricQuantity {
			amount: 100.0,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(1000.0, "km"), si_unit(MetricQuantity {
			amount: 1000.0,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(1000.0, "km"), si_unit(MetricQuantity {
			amount: 10_000.0,
			unit: Metric::Metre,
		}));

		assert_eq!(SiUnit(0.001, "mm"), si_unit(MetricQuantity {
			amount: -0.001,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(0.01, "cm"), si_unit(MetricQuantity {
			amount: -0.01,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(1.0, "m"), si_unit(MetricQuantity {
			amount: -1.0,
			unit: Metric::Metre,
		}));
		assert_eq!(SiUnit(1000.0, "km"), si_unit(MetricQuantity {
			amount: -1000.0,
			unit: Metric::Metre,
		}));

		assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
			amount: 0.1,
			unit: Metric::Gram,
		}));
		assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
			amount: 1.0,
			unit: Metric::Gram,
		}));
		assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
			amount: 10.0,
			unit: Metric::Gram,
		}));
		assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
			amount: 100.0,
			unit: Metric::Gram,
		}));
		assert_eq!(SiUnit(1000.0, "kg"), si_unit(MetricQuantity {
			amount: 1000.0,
			unit: Metric::Gram,
		}));
		assert_eq!(SiUnit(1000.0, "kg"), si_unit(MetricQuantity {
			amount: 10_1000.0,
			unit: Metric::Gram,
		}));

		assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
			amount: -1.0,
			unit: Metric::Gram,
		}));
		assert_eq!(SiUnit(1000.0, "kg"), si_unit(MetricQuantity {
			amount: -1000.0,
			unit: Metric::Gram,
		}));
	}
}