metrify/src/conversions.rs

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

pub fn convert(from: NonMetricQuantity) -> MetricQuantity {
	let conversion = get_conversion(from.unit);
	let amount = (from.amount - conversion.offset) * conversion.to.amount / conversion.from;
	let unit = conversion.to.unit;
	MetricQuantity { amount, unit }
}

struct Conversion {
	offset: f64,
	from: f64,
	to: MetricQuantity,
}

fn get_conversion(unit: NonMetric) -> Conversion {
	let inch_from = 10_000.0;
	let inch_to = 254.0;

	let pound_from = 100_000.0;
	let pound_to = 45359237.0;

	match unit {
		// Length
		NonMetric::Inch => Conversion {
			offset: 0.0,
			from: inch_from,
			to: MetricQuantity { amount: inch_to, unit: Metric::Metre },
		},
		NonMetric::Foot => Conversion {
			offset: 0.0,
			from: inch_from,
			to: MetricQuantity { amount: 12.0 * inch_to, unit: Metric::Metre },
		},
		NonMetric::Yard => Conversion {
			offset: 0.0,
			from: inch_from,
			to: MetricQuantity { amount: 3.0 * 12.0 * inch_to, unit: Metric::Metre },
		},
		NonMetric::Mile => Conversion {
			offset: 0.0,
			from: inch_from,
			to: MetricQuantity { amount: 1760.0 * 3.0 * 12.0 * inch_to, unit: Metric::Metre },
		},
		// Weight
		NonMetric::Ounce => Conversion {
			offset: 0.0,
			from: 16.0 * pound_from,
			to: MetricQuantity { amount: pound_to, unit: Metric::Gram },
		},
		NonMetric::Pound => Conversion {
			offset: 0.0,
			from: pound_from,
			to: MetricQuantity { amount: pound_to, unit: Metric::Gram },
		},
		NonMetric::Stone => Conversion {
			offset: 0.0,
			from: pound_from,
			to: MetricQuantity { amount: 14.0 * pound_to, unit: Metric::Gram },
		},
		// Temperature
		NonMetric::Fahrenheit => Conversion {
			offset: 32.0,
			from: 9.0,
			to: MetricQuantity { amount: 5.0, unit: Metric::Celsius },
		},
		// Area
		NonMetric::SquareInch => Conversion {
			offset: 0.0,
			from: inch_from * inch_from,
			to: MetricQuantity { amount: inch_to * inch_to, unit: Metric::SquareMetre },
		},
		NonMetric::SquareFoot => Conversion {
			offset: 0.0,
			from: inch_from * inch_from,
			to: MetricQuantity { amount: 12.0 * inch_to * 12.0 * inch_to, unit: Metric::SquareMetre },
		},
		NonMetric::Acre => Conversion {
			offset: 0.0,
			from: inch_from * inch_from,
			to: MetricQuantity { amount: 43_560.0 * 12.0 * inch_to * 12.0 * inch_to, unit: Metric::SquareMetre },
		},
		NonMetric::SquareMile => Conversion {
			offset: 0.0,
			from: inch_from * inch_from,
			to: MetricQuantity { amount: 1760.0 * 3.0 * 12.0 * inch_to * 1760.0 * 3.0 * 12.0 * inch_to, unit: Metric::SquareMetre },
		},
	}
}

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

	struct Test(NonMetric, f64);

	#[test]
	fn length() {
		let tests = [
			Test(NonMetric::Inch, 0.0254),
			Test(NonMetric::Foot, 0.3048),
			Test(NonMetric::Yard, 0.9144),
			Test(NonMetric::Mile, 1609.344),
		];
		run_tests(&tests, Metric::Metre);
	}

	#[test]
	fn weight() {
		let tests = [
			Test(NonMetric::Ounce, 28.349523125),
			Test(NonMetric::Pound, 453.59237),
			Test(NonMetric::Stone, 6350.29318),
		];
		run_tests(&tests, Metric::Gram);
	}

	#[test]
	fn temperature() {
		assert_eq!(convert(NonMetricQuantity {
			amount: -40.0,
			unit: NonMetric::Fahrenheit,
		}), MetricQuantity {
			amount: -40.0,
			unit: Metric::Celsius,
		});
		assert_eq!(convert(NonMetricQuantity {
			amount: 32.0,
			unit: NonMetric::Fahrenheit,
		}), MetricQuantity {
			amount: 0.0,
			unit: Metric::Celsius,
		});
	}

	#[test]
	fn area() {
		let tests = [
			Test(NonMetric::SquareInch, 0.00064516),
			Test(NonMetric::SquareFoot, 0.09290304),
			Test(NonMetric::Acre, 4046.8564224),
			Test(NonMetric::SquareMile, 2589988.110336),
		];
		run_tests(&tests, Metric::SquareMetre);
	}

	fn run_tests(tests: &[Test], unit: Metric) {
		for test in tests {
			let from = NonMetricQuantity {
				amount: 1.0,
				unit: test.0,
			};
			let to = MetricQuantity {
				amount: test.1,
				unit: unit,
			};
			assert_eq!(convert(from), to);
		}
	}
}