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

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

fn get_conversion(unit: NonMetric) -> Conversion {
	match unit {
		// Length
		NonMetric::Foot => Conversion {
			from: 10_000.0,
			to: MetricQuantity { amount: 3048.0, unit: Metric::Metre },
		},
		NonMetric::Inch => Conversion {
			from: 10_000.0,
			to: MetricQuantity { amount: 254.0, unit: Metric::Metre },
		},
		NonMetric::Yard => Conversion {
			from: 10_000.0,
			to: MetricQuantity { amount: 9144.0, unit: Metric::Metre },
		},
		NonMetric::Mile => Conversion {
			from: 1_000.0,
			to: MetricQuantity { amount: 1609344.0, unit: Metric::Metre },
		},
		// Weight
		NonMetric::Ounce => Conversion {
			from: 1_000_000_000.0,
			to: MetricQuantity { amount: 28349523125.0, unit: Metric::Gram },
		},
		NonMetric::Pound => Conversion {
			from: 100_000.0,
			to: MetricQuantity { amount: 45359237.0, unit: Metric::Gram },
		},
		NonMetric::Stone => Conversion {
			from: 100_000.0,
			to: MetricQuantity { amount: 635029318.0, unit: Metric::Gram },
		},
	}
}

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

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

	struct Test(NonMetric, f64);

	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);
		}
	}

	#[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);
	}
}