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 {
	const INCH_FROM: f64 = 10_000.0;
	const INCH_TO: f64 = 254.0;

	const POUND_FROM: f64 = 100_000.0;
	const POUND_TO: f64 = 45359237.0;

	const IMPERIAL_GALLON_FROM: f64 = 100_000.0;
	const IMPERIAL_GALLON_TO: f64 = 454609.0;

	const US_GALLON_FROM: f64 = INCH_FROM * INCH_FROM * INCH_FROM;
	const US_GALLON_TO: f64 = 231.0 * INCH_TO * INCH_TO * INCH_TO * 1000.0;

	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 },
		},
		// Mass
		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 },
		},
		NonMetric::ShortTon => Conversion {
			offset: 0.0,
			from: POUND_FROM,
			to: MetricQuantity { amount: 2000.0 * POUND_TO, unit: Metric::Gram },
		},
		NonMetric::LongTon => Conversion {
			offset: 0.0,
			from: POUND_FROM,
			to: MetricQuantity { amount: 2240.0 * 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::SquareYard => Conversion {
			offset: 0.0,
			from: INCH_FROM * INCH_FROM,
			to: MetricQuantity { amount: 3.0 * 12.0 * INCH_TO * 3.0 * 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 },
		},
		// Volume
		NonMetric::CubicInch => Conversion {
			offset: 0.0,
			from: INCH_FROM * INCH_FROM * INCH_FROM,
			to: MetricQuantity { amount: INCH_TO * INCH_TO * INCH_TO, unit: Metric::CubicMetre },
		},
		NonMetric::CubicFoot => Conversion {
			offset: 0.0,
			from: INCH_FROM * INCH_FROM * INCH_FROM,
			to: MetricQuantity { amount: 12.0 * INCH_TO * 12.0 * INCH_TO * 12.0 * INCH_TO, unit: Metric::CubicMetre },
		},
		NonMetric::CubicYard => Conversion {
			offset: 0.0,
			from: INCH_FROM * INCH_FROM * INCH_FROM,
			to: MetricQuantity { amount: 3.0 * 12.0 * INCH_TO * 3.0 * 12.0 * INCH_TO * 3.0 * 12.0 * INCH_TO, unit: Metric::CubicMetre },
		},
		// Fluid volume
		NonMetric::ImperialFluidOunce => Conversion {
			offset: 0.0,
			from: 20.0 * 2.0 * 4.0 * IMPERIAL_GALLON_FROM,
			to: MetricQuantity { amount: IMPERIAL_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::ImperialPint => Conversion {
			offset: 0.0,
			from: 2.0 * 4.0 * IMPERIAL_GALLON_FROM,
			to: MetricQuantity { amount: IMPERIAL_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::ImperialQuart => Conversion {
			offset: 0.0,
			from: 4.0 * IMPERIAL_GALLON_FROM,
			to: MetricQuantity { amount: IMPERIAL_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::ImperialGallon => Conversion {
			offset: 0.0,
			from: IMPERIAL_GALLON_FROM,
			to: MetricQuantity { amount: IMPERIAL_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::USTeaspoon => Conversion {
			offset: 0.0,
			from: 6.0 * 16.0 * 2.0 * 4.0 * US_GALLON_FROM,
			to: MetricQuantity { amount: US_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::USTablespoon => Conversion {
			offset: 0.0,
			from: 2.0 * 16.0 * 2.0 * 4.0 * US_GALLON_FROM,
			to: MetricQuantity { amount: US_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::USFluidOunce => Conversion {
			offset: 0.0,
			from: 16.0 * 2.0 * 4.0 * US_GALLON_FROM,
			to: MetricQuantity { amount: US_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::USCup => Conversion {
			offset: 0.0,
			from: 2.0 * 2.0 * 4.0 * US_GALLON_FROM,
			to: MetricQuantity { amount: US_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::USLiquidPint => Conversion {
			offset: 0.0,
			from: 2.0 * 4.0 * US_GALLON_FROM,
			to: MetricQuantity { amount: US_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::USLiquidQuart => Conversion {
			offset: 0.0,
			from: 4.0 * US_GALLON_FROM,
			to: MetricQuantity { amount: US_GALLON_TO, unit: Metric::Litre },
		},
		NonMetric::USGallon => Conversion {
			offset: 0.0,
			from: US_GALLON_FROM,
			to: MetricQuantity { amount: US_GALLON_TO, unit: Metric::Litre },
		},
	}
}

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

	struct Test(NonMetric, f64);

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

	#[test]
	fn mass() {
		run_tests(Metric::Gram, &[
			Test(NonMetric::Ounce, 28.349523125),
			Test(NonMetric::Pound, 453.59237),
			Test(NonMetric::Stone, 6350.29318),
			Test(NonMetric::ShortTon, 907184.74),
			Test(NonMetric::LongTon, 1016046.9088),
		]);
	}

	#[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() {
		run_tests(Metric::SquareMetre, &[
			Test(NonMetric::SquareInch, 0.00064516),
			Test(NonMetric::SquareFoot, 0.09290304),
			Test(NonMetric::SquareYard, 0.83612736),
			Test(NonMetric::Acre, 4046.8564224),
			Test(NonMetric::SquareMile, 2589988.110336),
		]);
	}

	#[test]
	fn volume() {
		run_tests(Metric::CubicMetre, &[
			Test(NonMetric::CubicInch, 1.6387064e-5),
			Test(NonMetric::CubicFoot, 0.028316846592),
			Test(NonMetric::CubicYard, 0.764554857984),
		]);
	}

	#[test]
	fn fluid_volume() {
		run_tests(Metric::Litre, &[
			Test(NonMetric::ImperialFluidOunce, 0.0284130625),
			Test(NonMetric::ImperialPint, 0.56826125),
			Test(NonMetric::ImperialQuart, 1.1365225),
			Test(NonMetric::ImperialGallon, 4.54609),
			Test(NonMetric::USTeaspoon, 0.00492892159375),
			Test(NonMetric::USTablespoon, 0.01478676478125),
			Test(NonMetric::USFluidOunce, 0.0295735295625),
			Test(NonMetric::USCup, 0.2365882365),
			Test(NonMetric::USLiquidPint, 0.473176473),
			Test(NonMetric::USLiquidQuart, 0.946352946),
			Test(NonMetric::USGallon, 3.785411784),
		]);
	}

	fn run_tests(unit: Metric, tests: &[Test]) {
		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);
		}
	}
}