mod conversions;
mod format;
mod parse;
mod units;

use conversions::convert;
use format::format;
use parse::{parse, ParseError};
use units::{Metric, MetricQuantity, NonMetric};

pub fn run(input: &str) -> Result<String, String> {
	let non_metric = match parse(input) {
		Ok(non_metric) => non_metric,
		Err(ParseError::NotValidNumber(string)) => {
			return Err(format!("Not a valid number: {string}"));
		}
		Err(ParseError::UnexpectedUnit(unit)) => {
			return Err(format!("Unexpected unit: {unit}"));
		}
		Err(ParseError::UnknownUnit(unit)) => {
			return Err(format!("Unknown unit: {unit}"));
		}
		Err(ParseError::ExpectedUnit) => {
			return Err("Expected a unit".to_string());
		}
		Err(ParseError::AmbiguousUnit(unit, prefix1, prefix2)) => {
			return Err(format!("Ambiguous unit '{unit}', use either '{prefix1} {unit}' or '{prefix2} {unit}'"));
		}
	};

	if non_metric.is_empty() {
		return Err("Expected quantity or quantities to convert".to_string());
	}

	let metric: Vec<MetricQuantity> = non_metric.clone().into_iter().map(convert).collect();

	// Make sure the results of the conversions can be summed together
	// This is the case if the units after conversion are the same and
	// they are not temperature units (i.e. degrees Celsius)
	let mut metric_unit = None;
	for index in 0..metric.len() {
		match metric_unit {
			Some(metric_unit) => {
				if metric[index].unit != metric_unit {
					let first_unit_name = unit_to_name(non_metric[0].unit);
					let unit_name = unit_to_name(non_metric[index].unit);
					return Err(format!("Incompatible units: {first_unit_name}, {unit_name}"));
				}
			}
			None => {
				metric_unit = Some(metric[index].unit);
			}
		}
	}
	if metric.len() > 1 && metric_unit == Some(Metric::Celsius) {
		return Err("Cannot sum together temperatures".to_string());
	}

	let amount = metric.into_iter().map(|quantity| { quantity.amount }).sum();

	let quantity = MetricQuantity {
		amount,
		unit: metric_unit.expect("we must have at least one quantity by this point"),
	};

	Ok(format(quantity))
}

fn unit_to_name(unit: NonMetric) -> &'static str {
	match unit {
		// Length
		NonMetric::Inch => "inches",
		NonMetric::Foot => "feet",
		NonMetric::Yard => "yards",
		NonMetric::Mile => "miles",
		// Mass
		NonMetric::Ounce => "ounces",
		NonMetric::Pound => "pounds",
		NonMetric::Stone => "stones",
		NonMetric::ShortTon => "short tons",
		NonMetric::LongTon => "long tons",
		// Temperature
		NonMetric::Fahrenheit => "degrees Fahrenheit",
		// Area
		NonMetric::SquareInch => "square inches",
		NonMetric::SquareFoot => "square feet",
		NonMetric::SquareYard => "square yards",
		NonMetric::Acre => "acres",
		NonMetric::SquareMile => "square miles",
		// Volume
		NonMetric::CubicInch => "cubic inches",
		NonMetric::CubicFoot => "cubic feet",
		NonMetric::CubicYard => "cubic yards",
		// Fluid volume
		NonMetric::ImperialFluidOunce => "imperial fluid ounces",
		NonMetric::ImperialPint => "imperial pints",
		NonMetric::ImperialQuart => "imperial quarts",
		NonMetric::ImperialGallon => "imperial gallons",
		NonMetric::USTeaspoon => "US teaspoons",
		NonMetric::USTablespoon => "US tablespoons",
		NonMetric::USFluidOunce => "US fluid ounces",
		NonMetric::USCup => "US cups",
		NonMetric::USLiquidPint => "US liquid pints",
		NonMetric::USLiquidQuart => "US liquid quarts",
		NonMetric::USGallon => "US gallons",
	}
}

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

	#[test]
	fn errors() {
		assert_eq!(run("1.0."), Err("Not a valid number: 1.0.".to_string()));
		assert_eq!(run("ft"), Err("Unexpected unit: ft".to_string()));
		assert_eq!(run("1 tf"), Err("Unknown unit: tf".to_string()));
		assert_eq!(run("1"), Err("Expected a unit".to_string()));
		assert_eq!(run(""), Err("Expected quantity or quantities to convert".to_string()));
		assert_eq!(run("1 fl oz"), Err("Ambiguous unit 'fl oz', use either 'imp fl oz' or 'US fl oz'".to_string()));
		assert_eq!(run("6 ft 1 lbs"), Err("Incompatible units: feet, pounds".to_string()));
		assert_eq!(run("0 °F 0 °F"), Err("Cannot sum together temperatures".to_string()));
	}

	#[test]
	fn conversions() {
		// Length
		assert_eq!(run("1 in"), Ok("2.54 cm".to_string()));
		assert_eq!(run("1 ft"), Ok("30.48 cm".to_string()));
		assert_eq!(run("1 yard"), Ok("91.44 cm".to_string()));
		assert_eq!(run("1 mile"), Ok("1.609 km".to_string()));
		// Mass
		assert_eq!(run("1 oz"), Ok("28.35 g".to_string()));
		assert_eq!(run("1 lb"), Ok("453.6 g".to_string()));
		assert_eq!(run("1 st"), Ok("6.35 kg".to_string()));
		assert_eq!(run("1 short ton"), Ok("907.2 kg".to_string()));
		assert_eq!(run("1 long ton"), Ok("1 016 kg".to_string()));
		// Temperature
		assert_eq!(run("-40 °F"), Ok("-40 °C".to_string()));
		assert_eq!(run("0 °F"), Ok("-17.78 °C".to_string()));
		assert_eq!(run("32 °F"), Ok("0 °C".to_string()));
		// Area
		assert_eq!(run("1 in²"), Ok("6.452 cm²".to_string()));
		assert_eq!(run("1 ft²"), Ok("929 cm²".to_string()));
		assert_eq!(run("1 yd²"), Ok("8 361 cm²".to_string()));
		assert_eq!(run("1 acre"), Ok("4 047 m²".to_string()));
		assert_eq!(run("1 mi²"), Ok("2.59 km²".to_string()));
		// Volume
		assert_eq!(run("1 in³"), Ok("16.39 cm³".to_string()));
		assert_eq!(run("1 ft³"), Ok("28 317 cm³".to_string()));
		assert_eq!(run("1 yd³"), Ok("764 555 cm³".to_string()));
		// Fluid volume
		assert_eq!(run("1 imp fl oz"), Ok("2.841 cl".to_string()));
		assert_eq!(run("1 imp pt"), Ok("5.683 dl".to_string()));
		assert_eq!(run("1 imp qt"), Ok("1.137 l".to_string()));
		assert_eq!(run("1 imp gal"), Ok("4.546 l".to_string()));
		assert_eq!(run("1 tsp"), Ok("4.929 ml".to_string()));
		assert_eq!(run("1 Tbsp"), Ok("1.479 cl".to_string()));
		assert_eq!(run("1 US fl oz"), Ok("2.957 cl".to_string()));
		assert_eq!(run("1 US cup"), Ok("2.366 dl".to_string()));
		assert_eq!(run("1 US pt"), Ok("4.732 dl".to_string()));
		assert_eq!(run("1 US qt"), Ok("9.464 dl".to_string()));
		assert_eq!(run("1 US gal"), Ok("3.785 l".to_string()));
	}
}