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

use conversions::convert;
use format::format;
use parse::{parse, ParseError};
use units::{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());
		}
	};

	if non_metric.len() == 0 {
		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
	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);
			}
		}
	}

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

	let quantity = MetricQuantity {
		amount: 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",
		// Weight
		NonMetric::Ounce => "ounces",
		NonMetric::Pound => "pounds",
		NonMetric::Stone => "stones",
	}
}

#[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("6 ft 1 lbs"), Err("Incompatible units: feet, pounds".to_string()));
	}
}