package net.mattmccutchen.measurements;

import java.util.*;

public class Unit {
	public static final Unit SECOND  = new Unit("s"   , 1.0, 1, 0, 0, 0, 0, 0);
	public static final Unit METER   = new Unit("m"   , 1.0, 0, 1, 0, 0, 0, 0);
	public static final Unit GRAM    = new Unit("g"   , 1.0, 0, 0, 1, 0, 0, 0);
	public static final Unit COULOMB = new Unit("coul", 1.0, 0, 0, 0, 1, 0, 0);
	public static final Unit KELVIN  = new Unit("K"   , 1.0, 0, 0, 0, 0, 1, 0);
	public static final Unit MOLE    = new Unit("mol" , 1.0, 0, 0, 0, 0, 0, 1);
	
	public static final Unit[] basicUnits = new Unit[] {
		SECOND, METER, GRAM, COULOMB, KELVIN, MOLE,
	}; // Don't mutate
	
	public static final Unit PERCENT    = new Unit("%", 1e-2, 0, 0, 0, 0, 0, 0);
	public static final Unit NEWTON     = new Unit("N", 1e+3,-2, 1, 1, 0, 0, 0);
	public static final Unit JOULE      = new Unit("J", 1e+3,-2, 2, 1, 0, 0, 0);
	public static final Unit WATT       = new Unit("W", 1e+3,-3, 2, 1, 0, 0, 0);
	public static final Unit VOLT       = new Unit("V", 1e+3,-2, 2, 1,-1, 0, 0);
	public static final Unit AMP        = new Unit("A", 1.0 ,-1, 0, 0, 1, 0, 0);
	public static final Unit LITER      = new Unit("L", 1e-3, 0, 3, 0, 0, 0, 0);
	
	public static final Unit[] allUnits = new Unit[] {
		SECOND, METER, GRAM, COULOMB, KELVIN, MOLE,
		PERCENT, NEWTON, JOULE, WATT, VOLT, AMP, LITER,
	}; // Don't mutate
	
	public final String symbol;
	public final double factor;
	public final int[] powers; // Don't mutate
	
	private Unit(String symbol, double factor, int... powers) {
		this.symbol = symbol;
		this.factor = factor;
		this.powers = powers;
	}
	
	private static final Map<String, Unit> unitsBySymbol; // Don't mutate
	private static final Map<Character, Double> prefixes; // Don't mutate
	
	public static Unit lookupBySymbol(String symbol) {
		Unit u = unitsBySymbol.get(symbol);
		if (u != null)
			return u;
		char pfx = symbol.charAt(0);
		symbol = symbol.substring(1);
		u = unitsBySymbol.get(symbol);
		Double mult1 = prefixes.get(pfx);
		if (u != null && mult1 != null)
			return new Unit(symbol, u.factor * mult1, u.powers);
		return null;
	}
	
	static {
		unitsBySymbol = new LinkedHashMap<String, Unit>();
		for (Unit u : allUnits)
			unitsBySymbol.put(u.symbol, u);
		
		prefixes = new LinkedHashMap<Character, Double>();
		prefixes.put('k', 1e+03);
		prefixes.put('M', 1e+06);
		prefixes.put('G', 1e+09);
		prefixes.put('T', 1e+12);
		prefixes.put('P', 1e+15);
		prefixes.put('E', 1e+18);
		prefixes.put('Z', 1e+21);
		prefixes.put('Y', 1e+24);
		prefixes.put('c', 1e-02);
		prefixes.put('m', 1e-03);
		prefixes.put('u', 1e-06); // micro -> u: oh well
		prefixes.put('n', 1e-09);
		prefixes.put('p', 1e-12);
		prefixes.put('f', 1e-15);
		prefixes.put('a', 1e-18);
		prefixes.put('z', 1e-21);
		prefixes.put('y', 1e-24);
	}
	
	public static Unit parseUnitString(String ustr) {
		double fctr = 1;
		int[] up = new int[Unit.basicUnits.length];
		StringTokenizer unitT = new StringTokenizer(ustr, " */", true);
		boolean invert = false;
		while (unitT.hasMoreTokens()) {
			String tok = unitT.nextToken();
			if (tok.equals("/")) {
				invert = !invert;
				continue;
			} else if (tok.equals(" ") || tok.equals("*"))
				continue;
			int caret = tok.indexOf('^');
			String symbol;
			int power;
			if (caret == -1) {
				power = 1;
				symbol = tok;
			} else {
				power = Integer.parseInt(tok.substring(caret + 1));
				symbol = tok.substring(0, caret);
			}
			Unit unit = Unit.lookupBySymbol(symbol);
			if (unit == null)
				throw new NullPointerException();
			if (invert)
				power = -power;
			fctr *= Math.pow(unit.factor, power);
			for (int i = 0; i < Unit.basicUnits.length; i++)
				up[i] += power * unit.powers[i];
		}
		return new Unit(ustr, fctr, up);
	}
}