/**
 * 
 */
package org.unitConverter.unit;

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Objects;
import java.util.Optional;

/**
 * A possibly uncertain value expressed in a linear unit.
 * 
 * Unless otherwise indicated, all methods in this class throw a
 * {@code NullPointerException} when an argument is null.
 * 
 * @author Adrien Hopkins
 * @since 2020-07-26
 */
public final class LinearUnitValue {
	private final LinearUnit unit;
	private final double value;
	private final double uncertainty;

	/**
	 * Gets an exact {@code UnitValue}
	 * 
	 * @param unit  unit to express with
	 * @param value value to express
	 * @return exact {@code UnitValue} instance
	 * @since 2020-07-26
	 */
	public static final LinearUnitValue getExact(LinearUnit unit, double value) {
		return new LinearUnitValue(Objects.requireNonNull(unit, "unit must not be null"), value, 0);
	}

	/**
	 * Gets an uncertain {@code UnitValue}
	 * 
	 * @param unit        unit to express with
	 * @param value       value to express
	 * @param uncertainty absolute uncertainty of value
	 * @return uncertain {@code UnitValue} instance
	 * @since 2020-07-26
	 */
	public static final LinearUnitValue of(LinearUnit unit, double value, double uncertainty) {
		return new LinearUnitValue(Objects.requireNonNull(unit, "unit must not be null"), value, uncertainty);
	}

	/**
	 * @param unit        unit to express as
	 * @param value       value to express
	 * @param uncertainty absolute uncertainty of value
	 * @since 2020-07-26
	 */
	private LinearUnitValue(LinearUnit unit, double value, double uncertainty) {
		this.unit = unit;
		this.value = value;
		this.uncertainty = uncertainty;
	}

	/**
	 * @param other a {@code LinearUnit}
	 * @return true iff this value can be represented with {@code other}.
	 * @since 2020-07-26
	 */
	public final boolean canConvertTo(LinearUnit other) {
		return this.unit.canConvertTo(other);
	}

	/**
	 * Returns a LinearUnitValue that represents the same value expressed in a
	 * different unit
	 * 
	 * @param other new unit to express value in
	 * @return value expressed in {@code other}
	 * @since 2020-07-26
	 */
	public final LinearUnitValue convertTo(LinearUnit other) {
		return LinearUnitValue.of(other, this.unit.convertTo(other, value), this.unit.convertTo(other, uncertainty));
	}

	/**
	 * Returns true if this and obj represent the same value, regardless of whether
	 * or not they are expressed in the same unit. So (1000 m).equals(1 km) returns
	 * true.
	 * 
	 * @since 2020-07-26
	 */
	@Override
	public boolean equals(Object obj) {
		if (!(obj instanceof LinearUnitValue))
			return false;
		LinearUnitValue other = (LinearUnitValue) obj;
		return Objects.equals(this.unit.getBase(), other.unit.getBase())
				&& Double.doubleToLongBits(this.unit.convertToBase(this.getValue())) == Double
						.doubleToLongBits(other.unit.convertToBase(other.getValue()))
				&& Double.doubleToLongBits(this.getRelativeUncertainty()) == Double
						.doubleToLongBits(other.getRelativeUncertainty());
	}
	
	/**
	 * @param other another {@code LinearUnitValue}
	 * @return true iff this and other are within each other's uncertainty range
	 * 
	 * @since 2020-07-26
	 */
	public boolean equivalent(LinearUnitValue other) {
		if (other == null || !Objects.equals(this.unit.getBase(), other.unit.getBase()))
			return false;
		double thisBaseValue = this.unit.convertToBase(this.value);
		double otherBaseValue = other.unit.convertToBase(other.value);
		double thisBaseUncertainty = this.unit.convertToBase(this.uncertainty);
		double otherBaseUncertainty = other.unit.convertToBase(other.uncertainty);
		return Math.abs(thisBaseValue - otherBaseValue) <= Math.min(thisBaseUncertainty, otherBaseUncertainty);
	}

	/**
	 * @return the unit
	 * 
	 * @since 2020-07-26
	 */
	public final LinearUnit getUnit() {
		return unit;
	}

	/**
	 * @return the value
	 * 
	 * @since 2020-07-26
	 */
	public final double getValue() {
		return value;
	}

	/**
	 * @return absolute uncertainty of value
	 * 
	 * @since 2020-07-26
	 */
	public final double getUncertainty() {
		return uncertainty;
	}

	/**
	 * @return relative uncertainty of value
	 * 
	 * @since 2020-07-26
	 */
	public final double getRelativeUncertainty() {
		return uncertainty / value;
	}
	
	@Override
	public int hashCode() {
		return Objects.hash(this.unit.getBase(), this.unit.convertToBase(this.getValue()), this.getRelativeUncertainty());
	}

	/**
	 * @return true iff the value has no uncertainty
	 * 
	 * @since 2020-07-26
	 */
	public final boolean isExact() {
		return uncertainty == 0;
	}
	
	/**
	 * Returns the sum of this value and another, expressed in this value's unit
	 * 
	 * @param addend
	 *            value to add
	 * @return sum of values
	 * @throws IllegalArgumentException
	 *             if {@code addend} has a unit that is not compatible for addition
	 * @since 2020-07-26
	 */
	public LinearUnitValue plus(LinearUnitValue addend) {
		Objects.requireNonNull(addend, "addend may not be null");
		
		if (!this.canConvertTo(addend.unit))
			throw new IllegalArgumentException(
					String.format("Incompatible units for addition \"%s\" and \"%s\".", this.unit, addend.unit));
		
		final LinearUnitValue otherConverted = addend.convertTo(this.unit);
		return LinearUnitValue.of(this.unit, this.value + otherConverted.value, Math.hypot(this.uncertainty, otherConverted.uncertainty));
	}
	
	/**
	 * Returns the difference of this value and another, expressed in this value's unit
	 * 
	 * @param subtrahend
	 *            value to subtract
	 * @return difference of values
	 * @throws IllegalArgumentException
	 *             if {@code subtrahend} has a unit that is not compatible for addition
	 * @since 2020-07-26
	 */
	public LinearUnitValue minus(LinearUnitValue subtrahend) {
		Objects.requireNonNull(subtrahend, "subtrahend may not be null");
		
		if (!this.canConvertTo(subtrahend.unit))
			throw new IllegalArgumentException(
					String.format("Incompatible units for subtraction \"%s\" and \"%s\".", this.unit, subtrahend.unit));
		
		final LinearUnitValue otherConverted = subtrahend.convertTo(this.unit);
		return LinearUnitValue.of(this.unit, this.value - otherConverted.value, Math.hypot(this.uncertainty, otherConverted.uncertainty));
	}

	@Override
	public String toString() {
		return this.toString(!this.isExact());
	}

	/**
	 * Returns a string representing the object. <br>
	 * If the attached unit has a name or symbol, the string looks like "12 km".
	 * Otherwise, it looks like "13 unnamed unit (= 2 m/s)".
	 * <p>
	 * If showUncertainty is true, strings like "35 ± 8" are shown instead of single
	 * numbers.
	 * <p>
	 * Non-exact values are rounded intelligently based on their uncertainty.
	 * 
	 * @since 2020-07-26
	 */
	public String toString(boolean showUncertainty) {
		Optional<String> primaryName = this.unit.getPrimaryName();
		Optional<String> symbol = this.unit.getSymbol();
		String chosenName = symbol.orElse(primaryName.orElse(null));

		final double baseValue = this.unit.convertToBase(this.value);
		final double baseUncertainty = this.unit.convertToBase(this.uncertainty);

		// get rounded strings
		final String valueString, baseValueString, uncertaintyString, baseUncertaintyString;
		if (this.isExact()) {
			valueString = Double.toString(value);
			baseValueString = Double.toString(baseValue);
			uncertaintyString = "0";
			baseUncertaintyString = "0";
		} else {
			final BigDecimal bigValue = BigDecimal.valueOf(this.value);
			final BigDecimal bigUncertainty = BigDecimal.valueOf(this.uncertainty);

			// round based on uncertainty
			// if uncertainty starts with 1 (ignoring zeroes and the decimal point), rounds
			// so that uncertainty has 2 significant digits.
			// otherwise, rounds so that uncertainty has 1 significant digits.
			// the value is rounded to the same number of decimal places as the uncertainty.
			BigDecimal roundedUncertainty = bigUncertainty
					.setScale(bigUncertainty.scale() - bigUncertainty.precision() + 2, RoundingMode.HALF_EVEN);
			if (roundedUncertainty.unscaledValue().intValue() >= 20) {
				roundedUncertainty = bigUncertainty.setScale(bigUncertainty.scale() - bigUncertainty.precision() + 1,
						RoundingMode.HALF_EVEN);
			}
			final BigDecimal roundedValue = bigValue.setScale(roundedUncertainty.scale(), RoundingMode.HALF_EVEN);

			valueString = roundedValue.toString();
			uncertaintyString = roundedUncertainty.toString();

			if (primaryName.isEmpty() && symbol.isEmpty()) {
				final BigDecimal bigBaseValue = BigDecimal.valueOf(baseValue);
				final BigDecimal bigBaseUncertainty = BigDecimal.valueOf(baseUncertainty);

				BigDecimal roundedBaseUncertainty = bigBaseUncertainty.setScale(
						bigBaseUncertainty.scale() - bigBaseUncertainty.precision() + 2, RoundingMode.HALF_EVEN);
				if (roundedBaseUncertainty.unscaledValue().intValue() >= 20) {
					roundedBaseUncertainty = bigBaseUncertainty.setScale(
							bigBaseUncertainty.scale() - bigBaseUncertainty.precision() + 1, RoundingMode.HALF_EVEN);
				}
				final BigDecimal roundedBaseValue = bigBaseValue.setScale(roundedBaseUncertainty.scale(),
						RoundingMode.HALF_EVEN);

				baseValueString = roundedBaseValue.toString();
				baseUncertaintyString = roundedBaseUncertainty.toString();
			} else {
				// unused
				baseValueString = "";
				baseUncertaintyString = "";
			}
		}

		// create string
		if (showUncertainty) {
			if (primaryName.isEmpty() && symbol.isEmpty()) {
				return String.format("(%s ± %s) unnamed unit (= %s ± %s %s)", valueString, uncertaintyString,
						baseValueString, baseUncertaintyString, this.unit.getBase());
			} else {
				return String.format("(%s ± %s) %s", valueString, uncertaintyString, chosenName);
			}
		} else {
			if (primaryName.isEmpty() && symbol.isEmpty()) {
				return String.format("%s unnamed unit (= %s %s)", valueString, baseValueString, this.unit.getBase());
			} else {
				return String.format("%s %s", valueString, chosenName);
			}
		}
	}
}