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

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

    /**
     * Gets an uncertain {@code LinearUnitValue}
     * 
     * @param unit                unit to express with
     * @param value               value to express
     * @param relativeUncertainty relative uncertainty of value
     * @return uncertain {@code LinearUnitValue} instance
     * @since 2020-07-28
     */
    public static final LinearUnitValue ofRelative(final LinearUnit unit, final double value,
	    final double relativeUncertainty) {
	return LinearUnitValue.of(unit, value, relativeUncertainty * value);
    }

    private final LinearUnit unit;
    private final double value;
    private final double uncertainty;

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

    /**
     * Divides this value by a scalar
     * 
     * @param divisor value to divide by
     * @return multiplied value
     * @since 2020-07-28
     */
    public LinearUnitValue dividedBy(final double divisor) {
	return LinearUnitValue.of(this.unit, this.value / divisor, this.uncertainty / divisor);
    }

    /**
     * Divides this value by another value
     * 
     * @param divisor value to multiply by
     * @return quotient
     * @since 2020-07-28
     */
    public LinearUnitValue dividedBy(final LinearUnitValue divisor) {
	return LinearUnitValue.ofRelative(this.unit.dividedBy(divisor.unit), this.value / divisor.value,
		Math.hypot(this.getRelativeUncertainty(), divisor.getRelativeUncertainty()));
    }

    /**
     * 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(final Object obj) {
	if (!(obj instanceof LinearUnitValue))
	    return false;
	final 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(final LinearUnitValue other) {
	if (other == null || !Objects.equals(this.unit.getBase(), other.unit.getBase()))
	    return false;
	final double thisBaseValue = this.unit.convertToBase(this.value);
	final double otherBaseValue = other.unit.convertToBase(other.value);
	final double thisBaseUncertainty = this.unit.convertToBase(this.uncertainty);
	final double otherBaseUncertainty = other.unit.convertToBase(other.uncertainty);
	return Math.abs(thisBaseValue - otherBaseValue) <= Math.min(thisBaseUncertainty, otherBaseUncertainty);
    }

    /**
     * @return relative uncertainty of value
     * 
     * @since 2020-07-26
     */
    public final double getRelativeUncertainty() {
	return this.uncertainty / this.value;
    }

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

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

    /**
     * @return the value
     * 
     * @since 2020-07-26
     */
    public final double getValue() {
	return this.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 this.uncertainty == 0;
    }

    /**
     * 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(final 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));
    }

    /**
     * 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(final 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));
    }

    /**
     * Multiplies this value by a scalar
     * 
     * @param multiplier value to multiply by
     * @return multiplied value
     * @since 2020-07-28
     */
    public LinearUnitValue times(final double multiplier) {
	return LinearUnitValue.of(this.unit, this.value * multiplier, this.uncertainty * multiplier);
    }

    /**
     * Multiplies this value by another value
     * 
     * @param multiplier value to multiply by
     * @return product
     * @since 2020-07-28
     */
    public LinearUnitValue times(final LinearUnitValue multiplier) {
	return LinearUnitValue.ofRelative(this.unit.times(multiplier.unit), this.value * multiplier.value,
		Math.hypot(this.getRelativeUncertainty(), multiplier.getRelativeUncertainty()));
    }

    /**
     * Raises a value to an exponent
     * 
     * @param exponent exponent to raise to
     * @return result of exponentiation
     * @since 2020-07-28
     */
    public LinearUnitValue toExponent(final int exponent) {
	return LinearUnitValue.ofRelative(this.unit.toExponent(exponent), Math.pow(this.value, exponent),
		this.getRelativeUncertainty() * Math.sqrt(exponent));
    }

    @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(final boolean showUncertainty) {
	final Optional<String> primaryName = this.unit.getPrimaryName();
	final Optional<String> symbol = this.unit.getSymbol();
	final 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(this.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);
	}
    }
}