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

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

import org.unitConverter.math.DecimalComparison;

/**
 * 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 {
	public static final LinearUnitValue ONE = getExact(SI.ONE, 1);
	
	/**
	 * 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;
	}
	
	/**
	 * @return this value as a {@code UnitValue}. All uncertainty information is
	 *         removed from the returned value.
	 * @since 2020-08-04
	 */
	public final UnitValue asUnitValue() {
		return UnitValue.of(this.unit, this.value);
	}
	
	/**
	 * @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
	 * @see #equals(Object, boolean)
	 */
	@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());
	}
	
	/**
	 * 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.
	 * <p>
	 * If avoidFPErrors is true, this method will attempt to avoid floating-point
	 * errors, at the cost of not always being transitive.
	 * 
	 * @since 2020-07-28
	 */
	public boolean equals(final Object obj, final boolean avoidFPErrors) {
		if (!avoidFPErrors)
			return this.equals(obj);
		if (!(obj instanceof LinearUnitValue))
			return false;
		final LinearUnitValue other = (LinearUnitValue) obj;
		return Objects.equals(this.unit.getBase(), other.unit.getBase())
				&& DecimalComparison.equals(this.unit.convertToBase(this.value),
						other.unit.convertToBase(other.value))
				&& DecimalComparison.equals(this.getRelativeUncertainty(),
						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
		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 {
			// truncate excess zeroes
			if (valueString.contains(".")) {
				while (valueString.endsWith("0")) {
					valueString = valueString.substring(0, valueString.length() - 1);
				}
				if (valueString.endsWith(".")) {
					valueString = valueString.substring(0, valueString.length() - 1);
				}
			}
			
			if (baseValueString.contains(".")) {
				while (baseValueString.endsWith("0")) {
					baseValueString = baseValueString.substring(0,
							baseValueString.length() - 1);
				}
				if (baseValueString.endsWith(".")) {
					baseValueString = baseValueString.substring(0,
							baseValueString.length() - 1);
				}
			}
			
			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);
		}
	}
}