/**
 * Copyright (C) 2021-2022 Adrien Hopkins
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
package sevenUnitsGUI;

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Optional;
import java.util.Scanner;
import java.util.Set;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import sevenUnits.ProgramInfo;
import sevenUnits.unit.BaseDimension;
import sevenUnits.unit.BaseUnit;
import sevenUnits.unit.BritishImperial;
import sevenUnits.unit.LinearUnit;
import sevenUnits.unit.LinearUnitValue;
import sevenUnits.unit.Metric;
import sevenUnits.unit.Unit;
import sevenUnits.unit.UnitDatabase;
import sevenUnits.unit.UnitPrefix;
import sevenUnits.unit.UnitType;
import sevenUnits.unit.UnitValue;
import sevenUnits.utils.Nameable;
import sevenUnits.utils.ObjectProduct;
import sevenUnits.utils.UncertainDouble;

/**
 * An object that handles interactions between the view and the backend code
 * 
 * @author Adrien Hopkins
 * @since 2021-12-15
 */
public final class Presenter {
	/** The place where settings are stored. */
	private static final Optional<Path> CONFIG_FILE = getConfigPath();
	/** The default place where units are stored. */
	private static final String DEFAULT_UNITS_FILEPATH = "/unitsfile.txt";
	/** The default place where dimensions are stored. */
	private static final String DEFAULT_DIMENSIONS_FILEPATH = "/dimensionfile.txt";
	/** The default place where exceptions are stored. */
	private static final String DEFAULT_EXCEPTIONS_FILEPATH = "/metric_exceptions.txt";
	
	/** Gets the configuration file, creating the directory if needed. */
	private static final Optional<Path> getConfigPath() {
		final Path configDir;
		if (System.getProperty("os.name").startsWith("Windows")) {
			final String envFolder = System.getenv("LOCALAPPDATA");
			if (envFolder == null || "".equals(envFolder)) {
				configDir = Path.of(System.getenv("USERPROFILE"), "AppData", "Local", "SevenUnits");
			} else {
				configDir = Path.of(envFolder, "SevenUnits");
			}
		} else {
			final String envFolder = System.getenv("XDG_CONFIG_HOME");
			if (envFolder == null || "".equals(envFolder)) {
				configDir = Path.of(System.getenv("HOME"), ".config", "SevenUnits");
			} else {
				configDir = Path.of(envFolder, "SevenUnits");
			}
		}

		// try to create config directory
		if (!Files.exists(configDir)) {
			try {
				Files.createDirectory(configDir);
			} catch (IOException e) {
				e.printStackTrace();
				return Optional.empty();
			}
		}

		return Optional.of(configDir.resolve("config.txt"));
	}

	/** Gets a Path from a pathname in the config file. */
	private static Path pathFromConfig(String pathname) {
		return CONFIG_FILE.map(configFile ->
			configFile.getParent().resolve(pathname)
		).orElse(Path.of(pathname));
	}

	/**
	 * Adds default units and dimensions to a database.
	 * 
	 * @param database database to add to
	 * @since 2019-04-14
	 * @since v0.2.0
	 */
	private static void addDefaults(final UnitDatabase database) {
		database.addUnit("metre", Metric.METRE);
		database.addUnit("kilogram", Metric.KILOGRAM);
		database.addUnit("gram", Metric.KILOGRAM.dividedBy(1000));
		database.addUnit("second", Metric.SECOND);
		database.addUnit("ampere", Metric.AMPERE);
		database.addUnit("kelvin", Metric.KELVIN);
		database.addUnit("mole", Metric.MOLE);
		database.addUnit("candela", Metric.CANDELA);
		database.addUnit("bit", Metric.BIT);
		database.addUnit("unit", Metric.ONE);
		// nonlinear units - must be loaded manually
		database.addUnit("tempCelsius", Metric.CELSIUS);
		database.addUnit("tempFahrenheit", BritishImperial.FAHRENHEIT);
		
		// load initial dimensions
		database.addDimension("Length", Metric.Dimensions.LENGTH);
		database.addDimension("Mass", Metric.Dimensions.MASS);
		database.addDimension("Time", Metric.Dimensions.TIME);
		database.addDimension("Temperature", Metric.Dimensions.TEMPERATURE);
	}
	
	/**
	 * @return text in About file
	 * @since 2022-02-19
	 */
	public static final String getAboutText() {
		return Presenter.getLinesFromResource("/about.txt").stream()
				.map(Presenter::withoutComments).collect(Collectors.joining("\n"))
				.replaceAll("\\[VERSION\\]", ProgramInfo.VERSION.toString());
	}
	
	/**
	 * Gets the text of a resource file as a set of strings (each one is one line
	 * of the text).
	 *
	 * @param filename filename to get resource from
	 * @return contents of file
	 * @since 2021-03-27
	 */
	private static final List<String> getLinesFromResource(String filename) {
		final List<String> lines = new ArrayList<>();
		
		try (InputStream stream = inputStream(filename);
				Scanner scanner = new Scanner(stream)) {
			while (scanner.hasNextLine()) {
				lines.add(scanner.nextLine());
			}
		} catch (final IOException e) {
			throw new AssertionError(
					"Error occurred while loading file " + filename, e);
		}
		
		return lines;
	}
	
	/**
	 * Gets an input stream for a resource file.
	 *
	 * @param filepath file to use as resource
	 * @return obtained Path
	 * @since 2021-03-27
	 */
	private static final InputStream inputStream(String filepath) {
		return Presenter.class.getResourceAsStream(filepath);
	}
	
	/**
	 * @return true iff a and b have any elements in common
	 * @since 2022-04-19
	 */
	private static final boolean sharesAnyElements(Set<?> a, Set<?> b) {
		for (final Object e : a) {
			if (b.contains(e))
				return true;
		}
		return false;
	}
	
	/**
	 * @return {@code line} with any comments removed.
	 * @since 2021-03-13
	 */
	private static final String withoutComments(String line) {
		final int index = line.indexOf('#');
		return index == -1 ? line : line.substring(0, index);
	}
	
	// ====== SETTINGS ======
	
	/**
	 * The view that this presenter communicates with
	 */
	private final View view;
	
	/**
	 * The database that this presenter communicates with (effectively the model)
	 */
	final UnitDatabase database;
	
	/**
	 * The rule used for parsing input numbers. Any number-string inputted into
	 * this program will be parsed using this method. <b>Not implemented yet.</b>
	 */
	private Function<String, UncertainDouble> numberParsingRule;
	
	/**
	 * The rule used for displaying the results of unit conversions. The result
	 * of unit conversions will be put into this function, and the resulting
	 * string will be used in the output.
	 */
	private Function<UncertainDouble, String> numberDisplayRule = StandardDisplayRules
			.uncertaintyBased();
	
	/**
	 * A predicate that determines whether or not a certain combination of
	 * prefixes is allowed. If it returns false, a combination of prefixes will
	 * not be allowed. Prefixes are put in the list from right to left.
	 */
	private Predicate<List<UnitPrefix>> prefixRepetitionRule = DefaultPrefixRepetitionRule.NO_RESTRICTION;
	
	/**
	 * A rule that accepts a prefixless name-unit pair and returns a map mapping
	 * names to prefixed versions of that unit (including the unit itself) that
	 * should be searchable.
	 */
	private Function<Map.Entry<String, LinearUnit>, Map<String, LinearUnit>> searchRule = PrefixSearchRule.NO_PREFIXES;
	
	/**
	 * The set of units that is considered neither metric nor nonmetric for the
	 * purposes of the metric-imperial one-way conversion. These units are
	 * included in both From and To, even if One Way Conversion is enabled.
	 */
	private final Set<String> metricExceptions;
	
	/**
	 * If this is true, views that show units as a list will have metric units
	 * removed from the From unit list and imperial/USC units removed from the To
	 * unit list.
	 */
	private boolean oneWayConversionEnabled = false;
	
	/**
	 * If this is false, duplicate units and prefixes will be removed from the
	 * unit view in views that show units as a list to choose from.
	 */
	private boolean showDuplicates = false;
	
	/**
	 * Creates a Presenter
	 * 
	 * @param view the view that this presenter communicates with
	 * @since 2021-12-15
	 */
	public Presenter(View view) {
		this.view = view;
		this.database = new UnitDatabase();
		addDefaults(this.database);
		
		// load units and prefixes
		try (final InputStream units = inputStream(DEFAULT_UNITS_FILEPATH)) {
			this.database.loadUnitsFromStream(units);
		} catch (final IOException e) {
			throw new AssertionError("Loading of unitsfile.txt failed.", e);
		}
		
		// load dimensions
		try (final InputStream dimensions = inputStream(
				DEFAULT_DIMENSIONS_FILEPATH)) {
			this.database.loadDimensionsFromStream(dimensions);
		} catch (final IOException e) {
			throw new AssertionError("Loading of dimensionfile.txt failed.", e);
		}
		
		// load metric exceptions
		try {
			this.metricExceptions = new HashSet<>();
			try (InputStream exceptions = inputStream(DEFAULT_EXCEPTIONS_FILEPATH);
					Scanner scanner = new Scanner(exceptions)) {
				while (scanner.hasNextLine()) {
					final String line = Presenter
							.withoutComments(scanner.nextLine());
					if (!line.isBlank()) {
						this.metricExceptions.add(line);
					}
				}
			}
		} catch (final IOException e) {
			throw new AssertionError("Loading of metric_exceptions.txt failed.",
					e);
		}
		
		// set default settings temporarily
		CONFIG_FILE.ifPresentOrElse(this::loadSettings, () -> {
			this.view.showErrorMessage("Config Loading Error", "Could not load config file - using default settings.");
		});
		
		// a Predicate that returns true iff the argument is a full base unit
		final Predicate<Unit> isFullBase = unit -> unit instanceof LinearUnit
				&& ((LinearUnit) unit).isBase();
		
		// print out unit counts
		System.out.printf(
				"Successfully loaded %d units with %d unit names (%d base units).%n",
				this.database.unitMapPrefixless(false).size(),
				this.database.unitMapPrefixless(true).size(),
				this.database.unitMapPrefixless(false).values().stream()
						.filter(isFullBase).count());
	}
	
	/**
	 * Applies a search rule to an entry in a name-unit map.
	 *
	 * @param e entry
	 * @return stream of entries, ready for flat-mapping
	 * @since 2022-07-06
	 */
	private final Stream<Map.Entry<String, Unit>> applySearchRule(
			Map.Entry<String, Unit> e) {
		final Unit u = e.getValue();
		if (u instanceof LinearUnit) {
			final String name = e.getKey();
			final Map.Entry<String, LinearUnit> linearEntry = Map.entry(name,
					(LinearUnit) u);
			return this.searchRule.apply(linearEntry).entrySet().stream().map(
					entry -> Map.entry(entry.getKey(), (Unit) entry.getValue()));
		} else
			return Stream.of(e);
	}
	
	/**
	 * Converts from the view's input expression to its output expression.
	 * Displays an error message if any of the required fields are invalid.
	 * 
	 * @throws UnsupportedOperationException if the view does not support
	 *                                       expression-based conversion (does
	 *                                       not implement
	 *                                       {@link ExpressionConversionView})
	 * @since 2021-12-15
	 */
	public void convertExpressions() {
		if (this.view instanceof ExpressionConversionView) {
			final ExpressionConversionView xcview = (ExpressionConversionView) this.view;
			
			final String fromExpression = xcview.getFromExpression();
			final String toExpression = xcview.getToExpression();
			
			// expressions must not be empty
			if (fromExpression.isEmpty()) {
				this.view.showErrorMessage("Parse Error",
						"Please enter a unit expression in the From: box.");
				return;
			}
			if (toExpression.isEmpty()) {
				this.view.showErrorMessage("Parse Error",
						"Please enter a unit expression in the To: box.");
				return;
			}
			
			// evaluate expressions
			final LinearUnitValue from;
			final Unit to;
			try {
				from = this.database.evaluateUnitExpression(fromExpression);
			} catch (final IllegalArgumentException | NoSuchElementException e) {
				this.view.showErrorMessage("Parse Error",
						"Could not recognize text in From entry: " + e.getMessage());
				return;
			}
			try {
				to = this.database.getUnitFromExpression(toExpression);
			} catch (final IllegalArgumentException | NoSuchElementException e) {
				this.view.showErrorMessage("Parse Error",
						"Could not recognize text in To entry: " + e.getMessage());
				return;
			}
			
			// convert and show output
			if (from.getUnit().canConvertTo(to)) {
				final UncertainDouble uncertainValue;
				
				// uncertainty is meaningless for non-linear units, so we will have
				// to erase uncertainty information for them
				if (to instanceof LinearUnit) {
					final var toLinear = (LinearUnit) to;
					uncertainValue = from.convertTo(toLinear).getValue();
				} else {
					final double value = from.asUnitValue().convertTo(to).getValue();
					uncertainValue = UncertainDouble.of(value, 0);
				}
				
				final UnitConversionRecord uc = UnitConversionRecord.valueOf(
						fromExpression, toExpression, "",
						this.numberDisplayRule.apply(uncertainValue));
				xcview.showExpressionConversionOutput(uc);
			} else {
				this.view.showErrorMessage("Conversion Error",
						"Cannot convert between \"" + fromExpression + "\" and \""
								+ toExpression + "\".");
			}
			
		} else
			throw new UnsupportedOperationException(
					"This function can only be called when the view is an ExpressionConversionView");
	}
	
	/**
	 * Converts from the view's input unit to its output unit. Displays an error
	 * message if any of the required fields are invalid.
	 * 
	 * @throws UnsupportedOperationException if the view does not support
	 *                                       unit-based conversion (does not
	 *                                       implement
	 *                                       {@link UnitConversionView})
	 * @since 2021-12-15
	 */
	public void convertUnits() {
		if (this.view instanceof UnitConversionView) {
			final UnitConversionView ucview = (UnitConversionView) this.view;
			
			final Optional<String> fromUnitOptional = ucview.getFromSelection();
			final Optional<String> toUnitOptional = ucview.getToSelection();
			final String inputValueString = ucview.getInputValue();
			
			// extract values from optionals
			final String fromUnitString, toUnitString;
			if (fromUnitOptional.isPresent()) {
				fromUnitString = fromUnitOptional.orElseThrow();
			} else {
				this.view.showErrorMessage("Unit Selection Error",
						"Please specify a From unit");
				return;
			}
			if (toUnitOptional.isPresent()) {
				toUnitString = toUnitOptional.orElseThrow();
			} else {
				this.view.showErrorMessage("Unit Selection Error",
						"Please specify a To unit");
				return;
			}
			
			// convert strings to data, checking if anything is invalid
			final Unit fromUnit, toUnit;
			final UncertainDouble uncertainValue;
			
			if (this.database.containsUnitName(fromUnitString)) {
				fromUnit = this.database.getUnit(fromUnitString);
			} else
				throw this.viewError("Nonexistent From unit: %s", fromUnitString);
			if (this.database.containsUnitName(toUnitString)) {
				toUnit = this.database.getUnit(toUnitString);
			} else
				throw this.viewError("Nonexistent To unit: %s", toUnitString);
			try {
				uncertainValue = UncertainDouble
						.fromRoundedString(inputValueString);
			} catch (final NumberFormatException e) {
				this.view.showErrorMessage("Value Error",
						"Invalid value " + inputValueString);
				return;
			}
			
			if (!fromUnit.canConvertTo(toUnit))
				throw this.viewError("Could not convert between %s and %s",
						fromUnit, toUnit);
				
			// convert - we will need to erase uncertainty for non-linear units, so
			// we need to treat linear and non-linear units differently
			final String outputValueString;
			if (fromUnit instanceof LinearUnit && toUnit instanceof LinearUnit) {
				final LinearUnit fromLinear = (LinearUnit) fromUnit;
				final LinearUnit toLinear = (LinearUnit) toUnit;
				final LinearUnitValue initialValue = LinearUnitValue.of(fromLinear,
						uncertainValue);
				final LinearUnitValue converted = initialValue.convertTo(toLinear);
				
				outputValueString = this.numberDisplayRule
						.apply(converted.getValue());
			} else {
				final UnitValue initialValue = UnitValue.of(fromUnit,
						uncertainValue.value());
				final UnitValue converted = initialValue.convertTo(toUnit);
				
				outputValueString = this.numberDisplayRule
						.apply(UncertainDouble.of(converted.getValue(), 0));
			}
			
			ucview.showUnitConversionOutput(
					UnitConversionRecord.valueOf(fromUnitString, toUnitString,
							inputValueString, outputValueString));
		} else
			throw new UnsupportedOperationException(
					"This function can only be called when the view is a UnitConversionView.");
	}
	
	/**
	 * @return true iff duplicate units are shown in unit lists
	 * @since 2022-03-30
	 */
	public boolean duplicatesShown() {
		return this.showDuplicates;
	}
	
	/**
	 * Gets a name for this dimension using the database
	 *
	 * @param dimension dimension to name
	 * @return name of dimension
	 * @since 2022-04-16
	 */
	final String getDimensionName(ObjectProduct<BaseDimension> dimension) {
		// find this dimension in the database and get its name
		// if it isn't there, use the dimension's toString instead
		return this.database.dimensionMap().values().stream()
				.filter(d -> d.equals(dimension)).findAny().map(Nameable::getName)
				.orElse(dimension.toString(Nameable::getName));
	}
	
	/**
	 * @return the rule that is used by this presenter to convert numbers into
	 *         strings
	 * @since 2022-04-10
	 */
	public Function<UncertainDouble, String> getNumberDisplayRule() {
		return this.numberDisplayRule;
	}
	
	/**
	 * @return the rule that is used by this presenter to convert strings into
	 *         numbers
	 * @since 2022-04-10
	 */
	@SuppressWarnings("unused") // not implemented yet
	private Function<String, UncertainDouble> getNumberParsingRule() {
		return this.numberParsingRule;
	}
	
	/**
	 * @return the rule that determines whether a set of prefixes is valid
	 * @since 2022-04-19
	 */
	public Predicate<List<UnitPrefix>> getPrefixRepetitionRule() {
		return this.prefixRepetitionRule;
	}
	
	/**
	 * @return the rule that determines which units are prefixed
	 * @since 2022-07-08
	 */
	public Function<Map.Entry<String, LinearUnit>, Map<String, LinearUnit>> getSearchRule() {
		return this.searchRule;
	}
	
	/**
	 * @return a search rule that shows all single prefixes
	 * @since 2022-07-08
	 */
	public Function<Map.Entry<String, LinearUnit>, Map<String, LinearUnit>> getUniversalSearchRule() {
		return PrefixSearchRule.getCoherentOnlyRule(
				new HashSet<>(this.database.prefixMap(true).values()));
	}
	
	/**
	 * @return the view associated with this presenter
	 * @since 2022-04-19
	 */
	public View getView() {
		return this.view;
	}
	
	/**
	 * @return whether or not the provided unit is semi-metric (i.e. an
	 *         exception)
	 * @since 2022-04-16
	 */
	final boolean isSemiMetric(Unit u) {
		// determine if u is an exception
		final var primaryName = u.getPrimaryName();
		final var symbol = u.getSymbol();
		return primaryName.isPresent()
				&& this.metricExceptions.contains(primaryName.orElseThrow())
				|| symbol.isPresent()
						&& this.metricExceptions.contains(symbol.orElseThrow())
				|| sharesAnyElements(this.metricExceptions, u.getOtherNames());
	}
	
	/**
	 * Loads settings from the user's settings file and applies them to the
	 * presenter.
	 *
	 * @param settingsFile file settings should be loaded from
	 * @since 2021-12-15
	 */
	void loadSettings(Path settingsFile) {
		try {
			// read file line by line
			final int lineNum = 0;
			for (final String line : Files.readAllLines(settingsFile)) {
				final int equalsIndex = line.indexOf('=');
				if (equalsIndex == -1)
					throw new IllegalStateException(
							"Settings file is malformed at line " + lineNum);
				
				final String param = line.substring(0, equalsIndex);
				final String value = line.substring(equalsIndex + 1);
				
				switch (param) {
				// set manually to avoid the unnecessary saving of the non-manual
				// methods
				case "custom_dimension_file":
					this.database.loadDimensionFile(pathFromConfig(value));
					break;
				case "custom_exception_file":
					Files.lines(pathFromConfig(value))
						.map(Presenter::withoutComments)
						.forEach(this.metricExceptions::add);
					break;
				case "custom_unit_file":
					this.database.loadUnitsFile(pathFromConfig(value));
					break;
				case "number_display_rule":
					this.numberDisplayRule = StandardDisplayRules
							.getStandardRule(value);
					break;
				case "prefix_rule":
					this.prefixRepetitionRule = DefaultPrefixRepetitionRule
							.valueOf(value);
					this.database.setPrefixRepetitionRule(this.prefixRepetitionRule);
					break;
				case "one_way":
					this.oneWayConversionEnabled = Boolean.valueOf(value);
					break;
				case "include_duplicates":
					this.showDuplicates = Boolean.valueOf(value);
					break;
				case "search_prefix_rule":
					if (PrefixSearchRule.NO_PREFIXES.toString().equals(value)) {
						this.searchRule = PrefixSearchRule.NO_PREFIXES;
					} else if (PrefixSearchRule.COMMON_PREFIXES.toString()
							.equals(value)) {
						this.searchRule = PrefixSearchRule.COMMON_PREFIXES;
					} else {
						this.searchRule = this.getUniversalSearchRule();
					}
					break;
				default:
					System.err.printf("Warning: unrecognized setting \"%s\".%n",
							param);
					break;
				}
			}
			if (this.view.getPresenter() != null) {
				this.updateView();
			}
		} catch (final IOException e) {}
	}
	
	/**
	 * @return true iff the One-Way Conversion feature is available (views that
	 *         show units as a list will have metric units removed from the From
	 *         unit list and imperial/USC units removed from the To unit list)
	 * 
	 * @since 2022-03-30
	 */
	public boolean oneWayConversionEnabled() {
		return this.oneWayConversionEnabled;
	}
	
	/**
	 * Completes creation of the presenter. This part of the initialization
	 * depends on the view's functions, so it cannot be run if the components
	 * they depend on are not created yet.
	 * 
	 * @since 2022-02-26
	 */
	public void postViewInitialize() {
		// unit conversion specific stuff
		if (this.view instanceof UnitConversionView) {
			final UnitConversionView ucview = (UnitConversionView) this.view;
			ucview.setDimensionNames(this.database.dimensionMap().keySet());
		}
		
		this.updateView();
	}
	
	void prefixSelected() {
		final Optional<String> selectedPrefixName = this.view
				.getViewedPrefixName();
		final Optional<UnitPrefix> selectedPrefix = selectedPrefixName
				.map(name -> this.database.containsPrefixName(name)
						? this.database.getPrefix(name)
						: null);
		selectedPrefix
				.ifPresent(prefix -> this.view.showPrefix(prefix.getNameSymbol(),
						String.valueOf(prefix.getMultiplier())));
	}
	
	/**
	 * Saves the presenter's current settings to its default filepath.
	 * 
	 * @return true iff this operation succeeded
	 * @since 2022-04-19
	 */
	public boolean saveSettings() {
		CONFIG_FILE.ifPresent(this::saveSettings);
		return CONFIG_FILE.isPresent();
	}
	
	/**
	 * Saves the presenter's settings to the user settings file.
	 * 
	 * @param settingsFile file settings should be saved to
	 * @since 2021-12-15
	 */
	void saveSettings(Path settingsFile) {
		try (BufferedWriter writer = Files.newBufferedWriter(settingsFile)) {
			writer.write(String.format("number_display_rule=%s\n",
					this.numberDisplayRule));
			writer.write(
					String.format("prefix_rule=%s\n", this.prefixRepetitionRule));
			writer.write(
					String.format("one_way=%s\n", this.oneWayConversionEnabled));
			writer.write(
					String.format("include_duplicates=%s\n", this.showDuplicates));
			writer.write(
					String.format("search_prefix_rule=%s\n", this.searchRule));
		} catch (final IOException e) {
			e.printStackTrace();
			this.view.showErrorMessage("I/O Error",
					"Error occurred while saving settings: "
							+ e.getLocalizedMessage());
		}
	}
	
	/**
	 * @param numberDisplayRule the new rule that will be used by this presenter
	 *                          to convert numbers into strings
	 * @since 2022-04-10
	 */
	public void setNumberDisplayRule(
			Function<UncertainDouble, String> numberDisplayRule) {
		this.numberDisplayRule = numberDisplayRule;
	}
	
	/**
	 * @param numberParsingRule the new rule that will be used by this presenter
	 *                          to convert strings into numbers
	 * @since 2022-04-10
	 */
	@SuppressWarnings("unused") // not implemented yet
	private void setNumberParsingRule(
			Function<String, UncertainDouble> numberParsingRule) {
		this.numberParsingRule = numberParsingRule;
	}
	
	/**
	 * @param oneWayConversionEnabled whether not one-way conversion should be
	 *                                enabled
	 * @since 2022-03-30
	 * @see {@link #isOneWayConversionEnabled}
	 */
	public void setOneWayConversionEnabled(boolean oneWayConversionEnabled) {
		this.oneWayConversionEnabled = oneWayConversionEnabled;
		this.updateView();
	}
	
	/**
	 * @param prefixRepetitionRule the rule that determines whether a set of
	 *                             prefixes is valid
	 * @since 2022-04-19
	 */
	public void setPrefixRepetitionRule(
			Predicate<List<UnitPrefix>> prefixRepetitionRule) {
		this.prefixRepetitionRule = prefixRepetitionRule;
		this.database.setPrefixRepetitionRule(prefixRepetitionRule);
	}
	
	/**
	 * @param searchRule A rule that accepts a prefixless name-unit pair and
	 *                   returns a map mapping names to prefixed versions of that
	 *                   unit (including the unit itself) that should be
	 *                   searchable.
	 * @since 2022-07-08
	 */
	public void setSearchRule(
			Function<Map.Entry<String, LinearUnit>, Map<String, LinearUnit>> searchRule) {
		this.searchRule = searchRule;
	}
	
	/**
	 * @param showDuplicateUnits whether or not duplicate units should be shown
	 * @since 2022-03-30
	 */
	public void setShowDuplicates(boolean showDuplicateUnits) {
		this.showDuplicates = showDuplicateUnits;
		this.updateView();
	}
	
	/**
	 * Shows a unit in the unit viewer
	 *
	 * @param u unit to show
	 * @since 2022-04-16
	 */
	private final void showUnit(Unit u) {
		final var nameSymbol = u.getNameSymbol();
		final boolean isBase = u instanceof BaseUnit
				|| u instanceof LinearUnit && ((LinearUnit) u).isBase();
		final var definition = isBase ? "(Base unit)" : u.toDefinitionString();
		final var dimensionString = this.getDimensionName(u.getDimension());
		final var unitType = UnitType.getType(u, this::isSemiMetric);
		this.view.showUnit(nameSymbol, definition, dimensionString, unitType);
	}
	
	/**
	 * Runs whenever a unit name is selected in the unit viewer. Gets the
	 * description of a unit and displays it.
	 * 
	 * @since 2022-04-10
	 */
	void unitNameSelected() {
		// get selected unit, if it's there and valid
		final Optional<String> selectedUnitName = this.view.getViewedUnitName();
		final Optional<Unit> selectedUnit = selectedUnitName
				.map(unitName -> this.database.containsUnitName(unitName)
						? this.database.getUnit(unitName)
						: null);
		selectedUnit.ifPresent(this::showUnit);
	}
	
	/**
	 * Updates the view's From and To units, if it has some
	 * 
	 * @since 2021-12-15
	 */
	public void updateView() {
		if (this.view instanceof UnitConversionView) {
			final UnitConversionView ucview = (UnitConversionView) this.view;
			final var selectedDimensionName = ucview.getSelectedDimensionName();
			
			// load units & prefixes into viewers
			this.view.setViewableUnitNames(
					this.database.unitMapPrefixless(this.showDuplicates).keySet());
			this.view.setViewablePrefixNames(
					this.database.prefixMap(this.showDuplicates).keySet());
			
			// get From and To units
			var fromUnits = this.database.unitMapPrefixless(this.showDuplicates)
					.entrySet().stream();
			var toUnits = this.database.unitMapPrefixless(this.showDuplicates)
					.entrySet().stream();
			
			// filter by dimension, if one is selected
			if (selectedDimensionName.isPresent()) {
				final var viewDimension = this.database
						.getDimension(selectedDimensionName.orElseThrow());
				fromUnits = fromUnits.filter(
						u -> viewDimension.equals(u.getValue().getDimension()));
				toUnits = toUnits.filter(
						u -> viewDimension.equals(u.getValue().getDimension()));
			}
			
			// filter by unit type, if desired
			if (this.oneWayConversionEnabled) {
				fromUnits = fromUnits.filter(u -> UnitType.getType(u.getValue(),
						this::isSemiMetric) != UnitType.METRIC);
				toUnits = toUnits.filter(u -> UnitType.getType(u.getValue(),
						this::isSemiMetric) != UnitType.NON_METRIC);
			}
			
			// set unit names
			ucview.setFromUnitNames(fromUnits.flatMap(this::applySearchRule)
					.map(Map.Entry::getKey).collect(Collectors.toSet()));
			ucview.setToUnitNames(toUnits.flatMap(this::applySearchRule)
					.map(Map.Entry::getKey).collect(Collectors.toSet()));
		}
	}
	
	/**
	 * @param message message to add
	 * @param args    string formatting arguments for message
	 * @return AssertionError stating that an error has happened in the view's
	 *         code
	 * @since 2022-04-09
	 */
	private AssertionError viewError(String message, Object... args) {
		return new AssertionError("View Programming Error (from " + this.view
				+ "): " + String.format(message, args));
	}
}