/**
 * Copyright (C) 2019 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 sevenUnits.unit;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.Assertions.fail;

import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Set;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;

import sevenUnits.utils.NameSymbol;
import sevenUnits.utils.UncertainDouble;

/**
 * A test for the {@link UnitDatabase} class. This is NOT part of this program's
 * public API.
 * 
 * @author Adrien Hopkins
 * @since 2019-04-14
 * @since v0.2.0
 */
class UnitDatabaseTest {
	private static final class SimpleEntry<K, V> implements Map.Entry<K, V> {
		private final K key;
		
		private V value;
		
		/**
		 * 
		 * @since 2021-10-07
		 */
		public SimpleEntry(K key, V value) {
			this.key = key;
			this.value = value;
		}
		
		@Override
		public boolean equals(Object obj) {
			if (this == obj)
				return true;
			if (!(obj instanceof Map.Entry<?, ?>))
				return false;
			final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
			return Objects.equals(this.key, other.getKey())
					&& Objects.equals(this.value, other.getValue());
		}
		
		@Override
		public K getKey() {
			return this.key;
		}
		
		@Override
		public V getValue() {
			return this.value;
		}
		
		@Override
		public int hashCode() {
			return (this.key == null ? 0 : this.key.hashCode())
					^ (this.value == null ? 0 : this.value.hashCode());
		}
		
		@Override
		public V setValue(V value) {
			final V oldValue = this.value;
			this.value = value;
			return oldValue;
		}
	}
	
	// some linear units and one nonlinear
	private static final Unit U = Metric.METRE;
	private static final Unit V = Metric.KILOGRAM;
	
	private static final Unit W = Metric.SECOND;
	// used for testing expressions
	// J = U^2 * V / W^2
	private static final LinearUnit J = Metric.KILOGRAM
			.times(Metric.METRE.toExponent(2))
			.dividedBy(Metric.SECOND.toExponent(2));
	
	private static final LinearUnit K = Metric.KELVIN;
	
	private static final Unit NONLINEAR = Unit.fromConversionFunctions(
			Metric.METRE.getBase(), o -> o + 1, o -> o - 1);
	// make the prefix values prime so I can tell which multiplications were made
	private static final UnitPrefix A = UnitPrefix.valueOf(2)
			.withName(NameSymbol.ofName("A"));
	private static final UnitPrefix B = UnitPrefix.valueOf(3)
			.withName(NameSymbol.ofName("B"));
	private static final UnitPrefix C = UnitPrefix.valueOf(5)
			.withName(NameSymbol.ofName("C"));
	private static final UnitPrefix AB = UnitPrefix.valueOf(7);
	
	private static final UnitPrefix BC = UnitPrefix.valueOf(11);
	
	/**
	 * Gets a map entry.
	 *
	 * @param <K>   type of key
	 * @param <V>   type of value
	 * @param key   key in entry
	 * @param value value in entry
	 * @return entry
	 * @since 2021-10-07
	 */
	private static <K, V> Map.Entry<K, V> entry(K key, V value) {
		return new SimpleEntry<>(key, value);
	}
	
	/**
	 * Loads the dimensionfile at src/test/resources/[path] to the database
	 * {@code loadTo}.
	 *
	 * @param loadTo database to load to
	 * @param path   path of file to load
	 * @since 2021-10-04
	 */
	private static void loadDimensionFile(UnitDatabase loadTo, String path) {
		try (final InputStream testFile = UnitDatabaseTest.class
				.getResourceAsStream(path)) {
			loadTo.loadDimensionsFromStream(testFile);
		} catch (final IOException e) {
			fail(e.getClass() + " occurred upon loading file \"" + path + "\".");
		}
	}
	
	/**
	 * Loads the unitfile at src/test/resources/[path] to the database
	 * {@code loadTo}.
	 *
	 * @param loadTo database to load to
	 * @param path   path of file to load
	 * @since 2021-09-22
	 */
	private static void loadUnitsFile(UnitDatabase loadTo, String path) {
		try (final InputStream testFile = UnitDatabaseTest.class
				.getResourceAsStream(path)) {
			loadTo.loadUnitsFromStream(testFile);
		} catch (final IOException e) {
			fail(e.getClass() + " occurred upon loading file \"" + path + "\".");
		}
	}
	
	/**
	 * A test for the {@link UnitDatabase#evaluateUnitExpression(String)}
	 * function. Simple because the expression parser has its own test.
	 * 
	 * @since 2021-09-27
	 */
	@Test
	public void testEvaluateExpression() {
		final UnitDatabase database = new UnitDatabase();
		
		database.addUnit("J", J);
		database.addUnit("K", K);
		
		database.addPrefix("A", A);
		database.addPrefix("B", B);
		database.addPrefix("C", C);
		
		final LinearUnitValue expected = LinearUnitValue.of(J,
				UncertainDouble.of(12, Math.sqrt(14.625)));
		// note: units are exact, each number has an uncertainty of 1
		final LinearUnitValue actual = database
				.evaluateUnitExpression("J + (2 * 3) J + (20 / 4) J");
		assertEquals(expected, actual);
		
		// check that negation works properly
		assertEquals(2,
				database.evaluateUnitExpression("J - -1 * J").getValueExact());
	}
	
	/**
	 * Test for {@link UnitDatabase#getUnit}, {@link UnitDatabase#getLinearUnit}
	 * and {@link UnitDatabase#getLinearUnitValue}.
	 * 
	 * @since 2021-10-07
	 */
	@Test
	public void testGetUnit() {
		final UnitDatabase database = new UnitDatabase();
		
		database.addUnit("m", Metric.METRE);
		database.addUnit("meter", Metric.METRE);
		database.addUnit("metre", Metric.METRE);
		database.addUnit("badname", Metric.METRE);
		database.addUnit("K", Metric.KELVIN);
		database.addUnit("degC", Metric.CELSIUS);
		
		// ensure getUnit returns units, regardless of whether the name is one of
		// the unit's names
		assertEquals(Metric.METRE, database.getUnit("m"));
		assertEquals(Metric.METRE, database.getUnit("metre"));
		assertEquals(Metric.METRE, database.getUnit("meter"));
		assertEquals(Metric.METRE, database.getUnit("badname"));
		assertThrows(NoSuchElementException.class,
				() -> database.getUnit("blabla"));
		
		assertEquals(Metric.KELVIN, database.getLinearUnit("K"));
		assertThrows(IllegalArgumentException.class,
				() -> database.getLinearUnit("degC"));
		assertEquals(Metric.KELVIN.times(373.15),
				database.getLinearUnit("degC(100)"));
	}
	
	/**
	 * Confirms that operations that shouldn't function for infinite databases
	 * throw an {@code IllegalStateException}.
	 * 
	 * @since 2019-05-03
	 */
//	@Test
//	@Timeout(value = 1, unit = TimeUnit.SECONDS)
	public void testInfiniteSetExceptions() {
		// load units
		final UnitDatabase infiniteDatabase = new UnitDatabase();
		
		infiniteDatabase.addUnit("J", J);
		infiniteDatabase.addUnit("K", K);
		
		infiniteDatabase.addPrefix("A", A);
		infiniteDatabase.addPrefix("B", B);
		infiniteDatabase.addPrefix("C", C);
		
		final Set<Entry<String, Unit>> entrySet = infiniteDatabase.unitMap()
				.entrySet();
		final Set<String> keySet = infiniteDatabase.unitMap().keySet();
		assertThrows(IllegalStateException.class, () -> entrySet.toArray());
		assertThrows(IllegalStateException.class, () -> keySet.toArray());
	}
	
	/**
	 * A bunch of tests for invalid dimension files
	 *
	 * @param num which file to test
	 * @since 2021-10-04
	 */
	@ParameterizedTest
	@ValueSource(ints = { 1, 2, 3 })
	public void testLoadingInvalidDimensionFile(int num) {
		final UnitDatabase database = new UnitDatabase();
		database.addDimension("LENGTH", Metric.Dimensions.LENGTH);
		database.addDimension("MASS", Metric.Dimensions.MASS);
		database.addDimension("TIME", Metric.Dimensions.TIME);
		final String filename = String.format("/test-dimensionfile-invalid%d.txt",
				num);
		final RuntimeException e = assertThrows(RuntimeException.class,
				() -> loadDimensionFile(database, filename));
		assertTrue(e instanceof IllegalArgumentException
				|| e instanceof NoSuchElementException);
	}
	
	/**
	 * A bunch of tests for invalid unit files
	 *
	 * @param num which file to test
	 * @since 2021-09-27
	 */
	@ParameterizedTest
	@ValueSource(ints = { 1, 2, 3, 4, 5 })
	public void testLoadingInvalidUnitFile(int num) {
		final UnitDatabase database = new UnitDatabase();
		final String filename = String.format("/test-unitsfile-invalid%d.txt",
				num);
		final RuntimeException e = assertThrows(RuntimeException.class,
				() -> loadUnitsFile(database, filename));
		assertTrue(e instanceof IllegalArgumentException
				|| e instanceof NoSuchElementException);
	}
	
	/**
	 * Tests loading a valid dimension-file with some derived dimensions.
	 * 
	 * @since 2021-10-04
	 */
	@Test
	public void testLoadingValidDimensions() {
		final UnitDatabase database = new UnitDatabase();
		database.addDimension("LENGTH", Metric.Dimensions.LENGTH);
		database.addDimension("MASS", Metric.Dimensions.MASS);
		database.addDimension("TIME", Metric.Dimensions.TIME);
		
		loadDimensionFile(database, "/test-dimensionfile-valid1.txt");
		assertEquals(Metric.Dimensions.ENERGY, database.getDimension("ENERGY"));
		assertEquals(Metric.Dimensions.POWER, database.getDimension("POWER"));
		
	}
	
	/**
	 * Tests loading a valid unitfile with some prefixes and no units.
	 * 
	 * @since 2021-09-22
	 */
	@Test
	public void testLoadingValidPrefixes() {
		final UnitDatabase database = new UnitDatabase();
		
		loadUnitsFile(database, "/test-unitsfile-valid2.txt");
		assertEquals(7, database.getPrefix("A").getMultiplier());
		assertEquals(11, database.getPrefix("B").getMultiplier());
		assertEquals(13, database.getPrefix("C").getMultiplier());
	}
	
	/**
	 * Tests loading a valid unitfile with some units and preloaded prefixes
	 * 
	 * @since 2021-09-22
	 */
	@Test
	public void testLoadingValidUnits() {
		final UnitDatabase database = new UnitDatabase();
		
		database.addUnit("U", U);
		database.addUnit("V", V);
		database.addUnit("W", W);
		database.addUnit("fj", J.times(5));
		database.addUnit("ej", J.times(8));
		
		database.addPrefix("A", A);
		database.addPrefix("B", B);
		database.addPrefix("C", C);
		
		loadUnitsFile(database, "/test-unitsfile-valid1.txt");
		
		final Unit expected1 = ((LinearUnit) U).withPrefix(A).withPrefix(B)
				.withPrefix(C);
		final Unit actual1 = database.getUnit("test1");
		assertEquals(expected1, actual1);
		
		final Unit expected2 = ((LinearUnit) W).withPrefix(B)
				.times(((LinearUnit) V).withPrefix(C));
		final Unit actual2 = database.getUnit("test2");
		assertEquals(expected2, actual2);
		
		final Unit expected3 = ((LinearUnit) U)
				.times(A.getMultiplier() + C.getMultiplier() - B.getMultiplier());
		final Unit actual3 = database.getUnit("test3");
		assertEquals(expected3, actual3);
		
		final UnitValue expected4 = UnitValue.of(U, 1);
		final UnitValue actual4 = database
				.evaluateUnitExpression("-5 * U + -3 * U + 12 * U - 3 * U")
				.asUnitValue();
		assertEquals(expected4, actual4);
		
		assertTrue(System.err.toString().length() > 0);
	}
	
	/**
	 * Tests the iterator of the prefixless unit map. These tests are simple, as
	 * the unit map iterator is simple.
	 * 
	 * @since 2021-10-07
	 */
	@Test
	public void testPrefixedUnitMapIterator() {
		final UnitDatabase database1 = new UnitDatabase();
		
		database1.addUnit("U", U);
		database1.addUnit("V", V);
		database1.addUnit("W", W);
		
		final Map<String, Unit> map1 = database1.unitMap();
		final Iterator<String> keyIterator1 = map1.keySet().iterator();
		final Iterator<Map.Entry<String, Unit>> entryIterator1 = map1.entrySet()
				.iterator();
		
		final Set<String> expectedKeys = Set.of("U", "V", "W");
		final Set<String> actualKeys = new HashSet<>();
		while (keyIterator1.hasNext()) {
			actualKeys.add(keyIterator1.next());
		}
		assertEquals(expectedKeys, actualKeys);
		assertEquals(expectedKeys, map1.keySet());
		
		final Set<Map.Entry<String, Unit>> expectedEntries = Set.of(entry("U", U),
				entry("V", V), entry("W", W));
		final Set<Map.Entry<String, Unit>> actualEntries = new HashSet<>();
		while (entryIterator1.hasNext()) {
			actualEntries.add(entryIterator1.next());
		}
		assertEquals(expectedEntries, actualEntries);
		assertEquals(expectedEntries, map1.entrySet());
	}
	
	/**
	 * Test that prefixes correctly apply to units.
	 * 
	 * @since 2019-04-14
	 * @since v0.2.0
	 */
	@Test
	public void testPrefixes() {
		final UnitDatabase database = new UnitDatabase();
		
		database.addUnit("U", U);
		database.addUnit("V", V);
		database.addUnit("W", W);
		
		database.addPrefix("A", A);
		database.addPrefix("B", B);
		database.addPrefix("C", C);
		
		// test the getPrefixesFromName method
		final List<UnitPrefix> expected = Arrays.asList(C, B, A);
		assertEquals(expected, database.getPrefixesFromName("ABCU"));
		
		// get the product
		final Unit abcuNonlinear = database.getUnit("ABCU");
		assert abcuNonlinear instanceof LinearUnit;
		
		final LinearUnit abcu = (LinearUnit) abcuNonlinear;
		assertEquals(A.getMultiplier() * B.getMultiplier() * C.getMultiplier(),
				abcu.getConversionFactor(), 1e-15);
	}
	
	/**
	 * Tests the functionnalites of the prefixless unit map.
	 * 
	 * <p>
	 * The map should be an auto-updating view of the units in the database.
	 * </p>
	 * 
	 * @since 2019-04-14
	 * @since v0.2.0
	 */
	@Test
	public void testPrefixlessUnitMap() {
		final UnitDatabase database = new UnitDatabase();
		final Map<String, Unit> prefixlessUnits = database
				.unitMapPrefixless(true);
		
		database.addUnit("U", U);
		database.addUnit("V", V);
		database.addUnit("W", W);
		
		// this should work because the map should be an auto-updating view
		assertTrue(prefixlessUnits.containsKey("U"));
		assertFalse(prefixlessUnits.containsKey("Z"));
		
		assertTrue(prefixlessUnits.containsValue(U));
		assertFalse(prefixlessUnits.containsValue(NONLINEAR));
	}
	
	/**
	 * Tests that the database correctly stores and retrieves units, ignoring
	 * prefixes.
	 * 
	 * @since 2019-04-14
	 * @since v0.2.0
	 */
	@Test
	public void testPrefixlessUnits() {
		final UnitDatabase database = new UnitDatabase();
		
		database.addUnit("U", U);
		database.addUnit("V", V);
		database.addUnit("W", W);
		
		assertTrue(database.containsUnitName("U"));
		assertFalse(database.containsUnitName("Z"));
		
		assertEquals(U, database.getUnit("U"));
		assertThrows(NoSuchElementException.class, () -> database.getUnit("Z"));
	}
	
	@Test
	public void testRemovableDuplicates() {
		final Map<String, Unit> unitMap = new HashMap<>();
		unitMap.put("meter", Metric.METRE);
		unitMap.put("metre", Metric.METRE);
		unitMap.put("m", Metric.METRE);
		unitMap.put("second", Metric.SECOND);
		
		assertTrue(UnitDatabase.isRemovableDuplicate(unitMap,
				entry("m", Metric.METRE)));
		assertTrue(UnitDatabase.isRemovableDuplicate(unitMap,
				entry("meter", Metric.METRE)));
		assertFalse(UnitDatabase.isRemovableDuplicate(unitMap,
				entry("metre", Metric.METRE)));
		assertFalse(UnitDatabase.isRemovableDuplicate(unitMap,
				entry("second", Metric.SECOND)));
	}
	
	@Test
	public void testToString() {
		final UnitDatabase database = new UnitDatabase();
		
		database.addUnit("J", J);
		database.addUnit("K", J);
		
		database.addPrefix("A", A);
		database.addPrefix("B", B);
		database.addPrefix("C", C);
		
		if ("Unit Database with 1 units, 3 unit prefixes and 0 dimensions"
				.equals(database.toString())) {
			fail("Database counts by number of units, not number of unit names.");
		}
		
		assertEquals(
				"Unit Database with 2 units, 3 unit prefixes and 0 dimensions",
				database.toString());
	}
	
	/**
	 * Test that unit expressions return the correct value.
	 * 
	 * @since 2019-04-14
	 * @since v0.2.0
	 */
	@Test
	public void testUnitExpressions() {
		// load units
		final UnitDatabase database = new UnitDatabase();
		
		database.addUnit("U", U);
		database.addUnit("V", V);
		database.addUnit("W", W);
		database.addUnit("fj", J.times(5));
		database.addUnit("ej", J.times(8));
		
		database.addPrefix("A", A);
		database.addPrefix("B", B);
		database.addPrefix("C", C);
		
		// first test - test prefixes and operations
		final Unit expected1 = J.withPrefix(A).withPrefix(B).withPrefix(C)
				.withPrefix(C);
		final Unit actual1 = database.getUnitFromExpression("ABV * CU^2 / W / W");
		
		assertEquals(expected1, actual1);
		
		// second test - test addition and subtraction
		final Unit expected2 = J.times(58);
		final Unit actual2 = database.getUnitFromExpression("2 fj + 6 ej");
		
		assertEquals(expected2, actual2);
		
		// test incorrect expressions
		assertThrows(IllegalArgumentException.class,
				() -> database.getUnitFromExpression("U + V"));
		assertThrows(IllegalArgumentException.class,
				() -> database.getUnitFromExpression("U - V"));
	}
	
	/**
	 * Tests both the unit name iterator and the name-unit entry iterator
	 * 
	 * @since 2019-04-14
	 * @since v0.2.0
	 */
	@Test
	public void testUnitIterator() {
		// load units
		final UnitDatabase database = new UnitDatabase();
		
		database.addUnit("J", J);
		database.addUnit("K", K);
		
		database.addPrefix("A", A);
		database.addPrefix("B", B);
		database.addPrefix("C", C);
		
		final int NUM_UNITS = database.unitMapPrefixless(true).size();
		final int NUM_PREFIXES = database.prefixMap(true).size();
		
		final Iterator<String> nameIterator = database.unitMap().keySet()
				.iterator();
		final Iterator<Entry<String, Unit>> entryIterator = database.unitMap()
				.entrySet().iterator();
		
		int expectedLength = 1;
		int unitsWithThisLengthSoFar = 0;
		
		// loop 1000 times
		for (int i = 0; i < 1000; i++) {
			// expected length of next
			if (unitsWithThisLengthSoFar >= NUM_UNITS
					* (int) Math.pow(NUM_PREFIXES, expectedLength - 1)) {
				expectedLength++;
				unitsWithThisLengthSoFar = 0;
			}
			
			// test that stuff is valid
			final String nextName = nameIterator.next();
			final Unit nextUnit = database.getUnit(nextName);
			final Entry<String, Unit> nextEntry = entryIterator.next();
			
			assertEquals(expectedLength, nextName.length());
			assertEquals(nextName, nextEntry.getKey());
			assertEquals(nextUnit, nextEntry.getValue());
			
			unitsWithThisLengthSoFar++;
		}
		
		// test toString for consistency
		final String entryIteratorString = entryIterator.toString();
		for (int i = 0; i < 3; i++) {
			assertEquals(entryIteratorString, entryIterator.toString());
		}
		
		final String nameIteratorString = nameIterator.toString();
		for (int i = 0; i < 3; i++) {
			assertEquals(nameIteratorString, nameIterator.toString());
		}
	}
	
	/**
	 * Determine, given a unit name that could mean multiple things, which
	 * meaning is chosen.
	 * <p>
	 * For example, "ABCU" could mean "A-B-C-U", "AB-C-U", or "A-BC-U". In this
	 * case, "AB-C-U" is the correct choice.
	 * </p>
	 * 
	 * @since 2019-04-14
	 * @since v0.2.0
	 */
	@Test
	public void testUnitPrefixCombinations() {
		// load units
		final UnitDatabase database = new UnitDatabase();
		
		database.addUnit("J", J);
		
		database.addPrefix("A", A);
		database.addPrefix("B", B);
		database.addPrefix("C", C);
		database.addPrefix("AB", AB);
		database.addPrefix("BC", BC);
		
		// test 1 - AB-C-J vs A-BC-J vs A-B-C-J
		final Unit expected1 = J.withPrefix(AB).withPrefix(C);
		final Unit actual1 = database.getUnit("ABCJ");
		
		assertEquals(expected1, actual1);
		
		// test 2 - ABC-J vs AB-CJ vs AB-C-J
		database.addUnit("CJ", J.times(13));
		database.addPrefix("ABC", UnitPrefix.valueOf(17));
		
		final Unit expected2 = J.times(17);
		final Unit actual2 = database.getUnit("ABCJ");
		
		assertEquals(expected2, actual2);
	}
}