package bjc.utils.funcutils;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.function.Function;
import java.util.function.Supplier;

import bjc.utils.funcdata.FunctionalList;
import bjc.utils.funcdata.IList;

/**
 * Utilities for manipulating FunctionalLists that don't belong in the class
 * itself
 *
 * @author ben
 *
 */
public class ListUtils {
	private static final int MAX_NTRIESPART = 50;

	/**
	 * Collapse a string of tokens into a single string without adding any
	 * spaces
	 *
	 * @param input
	 *                The list of tokens to collapse
	 * @return The collapsed string of tokens
	 */
	public static String collapseTokens(final IList<String> input) {
		if (input == null) throw new NullPointerException("Input must not be null");

		return collapseTokens(input, "");
	}

	/**
	 * Collapse a string of tokens into a single string, adding the desired
	 * separator after each token
	 *
	 * @param input
	 *                The list of tokens to collapse
	 * @param seperator
	 *                The separator to use for separating tokens
	 * @return The collapsed string of tokens
	 */
	public static String collapseTokens(final IList<String> input, final String seperator) {
		if (input == null)
			throw new NullPointerException("Input must not be null");
		else if (seperator == null) throw new NullPointerException("Seperator must not be null");

		if (input.getSize() < 1)
			return "";
		else if (input.getSize() == 1)
			return input.first();
		else {
			final StringBuilder state = new StringBuilder();

			int i = 1;
			for (final String itm : input.toIterable()) {
				state.append(itm);

				if (i != input.getSize()) {
					state.append(seperator);
				}

				i += 1;
			}

			return state.toString();
		}
	}

	/**
	 * Select a number of random items from the list without replacement
	 *
	 * @param <E>
	 *                The type of items to select
	 * @param list
	 *                The list to select from
	 * @param number
	 *                The number of items to selet
	 * @param rng
	 *                A function that creates a random number from 0 to the
	 *                desired number
	 * @return A new list containing the desired number of items randomly
	 *         selected from the specified list without replacement
	 */

	public static <E> IList<E> drawWithoutReplacement(final IList<E> list, final int number,
			final Function<Integer, Integer> rng) {
		final IList<E> selected = new FunctionalList<>(new ArrayList<>(number));

		final int total = list.getSize();

		final Iterator<E> itr = list.toIterable().iterator();
		E element = null;

		for (final int index = 0; itr.hasNext(); element = itr.next()) {
			// n - m
			final int winningChance = number - selected.getSize();

			// N - t
			final int totalChance = total - (index - 1);

			// Probability of selecting the t+1'th element
			if (NumberUtils.isProbable(winningChance, totalChance, rng)) {
				selected.add(element);
			}
		}

		return selected;
	}

	/**
	 * Select a number of random items from the list, with replacement
	 *
	 * @param <E>
	 *                The type of items to select
	 * @param list
	 *                The list to select from
	 * @param number
	 *                The number of items to selet
	 * @param rng
	 *                A function that creates a random number from 0 to the
	 *                desired number
	 * @return A new list containing the desired number of items randomly
	 *         selected from the specified list
	 */
	public static <E> IList<E> drawWithReplacement(final IList<E> list, final int number,
			final Function<Integer, Integer> rng) {
		final IList<E> selected = new FunctionalList<>(new ArrayList<>(number));

		for (int i = 0; i < number; i++) {
			selected.add(list.randItem(rng));
		}

		return selected;
	}

	/**
	 * Partition a list into a list of lists, where each element can count
	 * for more than one element in a partition
	 *
	 * @param <E>
	 *                The type of elements in the list to partition
	 *
	 * @param input
	 *                The list to partition
	 * @param counter
	 *                The function to determine the count for each element
	 *                for
	 * @param partitionSize
	 *                The number of elements to put in each partition
	 *
	 * @return A list partitioned according to the above rules
	 */
	public static <E> IList<IList<E>> groupPartition(final IList<E> input, final Function<E, Integer> counter,
			final int partitionSize) {
		if (input == null)
			throw new NullPointerException("Input list must not be null");
		else if (counter == null)
			throw new NullPointerException("Counter must not be null");
		else if (partitionSize < 1 || partitionSize > input.getSize()) {
			final String fmt = "%d is not a valid partition size. Must be between 1 and %d";
			final String msg = String.format(fmt, partitionSize, input.getSize());

			throw new IllegalArgumentException(msg);
		}

		/*
		 * List that holds our results
		 */
		final IList<IList<E>> returned = new FunctionalList<>();

		/*
		 * List that holds elements rejected during current pass
		 */
		final IList<E> rejected = new FunctionalList<>();

		final GroupPartIteration<E> it = new GroupPartIteration<>(returned, rejected, partitionSize, counter);

		/*
		 * Run up to a certain number of passes
		 */
		for (int numberOfIterations = 0; numberOfIterations < MAX_NTRIESPART
				&& !rejected.isEmpty(); numberOfIterations++) {
			input.forEach(it);

			if (rejected.isEmpty()) // Nothing was rejected, so
				// we're
				// done
				return returned;
		}

		throw new IllegalArgumentException("Heuristic (more than " + MAX_NTRIESPART
				+ " iterations of partitioning) detected unpartitionable list " + input.toString()
				+ "\nThe following elements were not partitioned: " + rejected.toString()
				+ "\nCurrent group in formation: " + it.currentPartition.toString()
				+ "\nPreviously formed groups: " + returned.toString());
	}

	/**
	 * Merge the contents of a bunch of lists together into a single list
	 *
	 * @param <E>
	 *                The type of value in this lists
	 * @param lists
	 *                The values in the lists to merge
	 * @return A list containing all the elements of the lists
	 */
	@SafeVarargs
	public static <E> IList<E> mergeLists(final IList<E>... lists) {
		final IList<E> returned = new FunctionalList<>();

		for (final IList<E> list : lists) {
			for (final E itm : list.toIterable()) {
				returned.add(itm);
			}
		}

		return returned;
	}

	/**
	 * Pad the provided list out to the desired size
	 *
	 * @param <E>
	 *                The type of elements in the list
	 * @param list
	 *                The list to pad out
	 * @param counter
	 *                The function to count elements with
	 * @param size
	 *                The desired size of the list
	 * @param padder
	 *                The function to get elements to pad with
	 * @return The list, padded to the desired size
	 * @throws IllegalArgumentException
	 *                 if the list couldn't be padded to the desired size
	 */
	public static <E> IList<E> padList(final IList<E> list, final Function<E, Integer> counter, final int size,
			final Supplier<E> padder) {
		int count = 0;

		final IList<E> returned = new FunctionalList<>();

		for (final E itm : list.toIterable()) {
			count += counter.apply(itm);

			returned.add(itm);
		}

		if (count % size != 0) {
			// We need to pad
			int needed = count % size;
			int threshold = 0;

			while (needed > 0 && threshold <= MAX_NTRIESPART) {
				final E val = padder.get();
				final int newCount = counter.apply(val);

				if (newCount <= needed) {
					returned.add(val);

					threshold = 0;

					needed -= newCount;
				} else {
					threshold += 1;
				}
			}

			if (threshold > MAX_NTRIESPART)
				throw new IllegalArgumentException("Heuristic (more than " + MAX_NTRIESPART
						+ " iterations of attempting to pad) detected unpaddable list ");
		}

		return returned;
	}
}