package org.bukkit.command.defaults;

import com.google.common.collect.ImmutableList;
import org.apache.commons.lang.ArrayUtils;
import org.apache.commons.lang.StringUtils;
import org.apache.commons.lang.Validate;
import org.apache.commons.lang.math.NumberUtils;
import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.command.CommandSender;
import org.bukkit.command.ConsoleCommandSender;
import org.bukkit.help.HelpMap;
import org.bukkit.help.HelpTopic;
import org.bukkit.help.HelpTopicComparator;
import org.bukkit.help.IndexHelpTopic;
import org.bukkit.util.ChatPaginator;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;

public class HelpCommand extends VanillaCommand
{
	public HelpCommand()
	{
		super("help");
		this.description = "Shows the help menu";
		this.usageMessage = "/help <pageNumber>\n/help <topic>\n/help <topic> <pageNumber>";
		this.setAliases(Arrays.asList(new String[]{"?"}));
		this.setPermission("bukkit.command.help");
	}

	@Override
	public boolean execute(CommandSender sender, String currentAlias, String[] args)
	{
		if(!testPermission(sender)) return true;

		String command;
		int pageNumber;
		int pageHeight;
		int pageWidth;

		if(args.length == 0)
		{
			command = "";
			pageNumber = 1;
		}
		else if(NumberUtils.isDigits(args[args.length - 1]))
		{
			command = StringUtils.join(ArrayUtils.subarray(args, 0, args.length - 1), " ");
			try
			{
				pageNumber = NumberUtils.createInteger(args[args.length - 1]);
			} catch(NumberFormatException exception)
			{
				pageNumber = 1;
			}
			if(pageNumber <= 0)
			{
				pageNumber = 1;
			}
		}
		else
		{
			command = StringUtils.join(args, " ");
			pageNumber = 1;
		}

		if(sender instanceof ConsoleCommandSender)
		{
			pageHeight = ChatPaginator.UNBOUNDED_PAGE_HEIGHT;
			pageWidth = ChatPaginator.UNBOUNDED_PAGE_WIDTH;
		}
		else
		{
			pageHeight = ChatPaginator.CLOSED_CHAT_PAGE_HEIGHT - 1;
			pageWidth = ChatPaginator.GUARANTEED_NO_WRAP_CHAT_PAGE_WIDTH;
		}

		HelpMap helpMap = Bukkit.getServer().getHelpMap();
		HelpTopic topic = helpMap.getHelpTopic(command);

		if(topic == null)
		{
			topic = helpMap.getHelpTopic("/" + command);
		}

		if(topic == null)
		{
			topic = findPossibleMatches(command);
		}

		if(topic == null || !topic.canSee(sender))
		{
			sender.sendMessage(ChatColor.RED + "No help for " + command);
			return true;
		}

		ChatPaginator.ChatPage page = ChatPaginator.paginate(topic.getFullText(sender), pageNumber, pageWidth, pageHeight);

		StringBuilder header = new StringBuilder();
		header.append(ChatColor.YELLOW);
		header.append("--------- ");
		header.append(ChatColor.WHITE);
		header.append("Help: ");
		header.append(topic.getName());
		header.append(" ");
		if(page.getTotalPages() > 1)
		{
			header.append("(");
			header.append(page.getPageNumber());
			header.append("/");
			header.append(page.getTotalPages());
			header.append(") ");
		}
		header.append(ChatColor.YELLOW);
		for(int i = header.length(); i < ChatPaginator.GUARANTEED_NO_WRAP_CHAT_PAGE_WIDTH; i++)
		{
			header.append("-");
		}
		sender.sendMessage(header.toString());

		sender.sendMessage(page.getLines());

		return true;
	}

	@Override
	public List<String> tabComplete(CommandSender sender, String alias, String[] args)
	{
		Validate.notNull(sender, "Sender cannot be null");
		Validate.notNull(args, "Arguments cannot be null");
		Validate.notNull(alias, "Alias cannot be null");

		if(args.length == 1)
		{
			List<String> matchedTopics = new ArrayList<String>();
			String searchString = args[0];
			for(HelpTopic topic : Bukkit.getServer().getHelpMap().getHelpTopics())
			{
				String trimmedTopic = topic.getName().startsWith("/") ? topic.getName().substring(1) : topic.getName();

				if(trimmedTopic.startsWith(searchString))
				{
					matchedTopics.add(trimmedTopic);
				}
			}
			return matchedTopics;
		}
		return ImmutableList.of();
	}

	protected HelpTopic findPossibleMatches(String searchString)
	{
		int maxDistance = (searchString.length() / 5) + 3;
		Set<HelpTopic> possibleMatches = new TreeSet<HelpTopic>(HelpTopicComparator.helpTopicComparatorInstance());

		if(searchString.startsWith("/"))
		{
			searchString = searchString.substring(1);
		}

		for(HelpTopic topic : Bukkit.getServer().getHelpMap().getHelpTopics())
		{
			String trimmedTopic = topic.getName().startsWith("/") ? topic.getName().substring(1) : topic.getName();

			if(trimmedTopic.length() < searchString.length())
			{
				continue;
			}

			if(Character.toLowerCase(trimmedTopic.charAt(0)) != Character.toLowerCase(searchString.charAt(0)))
			{
				continue;
			}

			if(damerauLevenshteinDistance(searchString, trimmedTopic.substring(0, searchString.length())) < maxDistance)
			{
				possibleMatches.add(topic);
			}
		}

		if(possibleMatches.size() > 0)
		{
			return new IndexHelpTopic("Search", null, null, possibleMatches, "Search for: " + searchString);
		}
		else
		{
			return null;
		}
	}

	/**
	 * Computes the Dameraur-Levenshtein Distance between two strings. Adapted
	 * from the algorithm at <a href="http://en.wikipedia.org/wiki/Damerau–Levenshtein_distance">Wikipedia: Damerau–Levenshtein distance</a>
	 *
	 * @param s1 The first string being compared.
	 * @param s2 The second string being compared.
	 * @return The number of substitutions, deletions, insertions, and
	 * transpositions required to get from s1 to s2.
	 */
	protected static int damerauLevenshteinDistance(String s1, String s2)
	{
		if(s1 == null && s2 == null)
		{
			return 0;
		}
		if(s1 != null && s2 == null)
		{
			return s1.length();
		}
		if(s1 == null && s2 != null)
		{
			return s2.length();
		}

		int s1Len = s1.length();
		int s2Len = s2.length();
		int[][] H = new int[s1Len + 2][s2Len + 2];

		int INF = s1Len + s2Len;
		H[0][0] = INF;
		for(int i = 0; i <= s1Len; i++)
		{
			H[i + 1][1] = i;
			H[i + 1][0] = INF;
		}
		for(int j = 0; j <= s2Len; j++)
		{
			H[1][j + 1] = j;
			H[0][j + 1] = INF;
		}

		Map<Character, Integer> sd = new HashMap<Character, Integer>();
		for(char Letter : (s1 + s2).toCharArray())
		{
			if(!sd.containsKey(Letter))
			{
				sd.put(Letter, 0);
			}
		}

		for(int i = 1; i <= s1Len; i++)
		{
			int DB = 0;
			for(int j = 1; j <= s2Len; j++)
			{
				int i1 = sd.get(s2.charAt(j - 1));
				int j1 = DB;

				if(s1.charAt(i - 1) == s2.charAt(j - 1))
				{
					H[i + 1][j + 1] = H[i][j];
					DB = j;
				}
				else
				{
					H[i + 1][j + 1] = Math.min(H[i][j], Math.min(H[i + 1][j], H[i][j + 1])) + 1;
				}

				H[i + 1][j + 1] = Math.min(H[i + 1][j + 1], H[i1][j1] + (i - i1 - 1) + 1 + (j - j1 - 1));
			}
			sd.put(s1.charAt(i - 1), i);
		}

		return H[s1Len + 1][s2Len + 1];
	}
}