/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package bjc.inflexion;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * General utils for dealing with english.
 *
 * @author student
 */
public class EnglishUtils {
	/**
	 * Pick an indefinite article ('a' or 'an') for a phrase.
	 * 
	 * @param phrase
	 *               The phrase to pick an article for.
	 * @return The article to use for the phrase.
	 */
	public static String pickIndefinite(String phrase) {
		Pattern pattern;
		Matcher matcher;
		String word, lowercaseWord;

		if (phrase.length() == 0) {
			return "a";
		}

		// Getting the first word
		pattern = Pattern.compile("(\\w+)\\s*.*");
		matcher = pattern.matcher(phrase);
		if (matcher.matches() == true) {
			word = matcher.group(1);
		} else {
			return "an";
		}

		lowercaseWord = word.toLowerCase();

		// Specific start of words that should be preceded by 'an'
		String[] altCases = {
				"euler", "heir", "honest", "hono"
		};
		for (String altCase : altCases) {
			if (lowercaseWord.startsWith(altCase) == true) {
				return "an";
			}
		}

		if (lowercaseWord.startsWith("hour") == true
				&& lowercaseWord.startsWith("houri") == false) {
			return "an";
		}

		// Single letter word which should be preceded by 'an'
		if (lowercaseWord.length() == 1) {
			if ("aedhilmnorsx".indexOf(lowercaseWord) >= 0) {
				return "an";
			}

			return "a";
		}

		// Capital words which should likely be preceded by 'an'
		if (word.matches(
				"(?!FJO|[HLMNS]Y.|RY[EO]|SQU|(F[LR]?|[HL]|MN?|N|RH?|S[CHKLMNPTVW]?|X(YL)?)[AEIOU])[FHLMNRSX][A-Z]")) {
			return "an";
		}

		// Special cases where a word that begins with a vowel should be preceded by 'a'
		String[] regexes = {
				"^e[uw]", "^onc?e\\b", "^uni([^nmd]|mo)", "^u[bcfhjkqrst][aeiou]"
		};

		for (String regex : regexes) {
			if (lowercaseWord.matches(regex + ".*") == true) {
				return "a";
			}
		}

		// Special capital words (UK, UN)
		if (word.matches("^U[NK][AIEO].*") == true) {
			return "a";
		} else if (word.equals(word.toUpperCase())) {
			if ("aedhilmnorsx".indexOf(lowercaseWord.substring(0, 1)) >= 0) {
				return "an";
			}

			return "a";
		}

		// Basic method of words that begin with a vowel being preceded by 'an'
		if ("aeiou".indexOf(lowercaseWord.substring(0, 1)) >= 0) {
			return "an";
		}

		// Instances where y followed by specific letters is preceded by 'an'
		if (lowercaseWord.matches("^y(b[lor]|cl[ea]|fere|gg|p[ios]|rou|tt).*")) {
			return "an";
		}

		return "a";
	}
}