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// Copyright 2008, 2013 Daniel de Kok
//
// 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 eu.danieldk.nlp.conllx.reader;

import com.google.common.base.Optional;
import eu.danieldk.nlp.conllx.CONLLToken;
import eu.danieldk.nlp.conllx.Sentence;
import eu.danieldk.nlp.conllx.SimpleSentence;
import eu.danieldk.nlp.conllx.Token;
import org.apache.commons.lang3.StringUtils;

import java.io.BufferedReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class CONLLReader implements CorpusReader {
    private final BufferedReader reader;

    private final boolean strict;

    /**
     * Construct a CoNLL corpus reader in non-strict mode. The caller should
     * ensure that the provided reader reads UTF-8.
     *
     * @param reader A buffered reader.
     */
    public CONLLReader(BufferedReader reader) {
        this(reader, false);
    }

    /**
     * Construct a CoNLL corpus reader. The caller should ensure that the provided
     * reader reads UTF-8. If a strictness is enabled, the reader will check if the
     * following is true:
     *
     * 
     *     Tokens are numbered consecutively, starting at 1.
     *     If tokens have a head, ensure that it refers to a token or 0.
     * 
     *
     * @param reader
     * @param strict
     */
    public CONLLReader(BufferedReader reader, boolean strict) {
        this.reader = reader;
        this.strict = strict;
    }

    @Override
    public void close() throws IOException {
        reader.close();
    }

    @Override
    public Sentence readSentence() throws IOException {
        List tokens = new ArrayList<>();

        String line;
        while ((line = reader.readLine()) != null) {
            String parts[] = StringUtils.split(line.trim(), '\t');

            // We are done with these tokens.
            if (parts.length == 0) {
                if (tokens.isEmpty())
                    continue;

                return constructSentence(tokens);
            }

            if (parts.length < 2)
                throw new IOException(String.format("Line has fewer than two columns: %s", line));

            Integer tokenId = Integer.parseInt(parts[0]);
            Optional form = valueForColumn(parts, 1);
            Optional lemma = valueForColumn(parts, 2);
            Optional courseTag = valueForColumn(parts, 3);
            Optional tag = valueForColumn(parts, 4);
            Optional features = valueForColumn(parts, 5);
            Optional head = intValueForColumn(parts, 6);
            Optional headRel = valueForColumn(parts, 7);
            Optional pHead = intValueForColumn(parts, 8);
            Optional pHeadRel = valueForColumn(parts, 9);

            Token token = new CONLLToken(tokenId, form, lemma, courseTag, tag, features, head, headRel,
                    pHead, pHeadRel);

            tokens.add(token);
        }

        // If the the file does not end with a blank line, we have left-overs.
        if (!tokens.isEmpty()) {
            return constructSentence(tokens);
        }

        return null;
    }

    /**
     * Construct a sentence. If strictness is used and invariants do not hold, convert
     * the exception to an IOException.
     */
    private Sentence constructSentence(List tokens) throws IOException {
        Sentence sentence;
        try {
            sentence = new SimpleSentence(tokens, strict);
        } catch (IllegalArgumentException e) {
            throw new IOException(e.getMessage());
        }
        return sentence;
    }

    private Optional valueForColumn(String[] columns, int column) {
        if (column >= columns.length)
            return Optional.absent();

        if (columns[column].equals("_"))
            return Optional.absent();

        return Optional.of(columns[column]);
    }

    private Optional intValueForColumn(String[] columns, int column) {
        if (column >= columns.length)
            return Optional.absent();

        if (columns[column].equals("_"))
            return Optional.absent();

        return Optional.of(Integer.parseInt(columns[column]));
    }
}