OperatorExtractValuesFromInsertStatement.java

package au.gov.amsa.mariweb;

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

import rx.Observable.Operator;
import rx.Subscriber;

/**
 * Note that this Operator does not support backpressure.
 */
public class OperatorExtractValuesFromInsertStatement implements Operator<List<String>, String> {

    private static final char COMMA = ',';
    private static final char QUOTE = '\'';
    private static final char ESCAPE = '\\';
    private static final char SPACE = ' ';

    @Override
    public Subscriber<? super String> call(final Subscriber<? super List<String>> child) {
        return new Subscriber<String>(child) {

            @Override
            public void onCompleted() {
                if (!child.isUnsubscribed())
                    child.onCompleted();
            }

            @Override
            public void onError(Throwable e) {
                if (!child.isUnsubscribed())
                    child.onError(e);
            }

            @Override
            public void onNext(String line) {
                if (!child.isUnsubscribed()) {
                    String clause = getClause(line);
                    parseValuesFromClause(clause, child);
                }
            }

        };
    }

    private String getClause(String s) {
        int i = s.indexOf("VALUES");
        return s.substring(i + "VALUES".length()).trim();
    }

    private static <T> T unexpected() {
        throw new RuntimeException();
    }

    private static final boolean DEBUG = false;
    private static final int CHECK_UNSUBSCRIBED_EVERY = 1000;

    static void parseValuesFromClause(String s, Subscriber<? super List<String>> subscriber) {
        int charPosition = 0;
        boolean isOpen = false;
        boolean isEscaped = false;
        boolean isInQuotes = false;
        List<String> values = new ArrayList<>();
        StringBuilder token = new StringBuilder();
        // check unsubscribed every 100 emissions to reduce the number of
        // volatile
        // reads of isUnsubscribed()
        long count = 0;

        char currentCh = '?';
        try {

            for (int i = 0; i < s.length(); i++) {
                char ch = s.charAt(i);
                currentCh = ch;
                if (DEBUG)
                    System.out.println(charPosition + ":'" + currentCh + "' open=" + isOpen
                            + ", escaped=" + isEscaped + ",inQuotes=" + isInQuotes + ",token="
                            + token + "values=" + values);
                if (ch == '(' && !isInQuotes) {
                    if (isOpen)
                        unexpected();
                    else
                        isOpen = true;
                } else if (ch == ')' && !isInQuotes) {
                    if (!isOpen)
                        unexpected();
                    else {
                        isOpen = false;
                        if (token.length() > 0) {
                            values.add(token.toString());
                            token = new StringBuilder();
                        }
                        if (++count % CHECK_UNSUBSCRIBED_EVERY == 0 && subscriber.isUnsubscribed())
                            return;
                        subscriber.onNext(values);
                        values = new ArrayList<String>();
                    }
                } else if (ch == QUOTE && !isInQuotes) {
                    isInQuotes = true;
                } else if (ch == QUOTE && !isEscaped) {
                    isInQuotes = false;
                } else if (ch == QUOTE) {
                    // must be escaped
                    token.append(QUOTE);
                    isEscaped = false;
                } else if (ch == ESCAPE && isInQuotes && isEscaped) {
                    token.append(ESCAPE);
                    isEscaped = false;
                } else if (ch == ESCAPE && isInQuotes) {
                    isEscaped = true;
                } else if (ch == ESCAPE) {
                    unexpected();
                } else if (ch == COMMA && !isInQuotes && isOpen) {
                    values.add(token.toString());
                    token = new StringBuilder();
                } else if (ch == COMMA && isInQuotes) {
                    token.append(COMMA);
                } else if (ch == COMMA) {
                    // ignore
                } else if (ch == SPACE && !isInQuotes) {
                    // ignore
                } else {
                    token.append(ch);
                    isEscaped = false;
                }
                charPosition++;
                if (token.length() > 2000)
                    throw new RuntimeException("token too long (>2000)");
                if (values.size() > 100)
                    throw new RuntimeException("too many columns found in a values clause (>100)");
            }
        } catch (RuntimeException e) {
            System.out.println("'" + currentCh + "' open=" + isOpen + ", escaped=" + isEscaped
                    + ",inQuotes=" + isInQuotes + ",token=" + token + "values=" + values);
            writeLineToFile(s);
            throw new RuntimeException("error at position " + charPosition
                    + ". line with problem written to target/error-line.txt", e);
        }
    }

    private static void writeLineToFile(String s) {
        try {
            FileOutputStream fos = new FileOutputStream("target/error-line.txt");
            fos.write(s.getBytes("US-ASCII"));
            fos.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

}