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/*
 * Copyright (c) 2015-2018 Rocket Partners, LLC
 * https://github.com/inversion-api
 *
 * 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 io.inversion.rql;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

public class RqlTokenizer {
    final char[] chars;
    int head = 0;

    boolean escaped  = false;
    char    quote    = 0;
    int     function = 0;

    StringBuilder next = new StringBuilder();

    public RqlTokenizer(String chars) {
        this.chars = chars.toCharArray();
    }

    public Stream stream() {
        return asList().stream();
    }

    public List asList() {
        List list = new ArrayList<>();
        String       next;
        while ((next = next()) != null)
            list.add(next);

        return list;
    }

    public String next() {
        if (head >= chars.length) {
            return null;
        }

        while (head < chars.length) {
            char c = chars[head];
            head += 1;

            if ((c == ' ' || c == '\t') && next.length() == 0)
                continue; //ignore leading whitespace

            if (isEscaped()) {
                append(c);
                escaped = false;
                continue;
            }

            if (c == '\\') {
                escaped = !escaped;
                continue;
            }

            if (c == '"' || c == '\'') {
                append(c);
                if (c == quote) {
                    //this has to be the closing quote
                    quote = 0;
                    break;
                } else if (next.length() == 1) {
                    //this has to be the starting quote
                    quote = c;
                    continue;
                } else {
                    continue;
                }
            }

            if (!inQuotes() && c == ',') {
                if (next.length() > 0)
                    break;

                continue;
            }

            if (!inQuotes() && c == '(') {
                append(c);
                function += 1;
                break;
            }

            if (!inQuotes() && ((!inFunction() && c == '=') || (inFunction() && c == ')'))) {
                if (next.length() == 0) {
                    append(c);
                    if (c == ')')
                        function -= 1;
                } else {
                    head--;
                }

                break;
            }

            if (!inQuotes() && c == ')' && !inFunction())
                error("Found ')' as the start of a token but no starting '(' was ever parsed: -> '" + new String(chars) + "'");

            append(c);
        }

        if (inQuotes())
            error("Unable to parse unterminated quoted string: \"" + String.valueOf(chars) + "\": -> '" + new String(chars) + "'");

        if (isEscaped())
            error("Unable to parse hanging escape character: \"" + String.valueOf(chars) + "\": -> '" + new String(chars) + "'");

        if (inFunction() && head == chars.length)
            error("Looks like you are missing a closing ')'");

        String str = next.toString().trim();
        next = new StringBuilder();
        return str;
    }

    protected void error(String msg) {
        throw new RuntimeException(msg);
    }

    protected boolean inQuotes() {
        return quote != 0;
    }

    protected boolean isEscaped() {
        return escaped;
    }

    protected boolean inFunction() {
        return function > 0;
    }

    protected void append(char c) {
        if (!inQuotes() && next.length() == 0 && c == ' ')
            return;
        next.append(c);
    }
}