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/*
 * Copyright 2017-2023 original authors
 *
 * 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
 *
 * https://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.micronaut.openapi.visitor;

import io.micronaut.core.annotation.Internal;
import io.micronaut.core.util.StringUtils;

/**
 * Number utils.
 */
@Internal
public final class NumberUtils {

    /**
     * Checks whether the String a valid Java number.
     *
     * Valid numbers include hexadecimal marked with the {@code 0x} or
     * {@code 0X} qualifier, octal numbers, scientific notation and
     * numbers marked with a type qualifier (e.g. 123L).
     *
     * Non-hexadecimal strings beginning with a leading zero are
     * treated as octal values. Thus, the string {@code 09} will return
     * {@code false}, since {@code 9} is not a valid octal value.
     * However, numbers beginning with {@code 0.} are treated as decimal.
     *
     * {@code null} and empty/blank {@code String} will return
     * {@code false}.
     *
     * Note, createNumber(String) should return a number for every
     * input resulting in {@code true}.
     *
     * @param str the {@code String} to check
     *
     * @return {@code true} if the string is a correctly formatted number
     *
     * @since 3.5
     */
    public static boolean isCreatable(final String str) {
        if (StringUtils.isEmpty(str)) {
            return false;
        }
        final char[] chars = str.toCharArray();
        int sz = chars.length;
        boolean hasExp = false;
        boolean hasDecPoint = false;
        boolean allowSigns = false;
        boolean foundDigit = false;
        // deal with any possible sign up front
        final int start = chars[0] == '-' || chars[0] == '+' ? 1 : 0;
        if (sz > start + 1 && chars[start] == '0' && str.indexOf('.') < 0) { // leading 0, skip if is a decimal number
            if (chars[start + 1] == 'x' || chars[start + 1] == 'X') { // leading 0x/0X
                int i = start + 2;
                if (i == sz) {
                    return false; // str == "0x"
                }
                // checking hex (it can't be anything else)
                for (; i < chars.length; i++) {
                    if ((chars[i] < '0' || chars[i] > '9')
                        && (chars[i] < 'a' || chars[i] > 'f')
                        && (chars[i] < 'A' || chars[i] > 'F')) {
                        return false;
                    }
                }
                return true;
            } else if (Character.isDigit(chars[start + 1])) {
                // leading 0, but not hex, must be octal
                int i = start + 1;
                for (; i < chars.length; i++) {
                    if (chars[i] < '0' || chars[i] > '7') {
                        return false;
                    }
                }
                return true;
            }
        }
        sz--; // don't want to loop to the last char, check it afterwords
        // for type qualifiers
        int i = start;
        // loop to the next to last char or to the last char if we need another digit to
        // make a valid number (e.g. chars[0..5] = "1234E")
        while (i < sz || i < sz + 1 && allowSigns && !foundDigit) {
            if (chars[i] >= '0' && chars[i] <= '9') {
                foundDigit = true;
                allowSigns = false;

            } else if (chars[i] == '.') {
                if (hasDecPoint || hasExp) {
                    // two decimal points or dec in exponent
                    return false;
                }
                hasDecPoint = true;
            } else if (chars[i] == 'e' || chars[i] == 'E') {
                // we've already taken care of hex.
                if (hasExp) {
                    // two E's
                    return false;
                }
                if (!foundDigit) {
                    return false;
                }
                hasExp = true;
                allowSigns = true;
            } else if (chars[i] == '+' || chars[i] == '-') {
                if (!allowSigns) {
                    return false;
                }
                allowSigns = false;
                foundDigit = false; // we need a digit after the E
            } else {
                return false;
            }
            i++;
        }
        if (i < chars.length) {
            if (chars[i] >= '0' && chars[i] <= '9') {
                // no type qualifier, OK
                return true;
            }
            if (chars[i] == 'e' || chars[i] == 'E') {
                // can't have an E at the last byte
                return false;
            }
            if (chars[i] == '.') {
                if (hasDecPoint || hasExp) {
                    // two decimal points or dec in exponent
                    return false;
                }
                // single trailing decimal point after non-exponent is ok
                return foundDigit;
            }
            if (!allowSigns
                && (chars[i] == 'd'
                || chars[i] == 'D'
                || chars[i] == 'f'
                || chars[i] == 'F')) {
                return foundDigit;
            }
            if (chars[i] == 'l'
                || chars[i] == 'L') {
                // not allowing L with an exponent or decimal point
                return foundDigit && !hasExp && !hasDecPoint;
            }
            // last character is illegal
            return false;
        }
        // allowSigns is true iff the val ends in 'E'
        // found digit it to make sure weird stuff like '.' and '1E-' doesn't pass
        return !allowSigns && foundDigit;
    }
}