/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * See LICENSE.txt included in this distribution for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at LICENSE.txt.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 2008, 2021, Oracle and/or its affiliates. All rights reserved.
 * Portions Copyright (c) 2017, 2020, Chris Fraire <cfraire@me.com>.
 */
package org.opengrok.indexer.util;

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

/**
 * Various String utility methods.
 *
 * @author austvik
 */
public final class StringUtils {

    /**
     * Matches a standard end-of-line indicator, identical to Common.lexh's {EOL}.
     */
    public static final Pattern STANDARD_EOL = Pattern.compile("\\r\\n?|\\n");

    /**
     * Matches an apostrophe not following a backslash escape or following an
     * even number¹ of backslash escapes.
     * <p>
     * ¹See {@link RegexUtils#getNotFollowingEscapePattern()} for a caveat
     * about the backslash assertion.
     */
    public static final Pattern APOS_NO_BSESC =
        Pattern.compile("\\'" + RegexUtils.getNotFollowingEscapePattern());

    /**
     * Matches the close of a C comment.
     */
    public static final Pattern END_C_COMMENT = Pattern.compile("\\*\\/");

    /**
     * Matches one of the same possible characters as CommonPath.lexh's {FPath}.
     */
    private static final String FPATH_CHAR_PAT = "[a-zA-Z0-9_\\-\\./]";

    private static final Pattern FPATH_CHAR_STARTSMATCH = Pattern.compile("^" + FPATH_CHAR_PAT);

    /** Private to enforce singleton. */
    private StringUtils() {
    }

    static final Pattern javaClassPattern =
        Pattern.compile("([a-z][A-Za-z]*\\.)+[A-Z][A-Za-z0-9]*");
    /**
     * Returns true if the string is possibly a Java class name, and only
     * matching a subset of possible class names to prevent false positives.
     * <p><ul>
     *     <li>class must be qualified with a package name</li>
     *     <li>package name must contain only letters and start lower case</li>
     *     <li>class name must be in CamelCase and start upper case</li>
     * </ul>
     *
     * @param s the string to be checked
     * @return true if string could be a java class name
    */
    public static boolean isPossiblyJavaClass(String s) {
        return javaClassPattern.matcher(s).matches();
    }

    /**
     * Convert value in milliseconds to readable time.
     * @param timeMs delta in milliseconds
     * @return human readable string
     */
    public static String getReadableTime(long timeMs) {
        StringBuilder output = new StringBuilder();
        long timeDelta = timeMs;

        int milliseconds = (int) (timeDelta % 1000);
        timeDelta /= 1000;
        int seconds = (int) (timeDelta % 60);
        timeDelta /= 60;
        int minutes = (int) (timeDelta % 60);
        timeDelta /= 60;
        int hours = (int) (timeDelta % 24);
        int days = (int) (timeDelta / 24);

        if (days != 0) {
            output.append(days);
            output.append(" day");
            if (days > 1) {
                output.append("s");
            }
        }
        if ((hours != 0) || (minutes != 0)) {
            if (output.length() > 0) {
                // Use zero-padded hours here as it's longer than a day.
                output.append(String.format(" %02d:%02d:%02d", hours, minutes, seconds));
            } else {
                // Don't pad hours if less than a day.
                output.append(String.format("%d:%02d:%02d", hours, minutes, seconds));
            }
        } else if (output.length() > 0) {
            /*
             * If a day+ with zero hours and zero minutes, just report the days.
             * E.g. "1 day", and not "1 day 35 ms".
             */
            return output.toString();
        } else if (seconds != 0) {
            output.append(String.format("%d.%d seconds", seconds, milliseconds));
        } else if (milliseconds != 0) {
            output.append(String.format("%d ms", milliseconds));
        }

        return (output.length() == 0 ? "0 ms" : output.toString());
    }

    /**
     * Finds n-th index of a given substring in a string.
     *
     * @param str an original string
     * @param substr a substring to match
     * @param n n-th occurrence
     * @return the index of the first character of the substring in the original
     * string where the substring occurred n-th times in the string. If the n-th
     * candidate does not exist, -1 is returned.
     */
    public static int nthIndexOf(String str, String substr, int n) {
        int pos = -1;
        while (n > 0) {
            if (pos >= str.length()) {
                return -1;
            }
            if ((pos = str.indexOf(substr, pos + 1)) == -1) {
                break;
            }
            n--;
        }
        return pos;
    }

    /**
     * Count the number of ending pushback characters from a matched URI.
     * <p>
     * jflex does not support negative lookbehind, so modifying a URI matcher
     * to backtrack on ending characters that are otherwise normally valid
     * (e.g. '.') is difficult. Instead, this method allows counting and
     * pushing back.
     * @param value the URI to test
     * @return the number of characters greater than or equal to zero which
     * could be pushed back.
     */
    public static int countURIEndingPushback(String value) {
        int n = 0;
        for (int i = value.length() - 1; i >= 0; --i) {
            char c = value.charAt(i);
            if (c == '.') {
                ++n;
            } else {
                break;
            }
        }
        return n;
    }

    /**
     * Determines if the specified {@code pattern} matches in the specified
     * {@code value}.
     * @param value the string to inspect
     * @param pattern the pattern to match
     * @return the index of the first occurrence of the specified pattern, or
     * -1 if there is no such occurrence
     */
    public static int patindexOf(String value, Pattern pattern) {
        Matcher m = pattern.matcher(value);
        if (!m.find()) {
            return -1;
        }
        return m.start();
    }

    /**
     * Determines if the {@code value} starts with a character in
     * CommonPath.lexh's {FPath}.
     * @param value the input to test
     * @return true if {@code value} matches at its start
     */
    public static boolean startsWithFpathChar(String value) {
        return FPATH_CHAR_STARTSMATCH.matcher(value).matches();
    }

    /**
     * Determines if the specified pattern, {@code pat}, matches the specified
     * {@code capture}, and computes an eligible pushback.
     * @param capture a defined input
     * @param pat a pattern, or null to skip computation
     * @return a positive value if {@code pat} matches in {@code capture} at or
     * after the second character to indicate the number of characters to
     * pushback including the first-matched character; otherwise 0 to indicate
     * no match or a match at the 0-th character. (The 0-th chracter is
     * ineligible for fear of looping non-stop upon pushing back the entire
     * {@code yytext()}.)
     */
    public static int countPushback(String capture, Pattern pat) {
        if (pat != null) {
            int o = StringUtils.patindexOf(capture, pat);
            if (o >= 0) {
                int n = capture.length() - o;
                // Push back if positive, but not if equal to the full length.
                if (n > 0 && n < capture.length()) {
                    return n;
                }
            }
        }
        return 0;
    }

    /**
     * Determine the length of the next whitespace- or ISO control
     * character-related sequence within a string.
     * @param str a defined instance
     * @param off the starting offset within {@code str}
     * @param shouldMatch a value indicating whether to match all contiguous
     *                    whitespace or ISO control characters ({@code true}) or
     *                    all contiguous non-whitespace and non-control
     *                    characters ({@code false}) starting at {@code off}
     * @return a length greater than or equal to zero
     */
    public static int whitespaceOrControlLength(String str, int off, boolean shouldMatch) {
        int i = 0;
        while (off + i < str.length()) {
            int cp = Character.codePointAt(str, off + i);
            if ((Character.isWhitespace(cp) || Character.isISOControl(cp)) != shouldMatch) {
                return i;
            }
            i += Character.charCount(cp);
        }
        return str.length() - off;
    }
}