/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * 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 com.android.inputmethod.latin.utils;

import android.text.TextUtils;

import com.android.inputmethod.annotations.UsedForTesting;
import com.android.inputmethod.latin.Constants;

import java.util.ArrayList;
import java.util.Locale;

public final class StringUtils {
    private static final String TAG = StringUtils.class.getSimpleName();
    public static final int CAPITALIZE_NONE = 0;  // No caps, or mixed case
    public static final int CAPITALIZE_FIRST = 1; // First only
    public static final int CAPITALIZE_ALL = 2;   // All caps

    private static final String EMPTY_STRING = "";

    private StringUtils() {
        // This utility class is not publicly instantiable.
    }

    public static int codePointCount(final String text) {
        if (TextUtils.isEmpty(text)) return 0;
        return text.codePointCount(0, text.length());
    }

    public static String newSingleCodePointString(int codePoint) {
        if (Character.charCount(codePoint) == 1) {
            // Optimization: avoid creating an temporary array for characters that are
            // represented by a single char value
            return String.valueOf((char) codePoint);
        }
        // For surrogate pair
        return new String(Character.toChars(codePoint));
    }

    public static boolean containsInArray(final String text, final String[] array) {
        for (final String element : array) {
            if (text.equals(element)) return true;
        }
        return false;
    }

    /**
     * Comma-Splittable Text is similar to Comma-Separated Values (CSV) but has much simpler syntax.
     * Unlike CSV, Comma-Splittable Text has no escaping mechanism, so that the text can't contain
     * a comma character in it.
     */
    private static final String SEPARATOR_FOR_COMMA_SPLITTABLE_TEXT = ",";

    public static boolean containsInCommaSplittableText(final String text,
            final String extraValues) {
        if (TextUtils.isEmpty(extraValues)) {
            return false;
        }
        return containsInArray(text, extraValues.split(SEPARATOR_FOR_COMMA_SPLITTABLE_TEXT));
    }

    public static String joinCommaSplittableText(final String head, final String tail) {
        if (TextUtils.isEmpty(head) && TextUtils.isEmpty(tail)) {
            return EMPTY_STRING;
        }
        // Here either head or tail is not null.
        if (TextUtils.isEmpty(head)) {
            return tail;
        }
        if (TextUtils.isEmpty(tail)) {
            return head;
        }
        return head + SEPARATOR_FOR_COMMA_SPLITTABLE_TEXT + tail;
    }

    public static String appendToCommaSplittableTextIfNotExists(final String text,
            final String extraValues) {
        if (TextUtils.isEmpty(extraValues)) {
            return text;
        }
        if (containsInCommaSplittableText(text, extraValues)) {
            return extraValues;
        }
        return extraValues + SEPARATOR_FOR_COMMA_SPLITTABLE_TEXT + text;
    }

    public static String removeFromCommaSplittableTextIfExists(final String text,
            final String extraValues) {
        if (TextUtils.isEmpty(extraValues)) {
            return EMPTY_STRING;
        }
        final String[] elements = extraValues.split(SEPARATOR_FOR_COMMA_SPLITTABLE_TEXT);
        if (!containsInArray(text, elements)) {
            return extraValues;
        }
        final ArrayList<String> result = CollectionUtils.newArrayList(elements.length - 1);
        for (final String element : elements) {
            if (!text.equals(element)) {
                result.add(element);
            }
        }
        return TextUtils.join(SEPARATOR_FOR_COMMA_SPLITTABLE_TEXT, result);
    }

    /**
     * Remove duplicates from an array of strings.
     *
     * This method will always keep the first occurrence of all strings at their position
     * in the array, removing the subsequent ones.
     */
    public static void removeDupes(final ArrayList<String> suggestions) {
        if (suggestions.size() < 2) return;
        int i = 1;
        // Don't cache suggestions.size(), since we may be removing items
        while (i < suggestions.size()) {
            final String cur = suggestions.get(i);
            // Compare each suggestion with each previous suggestion
            for (int j = 0; j < i; j++) {
                final String previous = suggestions.get(j);
                if (TextUtils.equals(cur, previous)) {
                    suggestions.remove(i);
                    i--;
                    break;
                }
            }
            i++;
        }
    }

    public static String capitalizeFirstCodePoint(final String s, final Locale locale) {
        if (s.length() <= 1) {
            return s.toUpperCase(locale);
        }
        // Please refer to the comment below in
        // {@link #capitalizeFirstAndDowncaseRest(String,Locale)} as this has the same shortcomings
        final int cutoff = s.offsetByCodePoints(0, 1);
        return s.substring(0, cutoff).toUpperCase(locale) + s.substring(cutoff);
    }

    public static String capitalizeFirstAndDowncaseRest(final String s, final Locale locale) {
        if (s.length() <= 1) {
            return s.toUpperCase(locale);
        }
        // TODO: fix the bugs below
        // - This does not work for Greek, because it returns upper case instead of title case.
        // - It does not work for Serbian, because it fails to account for the "lj" character,
        // which should be "Lj" in title case and "LJ" in upper case.
        // - It does not work for Dutch, because it fails to account for the "ij" digraph when it's
        // written as two separate code points. They are two different characters but both should
        // be capitalized as "IJ" as if they were a single letter in most words (not all). If the
        // unicode char for the ligature is used however, it works.
        final int cutoff = s.offsetByCodePoints(0, 1);
        return s.substring(0, cutoff).toUpperCase(locale) + s.substring(cutoff).toLowerCase(locale);
    }

    private static final int[] EMPTY_CODEPOINTS = {};

    public static int[] toCodePointArray(final String string) {
        final int length = string.length();
        if (length <= 0) {
            return EMPTY_CODEPOINTS;
        }
        final int[] codePoints = new int[string.codePointCount(0, length)];
        int destIndex = 0;
        for (int index = 0; index < length; index = string.offsetByCodePoints(index, 1)) {
            codePoints[destIndex] = string.codePointAt(index);
            destIndex++;
        }
        return codePoints;
    }

    // This method assumes the text is not null. For the empty string, it returns CAPITALIZE_NONE.
    public static int getCapitalizationType(final String text) {
        // If the first char is not uppercase, then the word is either all lower case or
        // camel case, and in either case we return CAPITALIZE_NONE.
        final int len = text.length();
        int index = 0;
        for (; index < len; index = text.offsetByCodePoints(index, 1)) {
            if (Character.isLetter(text.codePointAt(index))) {
                break;
            }
        }
        if (index == len) return CAPITALIZE_NONE;
        if (!Character.isUpperCase(text.codePointAt(index))) {
            return CAPITALIZE_NONE;
        }
        int capsCount = 1;
        int letterCount = 1;
        for (index = text.offsetByCodePoints(index, 1); index < len;
                index = text.offsetByCodePoints(index, 1)) {
            if (1 != capsCount && letterCount != capsCount) break;
            final int codePoint = text.codePointAt(index);
            if (Character.isUpperCase(codePoint)) {
                ++capsCount;
                ++letterCount;
            } else if (Character.isLetter(codePoint)) {
                // We need to discount non-letters since they may not be upper-case, but may
                // still be part of a word (e.g. single quote or dash, as in "IT'S" or "FULL-TIME")
                ++letterCount;
            }
        }
        // We know the first char is upper case. So we want to test if either every letter other
        // than the first is lower case, or if they are all upper case. If the string is exactly
        // one char long, then we will arrive here with letterCount 1, and this is correct, too.
        if (1 == capsCount) return CAPITALIZE_FIRST;
        return (letterCount == capsCount ? CAPITALIZE_ALL : CAPITALIZE_NONE);
    }

    public static boolean isIdenticalAfterUpcase(final String text) {
        final int length = text.length();
        int i = 0;
        while (i < length) {
            final int codePoint = text.codePointAt(i);
            if (Character.isLetter(codePoint) && !Character.isUpperCase(codePoint)) {
                return false;
            }
            i += Character.charCount(codePoint);
        }
        return true;
    }

    public static boolean isIdenticalAfterDowncase(final String text) {
        final int length = text.length();
        int i = 0;
        while (i < length) {
            final int codePoint = text.codePointAt(i);
            if (Character.isLetter(codePoint) && !Character.isLowerCase(codePoint)) {
                return false;
            }
            i += Character.charCount(codePoint);
        }
        return true;
    }

    /**
     * Returns true if all code points in text are whitespace, false otherwise. Empty is true.
     */
    // Interestingly enough, U+00A0 NO-BREAK SPACE and U+200B ZERO-WIDTH SPACE are not considered
    // whitespace, while EN SPACE, EM SPACE and IDEOGRAPHIC SPACES are.
    public static boolean containsOnlyWhitespace(final String text) {
        final int length = text.length();
        int i = 0;
        while (i < length) {
            final int codePoint = text.codePointAt(i);
            if (!Character.isWhitespace(codePoint)) {
                return false;
            }
            i += Character.charCount(codePoint);
        }
        return true;
    }

    public static boolean isIdenticalAfterCapitalizeEachWord(final String text,
            final String separators) {
        boolean needCapsNext = true;
        final int len = text.length();
        for (int i = 0; i < len; i = text.offsetByCodePoints(i, 1)) {
            final int codePoint = text.codePointAt(i);
            if (Character.isLetter(codePoint)) {
                if ((needCapsNext && !Character.isUpperCase(codePoint))
                        || (!needCapsNext && !Character.isLowerCase(codePoint))) {
                    return false;
                }
            }
            // We need a capital letter next if this is a separator.
            needCapsNext = (-1 != separators.indexOf(codePoint));
        }
        return true;
    }

    // TODO: like capitalizeFirst*, this does not work perfectly for Dutch because of the IJ digraph
    // which should be capitalized together in *some* cases.
    public static String capitalizeEachWord(final String text, final String separators,
            final Locale locale) {
        final StringBuilder builder = new StringBuilder();
        boolean needCapsNext = true;
        final int len = text.length();
        for (int i = 0; i < len; i = text.offsetByCodePoints(i, 1)) {
            final String nextChar = text.substring(i, text.offsetByCodePoints(i, 1));
            if (needCapsNext) {
                builder.append(nextChar.toUpperCase(locale));
            } else {
                builder.append(nextChar.toLowerCase(locale));
            }
            // We need a capital letter next if this is a separator.
            needCapsNext = (-1 != separators.indexOf(nextChar.codePointAt(0)));
        }
        return builder.toString();
    }

    /**
     * Approximates whether the text before the cursor looks like a URL.
     *
     * This is not foolproof, but it should work well in the practice.
     * Essentially it walks backward from the cursor until it finds something that's not a letter,
     * digit, or common URL symbol like underscore. If it hasn't found a period yet, then it
     * does not look like a URL.
     * If the text:
     * - starts with www and contains a period
     * - starts with a slash preceded by either a slash, whitespace, or start-of-string
     * Then it looks like a URL and we return true. Otherwise, we return false.
     *
     * Note: this method is called quite often, and should be fast.
     *
     * TODO: This will return that "abc./def" and ".abc/def" look like URLs to keep down the
     * code complexity, but ideally it should not. It's acceptable for now.
     */
    public static boolean lastPartLooksLikeURL(final CharSequence text) {
        int i = text.length();
        if (0 == i) return false;
        int wCount = 0;
        int slashCount = 0;
        boolean hasSlash = false;
        boolean hasPeriod = false;
        int codePoint = 0;
        while (i > 0) {
            codePoint =  Character.codePointBefore(text, i);
            if (codePoint < Constants.CODE_PERIOD || codePoint > 'z') {
                // Handwavy heuristic to see if that's a URL character. Anything between period
                // and z. This includes all lower- and upper-case ascii letters, period,
                // underscore, arrobase, question mark, equal sign. It excludes spaces, exclamation
                // marks, double quotes...
                // Anything that's not a URL-like character causes us to break from here and
                // evaluate normally.
                break;
            }
            if (Constants.CODE_PERIOD == codePoint) {
                hasPeriod = true;
            }
            if (Constants.CODE_SLASH == codePoint) {
                hasSlash = true;
                if (2 == ++slashCount) {
                    return true;
                }
            } else {
                slashCount = 0;
            }
            if ('w' == codePoint) {
                ++wCount;
            } else {
                wCount = 0;
            }
            i = Character.offsetByCodePoints(text, i, -1);
        }
        // End of the text run.
        // If it starts with www and includes a period, then it looks like a URL.
        if (wCount >= 3 && hasPeriod) return true;
        // If it starts with a slash, and the code point before is whitespace, it looks like an URL.
        if (1 == slashCount && (0 == i || Character.isWhitespace(codePoint))) return true;
        // If it has both a period and a slash, it looks like an URL.
        if (hasPeriod && hasSlash) return true;
        // Otherwise, it doesn't look like an URL.
        return false;
    }

    public static boolean isEmptyStringOrWhiteSpaces(final String s) {
        final int N = codePointCount(s);
        for (int i = 0; i < N; ++i) {
            if (!Character.isWhitespace(s.codePointAt(i))) {
                return false;
            }
        }
        return true;
    }

    @UsedForTesting
    public static String byteArrayToHexString(final byte[] bytes) {
        if (bytes == null || bytes.length == 0) {
            return EMPTY_STRING;
        }
        final StringBuilder sb = new StringBuilder();
        for (byte b : bytes) {
            sb.append(String.format("%02x", b & 0xff));
        }
        return sb.toString();
    }

    /**
     * Convert hex string to byte array. The string length must be an even number.
     */
    @UsedForTesting
    public static byte[] hexStringToByteArray(final String hexString) {
        if (TextUtils.isEmpty(hexString)) {
            return null;
        }
        final int N = hexString.length();
        if (N % 2 != 0) {
            throw new NumberFormatException("Input hex string length must be an even number."
                    + " Length = " + N);
        }
        final byte[] bytes = new byte[N / 2];
        for (int i = 0; i < N; i += 2) {
            bytes[i / 2] = (byte) ((Character.digit(hexString.charAt(i), 16) << 4)
                    + Character.digit(hexString.charAt(i + 1), 16));
        }
        return bytes;
    }
}