rippled/modules/beast_core/text/beast_TextDiff.cpp

//------------------------------------------------------------------------------
/*
    This file is part of Beast: https://github.com/vinniefalco/Beast
    Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>

    Portions of this file are from JUCE.
    Copyright (c) 2013 - Raw Material Software Ltd.
    Please visit http://www.juce.com

    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.

    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================

struct TextDiffHelpers
{
    enum { minLengthToMatch = 3 };

    struct StringRegion
    {
        StringRegion (const String& s) noexcept
            : text (s.getCharPointer()), start (0), length (s.length()) {}

        StringRegion (const String::CharPointerType t, int s, int len)  noexcept
            : text (t), start (s), length (len) {}

        String::CharPointerType text;
        int start, length;
    };

    static void addInsertion (TextDiff& td, const String::CharPointerType text, int index, int length)
    {
        TextDiff::Change c;
        c.insertedText = String (text, (size_t) length);
        c.start = index;
        c.length = length;
        td.changes.add (c);
    }

    static void addDeletion (TextDiff& td, int index, int length)
    {
        TextDiff::Change c;
        c.start = index;
        c.length = length;
        td.changes.add (c);
    }

    static void diffSkippingCommonStart (TextDiff& td, const StringRegion& a, const StringRegion& b)
    {
        String::CharPointerType sa (a.text);
        String::CharPointerType sb (b.text);
        const int maxLen = bmax (a.length, b.length);

        for (int i = 0; i < maxLen; ++i, ++sa, ++sb)
        {
            if (*sa != *sb)
            {
                diffRecursively (td, StringRegion (sa, a.start + i, a.length - i),
                                     StringRegion (sb, b.start + i, b.length - i));
                break;
            }
        }
    }

    static void diffRecursively (TextDiff& td, const StringRegion& a, const StringRegion& b)
    {
        int indexA, indexB;
        const int len = findLongestCommonSubstring (a.text, a.length,
                                                    b.text, b.length,
                                                    indexA, indexB);

        if (len >= minLengthToMatch)
        {
            if (indexA > 0 && indexB > 0)
                diffSkippingCommonStart (td, StringRegion (a.text, a.start, indexA),
                                             StringRegion (b.text, b.start, indexB));
            else if (indexA > 0)
                addDeletion (td, b.start, indexA);
            else if (indexB > 0)
                addInsertion (td, b.text, b.start, indexB);

            diffRecursively (td, StringRegion (a.text + indexA + len, a.start + indexA + len, a.length - indexA - len),
                                 StringRegion (b.text + indexB + len, b.start + indexB + len, b.length - indexB - len));
        }
        else
        {
            if (a.length > 0)   addDeletion (td, b.start, a.length);
            if (b.length > 0)   addInsertion (td, b.text, b.start, b.length);
        }
    }

    static int findLongestCommonSubstring (String::CharPointerType a, const int lenA,
                                           const String::CharPointerType b, const int lenB,
                                           int& indexInA, int& indexInB)
    {
        if (lenA == 0 || lenB == 0)
            return 0;

        HeapBlock<int> lines;
        lines.calloc (2 + 2 * (size_t) lenB);

        int* l0 = lines;
        int* l1 = l0 + lenB + 1;

        int bestLength = 0;
        indexInA = indexInB = 0;

        for (int i = 0; i < lenA; ++i)
        {
            const beast_wchar ca = a.getAndAdvance();
            String::CharPointerType b2 (b);

            for (int j = 0; j < lenB; ++j)
            {
                if (ca != b2.getAndAdvance())
                {
                    l1[j + 1] = 0;
                }
                else
                {
                    const int len = l0[j] + 1;
                    l1[j + 1] = len;

                    if (len > bestLength)
                    {
                        bestLength = len;
                        indexInA = i;
                        indexInB = j;
                    }
                }
            }

            std::swap (l0, l1);
        }

        indexInA -= bestLength - 1;
        indexInB -= bestLength - 1;
        return bestLength;
    }
};

TextDiff::TextDiff (const String& original, const String& target)
{
    TextDiffHelpers::diffSkippingCommonStart (*this, original, target);
}

String TextDiff::appliedTo (String text) const
{
    for (int i = 0; i < changes.size(); ++i)
        text = changes.getReference(i).appliedTo (text);

    return text;
}

bool TextDiff::Change::isDeletion() const noexcept
{
    return insertedText.isEmpty();
}

String TextDiff::Change::appliedTo (const String& text) const noexcept
{
    return text.substring (0, start) + (isDeletion() ? text.substring (start + length)
                                                     : (insertedText + text.substring (start)));
}

//==============================================================================

class DiffTests  : public UnitTest
{
public:
    DiffTests() : UnitTest ("TextDiff") {}

    static String createString()
    {
        beast_wchar buffer[50] = { 0 };
        Random r;

        for (int i = r.nextInt (49); --i >= 0;)
        {
            if (r.nextInt (10) == 0)
            {
                do
                {
                    buffer[i] = (beast_wchar) (1 + r.nextInt (0x10ffff - 1));
                }
                while (! CharPointer_UTF16::canRepresent (buffer[i]));
            }
            else
                buffer[i] = (beast_wchar) ('a' + r.nextInt (3));
        }

        return CharPointer_UTF32 (buffer);
    }

    void testDiff (const String& a, const String& b)
    {
        TextDiff diff (a, b);
        const String result (diff.appliedTo (a));
        expectEquals (result, b);
    }

    void runTest()
    {
        beginTest ("TextDiff");

        testDiff (String::empty, String::empty);
        testDiff ("x", String::empty);
        testDiff (String::empty, "x");
        testDiff ("x", "x");
        testDiff ("x", "y");
        testDiff ("xxx", "x");
        testDiff ("x", "xxx");

        for (int i = 5000; --i >= 0;)
        {
            String s (createString());
            testDiff (s, createString());
            testDiff (s + createString(), s + createString());
        }
    }
};

#if BEAST_UNIT_TESTS
static DiffTests diffTests;
#endif