using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace Umbraco.Core.Strings
{
    /// <summary>    
    /// This Class implements the Difference Algorithm published in
    /// "An O(ND) Difference Algorithm and its Variations" by Eugene Myers
    /// Algorithmica Vol. 1 No. 2, 1986, p 251.  
    /// 
    /// The algorithm itself is comparing 2 arrays of numbers so when comparing 2 text documents
    /// each line is converted into a (hash) number. See DiffText().     
    /// 
    /// diff.cs: A port of the algorithm to C#
    /// Copyright (c) by Matthias Hertel, http://www.mathertel.de
    /// This work is licensed under a BSD style license. See http://www.mathertel.de/License.aspx    
    /// </summary>    
    internal class Diff
    {
        /// <summary>Data on one input file being compared.  
        /// </summary>
        internal class DiffData
        {

            /// <summary>Number of elements (lines).</summary>
            internal int Length;

            /// <summary>Buffer of numbers that will be compared.</summary>
            internal int[] Data;

            /// <summary>
            /// Array of booleans that flag for modified data.
            /// This is the result of the diff.
            /// This means deletedA in the first Data or inserted in the second Data.
            /// </summary>
            internal bool[] Modified;

            /// <summary>
            /// Initialize the Diff-Data buffer.
            /// </summary>
            /// <param name="initData">reference to the buffer</param>
            internal DiffData(int[] initData)
            {
                Data = initData;
                Length = initData.Length;
                Modified = new bool[Length + 2];
            } // DiffData

        } // class DiffData

        /// <summary>details of one difference.</summary>
        public struct Item
        {
            /// <summary>Start Line number in Data A.</summary>
            public int StartA;
            /// <summary>Start Line number in Data B.</summary>
            public int StartB;

            /// <summary>Number of changes in Data A.</summary>
            public int DeletedA;
            /// <summary>Number of changes in Data B.</summary>
            public int InsertedB;
        } // Item

        /// <summary>
        /// Shortest Middle Snake Return Data
        /// </summary>
        private struct Smsrd
        {
            internal int X, Y;
            // internal int u, v;  // 2002.09.20: no need for 2 points 
        }

        /// <summary>
        /// Find the difference in 2 texts, comparing by textlines.
        /// </summary>
        /// <param name="textA">A-version of the text (usualy the old one)</param>
        /// <param name="textB">B-version of the text (usualy the new one)</param>
        /// <returns>Returns a array of Items that describe the differences.</returns>
        public static Item[] DiffText(string textA, string textB)
        {
            return (DiffText(textA, textB, false, false, false));
        } // DiffText

        /// <summary>
        /// Find the difference in 2 texts, comparing by textlines. 
        /// This method uses the DiffInt internally by 1st converting the string into char codes
        /// then uses the diff int method
        /// </summary>
        /// <param name="textA">A-version of the text (usualy the old one)</param>
        /// <param name="textB">B-version of the text (usualy the new one)</param>
        /// <returns>Returns a array of Items that describe the differences.</returns>
        public static Item[] DiffText1(string textA, string textB)
        {
            return DiffInt(DiffCharCodes(textA, false), DiffCharCodes(textB, false));
        }


        /// <summary>
        /// Find the difference in 2 text documents, comparing by textlines.
        /// The algorithm itself is comparing 2 arrays of numbers so when comparing 2 text documents
        /// each line is converted into a (hash) number. This hash-value is computed by storing all
        /// textlines into a common hashtable so i can find dublicates in there, and generating a 
        /// new number each time a new textline is inserted.
        /// </summary>
        /// <param name="textA">A-version of the text (usualy the old one)</param>
        /// <param name="textB">B-version of the text (usualy the new one)</param>
        /// <param name="trimSpace">When set to true, all leading and trailing whitespace characters are stripped out before the comparation is done.</param>
        /// <param name="ignoreSpace">When set to true, all whitespace characters are converted to a single space character before the comparation is done.</param>
        /// <param name="ignoreCase">When set to true, all characters are converted to their lowercase equivivalence before the comparation is done.</param>
        /// <returns>Returns a array of Items that describe the differences.</returns>
        public static Item[] DiffText(string textA, string textB, bool trimSpace, bool ignoreSpace, bool ignoreCase)
        {
            // prepare the input-text and convert to comparable numbers.
            var h = new Hashtable(textA.Length + textB.Length);

            // The A-Version of the data (original data) to be compared.
            var dataA = new DiffData(DiffCodes(textA, h, trimSpace, ignoreSpace, ignoreCase));

            // The B-Version of the data (modified data) to be compared.
            var dataB = new DiffData(DiffCodes(textB, h, trimSpace, ignoreSpace, ignoreCase));

            h = null; // free up hashtable memory (maybe)

            var max = dataA.Length + dataB.Length + 1;
            // vector for the (0,0) to (x,y) search
            var downVector = new int[2 * max + 2];
            // vector for the (u,v) to (N,M) search
            var upVector = new int[2 * max + 2];

            Lcs(dataA, 0, dataA.Length, dataB, 0, dataB.Length, downVector, upVector);

            Optimize(dataA);
            Optimize(dataB);
            return CreateDiffs(dataA, dataB);
        } // DiffText


        /// <summary>
        /// Diffs the char codes.
        /// </summary>
        /// <param name="aText">A text.</param>
        /// <param name="ignoreCase">if set to <c>true</c> [ignore case].</param>
        /// <returns></returns>
        private static int[] DiffCharCodes(string aText, bool ignoreCase)
        {
            if (ignoreCase)
                aText = aText.ToUpperInvariant();

            var codes = new int[aText.Length];

            for (int n = 0; n < aText.Length; n++)
                codes[n] = (int)aText[n];

            return (codes);
        } // DiffCharCodes

        /// <summary>
        /// If a sequence of modified lines starts with a line that contains the same content
        /// as the line that appends the changes, the difference sequence is modified so that the
        /// appended line and not the starting line is marked as modified.
        /// This leads to more readable diff sequences when comparing text files.
        /// </summary>
        /// <param name="data">A Diff data buffer containing the identified changes.</param>
        private static void Optimize(DiffData data)
        {
            var startPos = 0;
            while (startPos < data.Length)
            {
                while ((startPos < data.Length) && (data.Modified[startPos] == false))
                    startPos++;
                int endPos = startPos;
                while ((endPos < data.Length) && (data.Modified[endPos] == true))
                    endPos++;

                if ((endPos < data.Length) && (data.Data[startPos] == data.Data[endPos]))
                {
                    data.Modified[startPos] = false;
                    data.Modified[endPos] = true;
                }
                else
                {
                    startPos = endPos;
                } // if
            } // while
        } // Optimize


        /// <summary>
        /// Find the difference in 2 arrays of integers.
        /// </summary>
        /// <param name="arrayA">A-version of the numbers (usualy the old one)</param>
        /// <param name="arrayB">B-version of the numbers (usualy the new one)</param>
        /// <returns>Returns a array of Items that describe the differences.</returns>
        public static Item[] DiffInt(int[] arrayA, int[] arrayB)
        {
            // The A-Version of the data (original data) to be compared.
            var dataA = new DiffData(arrayA);

            // The B-Version of the data (modified data) to be compared.
            var dataB = new DiffData(arrayB);

            var max = dataA.Length + dataB.Length + 1;
            // vector for the (0,0) to (x,y) search
            var downVector = new int[2 * max + 2];
            // vector for the (u,v) to (N,M) search
            var upVector = new int[2 * max + 2];

            Lcs(dataA, 0, dataA.Length, dataB, 0, dataB.Length, downVector, upVector);
            return CreateDiffs(dataA, dataB);
        } // Diff


        /// <summary>
        /// This function converts all textlines of the text into unique numbers for every unique textline
        /// so further work can work only with simple numbers.
        /// </summary>
        /// <param name="aText">the input text</param>
        /// <param name="h">This extern initialized hashtable is used for storing all ever used textlines.</param>
        /// <param name="trimSpace">ignore leading and trailing space characters</param>
        /// <param name="ignoreSpace"></param>
        /// <param name="ignoreCase"></param>
        /// <returns>a array of integers.</returns>
        private static int[] DiffCodes(string aText, IDictionary h, bool trimSpace, bool ignoreSpace, bool ignoreCase)
        {
            // get all codes of the text
            var lastUsedCode = h.Count;

            // strip off all cr, only use lf as textline separator.
            aText = aText.Replace("\r", "");
            var lines = aText.Split('\n');

            var codes = new int[lines.Length];

            for (int i = 0; i < lines.Length; ++i)
            {
                string s = lines[i];
                if (trimSpace)
                    s = s.Trim();

                if (ignoreSpace)
                {
                    s = Regex.Replace(s, "\\s+", " ");            // TODO: optimization: faster blank removal.
                }

                if (ignoreCase)
                    s = s.ToLower();

                object aCode = h[s];
                if (aCode == null)
                {
                    lastUsedCode++;
                    h[s] = lastUsedCode;
                    codes[i] = lastUsedCode;
                }
                else
                {
                    codes[i] = (int)aCode;
                } // if
            } // for
            return (codes);
        } // DiffCodes


        /// <summary>
        /// This is the algorithm to find the Shortest Middle Snake (SMS).
        /// </summary>
        /// <param name="dataA">sequence A</param>
        /// <param name="lowerA">lower bound of the actual range in DataA</param>
        /// <param name="upperA">upper bound of the actual range in DataA (exclusive)</param>
        /// <param name="dataB">sequence B</param>
        /// <param name="lowerB">lower bound of the actual range in DataB</param>
        /// <param name="upperB">upper bound of the actual range in DataB (exclusive)</param>
        /// <param name="downVector">a vector for the (0,0) to (x,y) search. Passed as a parameter for speed reasons.</param>
        /// <param name="upVector">a vector for the (u,v) to (N,M) search. Passed as a parameter for speed reasons.</param>
        /// <returns>a MiddleSnakeData record containing x,y and u,v</returns>
        private static Smsrd Sms(DiffData dataA, int lowerA, int upperA, DiffData dataB, int lowerB, int upperB, int[] downVector, int[] upVector)
        {
            int max = dataA.Length + dataB.Length + 1;

            int downK = lowerA - lowerB; // the k-line to start the forward search
            int upK = upperA - upperB; // the k-line to start the reverse search

            int delta = (upperA - lowerA) - (upperB - lowerB);
            bool oddDelta = (delta & 1) != 0;

            // The vectors in the publication accepts negative indexes. the vectors implemented here are 0-based
            // and are access using a specific offset: UpOffset UpVector and DownOffset for DownVektor
            int downOffset = max - downK;
            int upOffset = max - upK;

            int maxD = ((upperA - lowerA + upperB - lowerB) / 2) + 1;

            // Debug.Write(2, "SMS", String.Format("Search the box: A[{0}-{1}] to B[{2}-{3}]", LowerA, UpperA, LowerB, UpperB));

            // init vectors
            downVector[downOffset + downK + 1] = lowerA;
            upVector[upOffset + upK - 1] = upperA;

            for (int d = 0; d <= maxD; d++)
            {

                // Extend the forward path.
                Smsrd ret;
                for (int k = downK - d; k <= downK + d; k += 2)
                {
                    // Debug.Write(0, "SMS", "extend forward path " + k.ToString());

                    // find the only or better starting point
                    int x, y;
                    if (k == downK - d)
                    {
                        x = downVector[downOffset + k + 1]; // down
                    }
                    else
                    {
                        x = downVector[downOffset + k - 1] + 1; // a step to the right
                        if ((k < downK + d) && (downVector[downOffset + k + 1] >= x))
                            x = downVector[downOffset + k + 1]; // down
                    }
                    y = x - k;

                    // find the end of the furthest reaching forward D-path in diagonal k.
                    while ((x < upperA) && (y < upperB) && (dataA.Data[x] == dataB.Data[y]))
                    {
                        x++; y++;
                    }
                    downVector[downOffset + k] = x;

                    // overlap ?
                    if (oddDelta && (upK - d < k) && (k < upK + d))
                    {
                        if (upVector[upOffset + k] <= downVector[downOffset + k])
                        {
                            ret.X = downVector[downOffset + k];
                            ret.Y = downVector[downOffset + k] - k;
                            // ret.u = UpVector[UpOffset + k];      // 2002.09.20: no need for 2 points 
                            // ret.v = UpVector[UpOffset + k] - k;
                            return (ret);
                        } // if
                    } // if

                } // for k

                // Extend the reverse path.
                for (int k = upK - d; k <= upK + d; k += 2)
                {
                    // Debug.Write(0, "SMS", "extend reverse path " + k.ToString());

                    // find the only or better starting point
                    int x, y;
                    if (k == upK + d)
                    {
                        x = upVector[upOffset + k - 1]; // up
                    }
                    else
                    {
                        x = upVector[upOffset + k + 1] - 1; // left
                        if ((k > upK - d) && (upVector[upOffset + k - 1] < x))
                            x = upVector[upOffset + k - 1]; // up
                    } // if
                    y = x - k;

                    while ((x > lowerA) && (y > lowerB) && (dataA.Data[x - 1] == dataB.Data[y - 1]))
                    {
                        x--; y--; // diagonal
                    }
                    upVector[upOffset + k] = x;

                    // overlap ?
                    if (!oddDelta && (downK - d <= k) && (k <= downK + d))
                    {
                        if (upVector[upOffset + k] <= downVector[downOffset + k])
                        {
                            ret.X = downVector[downOffset + k];
                            ret.Y = downVector[downOffset + k] - k;
                            // ret.u = UpVector[UpOffset + k];     // 2002.09.20: no need for 2 points 
                            // ret.v = UpVector[UpOffset + k] - k;
                            return (ret);
                        } // if
                    } // if

                } // for k

            } // for D

            throw new ApplicationException("the algorithm should never come here.");
        } // SMS


        /// <summary>
        /// This is the divide-and-conquer implementation of the longes common-subsequence (LCS) 
        /// algorithm.
        /// The published algorithm passes recursively parts of the A and B sequences.
        /// To avoid copying these arrays the lower and upper bounds are passed while the sequences stay constant.
        /// </summary>
        /// <param name="dataA">sequence A</param>
        /// <param name="lowerA">lower bound of the actual range in DataA</param>
        /// <param name="upperA">upper bound of the actual range in DataA (exclusive)</param>
        /// <param name="dataB">sequence B</param>
        /// <param name="lowerB">lower bound of the actual range in DataB</param>
        /// <param name="upperB">upper bound of the actual range in DataB (exclusive)</param>
        /// <param name="downVector">a vector for the (0,0) to (x,y) search. Passed as a parameter for speed reasons.</param>
        /// <param name="upVector">a vector for the (u,v) to (N,M) search. Passed as a parameter for speed reasons.</param>
        private static void Lcs(DiffData dataA, int lowerA, int upperA, DiffData dataB, int lowerB, int upperB, int[] downVector, int[] upVector)
        {
            // Debug.Write(2, "LCS", String.Format("Analyse the box: A[{0}-{1}] to B[{2}-{3}]", LowerA, UpperA, LowerB, UpperB));

            // Fast walkthrough equal lines at the start
            while (lowerA < upperA && lowerB < upperB && dataA.Data[lowerA] == dataB.Data[lowerB])
            {
                lowerA++; lowerB++;
            }

            // Fast walkthrough equal lines at the end
            while (lowerA < upperA && lowerB < upperB && dataA.Data[upperA - 1] == dataB.Data[upperB - 1])
            {
                --upperA; --upperB;
            }

            if (lowerA == upperA)
            {
                // mark as inserted lines.
                while (lowerB < upperB)
                    dataB.Modified[lowerB++] = true;

            }
            else if (lowerB == upperB)
            {
                // mark as deleted lines.
                while (lowerA < upperA)
                    dataA.Modified[lowerA++] = true;

            }
            else
            {
                // Find the middle snakea and length of an optimal path for A and B
                Smsrd smsrd = Sms(dataA, lowerA, upperA, dataB, lowerB, upperB, downVector, upVector);
                // Debug.Write(2, "MiddleSnakeData", String.Format("{0},{1}", smsrd.x, smsrd.y));

                // The path is from LowerX to (x,y) and (x,y) to UpperX
                Lcs(dataA, lowerA, smsrd.X, dataB, lowerB, smsrd.Y, downVector, upVector);
                Lcs(dataA, smsrd.X, upperA, dataB, smsrd.Y, upperB, downVector, upVector);  // 2002.09.20: no need for 2 points 
            }
        } // LCS()


        /// <summary>Scan the tables of which lines are inserted and deleted,
        /// producing an edit script in forward order.  
        /// </summary>
        /// dynamic array
        private static Item[] CreateDiffs(DiffData dataA, DiffData dataB)
        {
            ArrayList a = new ArrayList();
            Item aItem;
            Item[] result;

            int lineA = 0;
            int lineB = 0;
            while (lineA < dataA.Length || lineB < dataB.Length)
            {
                if ((lineA < dataA.Length) && (!dataA.Modified[lineA])
                  && (lineB < dataB.Length) && (!dataB.Modified[lineB]))
                {
                    // equal lines
                    lineA++;
                    lineB++;

                }
                else
                {
                    // maybe deleted and/or inserted lines
                    int startA = lineA;
                    int startB = lineB;

                    while (lineA < dataA.Length && (lineB >= dataB.Length || dataA.Modified[lineA]))
                        // while (LineA < DataA.Length && DataA.modified[LineA])
                        lineA++;

                    while (lineB < dataB.Length && (lineA >= dataA.Length || dataB.Modified[lineB]))
                        // while (LineB < DataB.Length && DataB.modified[LineB])
                        lineB++;

                    if ((startA < lineA) || (startB < lineB))
                    {
                        // store a new difference-item
                        aItem = new Item();
                        aItem.StartA = startA;
                        aItem.StartB = startB;
                        aItem.DeletedA = lineA - startA;
                        aItem.InsertedB = lineB - startB;
                        a.Add(aItem);
                    } // if
                } // if
            } // while

            result = new Item[a.Count];
            a.CopyTo(result);

            return (result);
        }

    } // class Diff

    
}