// Copyright © 2016 The CefSharp Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.

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

namespace CefSharp.Example.Filters
{
    //NOTE: You need to make sure that your queries are in chronological order since the stream doesn't rewind
    public class FindReplaceMultiResponseFilter : IResponseFilter
    {
        private static readonly Encoding encoding = Encoding.UTF8;

        /// <summary>
        ///     The portion of the find string that is currently matching.
        /// </summary>
        private int findMatchOffset;

        /// <summary>
        ///     Overflow from the output buffer.
        /// </summary>
        private readonly List<byte> overflow = new List<byte>();

        /// <summary>
        ///     Number of times the the string was found/replaced.
        /// </summary>
        private int replaceCount;

        private List<KeyValuePair<string, string>> dictionary;

        public FindReplaceMultiResponseFilter(List<KeyValuePair<string, string>> dictionary)
        {
            this.dictionary = dictionary;
        }

        bool IResponseFilter.InitFilter()
        {
            return true;
        }

        FilterStatus IResponseFilter.Filter(Stream dataIn, out long dataInRead, Stream dataOut, out long dataOutWritten)
        {
            // All data will be read.
            dataInRead = dataIn == null ? 0 : dataIn.Length;
            dataOutWritten = 0;

            // Write overflow then reset
            if (overflow.Count > 0)
            {
                // Write the overflow from last time.
                WriteOverflow(dataOut, ref dataOutWritten);
            }

            // Evaluate each character in the input buffer. Track how many characters in
            // a row match findString. If findString is completely matched then write
            // replacement. Otherwise, write the input characters as-is.
            for (var i = 0; i < dataInRead; ++i)
            {
                var readByte = (byte)dataIn.ReadByte();
                var charForComparison = Convert.ToChar(readByte);

                if (replaceCount < dictionary.Count)
                {
                    var replace = dictionary.ElementAt(replaceCount);
                    if (charForComparison == replace.Key[findMatchOffset])
                    {
                        //We have a match, increment the counter
                        findMatchOffset++;

                        // If all characters match the string specified
                        if (findMatchOffset == replace.Key.Length)
                        {
                            // Complete match of the find string. Write the replace string.
                            WriteString(replace.Value, replace.Value.Length, dataOut, ref dataOutWritten);


                            // Start over looking for a match.
                            findMatchOffset = 0;
                            replaceCount++;
                        }
                        continue;
                    }
                    // Character did not match the find string.
                    if (findMatchOffset > 0)
                    {
                        // Write the portion of the find string that has matched so far.
                        WriteString(replace.Key, findMatchOffset, dataOut, ref dataOutWritten);

                        // Start over looking for a match.
                        findMatchOffset = 0;
                    }
                }

                // Write the current character.
                WriteSingleByte(readByte, dataOut, ref dataOutWritten);
            }

            if (overflow.Count > 0)
            {
                //If we end up with overflow data then we'll need to return NeedMoreData
                // On the next pass the data will be written, then the next batch will be processed.
                return FilterStatus.NeedMoreData;
            }

            // If a match is currently in-progress we need more data. Otherwise, we're
            // done.
            return findMatchOffset > 0 ? FilterStatus.NeedMoreData : FilterStatus.Done;
        }

        private void WriteOverflow(Stream dataOut, ref long dataOutWritten)
        {
            // Number of bytes remaining in the output buffer.
            var remainingSpace = dataOut.Length - dataOutWritten;
            // Maximum number of bytes we can write into the output buffer.
            var maxWrite = Math.Min(overflow.Count, remainingSpace);

            // Write the maximum portion that fits in the output buffer.
            if (maxWrite > 0)
            {
                dataOut.Write(overflow.ToArray(), 0, (int)maxWrite);
                dataOutWritten += maxWrite;
            }

            if (maxWrite < overflow.Count)
            {
                // Need to write more bytes than will fit in the output buffer. 
                // Remove the bytes that were written already
                overflow.RemoveRange(0, (int)(maxWrite - 1));
            }
            else
            {
                overflow.Clear();
            }
        }

        private void WriteString(string str, int stringSize, Stream dataOut, ref long dataOutWritten)
        {
            // Number of bytes remaining in the output buffer.
            var remainingSpace = dataOut.Length - dataOutWritten;
            // Maximum number of bytes we can write into the output buffer.
            var maxWrite = Math.Min(stringSize, remainingSpace);

            // Write the maximum portion that fits in the output buffer.
            if (maxWrite > 0)
            {
                var bytes = encoding.GetBytes(str);
                dataOut.Write(bytes, 0, (int)maxWrite);
                dataOutWritten += maxWrite;
            }

            if (maxWrite < stringSize)
            {
                // Need to write more bytes than will fit in the output buffer. Store the
                // remainder in the overflow buffer.
                overflow.AddRange(encoding.GetBytes(str.Substring((int)maxWrite, (int)(stringSize - maxWrite))));
            }
        }

        private void WriteSingleByte(byte data, Stream dataOut, ref long dataOutWritten)
        {
            // Number of bytes remaining in the output buffer.
            var remainingSpace = dataOut.Length - dataOutWritten;

            // Write the byte to the buffer or add it to the overflow
            if (remainingSpace > 0)
            {
                dataOut.WriteByte(data);
                dataOutWritten += 1;
            }
            else
            {
                // Need to write more bytes than will fit in the output buffer. Store the
                // remainder in the overflow buffer.
                overflow.Add(data);
            }
        }

        void IDisposable.Dispose()
        {
        }
    }
}