using System;
using System.IO;
using System.Collections;
using Microsoft.SPOT;

namespace Netduino_ReadFile
{
    // Only works with ASCII streams
    public class FastLineReader
    {
        protected Stream mInputStream;
        protected byte[] mFileBuffer;
        protected int mFileBufferPos;
        protected int mFileBufferLen;
        protected int mBufferSize;

        public bool EndOfStream { get; protected set; }

        /// <summary>
        ///
        /// </summary>
        /// <param name="s"></param>
        /// <param name="bufferSize">this should be your expected max line length. it is ok if too small</param>
        public FastLineReader(Stream s, int bufferSize = 256)
        {
            mInputStream = s;
            mBufferSize = bufferSize;
            mFileBuffer = new byte[bufferSize];
            mFileBufferPos = 0;
            mFileBufferLen = 0;
            EndOfStream = false;
        }

        public String ReadLine()
        {
            var lineBuffer = new char[mBufferSize];
            int lineBufferPos = 0;

            bool foundLF = false;
            while(!foundLF)
            {
                if (mFileBufferPos >= mFileBufferLen)
                {
                    mFileBufferPos = 0;
                    mFileBufferLen = mInputStream.Read(mFileBuffer, mFileBufferPos, mFileBuffer.Length);
                    if (mFileBufferLen == 0)
                    {
                        EndOfStream = true;
                        break; // empty file or we're finished
                    }
                }

                int lfLocation = mFileBufferLen - 1;
                for (int x = mFileBufferPos; x < mFileBufferLen; ++x)
                {
                    if (mFileBuffer[x] == '\n')
                    {
                        lfLocation = x;
                        foundLF = true;
                        break;
                    }
                }
                var dataSize = (lfLocation + 1 - mFileBufferPos); // lfLocation is 0 based, need to increment by 1 for size

                if ((lineBufferPos + dataSize) > lineBuffer.Length)
                {
                    var tempBuffer = new char[lineBufferPos + dataSize];
                    Array.Copy(lineBuffer, tempBuffer, lineBuffer.Length);
                    lineBuffer = tempBuffer;
                }

                for (int x = mFileBufferPos; x <= lfLocation; ++x)
                {
                    lineBuffer[lineBufferPos++] = (char)mFileBuffer[x];
                }
                mFileBufferPos = lfLocation + 1;
            }

            return new String(lineBuffer, 0, lineBufferPos);
        }
    }
}