function [ncs] = read_neuralynx_ncs(filename, begrecord, endrecord)

% READ_NEURALYNX_NCS reads a single continuous channel file
%
% Use as
%   [ncs] = read_neuralynx_ncs(filename)
%   [ncs] = read_neuralynx_ncs(filename, begrecord, endrecord)

% Copyright (C) 2005-2007, Robert Oostenveld
%
% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org
% for the documentation and details.
%
%    FieldTrip is free software: you can redistribute it and/or modify
%    it under the terms of the GNU General Public License as published by
%    the Free Software Foundation, either version 3 of the License, or
%    (at your option) any later version.
%
%    FieldTrip is distributed in the hope that it will be useful,
%    but WITHOUT ANY WARRANTY; without even the implied warranty of
%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%    GNU General Public License for more details.
%
%    You should have received a copy of the GNU General Public License
%    along with FieldTrip. If not, see <http://www.gnu.org/licenses/>.
%
% $Id$

persistent mexWarning
if isempty(mexWarning)
  mexWarning = false;
end

if nargin<2
  begrecord = 1;
end
if nargin<3
  endrecord = inf;
end

% Using mex files will decrease reading times 2-10-fold on big files
% I had 0.5 sec vs 3.1 sec on 20kHz 600sec file

% determine whether precompiled Nlx2MatCSC from Neualynx is available

isMexv6 = false;
isMexv3 = false;
if ispc
  % first look for Neuralynx version 6 libs
  isMexv6 = ft_hastoolbox('neuralynx_v6', 3);   % don't give warning
  if ~isMexv6
    % look for Ueli's libs as alternative
    isMexv3 = ft_hastoolbox('neuralynx_v3', 3); % don't give warning
  end
elseif ismac || isunix
  % look for Ueli's libs only
  isMexv3 = ft_hastoolbox('neuralynx_v3', 3);   % don't give warning
end

if ~isMexv6 && ~isMexv3
  msgId = 'FieldTrip:fileio:neuralynx_mex';
  ft_warning('once', msgId);
  ft_warning(msgId, 'reading Neuralynx CSC files is faster if you install the MATLAB importer mex files, see http://neuralynx.com/research_software/file_converters_and_utilities/ or https://www.urut.ch/new/serendipity/index.php?/pages/nlxtomatlab.html');
end

if isMexv6 || isMexv3
  % Neuralynx mex files use C-style flags, so let's name them for convinience
  READ_ALL = ones(1,5);
  flags = num2cell(diag(READ_ALL), [1,5]);
  [READ_TST, READ_CHAN, READ_FREQ, READ_VAL, READ_SAMP] = flags{:};
  % the request vector will look like:
  %     >> TST_FLAG+FREQ_FLAG+SAMP_FLAG
  %     >> ans =
  %              1
  %              0
  %              1
  %              0
  %              1
  HEADER_NO  = 0;
  HEADER_YES = 1;
  EXTRACT_RECORD_RANGE = 2;
end

% the file starts with a 16*1024 bytes header in ascii, followed by a number of records
hdr = neuralynx_getheader(filename);
fid = fopen_or_error(filename, 'rb', 'ieee-le');

% determine the length of the file
fseek(fid, 0, 'eof');
headersize = 16384;
recordsize = 1044;
NRecords   = floor((ftell(fid) - headersize)/recordsize);

if NRecords>0
  
  % read out part of the dataset to detect whether there were jumps
  NRecords_to_read = min(NRecords, 100); % read out maximum 100 blocks of data
  
  if isMexv6
    [TimeStamp, ChanNumber, SampFreq] = Nlx2MatCSC(filename, READ_TST+READ_CHAN+READ_FREQ, HEADER_NO, EXTRACT_RECORD_RANGE, [1, NRecords_to_read]);
    TimeStamp = uint64(TimeStamp); % to match signature of ft_read_... output, as mex gives us doubles
  elseif isMexv3
    % note that the indexing in the mex file is 0-offset (C++ style) rather than 1-offset (MATLAB style)
    [TimeStamp, ChanNumber, SampFreq] = Nlx2MatCSC_v3(filename, READ_TST+READ_CHAN+READ_FREQ, HEADER_NO, EXTRACT_RECORD_RANGE, [0, NRecords_to_read-1]);
    TimeStamp = uint64(TimeStamp); % to match signature of ft_read_... output, as mex gives us doubles
  else
    TimeStamp        = zeros(1, NRecords_to_read, 'uint64');
    ChanNumber       = zeros(1, NRecords_to_read);
    SampFreq         = zeros(1, NRecords_to_read);
    for k=1:NRecords_to_read
      
      % set to the correct position
      status = fseek(fid, headersize + (k-1)*recordsize, 'bof');
      if status~=0
        ft_error('cannot jump to the requested record');
      end
      
      % read a single continuous data record
      TimeStamp(k)    = fread(fid,   1, 'uint64=>uint64');
      ChanNumber(k)   = fread(fid,   1, 'int32');
      SampFreq(k)     = fread(fid,   1, 'int32');
    end
  end % if isMexv6
  
  % explicitly sort the timestamps to deal with negative timestamp jumps that can occur
  ts1 = TimeStamp(1);
  dts = double(TimeStamp - TimeStamp(1));
  dts = unique(dts);
  dts = sort(dts);
  TimeStamp = uint64(dts) + ts1;
  
  % for this block of data: automatically detect the gaps;
  % there's a gap if no round off error of the sampling frequency could
  % explain the jump (which is always > one block)
  Fs       = mode(double(SampFreq));
  if abs(Fs/hdr.SamplingFrequency-1)>0.01
    ft_warning('the sampling frequency as read out from the header equals %2.2f and differs from the mode sampling frequency as read out from the data %2.2f\n', hdr.SamplingFrequency, Fs);
    
    % check which one was correct
    d = double(TimeStamp(2:end)-TimeStamp(1:end-1));
    fsEst = 1e6./mode(d);
    indx = nearest([Fs hdr.SamplingFrequency], fsEst);
    if indx==1
      ft_warning('correcting the header frequency from %2.2f to %2.2f', hdr.SamplingFrequency, Fs);
      hdr.SamplingFrequency = Fs;
    end
  end
  
  % detect the number of timestamps per block while avoiding influencce of gaps
  d = double(TimeStamp(2:end)-TimeStamp(1:end-1));
  maxJump  = ceil(10^6./(Fs-1))*512;
  gapCorrectedTimeStampPerSample =  nanmean(d(d<maxJump))/512;
  
  % read the timestamp from the first and last record
  if (ispc), fclose(fid); end
  ts1 = neuralynx_timestamp(filename, 1);
  tsE = neuralynx_timestamp(filename, inf);
  if (ispc), fid = fopen_or_error(filename, 'rb', 'ieee-le'); end
  
  hdr.FirstTimeStamp  = ts1;
  hdr.LastTimeStamp   = tsE;
  
  % compare whether there's at least a block missing
  minJump = min(d);
  ts_range_predicted = (NRecords-1)*512*gapCorrectedTimeStampPerSample;
  ts_range_observed  = double(tsE-ts1);
  if abs(ts_range_predicted-ts_range_observed)>minJump
    ft_warning('discontinuous recording, predicted number of timestamps and observed number of timestamps differ by %2.2f\nPlease consult http://www.fieldtriptoolbox.org/faq/discontinuous_neuralynx', abs(ts_range_predicted-ts_range_observed) );
  end
  
else
  hdr.FirstTimeStamp = nan;
  hdr.LastTimeStamp  = nan;
end

if begrecord==0 && endrecord==0
  % only read the header
elseif begrecord<1
  ft_error('cannot read before the first record');
elseif begrecord>NRecords
  ft_error('cannot read beyond the last record')
elseif endrecord>NRecords
  endrecord = NRecords;
end

if begrecord>=1 && endrecord>=begrecord
  % leave numrecord information here for proper synchronisation
  numrecord    = (endrecord-begrecord+1);
  if isMexv6
    % ft_warning('Reading with neuralynx_v6 mex files');
    [TimeStamp, ChanNumber, SampFreq, NumValidSamp, Samp] = Nlx2MatCSC(filename, READ_ALL, HEADER_NO, EXTRACT_RECORD_RANGE, [begrecord, endrecord]);
    TimeStamp = uint64(TimeStamp); % to match signature of ft_read_... output
  elseif isMexv3
    % ft_warning('Reading with neuralynx_v3 mex files');
    % note that the indexing in the mex file is 0-offset (C++ style) rather than 1-offset (MATLAB style)
    [TimeStamp, ChanNumber, SampFreq, NumValidSamp, Samp] = Nlx2MatCSC_v3(filename, READ_ALL, HEADER_NO, EXTRACT_RECORD_RANGE, [begrecord-1, endrecord-1]);
    TimeStamp = uint64(TimeStamp); % to match signature of ft_read_... output
  else
    % ft_warning('Reading with native MATLAB code');
    % rewind to the first record to be read
    status = fseek(fid, headersize + (begrecord-1)*recordsize, 'bof');
    if status~=0
      ft_error('cannot jump to the requested record');
    end
    
    TimeStamp    = zeros(1,numrecord,'uint64');
    ChanNumber   = zeros(1,numrecord);
    SampFreq     = zeros(1,numrecord);
    NumValidSamp = zeros(1,numrecord);
    Samp         = zeros(512,numrecord);  % this allows easy reshaping into a 1xNsamples vector
    
    for k=1:numrecord
      % read a single continuous data record
      TimeStamp(k)    = fread(fid,   1, 'uint64=>uint64');
      ChanNumber(k)   = fread(fid,   1, 'int32');
      SampFreq(k)     = fread(fid,   1, 'int32');
      NumValidSamp(k) = fread(fid,   1, 'int32');
      Samp(:,k)       = fread(fid, 512, 'int16');
      % mark the invalid samples
      Samp((NumValidSamp(k)+1):end,k) = nan;
    end
    
  end % if isMexv6
  
  ts1 = TimeStamp(1);
  dts = double(TimeStamp-ts1); % no problem with doubles here as numbers are small
  
  [val,indx] = sort(dts);
  [A,I] = unique(val); % consider only the unique values
  indx = indx(I);
  
  % store the record data in the output structure
  ncs.TimeStamp    = uint64(dts(indx)) + ts1; % convert back to original class
  ncs.ChanNumber   = ChanNumber(indx);
  ncs.SampFreq     = SampFreq(indx);
  ncs.NumValidSamp = NumValidSamp(indx);
  % apply the scaling factor from ADBitVolts and convert to uV
  ncs.dat          = Samp(:,indx) * hdr.ADBitVolts * 1e6;
end
fclose(fid);

% store the header info in the output structure
ncs.NRecords = NRecords;
ncs.hdr      = hdr;
