function get_latest_met(info)
% get_latest_metar(info)
%
% Last modified:  Time-stamp: <2005-01-19 17:05:09 haines>
%
% Abstract: Function that loads, parses metar obs, appends new data, and saves with all data 
%
% Usage: get_latest_metar(info)
  
% Processing steps
% (1) load previous month and current month data from raw ascii files,
%      adding year and month to each line
% (2) append current to previous 
% (3) subset data for latest 48 hours
% (4) decode each METAR record to get WDIR, WSPD, ATEMP, DEWP, ALTIMETER
% (5) calculate u, v, seallevel pressure (if needed), and time stuff
% (5) create new file of global attributes, dimensions, and variables
% (6) save (ncclose) file

% Author: Sara Haines, Sep 18, 2003 
  
  have_this_month = 0;
  have_prev_month = 0;
  
  x = dir([info.rawdirname '/*.dat']);
  for i=1:length(x)
    % x(i).name
    if strfind(x(i).name, info.month_str)
      have_this_month = 1;
      rawfile_this_month = [info.rawdirname '/' x(i).name];
    elseif strfind(x(i).name, info.prev_month_str)
      have_prev_month = 1;
      rawfile_prev_month = [info.rawdirname '/' x(i).name];
    end
  end
  
  % have_this_month
  % have_prev_month

  % (1) load previous month and current month data from raw ascii files,
  %      adding year and month to each line

  % make it MM/DD/YYY (e.g. 04/01/2000)
  this_dv = datevec([info.month_str(6:7) '/01/' info.month_str(1:4)]);
  this_year = this_dv(1);
  this_month = this_dv(2);
  prev_dv = datevec(datenum(this_year,this_month,-1,0,0,0)); % e.g. 2003_04
  prev_year = prev_dv(1);
  prev_month = prev_dv(2);
	     
  if (have_this_month & have_prev_month)
    % if have both append this month data to previous month data
    
    % read a file into a cell array of strings and read date stamp
    raw_prev_data = textread(rawfile_prev_month,'%s','delimiter','\n','whitespace','');
    % this assumes that *all* METAR obs time of form DDhhmmZ (e.g. 171450Z)
    [DD hh mm] = textread(rawfile_prev_month, ['%*s %2d%2d%2d%*s %*s%*[^\n]']);
    dn_prev = datenum(prev_year*ones(size(DD)),prev_month*ones(size(DD)),DD, ...
		      hh, mm, zeros(size(DD)));

    % read a file into a cell array of strings and read date stamp
    raw_this_data = textread(rawfile_this_month,'%s','delimiter','\n','whitespace','');
    % this assumes that *all* METAR obs time of form DDhhmmZ (e.g. 171450Z)
    [DD hh mm] = textread(rawfile_this_month, ['%*s %2d%2d%2d%*s %*s%*[^\n]']);
    dn_this = datenum(this_year*ones(size(DD)),this_month*ones(size(DD)),DD, ...
		      hh, mm, zeros(size(DD)));
    
    
  elseif (have_this_month & ~have_prev_month)
    % if only this month just only use this month
    
    % no previous data
    raw_prev_data = []; dn_prev = [];

    % read a file into a cell array of strings and read date stamp
    raw_this_data = textread(rawfile_this_month,'%s','delimiter','\n','whitespace','');
    % this assumes that *all* METAR obs time of form DDhhmmZ (e.g. 171450Z)
    [DD hh mm] = textread(rawfile_this_month, ['%*s %2d%2d%2d%*s %*s%*[^\n]']);
    dn_this = datenum(this_year*ones(size(DD)),this_month*ones(size(DD)),DD, ...
		      hh, mm, zeros(size(DD)));
    
  else
    % if don't have any data for this or previous, don't write out new netcdf file
    fprintf(2, ['... ... no current metar data to read\n']);
  end
  
  if have_this_month
    
    % (2) append current to previous 
    % 
    raw_data = [raw_prev_data; raw_this_data];
    dn = [dn_prev; dn_this];
    
    % size(dn)
    
    % (3) subset data to within the last 48 hours (2 days)
    current_dn = info.current_time_dn;
    two_days_ago = current_dn-2; % datenum is in units of days
    which_latest = find(two_days_ago<=dn & dn<current_dn);
    
    % whos
    
    dn = dn(which_latest);
    raw_data = raw_data(which_latest);
    
    % size(dn)
    
    % (4) decode each METAR record to get 
    % wspd, wdir, maxwspd, atemp, dewp, baro, slp (sometimes)
    % (do we want visibility, sky conditions, etc, eventually?)
    wspd=[]; wdir=[]; maxwspd=[]; atemp=[]; dewp=[]; baro=[]; slp=[];
    for i=1:length(raw_data)
      raw_str = char(raw_data(i));
      obs = parse_metar(raw_str);
      
      % raw_str
      % obs
      
      wspd = [wspd; obs.wspd];
      wdir = [wdir; obs.wdir];
      maxwspd = [maxwspd; obs.maxwspd];
      atemp = [atemp; obs.atemp];
      dewp = [dewp; obs.dewp];
      baro = [baro; obs.baro];
      slp = [slp; obs.slp];
    end
    
    % (5) calculations and other time variables for output
    % (5a) uv wind components (eastward and northward)
    % winds in met-convention need to be rotated 180 deg
    
    r=pi/180;
    
    WVE = wspd .*(sin((wdir-180)*r));
    WVN = wspd .*(cos((wdir-180)*r));
    
    % (5b) calculate sea-level pressure based on atemp, baro and station
    % altitude (z), if slp missing (-9999) but atemp and baro are not.
    
    which_calc_slp = find(slp==-9999 & baro~=-9999 & atemp~=-9999);
    if length(which_calc_slp)>0
      
      % this procedure from class notes from Grant Petty
      % http://rain.aos.wisc.edu/~gpetty/aos330/lab1_slp_adjust.pdf
      atempK = atemp(which_calc_slp)+273.1; % units deg K
      Rd = 287.1; % gas constant for dry air (Rd) units of J/(kg K)
      g = 9.807; % gravitional force units of m/s^2
      
      % height (meters) of airport above sea level	
      z0 = info.location_elev; 
      
      H = (Rd.*atempK)/g; 
      % scale height depending on air temperature
      % air pressure at sea level units of mbar quivalent to hPa (hecto-Pascal)
      slp(which_calc_slp) = baro(which_calc_slp).*(exp(z0./H));
      
      % clean up
      clear atempK z0 H;
    end
    
    
    % (5c) time variables for wind product exercise
    %     (i) seconds since  1970-1-1 00:00:00 UTC
    seacoos_time_1970 = (dn-datenum(1970, 1, 1, 0, 0, 0))*24*60*60;
    seacoos_time_1970 = round(seacoos_time_1970);

    %     (ii) matlab datenum (source_time)
    % don't need to do anything. 
    % dn
    
    %     (iii) date_time_string
    date_time_string = datestr(dn,'yyyy-mm-dd HH:MM:SS' );
    
    end
    
  end
  
  ncfile_v20 = [info.out_nc_v20_dir '/nws-' info.platform_name '-' ...
	    info.package_name '-latest.nc'];
  
  % delete old netcdf file of latest data
  if exist(ncfile_v20, 'file')
    delete(ncfile_v20);
  end
  
  % one or more obs in desired time period?
  have_dn = exist('dn');
  if have_dn
    have_latest = length(dn)>0;
  else
    have_latest = 0;
  end
  
  % (5) create new file of global attributes, dimensions, and variables
  % if have data then create new netcdf file and populate
  if have_this_month & have_latest

    fprintf(2, ['... ... writing %s\n'], ncfile_v20);
    nc = netcdf(ncfile_v20, 'clobber');     
    netcdf_create_v20;
    nc = close(nc);
    
  end
  

%