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##
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## -*- texinfo -*-
## @deftypefn  {} {} datetick ()
## @deftypefnx {} {} datetick (@var{axis_str})
## @deftypefnx {} {} datetick (@var{date_format})
## @deftypefnx {} {} datetick (@var{axis_str}, @var{date_format})
## @deftypefnx {} {} datetick (@dots{}, "keeplimits")
## @deftypefnx {} {} datetick (@dots{}, "keepticks")
## @deftypefnx {} {} datetick (@var{hax}, @dots{})
## Add date-formatted tick labels to an axis.
##
## The axis to apply the ticks to is determined by @var{axis_str} which can
## take the values @qcode{"x"}, @qcode{"y"}, or @qcode{"z"}.  The default
## value is @qcode{"x"}.
##
## The formatting of the labels is determined by the variable
## @var{date_format}, which can either be a string or positive integer that
## @code{datestr} accepts.
##
## If the first argument @var{hax} is an axes handle, then plot into this axes,
## rather than the current axes returned by @code{gca}.
##
## @seealso{datenum, datestr}
## @end deftypefn

function datetick (varargin)

  [hax, varargin, nargin] = __plt_get_axis_arg__ ("datetick", varargin{:});

  oldfig = [];
  if (! isempty (hax))
    oldfig = get (0, "currentfigure");
  endif
  if (isempty (hax))
    hax = gca ();
  endif

  unwind_protect
    ## FIXME: This will bring the axes to the top of the stack.
    ##        This may not be desirable if there are multiple axes objects,
    ##        such as can occur with plotyy.
    axes (hax);
    __datetick__ (varargin{:});
  unwind_protect_cleanup
    if (! isempty (oldfig))
      set (0, "currentfigure", oldfig);
    endif
  end_unwind_protect

endfunction


%!demo
%! clf;
%! yr = 1900:10:2000;
%! pop = [76.094, 92.407, 106.461, 123.077 131.954, 151.868, 179.979, ...
%!        203.984, 227.225, 249.623, 282.224];
%! plot (datenum (yr, 1, 1), pop);
%! xlabel ("Year");
%! ylabel ("US population (millions)");
%! title ("datetick() with 4-digit year format");
%! datetick ("x", "YYYY");

%!demo
%! clf;
%! yr = 1988:2:2002;
%! yr = datenum (yr,1,1);
%! pr = [12.1 13.3 12.6 13.1 13.3 14.1 14.4 15.2];
%! plot (yr, pr, "-o");
%! xlabel ("year");
%! ylabel ("average price");
%! title ("datetick() with MM/DD/YY format");
%! ax = gca ();
%! set (ax, "xtick", datenum (1990:5:2005,1,1));
%! datetick ("x", 2, "keepticks");
%! set (ax, "ytick", 12:16);

%!test
%! hf = figure ("visible", "off");
%! unwind_protect
%!   hax = axes ();
%!   plot ([213:364 0:28], randn (1,181));
%!   datetick ("x", 3);
%!   xticks = get (hax, "xtick");
%!   assert (xticks, [-30 32 92 153 214 275 336 398]);
%! unwind_protect_cleanup
%!   close (hf);
%! end_unwind_protect

function __datetick__ (varargin)

  keeplimits = false;
  idx = strcmpi (varargin, "keeplimits");
  if (any (idx))
    keeplimits = true;
    varargin = varargin(! idx);
  endif
  keepticks = false;
  idx = strcmpi (varargin, "keepticks");
  if (any (idx))
    keepticks = true;
    varargin = varargin(! idx);
  endif

  nargin = numel (varargin);
  form = [];
  ax = "x";

  if (nargin != 0)
    arg = varargin{1};
    if (ischar (arg) && any (strcmpi (arg, {"x", "y", "z"})))
      ax = lower (arg);
      if (nargin > 1)
        form = varargin{2};
        varargin(1:2) = [];
      else
        varargin(1) = [];
      endif
    else
      form = arg;
      varargin(1) = [];
    endif
  endif

  ## Don't publish the existence of this variable for use with dateaxis
  if (length (varargin) > 0)
    startdate = varargin{1};
  else
    startdate = [];
  endif

  if (! isempty (form))
    if (isnumeric (form))
      if (! isscalar (form) || form < 0 || form != fix (form))
        error ("datetick: FORM argument must be a positive integer");
      endif
    elseif (! ischar (form))
      error ("datetick: FORM argument must be a valid date format string");
    endif
  endif

  if (keepticks)
    ticks = get (gca (), [ax "tick"]);
  else
    ## Need to do our own axis tick position calculation as
    ## year, etc., don't fall back to nice datenum values.
    if (keeplimits)
      limits = get (gca (), [ax "lim"]);
      xmin = limits(1);
      xmax = limits(2);
    else
      objs = findall (gca ());
      xmin = xmax = NaN;
      for i = 1 : numel (objs)
        fld = get (objs(i));
        if (isfield (fld, [ax "data"]))
          xdata = getfield (fld, [ax "data"])(:);
          xmin = min (xmin, min (xdata));
          xmax = max (xmax, max (xdata));
        endif
      endfor
    endif

    if (isnan (xmin) || isnan (xmax))
      xmin = 0;
      xmax = 1;
    elseif (xmin == xmax)
      xmax = xmin + 1;
    endif

    N = 3;
    if (xmax - xmin < N)
      ## Day scale or less
      if (xmax - xmin < N / 24 / 60 / 60)
        scl = 1 / 24 / 60 / 60;
      elseif (xmax - xmin < N / 24 / 60)
        scl = 1 / 24 / 60;
      else
        scl = 1 / 24;
      endif
      sep = __calc_tick_sep__ (xmin / scl , xmax / scl);
      xmin = sep * floor (xmin / scl / sep);
      xmax = sep * ceil (xmax / scl / sep);
      nticks = (xmax - xmin) / sep + 1;
      xmin *= scl;
      xmax *= scl;
      ticks = xmin + [0 : nticks - 1] / (nticks - 1) * (xmax - xmin);
    else
      [ymin, mmin, dmin] = datevec (xmin);
      [ymax, mmax, dmax] = datevec (xmax);
      minyear = ymin + (mmin - 1) / 12 + (dmin - 1) / 12 / 30.5;
      maxyear = ymax + (mmax - 1) / 12 + (dmax - 1) / 12 / 30.5;
      minmonth = mmin + (dmin - 1) / 30.5;
      maxmonth = (ymax  - ymin) * 12 + mmax + (dmax - 1) / 30.5;

      if (maxmonth - minmonth < N)
        sep = __calc_tick_sep__ (xmin, xmax);
        xmin = sep * floor (xmin / sep);
        xmax = sep * ceil (xmax / sep);
        nticks = (xmax - xmin) / sep + 1;
        ticks = xmin + [0 : nticks - 1] / (nticks - 1) * (xmax - xmin);
      elseif (maxyear - minyear < N)
        sep = __calc_tick_sep__ (minmonth, maxmonth);
        minyear = floor (minyear);
        minmonth = sep * floor (minmonth / sep);
        minmonth = ifelse (minmonth == 0, 1, minmonth);
        maxmonth = sep * ceil (maxmonth / sep);
        rangemonth = (minmonth:sep:maxmonth)';
        tickdays = round (1 + 28*mod (rangemonth, 1));
        ticks = datenum ([repmat(minyear, size(rangemonth)), ...
                          floor(rangemonth), ...
                          tickdays]);
      else
        sep = __calc_tick_sep__ (minyear, maxyear);
        minyear = sep * floor (minyear / sep);
        maxyear = sep * ceil (maxyear / sep);
        rangeyear = (minyear:sep:maxyear)';
        tickmonth = round (1 + 12*mod (rangeyear, 1));
        ticks = datenum ([floor(rangeyear), ...
                          tickmonth, ...
                          ones(rows (rangeyear), 1)]);
      endif
    endif
  endif

  if (isempty (form))
    r = max (ticks) - min (ticks);
    if (r < 10/60/24)
      ## minutes and seconds
      form = 13;
    elseif (r < 2)
      ## hours
      form = 15;
    elseif (r < 15)
      ## days
      form = 8;
    elseif (r < 365)
      ## FIXME: FORM should be 19 for European users who use dd/mm
      ## instead of mm/dd.  How can that be determined automatically?
      ## months
      form = 6;
    elseif (r < 90*12)
      ## quarters
      form = 27;
    else
      ## years
      form = 10;
    endif
  endif

  if (length (ticks) == 6)
    ## Careful that its not treated as a datevec
    if (! isempty (startdate))
      sticks = strvcat (datestr (ticks(1:end-1) - ticks(1) + startdate, form),
      datestr (ticks(end) - ticks(1) + startdate, form));
    else
      sticks = strvcat (datestr (ticks(1:end-1), form),
      datestr (ticks(end), form));
    endif
  else
    if (! isempty (startdate))
      sticks = datestr (ticks - ticks(1) + startdate, form);
    else
      sticks = datestr (ticks, form);
    endif
  endif

  sticks = mat2cell (sticks, ones (rows (sticks), 1), columns (sticks));

  if (keepticks)
    if (keeplimits)
      set (gca (), [ax "ticklabel"], sticks);
    else
      set (gca (), [ax "ticklabel"], sticks,
                   [ax "lim"], [min(ticks), max(ticks)]);
    endif
  else
    if (keeplimits)
      set (gca (), [ax "tick"], ticks, [ax "ticklabel"], sticks);
    else
      set (gca (), [ax "tick"], ticks, [ax "ticklabel"], sticks,
                   [ax "lim"], [min(ticks), max(ticks)]);
    endif
  endif

endfunction

function [a, b] = __magform__ (x)

  if (x == 0)
    a = b = 0;
  else
    l = log10 (abs (x));
    r = rem (l, 1);
    a = 10 .^ r;
    b = fix (l - r);
    if (a < 1)
      a *= 10;
      b -= 1;
    endif
    if (x < 0)
      a = -a;
    endif
  endif

endfunction

## A translation from Tom Holoryd's python code at
## http://kurage.nimh.nih.gov/tomh/tics.py
function sep = __calc_tick_sep__ (lo, hi)
  persistent sqrt_2  = sqrt (2.0);
  persistent sqrt_10 = sqrt (10.0);
  persistent sqrt_50 = sqrt (50.0);

  ticint = 5;

  ## Reference: Lewart, C. R., "Algorithms SCALE1, SCALE2, and
  ## SCALE3 for Determination of Scales on Computer Generated
  ## Plots", Communications of the ACM, 10 (1973), 639-640.
  ## Also cited as ACM Algorithm 463.

  [a, b] = __magform__ ((hi - lo) / ticint);

  if (a < sqrt_2)
    x = 1;
  elseif (a < sqrt_10)
    x = 2;
  elseif (a < sqrt_50)
    x = 5;
  else
    x = 10;
  endif

  sep = x * 10 .^ b;

endfunction
