function params=parse_pv_pairs(params,pv_pairs)
% parse_pv_pairs: parses sets of property value pairs, allows defaults
% usage: params=parse_pv_pairs(default_params,pv_pairs)
%
% arguments: (input)
%  default_params - structure, with one field for every potential
%             property/value pair. Each field will contain the default
%             value for that property. If no default is supplied for a
%             given property, then that field must be empty.
%
%  pv_array - cell array of property/value pairs.
%             Case is ignored when comparing properties to the list
%             of field names. Also, any unambiguous shortening of a
%             field/property name is allowed.
%
% arguments: (output)
%  params   - parameter struct that reflects any updated property/value
%             pairs in the pv_array.
%
% Example usage:
% First, set default values for the parameters. Assume we
% have four parameters that we wish to use optionally in
% the function examplefun.
%
%  - 'viscosity', which will have a default value of 1
%  - 'volume', which will default to 1
%  - 'pie' - which will have default value 3.141592653589793
%  - 'description' - a text field, left empty by default
%
% The first argument to examplefun is one which will always be
% supplied.
%
%   function examplefun(dummyarg1,varargin)
%   params.Viscosity = 1;
%   params.Volume = 1;
%   params.Pie = 3.141592653589793
%
%   params.Description = '';
%   params=parse_pv_pairs(params,varargin);
%   params
%
% Use examplefun, overriding the defaults for 'pie', 'viscosity'
% and 'description'. The 'volume' parameter is left at its default.
%
%   examplefun(rand(10),'vis',10,'pie',3,'Description','Hello world')
%
% params = 
%     Viscosity: 10
%        Volume: 1
%           Pie: 3
%   Description: 'Hello world'
%
% Note that capitalization was ignored, and the property 'viscosity'
% was truncated as supplied. Also note that the order the pairs were
% supplied was arbitrary.

npv = length(pv_pairs);
n = npv/2;

if n~=floor(n)
  error 'Property/value pairs must come in PAIRS.'
end
if n<=0
  % just return the defaults
  return
end

if ~isstruct(params)
  error 'No structure for defaults was supplied'
end

% there was at least one pv pair. process any supplied
propnames = fieldnames(params);
lpropnames = lower(propnames);
for i=1:n
  p_i = lower(pv_pairs{2*i-1});
  v_i = pv_pairs{2*i};
  
  ind = strmatch(p_i,lpropnames,'exact');
  if isempty(ind)
    ind = find(strncmp(p_i,lpropnames,length(p_i)));
    if isempty(ind)
      error(['No matching property found for: ',pv_pairs{2*i-1}])
    elseif length(ind)>1
      error(['Ambiguous property name: ',pv_pairs{2*i-1}])
    end
  end
  p_i = propnames{ind};
  
  % override the corresponding default in params
  params = setfield(params,p_i,v_i); %#ok
  
end

end % parse_pv_pairs