function varargout = imformats(varargin)

%IMFORMATS  Manage file format registry.

%   FORMATS = IMFORMATS returns a structure containing all of the values in

%   the file format registry.  The fields in this structure are:

%

%        ext         - A cell array of file extensions for this format

%        isa         - Function to determine if a file "IS A" certain type

%        info        - Function to read information about a file

%        read        - Function to read image data from a file

%        write       - Function to write MATLAB data to a file

%        alpha       - 1 if the format has an alpha channel, 0 otherwise

%        description - A text description of the file format

% 

%   The values for the isa, info, read, and write fields must be functions

%   which are on the MATLAB search path or function handles.

%

%   FORMATS = IMFORMATS(FMT) searches the known formats for a format with

%   extension given in the character vector or string scalar "FMT."  If

%   found, a structure is returned containing the characteristics and

%   function names.  Otherwise an empty structure is returned.

% 

%   FORMATS = IMFORMATS(FORMAT_STRUCT) sets the format registry to contain

%   the values in the "FORMAT_STRUCT" structure.  The output structure

%   FORMATS contains the new registry settings.  See the "Warning" statement

%   below.

% 

%   FORMATS = IMFORMATS('add', FORMAT_STRUCT) adds the values in the

%   "FORMAT_STRUCT" structure to the format registry.

%

%   FORMATS = IMFORMATS('factory') resets the file format registry to the

%   default format registry values.  This removes any user-specified

%   settings.

%

%   FORMATS = IMFORMATS('remove', FMT) removes the format with extension

%   FMT from the format registry.

%

%   FORMATS = IMFORMATS('update', FMT, FORMAT_STRUCT) change the format

%   registry values for the format with extension FMT to have the values

%   stored in FORMAT_STRUCT.

% 

%   IMFORMATS without any input or output arguments prettyprints a table of

%   file format information for the supported formats.

%

%   Warning:

%

%     Using IMFORMATS to change the format registry is an advanced feature.

%     Incorrect usage may prevent loading of image files.  Use IMFORMATS

%     with the 'factory' setting to return the format registry to a workable

%     state. 

%   

%   Note:

%

%     Changes to the format registry do not persist between MATLAB sessions.

%     To have a format always available when you start MATLAB, add the

%     appropriate IMFORMATS commands to the startup.m file in

%     $MATLAB/toolbox/local. 

%

%   See also IMREAD, IMWRITE, IMFINFO, PATH.

%   Copyright 1984-2019 The MathWorks, Inc.

% Verify correct number of arguments

narginchk(0, 3); 

nargoutchk(0, 1); 

if nargin > 0 

    [varargin{:}] = convertStringsToChars(varargin{:}); 

end 

% Declare format structure as persistent variable

persistent fmts; 

% If format structure is empty (first time)

if (isempty(fmts)) 

    % Build default format structure

    fmts = build_registry;

    mlock

end 

% Determine what to do based on number of input arguments

switch(nargin) 

case 0 

    % 0 inputs: Informational only

    if (nargout == 0)

        % Pretty-print the registry

        pretty_print_registry(fmts)

    else

        % Return the registry as a struct

        varargout{1} = fmts;

    end

case 1 

    % 1 input: Look for specific format or modify registry

    if (isstruct(varargin{1})) 

        varargin{1} = matlab.io.internal.imagesci.convertStringsInStruct(varargin{1});

        % Change the registry to contain the structure

        fmts = update_registry(varargin{1});

        varargout{1} = fmts;

        % reset cached format from the last call of imread

        % as changes to imformats could have made it stale

        cachedFormat([]);

    elseif (isequal(lower(varargin{1}), 'factory')) 

        % Reset the registry to the default values

        fmts = build_registry;

        varargout{1} = fmts;

        % reset cached format from the last call of imread

        % as changes to imformats could have made it stale

        cachedFormat([]);

    elseif (ischar(varargin{1})) 

        if isempty(varargin{1}) 

            error(message('MATLAB:imagesci:imformats:badInputType'));

        end 

        % Look for a particular format in the registry

        varargout{1} = find_in_registry(fmts, varargin{1}); 

    else

        % Error out, wrong input argument type

        error(message('MATLAB:imagesci:imformats:badInputType'))

    end 

otherwise

    % n inputs: Modify the registry using a command.

    command = validatestring(varargin{1},{'add','update','remove'});

    switch (lower(command))

        case 'add'

            fmts = add_entry(fmts, varargin{2:end});

        case 'update'

            fmts = update_entry(fmts, varargin{2:end});

        case 'remove'

            fmts = remove_entry(fmts, varargin{2:end});

    end

    varargout{1} = fmts;

    % reset cached format from the last call of imread

    % as changes to imformats could have made it stale

    cachedFormat([]);

end 

% Protect current file's persistent variables from CLEAR

mlock;