jsonwrite.m

function varargout = jsonwrite(varargin)
% Serialize a JSON (JavaScript Object Notation) structure
% FORMAT jsonwrite(filename,json)
% filename - JSON filename
% json     - JSON structure
%
% FORMAT S = jsonwrite(json)
% json     - JSON structure
% S        - serialized JSON structure (string)
%
% FORMAT [...] = jsonwrite(...,opts)
% opts     - structure of optional parameters:
%              indent: string to use for indentation [Default: '']
%              replacementStyle: string to control how non-alphanumeric
%                characters are replaced [Default: 'underscore']
% 
% References:
%   JSON Standard: http://www.json.org/

% Guillaume Flandin
% $Id: jsonwrite.m 7025 2017-02-22 10:03:58Z guillaume $


%-Input parameters
%--------------------------------------------------------------------------
opts         = struct('indent','','replacementstyle','underscore');
opt          = struct([]);
if nargin > 1
    if ischar(varargin{1})
        filename = varargin{1};
        json     = varargin{2};
    else
        filename = '';
        json = varargin{1};
        opt  = varargin{2};
    end
    if nargin > 2
        opt  = varargin{3};
    end
else
    filename = '';
    json     = varargin{1};
end
fn = fieldnames(opt);
for i=1:numel(fn)
    if ~isfield(opts,lower(fn{i})), warning('Unknown option "%s".',fn{i}); end
    opts.(lower(fn{i})) = opt.(fn{i});
end
optregistry(opts);

%-JSON serialization
%--------------------------------------------------------------------------
fmt('init',sprintf(opts.indent));
S = jsonwrite_var(json,~isempty(opts.indent));

%-Output
%--------------------------------------------------------------------------
if isempty(filename)
    varargout = { S };
else
    fid = fopen(filename,'wt');
    if fid == -1
        error('Unable to open file "%s" for writing.',filename);
    end
    fprintf(fid,'%s',S);
    fclose(fid);
end


%==========================================================================
function S = jsonwrite_var(json,tab)
if nargin < 2, tab = ''; end
if isstruct(json) || isa(json,'containers.Map')
    S = jsonwrite_struct(json,tab);
elseif iscell(json)
    S = jsonwrite_cell(json,tab);
elseif ischar(json)
    if size(json,1) <= 1
        S = jsonwrite_char(json);
    else
        S = jsonwrite_cell(cellstr(json),tab);
    end
elseif isnumeric(json) || islogical(json)
    S = jsonwrite_numeric(json);
elseif isa(json,'string')
    if numel(json) == 1
        S = jsonwrite_char(char(json));
    else
        json = arrayfun(@(x)x,json,'UniformOutput',false);
        json(cellfun(@(x) ismissing(x),json)) = {NaN}; % to be saved as null
        idx = find(size(json)~=1);
        if numel(idx) == 1 % vector
            S = jsonwrite_cell(json,tab);
        else % array
            S = jsonwrite_cell(num2cell(json,setdiff(1:ndims(json),idx(1))),tab);
        end
    end
elseif isa(json,'datetime') || isa(json,'categorical')
    S = jsonwrite_var(string(json));
elseif isa(json,'table')
    S = struct;
    s = size(json);
    vn = json.Properties.VariableNames;
    for i=1:s(1)
        for j=1:s(2)
            S(i).(vn{j}) = json{i,j};
        end
    end
    S = jsonwrite_struct(S,tab);
else
    if numel(json) ~= 1
        json = arrayfun(@(x)x,json,'UniformOutput',false);
        S = jsonwrite_cell(json,tab);
    else
        p = properties(json);
        if isempty(p), p = fieldnames(json); end % for pre-classdef
        s = struct;
        for i=1:numel(p)
            s.(p{i}) = json.(p{i});
        end
        S = jsonwrite_struct(s,tab);
        %error('Class "%s" is not supported.',class(json));
    end
end

%==========================================================================
function S = jsonwrite_struct(json,tab)
if numel(json) == 1
    if isstruct(json), fn = fieldnames(json); else fn = keys(json); end
    S = ['{' fmt('\n',tab)];
    for i=1:numel(fn)
        key = fn{i};
        if strcmp(optregistry('replacementStyle'),'hex')
            key = regexprep(key,...
                'x0x([0-9a-fA-F]+)_', '${native2unicode(hex2dec($1))}');
        end
        if isstruct(json), val = json.(fn{i}); else val = json(fn{i}); end
        S = [S fmt(tab) jsonwrite_char(key) ':' fmt(' ',tab) ...
            jsonwrite_var(val,tab+1)];
        if i ~= numel(fn), S = [S ',']; end
        S = [S fmt('\n',tab)];
    end
    S = [S fmt(tab-1) '}'];
else
    S = jsonwrite_cell(arrayfun(@(x) {x},json),tab);
end

%==========================================================================
function S = jsonwrite_cell(json,tab)
if numel(json) == 0 ...
        || (numel(json) == 1 && iscellstr(json)) ...
        || all(all(cellfun(@isnumeric,json))) ...
        || all(all(cellfun(@islogical,json)))
    tab = '';
end
S = ['[' fmt('\n',tab)];
for i=1:numel(json)
    S = [S fmt(tab) jsonwrite_var(json{i},tab+1)];
    if i ~= numel(json), S = [S ',']; end
    S = [S fmt('\n',tab)];
end
S = [S fmt(tab-1) ']'];

%==========================================================================
function S = jsonwrite_char(json)
% any-Unicode-character-except-"-or-\-or-control-character
% \" \\ \/ \b \f \n \r \t \u four-hex-digits
json = strrep(json,'\','\\');
json = strrep(json,'"','\"');
json = strrep(json,'/','\/');
json = strrep(json,sprintf('\b'),'\b');
json = strrep(json,sprintf('\f'),'\f');
json = strrep(json,sprintf('\n'),'\n');
json = strrep(json,sprintf('\r'),'\r');
json = strrep(json,sprintf('\t'),'\t');
S = ['"' json '"'];

%==========================================================================
function S = jsonwrite_numeric(json)
if any(imag(json(:)))
    error('Complex numbers not supported.');
end
if numel(json) == 0
    S = jsonwrite_cell({});
    return;
elseif numel(json) > 1
    idx = find(size(json)~=1);
    if numel(idx) == 1 % vector
        S = jsonwrite_cell(num2cell(json),'');
    else % array
        S = jsonwrite_cell(num2cell(json,setdiff(1:ndims(json),idx(1))),'');
    end
    return;
end
if islogical(json)
    if json, S = 'true'; else S = 'false'; end
else
    S = num2str(json,16);
end

%==========================================================================
function b = fmt(varargin)
persistent tab;
if nargin == 2 && isequal(varargin{1},'init')
    tab = varargin{2};
end
b = '';
if nargin == 1
    if varargin{1} > 0, b = repmat(tab,1,varargin{1}); end
elseif nargin == 2
    if ~isempty(tab) && ~isempty(varargin{2}), b = sprintf(varargin{1}); end
end

%==========================================================================
function val = optregistry(opts)
persistent options
if isstruct(opts)
    options = opts;
else
    val = options.(lower(opts));
end