function SE = strel(varargin)
%
% Function File: SE = strel(shape, parameters);
%
% Inputs: shape = 'diamond', 'octagon', 'pair', 'rectangle', 'square', 'line',
%                 'periodicline', 'ball', 'arbitrary', 'disk'
%         parameters = tuning for shape selected (NYI - not yet implemented)
%           "diamond" - R = integer radius greater than 0
%           "octagon" - NYI
%           "pair" - OFFSET = integer 2-element array [X Y]
%           "rectangle" - DIMENSION = 2 greater than 0 integer array [M N]
%           "square" - EDGE = integer edge greater than 0
%           "line" - NYI
%           "periodicline" - NYI
%           "ball" - NYI
%           "arbitrary" - NYI
%           "disk" - R = integer radius greater than 0
%                  - N = use 0, 4, 6 or 8 periodic lines (default 0) (NYI)
%                        (default will be 4, for now 0: it works 'slower')  
%
% Output: SE = structure element as logical array
%
% Copyright (C) Roberto Metere. All rights reserved.
% License: GPLv3

version = '0.5.1';
author = 'Roberto Metere';
bugreport = 'address@hidden';
% ------------------------------------

% Two arguments as minimum
if (nargin == 0)
	usage = [' -- Function File: SE = strel(shape, parameters)' "\n\n"];
	usage = [usage " shape = 'diamond', 'octagon', 'pair', 'rectangle', 'square', 'line', \n"];
	usage = [usage "         'periodicline', 'ball', 'arbitrary', 'disk'\n\n"];
	usage = [usage ' parameters (NYI - not yet implemented)' "\n"];
	usage = [usage '  "diamond" - R = integer radius greater than 0' "\n"];
	usage = [usage '  "octagon" - NYI' "\n"];
	usage = [usage '  "pair" - OFFSET = integer 2-element array [X Y]' "\n"];
	usage = [usage '  "rectangle" - DIMENSION = 2 greater than 0 integer array [M N]' "\n"];
	usage = [usage '  "square" - EDGE = integer edge greater than 0' "\n"];
	usage = [usage '  "line" - NYI' "\n"];
	usage = [usage '  "periodicline" - NYI' "\n"];
	usage = [usage '  "ball" - NYI' "\n"];
	usage = [usage '  "arbitrary" - NYI' "\n"];
	usage = [usage '  "disk" - R = integer radius greater than 0' "\n"];
	usage = [usage '         - N = use 0, 4, 6 or 8 periodic lines (default 4) (NYI)' "\n"];
	help strel
	error(['Invalid call to strel version ' version '.  Correct usage is:' "\n\n" usage "\n\n"]);
else
	% get only shape for now
	shape = varargin{1};
end

% Not yet implemented, sorry
switch (shape)
	case {'octagon', 'line', 'periodicline', 'ball', 'arbitrary'}
		error(['Shape "' shape '" not yet implemented']);

	otherwise % Just for completeness
end

% Get other parameters
switch (shape)
	case {'diamond', 'octagon', 'pair', 'rectangle', 'square'}
		if (nargin == 2)
			arg1 = varargin{nargin};
		else
			error(['Shape "' shape '" needs (at least) 1 parameter']);
		end

	case {'line', 'periodicline'}
		if (nargin == 3)
			arg1 = varargin{nargin - 1};
			arg2 = varargin{nargin};
		else
			error(['Shape "' shape '" needs (at least) 2 parameters']);
		end

	case 'ball'
		if (nargin == 4)
			arg1 = varargin{nargin - 2};
			arg2 = varargin{nargin - 1};
			arg3 = varargin{nargin};
		else
			error(['Shape "' shape '" needs (at least) 3 parameters']);
		end
	
	case {'arbitrary', 'disk'}
		if (nargin == 2)
			arg1 = varargin{nargin};
		else
			if (nargin == 3)
				arg1 = varargin{nargin - 1};
				arg2 = varargin{nargin};
			else
				error('strel');
			end
		end

	otherwise
		error(['Unknown shape "' shape '"']);
end

% Compute structure element
switch (shape)
	case 'square'
		if (size(arg1) == [1 1])
			if ((arg1 == uint8(arg1)) && isnumeric(arg1))
				if (arg1 > 0)
					arg1 = uint8(arg1);
					SE = ones(arg1, arg1, 'logical');
				else
					error(['Square edge must be a positive integer']);
				end
			else
				error(['Square edge must be a number']);
			end
		else
			error(['Square edge must be a positive integer']);
		end

	case 'rectangle'
		if ((arg1 == uint8(arg1)) && isnumeric(arg1))
			if ((size(arg1) == [1 2]) || (size(arg1) == [2 1]));
				if ((arg1(1) >= 0) && (arg1(2) >= 0))
					SE = ones(arg1(1), arg1(2), 'logical');
				else
					error(['Only positive value for rectangle dimensions allowed']);
				end
			else
				error(['Rectangle dimensions must be exactly a 2-integer array']);
			end
		else
			error(['Rectangle dimensions must be a 2-integer array']);
		end

	case 'diamond'
		if (size(arg1) == [1 1])
			if ((arg1 == uint8(arg1)) && isnumeric(arg1))
				if (arg1 > 0)
					n = int32(2*arg1 + 1);
					c = (n + 1)/2;
					SE = zeros([n n], 'logical');
					for i = 1:n
						m = n - abs(2*(i - c));
						for j = c - m/2 + 1:c + m/2 - 1
							SE(i, j) = 1;
						end
					end
				else
					error(['The parameter must be greater than 0']);
				end
			else
				error(['The parameter must be an integer']);
			end
		else
			error(['The parameter must be an integer']);
		end

	case 'pair'
		if ((arg1 == int8(arg1)) && isnumeric(arg1))
			if ((size(arg1) == [1 2]) || (size(arg1) == [2 1]));
				m = abs(2*arg1(1)) + 1;
				n = abs(2*arg1(2)) + 1;
				cy = (m + 1)/2;
				cx = (n + 1)/2;
				SE = zeros([m n], 'logical');
				SE(cy, cx) = 1;
				SE(cy + arg1(1), cx + arg1(2) ) = 1;
			else
				error(['Offset must be a 2-integer array']);
			end
		else
			error(['Offset must be a numeric array']);
		end

	case 'disk'
		if (size(arg1) == [1 1])
			% Default value of N
			if (nargin <= 2)
				arg2 = 4;
			else
				warning(['Shape "' shape '" still ignores second argument (partially implemented)']);
			end
			if (size(arg2) == [1 1])
				if (arg1 > 0)
					switch (arg2)
						case {0, 4, 6, 8}
							radius = arg1;
							n = 2*radius + 1;
							radius2 = radius*radius;
							SE = zeros([n n], 'logical');
							for i = 1:n
								for j = 1:n
									pitagora = (i - int32(radius) - 1)^2 + (j - int32(radius) - 1)^2;
									if (pitagora <= radius2)
										SE(i, j) = 1;
									end
								end
							end

						otherwise
							error(['Number of periodic lines structuring elements may assume only values: 0, 4, 6 or 8.']);
					end
				else
					error(['Radius must be a strictly positive integer']);
				end
			else
				error(['Number of periodic lines structuring elements must be an integer']);
			end
		else
			error(['Radius must be an integer']);
		end

	otherwise
		error(['Bug: execution should never reach this line. Please report this bug to ' author ' <' bugreport '>']);
end