function hAnnot = arrow(startPoint, endPoint, ax, arrowType, varargin)
% ARROW Draws an annotation of specified type between two data points.
% 
%   hAnnot = ARROW(startPoint, endPoint, ax, arrowType) creates an 
%   annotation from the coordinate specified by startPoint to the coordinate 
%   specified by endPoint. The annotation type can be 'arrow', 'doublearrow',
%   'textarrow', etc.
%
%   hAnnot = ARROW(startPoint, endPoint, ax, arrowType, Name, Value) allows
%   additional customization of the annotation properties (e.g., color, 
%   arrowhead size, line width, etc.).
%
%   INPUT:
%     startPoint - 1x2 array, [x1, y1], coordinates of the start point 
%                  in the data space of the current axes.
%     endPoint   - 1x2 array, [x2, y2], coordinates of the end point 
%                  in the data space of the current axes.
%     ax         - (optional) Axes handle. If omitted, the current axes 
%                  (gca) will be used.
%     arrowType  - (optional) Type of annotation ('arrow', 'doublearrow', 
%                  'textarrow', etc.). Default is 'arrow'.
%     Name, Value - (optional) Name-value pairs to customize the annotation's 
%                   appearance (e.g., 'Color', 'LineWidth', etc.).
%
%   OUTPUT:
%     hAnnot     - Handle to the created annotation object.
%
%   Example:
%     figure;
%     x = linspace(0, 10, 100);
%     y = sin(x);
%     plot(x, y);
%     arrow([2, sin(2)], [8, sin(8)], gca, 'textarrow', 'Color', 'r', 'String', 'Text');
%
%   Notes:
%     The function automatically converts the data coordinates to normalized
%     figure coordinates for annotation purposes.

    % Input validation
    if nargin < 2
        error('arrow:InsufficientInputs', 'Both startPoint and endPoint must be specified.');
    end
    if nargin < 3 || isempty(ax)
        ax = gca; % If axes handle is not provided, use the current axes
    end
    if nargin < 4 || isempty(arrowType)
        arrowType = 'arrow'; % Default arrow type is 'arrow'
    end
    if numel(startPoint) ~= 2 || numel(endPoint) ~= 2
        error('arrow:InvalidInput', 'startPoint and endPoint must be 1x2 arrays representing [x, y] coordinates.');
    end

    % Get the current axes position in normalized figure units
    ax_pos = ax.Position;

    % Convert data coordinates to normalized figure coordinates
    startNorm = [(startPoint(1) - ax.XLim(1)) / diff(ax.XLim), ...
                 (startPoint(2) - ax.YLim(1)) / diff(ax.YLim)];
    endNorm = [(endPoint(1) - ax.XLim(1)) / diff(ax.XLim), ...
               (endPoint(2) - ax.YLim(1)) / diff(ax.YLim)];

    % Map normalized data coordinates to figure normalized coordinates
    startAnnot = [ax_pos(1) + startNorm(1) * ax_pos(3), ...
                  ax_pos(2) + startNorm(2) * ax_pos(4)];
    endAnnot = [ax_pos(1) + endNorm(1) * ax_pos(3), ...
                ax_pos(2) + endNorm(2) * ax_pos(4)];

    % Create the specified type of annotation
    hAnnot = annotation(arrowType, [startAnnot(1) endAnnot(1)], ...
                                 [startAnnot(2) endAnnot(2)], ...
                                 varargin{:});  % Pass additional name-value pairs

end