function [ good_epochs ] = visual_check( epochs, fs)

%VISUAL_CHECK Summary of this function goes here

%   Detailed explanation goes here

     %% Initiations

    [epoch_num, epoch_len ]= size(epochs);

    time_start = 0;

    time_end = epoch_len/fs;

    time_axis = linspace(time_start, time_end, epoch_len);

    frequencies = 1:120;

    global plot_data;

    global my_handles;

    plot_data.epochs = epochs;

    plot_data.time_axis = time_axis;

    plot_data.epoch_num = epoch_num;

    plot_data.bad_epochs_list = [];

    plot_data.bad_epoch_num = 0;

    plot_data.epoch_index = 1;

    plot_data.epoch_info = sprintf('Epoch %d of %d, labeled as %s', plot_data.epoch_index, plot_data.epoch_num, is_epoch_good);

    %% calculate psd for all epochs

    [plot_data.PSDs, plot_data.frequency_axis] = pwelch(epochs', [], [], frequencies, fs);

    plot_data.PSDs = plot_data.PSDs';

    %% put ui components

    my_handles.main_window = figure;

    my_handles.main_window.Color = [1,1,1];

    figure_width = 1000;

    figure_height = 600;

    my_handles.main_window.InnerPosition=[0,0,figure_width, figure_height];

    margin_width = 5;

    ui_size_width = 50;

    ui_size_height = 30;

    position = [0,0, ui_size_width,ui_size_height];

    my_handles.left_button = uicontrol('Style', 'pushbutton', 'String', '<-', 'FontSize', 14, 'FontWeight', 'Bold', 'Position', position, 'BackgroundColor', [0.8078, 0.3725, 0.3725],'ForegroundColor', [1,1,1],'Callback', @cbc_left_btn);

    position(1) = position(1) + ui_size_width + margin_width;

    my_handles.text_edit = uicontrol('Style', 'edit','String', '1', 'FontSize', 14, 'Position', position);

    position(1) = position(1) + ui_size_width + margin_width;

    my_handles.go_button = uicontrol('Style', 'pushbutton','String', 'Go', 'FontSize', 14, 'FontWeight', 'Bold', 'Position', position, 'BackgroundColor', [0.8078, 0.3725, 0.3725],'ForegroundColor', [1,1,1],'Callback', @cbc_go_btn);

    position(1) = position(1) + ui_size_width + margin_width;

    my_handles.right_button = uicontrol('Style', 'pushbutton','String', '->', 'FontSize', 14, 'FontWeight', 'Bold', 'Position', position, 'BackgroundColor', [0.8078, 0.3725, 0.3725],'ForegroundColor', [1,1,1],'Callback', @cbc_right_btn);

    position(1) = position(1) + 4*ui_size_height + margin_width;

    position(3) = 4*ui_size_width;

    my_handles.label_as_bad_button = uicontrol('Style', 'pushbutton','String', 'Label as bad', 'FontSize', 14, 'FontWeight', 'Bold', 'Position', position, 'BackgroundColor', [0.8078, 0.3725, 0.3725],'ForegroundColor', [1,1,1],'Callback', @cbc_label_as_bad_btn);

    position(1) = position(1) + 8*ui_size_height + margin_width;

    position(3) = 4*ui_size_width;

    my_handles.finish_button = uicontrol('Style', 'pushbutton','String', 'Finish Label', 'FontSize', 14, 'FontWeight', 'Bold', 'Position', position, 'BackgroundColor', [0.8078, 0.3725, 0.3725],'ForegroundColor', [1,1,1],'Callback', @cbc_finish_label_btn);

    %% refresh plot

    refresh_plot();

    %% wait for return

    uiwait(my_handles.main_window);

    %% return updated epochs

    good_epochs = epochs;

    good_epochs(plot_data.bad_epochs_list,:) = [];

    disp('finished');

end

%% private functions

%% callbacks

function cbc_left_btn(hObject, event, handles)

        global plot_data;

        if(plot_data.epoch_index > 1)

            plot_data.epoch_index = plot_data.epoch_index - 1;

        end

        plot_data.epoch_info = sprintf('Epoch %d of %d, labeled as %s', plot_data.epoch_index, plot_data.epoch_num, is_epoch_good);

        refresh_plot();

end

function cbc_right_btn(hObject, event, handles)

        global plot_data;

        if(plot_data.epoch_index < plot_data.epoch_num)

            plot_data.epoch_index = plot_data.epoch_index + 1;

        end

        plot_data.epoch_info = sprintf('Epoch %d of %d, labeled as %s', plot_data.epoch_index, plot_data.epoch_num, is_epoch_good);

        refresh_plot();

end

function cbc_go_btn(hObject, event, handles)

        global plot_data;

        global my_handles;

        go_to_index = str2num(my_handles.text_edit.String);

        if( go_to_index > plot_data.epoch_num | go_to_index < 1)

            go_to_index = 1;

        end

        plot_data.epoch_index = go_to_index;

        plot_data.epoch_info = sprintf('Epoch %d of %d, labeled as %s', plot_data.epoch_index, plot_data.epoch_num, is_epoch_good);

        refresh_plot();

end

function cbc_label_as_bad_btn(hObject, event, handles)

    global plot_data;

    plot_data.bad_epochs_list = [plot_data.bad_epochs_list plot_data.epoch_index];

    plot_data.bad_epochs_list = unique(plot_data.bad_epochs_list);

    plot_data.bad_epoch_num = length(plot_data.bad_epochs_list);

    plot_data.epoch_info = sprintf('Epoch %d of %d, labeled as %s', plot_data.epoch_index, plot_data.epoch_num, is_epoch_good);

    refresh_plot();

    disp(['a bad epoch was just labeld: epoch ', num2str(plot_data.epoch_index)]);

end

function cbc_finish_label_btn(hObject, event, handles)

    global my_handles

    close(my_handles.main_window);

end

%% internal functions

    function [] = refresh_plot()

        %% plot in time field

        global plot_data;

        global my_handles;

        time_axis = plot_data.time_axis;

        epoch = plot_data.epochs(plot_data.epoch_index,:);

        subplot(1,2,1);

        plot(time_axis, epoch);

        xlabel('Time (s)');

        ylabel(['epoch ', num2str(plot_data.epoch_index)]);

        title('Epoch in time field');

        my_handles.text_edit.String = num2str(plot_data.epoch_index);

        %% plot PSD

        subplot(1,2,2);

        frequency_axis = plot_data.frequency_axis;

        PSD = plot_data.PSDs(plot_data.epoch_index, :);

        area(frequency_axis, PSD, 'EdgeColor', [0.1,0.6,0.1], 'FaceColor', [0.1,0.6,0.1], 'FaceAlpha', 0.4);

        xlabel('Frequency (Hz)');

        title('Epoch in frequency field');

        %sgtitle(plot_data.epoch_info);

    end

    function [tag] = is_epoch_good()

        global plot_data;

        bad_flag = ismember(plot_data.epoch_index, plot_data.bad_epochs_list);

        if(bad_flag)

            tag = 'bad';

        else

            tag = 'good';

        end

    end