Addresses #11

.gitignore

@@ -4,6 +4,7 @@ storage/sqlite_db_edit
 backend/1-5_raw_output.log
 *.log
 some_file_location
+/frontend/static/images/dashboard_histogram.png
 
 # Compiled python modules.
 *.pyc

frontend/templates/dashboard.html

@@ -35,7 +35,7 @@
                 <input type="checkbox" onclick="toggleAutoRefresh(this);" id="reloadCB"> Auto refresh dashboard every 5 seconds
             </div>
             <div class="panel-body">
-                <img id="img" src="/histogram.png?start_time=-120&end_time=9000000000&bin_size_seconds=2"/>
+                <img id="img" src="{{ url_for('static',filename='images/dashboard_histogram.png') }}"/>
             </div>
         </div>
     </div>

frontend/web_ui.py

@@ -360,12 +360,8 @@ def about_page():
     return render_template('about.html')
 
 
-@app.route('/histogram.png')
+# returns the histogram as a png byte stream
-def build_plot():
+def build_histogram(start_time, end_time, bin_size_seconds):
-    # get user set parameters
-    start_time = request.args.get('start_time', type=int)
-    end_time = request.args.get('end_time', type=int)
-    bin_size_seconds = request.args.get('bin_size_seconds', type=int)
     plot_title = ''
 
     # get some data
@@ -374,7 +370,8 @@ def build_plot():
     cursor = conn.cursor()
     # only get the last n seconds if the start time was negative
     if start_time < 0:
-        plot_title += "Histogram of events over the last {0:.1f} minutes\nbin size: {1:d} [s]".format(-start_time/60., bin_size_seconds)
+        plot_title += "Histogram of events over the last {0:.1f} minutes\nbin size: {1:d} [s]".format(-start_time / 60.,
+                                                                                                      bin_size_seconds)
         cursor.execute("SELECT * FROM Events ORDER BY UTCUnixTime DESC, SubSeconds DESC;")
         start_time = cursor.fetchone()[0] + start_time
         end_time = 9000000000
@@ -426,13 +423,45 @@ def build_plot():
     plt.savefig(img, format='png')
     img.seek(0)
     plt.close()
-    response = make_response(img.getvalue())
+    return img.getvalue()
+
+@app.route('/histogram.png')
+def serve_histogram_request():
+    # get user set parameters
+    start_time = request.args.get('start_time', type=int)
+    end_time = request.args.get('end_time', type=int)
+    bin_size_seconds = request.args.get('bin_size_seconds', type=int)
+
+    # render the plot
+    img = build_histogram(start_time, end_time, bin_size_seconds)
+
+    # return the plot
+    response = make_response(img)
     response.headers['Content-Type'] = 'image/png'
     return response
 
+def periodically_render_dashboard_histogram():
+    while True:
+        # standard values for the dashboard histogram
+        start_time = -120
+        end_time = 9000000000
+        bin_size_seconds = 2
+        # place where we need to save the image
+        path_to_static_image = "static/images/dashboard_histogram.png"
 
+        # render the plot
+        img = build_histogram(start_time, end_time, bin_size_seconds)
+
+        # save the image to disk
+        with open(path_to_static_image, 'wb') as f:
+            f.write(img)
+
+        # wait four seconds until we render the next plot
+        time.sleep(4)
 
 if __name__ == '__main__':
     # do necessary inits
     initDB()
+    # Launch the periodical histogram renderer for the dashboard
+    thread.start_new_thread(periodically_render_dashboard_histogram, ())
     app.run()