Implemented coutdown timer to start of presentation

This implementation should be considered a hack for now. It has to be
refactored in the future. For example if you start your presentation timer
early by pressing one of the navigation keys during a countdown is running you
are not able to go back into the countdown mode by pressing POS1 for example.

src/classes/options.vala

@@ -61,5 +61,11 @@ namespace org.westhoffswelt.pdfpresenter {
          * the presenter window
          */
         public static uint current_size = 60;
+
+        /**
+         * Time the talk starts at, to calculate and display a countdown to
+         * this time.
+         */
+        public static string? start_time = null;
     }
 }

src/classes/timer_label.vala

@@ -63,6 +63,22 @@ namespace org.westhoffswelt.pdfpresenter {
          */
         protected uint last_minutes = 5;
 
+        /**
+         * Supportes states aka. modes of the timer
+         *
+         * These states are used to indicate if the talk has already started or
+         * it is been counted down to it's beginning, for example
+         */
+        protected enum MODE {
+            pretalk,
+            talk
+        }
+
+        /**
+         * The mode the timer is currently in
+         */
+        protected MODE current_mode;
+
         /**
          * Color used for normal timer rendering
          *
@@ -88,11 +104,31 @@ namespace org.westhoffswelt.pdfpresenter {
         public Color negative_color;
 
         /**
-         * Default constructor taking the initial time as argument
+         * Default constructor taking the initial time as argument, as well as
+         * the time to countdown until the talk actually starts.
+         *
+         * The second argument is optional. If no countdown_time is specified
+         * the countdown will be disabled. The timer is paused in such a case
+         * at the given intial_time.
          */
-        public TimerLabel( int initial_time ) {
+        public TimerLabel( int initial_time, int countdown_time = 0 ) {
             this.initial_time = initial_time;
-            this._time = initial_time;
+
+            if ( countdown_time != 0 ) 
+            {
+                this.current_mode = MODE.pretalk;
+                this._time = countdown_time;
+                // Auto start the timer after realization of the timer widget
+                this.realize.connect( () => 
+                {
+                    this.start();
+                });
+            }
+            else 
+            {
+                this.current_mode = MODE.talk;
+                this._time = initial_time;
+            }
 
             // By default the colors are white, yellow and red
             Color.parse( "white", out this.normal_color );
@@ -104,7 +140,17 @@ namespace org.westhoffswelt.pdfpresenter {
          * Start the timer
          */
         public void start() {
-            if ( this.initial_time != 0 && this.timeout == 0 ) {
+            // Check if there is a countdown_timer running, in which case it
+            // will be aborted and a jump to talk mode is executed.
+            if ( this.timeout != 0 && this.current_mode == MODE.pretalk ) 
+            {
+                this.current_mode = MODE.talk;
+                this.reset();
+                this.start();
+            }
+            // Start the timer if it is not running and the currently set time
+            // is non zero
+            else if ( this._time != 0 && this.timeout == 0 ) {
                 this.timeout = Timeout.add( 1000, this.on_timeout );
             }
         }
@@ -123,10 +169,19 @@ namespace org.westhoffswelt.pdfpresenter {
          * Reset the timer to its initial value
          *
          * Furthermore the stop state will be restored
+         * If the countdown is running the reset will simply be ignored because
+         * it does not make sense at all.
+         *
+         * In presentation mode the time will be reset to the initial
+         * presentation time.
          */
         public void reset() {
-            this.stop();
-            this._time = this.initial_time;
+            if ( this.current_mode != MODE.pretalk ) 
+            {
+                this.stop();
+                this._time = this.initial_time;
+            }
+
             this.format_time();
         }
 
@@ -141,7 +196,15 @@ namespace org.westhoffswelt.pdfpresenter {
          * Update the timer on every timeout step (every second)
          */
         protected bool on_timeout() {
-            --this._time;
+            if ( this._time-- == 0 && this.current_mode == MODE.pretalk ) 
+            {
+                // The zero has been reached on the way down to a presentation
+                // start time. Therefore a mode switch is needed
+                this.current_mode = MODE.talk;
+                this.reset();
+                this.start();
+            }
+
             this.format_time();
             return true;
         }
@@ -154,9 +217,16 @@ namespace org.westhoffswelt.pdfpresenter {
             uint time;
             uint hours, minutes, seconds;
 
-            // The default prefix is an empty string, as the time is normally not
-            // negative ;)
+            // In pretalk mode we display a negative sign before the the time,
+            // to indicate that we are actually counting down to the start of
+            // the presentation.
+            // Normally the default is a positive number. Therefore a negative
+            // sign is not needed and the prefix is just an empty string.
             string prefix = "";
+            if ( this.current_mode == MODE.pretalk ) 
+            {
+                prefix = "-";
+            }
 
             if ( this._time >= 0 ) {
                 // Time is positive

src/classes/window/presenter.vala

@@ -146,9 +146,24 @@ namespace org.westhoffswelt.pdfpresenter.Window {
                 (int)Math.floor( bottom_height * 0.8 * 0.75 ) * Pango.SCALE
             );
 
+            // Calculate the countdown to display until the presentation has to
+            // start
+            int countdown = 0;
+            if ( Options.start_time != null ) 
+            {
+                var start_time = this.parseStartTime( 
+                    Options.start_time 
+                );
+
+                var tm = Time.local( time_t() );
+                var now = tm.mktime();
+
+                countdown = (int)Math.fmax( 0, start_time - now );
+            }
+
             // The countdown timer is centered in the 90% bottom part of the screen
             // It takes 3/4 of the available width
-            this.timer = new TimerLabel( (int)Options.duration * 60 );
+            this.timer = new TimerLabel( (int)Options.duration * 60, countdown );
             this.timer.set_justify( Justification.CENTER );
             this.timer.modify_font( font );
             this.timer.set_size_request( 
@@ -338,5 +353,15 @@ namespace org.westhoffswelt.pdfpresenter.Window {
             );
             observer.show();
         }
+
+        /**
+         * Parse the given start time string to a Time object
+         */
+        private time_t parseStartTime( string start_time ) 
+        {
+            var tm = Time.local( time_t() );
+            tm.strptime( start_time, "%H:%M:%S" );
+            return tm.mktime();
+        }
     }
 }

src/pdf_presenter_console.vala

@@ -62,6 +62,7 @@ namespace org.westhoffswelt.pdfpresenter {
          */
         const OptionEntry[] options = {
             { "duration", 'd', 0, OptionArg.INT, ref Options.duration, "Duration in minutes of the presentation used for timer display. (Default 45 minutes)", "N" },
+            { "start-time", 't', 0, OptionArg.STRING, ref Options.start_time, "Start time of the presentation to be used as a countdown. (Format: hh:mm:ss (24h))", "T" },
             { "last-minutes", 'l', 0, OptionArg.INT, ref Options.last_minutes, "Time in minutes, from which on the timer changes its color. (Default 5 minutes)", "N" },
             { "current-size", 'u', 0, OptionArg.INT, ref Options.current_size, "Percentage of the presenter screen to be used for the current slide. (Default 60)", "N" },
             { "switch-screens", 's', 0, 0, ref Options.display_switch, "Switch the presentation and the presenter screen.", null },