To choose a date and get the week and enable select with specific values

Question

I wonder if they can help me because I’ve been "cracking my brain" for days:

1. Clicking a text input opens a calendar and then I choose a date;
2. I need another input text to calculate the day of the week (Tuesday or Thursday only) based on the chosen date
3. And through the input text of the day of the week, should be visibled the select to choose the time: TUESDAY = 14:30, 14:50, 15:10, 15:30 and 15:40 and THURSDAY = 09:40, 10:10, 10:30, 10:50 and 11:10

I’m trying to get the date with the document.getElementById, but precisely in this field nothing happens! It will be because of the calendar...

function escrever(el) {
    var isso = document.getElementById('calendSemana').value = el.value; 

    //var dias_semana = new Array("Domingo", "Segunda-feira", "Terça-feira", "Quarta-feira", "Quinta-feira", "Sexta-feira", "Sábado");
    //var data = new Date();
    //var dia = data.getDay();

    //document.write(dias_semana[dia]);

    //linhasOcultas = (dias_semana[dia]);

    //document.getElementById("#calendSemana").value(linhasOcultas);

    //var campoValor = document.getElementById("celular").value;
    //document.write(linhasOcultas);
    //document.getElementById('calendSemana').value += campoValor;

    //document.write("<input type='text' class='inputcad' id='calendSemana' name='calendSemana' maxlength='10' value='"+isso+"'>");

    //document.getElementById('#calendSemana').value = document.getElementById('#data_3').value;

    //document.getElementById('calendSemana').innerHTML = el.value;

}

---

<script type="text/javascript">
     function mostraDiv(valor) {
          if(valor == "Terça")
          {
                document.getElementById("TER").style.display = "block";
                document.getElementById("QUI").style.display = "none";
          }
          else if(valor == "Quinta")
          {
                document.getElementById("TER").style.display = "none";
                document.getElementById("QUI").style.display = "block";
          }
          else if(valor == "Selecione")
          {
                document.getElementById("TER").style.display = "none";
                document.getElementById("QUI").style.display = "none";
          }
}
</script>

<select name='dia' id='dia' class='inputselec' onchange='mostraDiv(this.value)'>
<option value="<? echo $_SESSION['dia_c']; ?>"><? if(empty($_SESSION['dia_c'])) { echo "Selecione"; } else { echo $_SESSION['dia_c']; } ?></option>
<option value='Terça'>Terça-feira</option>      
<option value='Quinta'>Quinta-feira</option>
</select>

<div id='TER' style='display:none'>
<select name='terca' id='terca' class='inputselec'>
<option value="<? echo $_SESSION['terca_c']; ?>"><? if(empty($_SESSION['terca_c'])) { echo "Horário"; } else { echo $_SESSION['terca_c']; } ?></option>
<option value='14:30'>14:30</option>
<option value='14:50'>14:50</option>
<option value='15:10'>15:10</option>
<option value='15:30'>15:30</option>
<option value='15:40'>15:40</option>
</select>
</div>
<div id='QUI' style='display:<? echo $mostraQ ?>'>
<select name='quinta' class='inputselec'>
<option value="<? echo $_SESSION['quinta_c']; ?>"><? if(empty($_SESSION['quinta_c'])) { echo "Horário"; } else { echo $_SESSION['quinta_c']; } ?></option>
<option value='09:40'>09:40</option>
<option value='10:10'>10:10</option>
<option value='10:30'>10:30</option>
<option value='10:50'>10:50</option>
<option value='11:10'>11:10</option>
</select>
</div>

I thank very much to those who can help me... Light and Peace!