Calculate a date column in a Google Spreadsheet based on other columns

Question

I have made a Google Sheet for handling my medication.

In column A, I have a dropdown of medication that I take. The time I initially take the medication isn't important, but what is important is when I take the next pill and it is different for each one. One pill, after taking it, I need to take the next one 6 hours later while another, I don't take until 24 hours later. I go to sleep at different times every day so when I take the initial pill depends on when I wake up or when I eat breakfast or such. The most important one is the one that I need to wait 6 hours before I can take it again. That is my pain pill.

So far, I have the sheet setup so that I have the drop down list of medication and column 2 inputs the exact date and time that I take the pill. The 3rd column, I have a formula that is set to take column 2 and add 6 hours to it which is not correct for all meds, so that is where I need help. I know it can be done, but I don't know who to ask. If I can get it so that the 3rd column will see what medication I chose then depending on which one it will put the time that I need to take the next one. Here is what I have so far but using a formula to add 6 hours which applies to all and that is why the formula won't work:

Worksheet :

Medication        Pill-taken-at        +6 hours
----------------------------------------------------------
Mycoxofloppin     2018-03-17 12:44     2018-03-17 18:44 
Maryjaneaspliff   2018-03-16 04:20     2018-03-16 10:20

Script :

function onEdit(e) {
  var timezone = "GMT-5";
  var timestamp_format = "yyyy-MM-dd   hh:mm";
  var ss = e.source.getActiveSheet();
  var start = 2;
  var end = 4;
  var row = e.range.getRow();
  if (e.range.getColumn() == 1){
    ss.getRange(row, start).setValue(new Date());
  }
}

Answer 1

Range::getValue gets you the value of a cell in Google Sheets' API. I'm assuming that your cells are typed as DateTime so getValue() will give you a JavaScript Date value that you can easily perform date-calculations on.

You don't need to worry about timezones or date formats if your cells are typed correctly. ("typed" as in "data-type", not "keyboard typing").

function onEdit(event) {

    var range = event.range;
    if( range.getColumn() != 1 && range.getColumn() != 2 ) {
        // Only update when column 1 or 2 are updated.
        return;
    }
    var rowNumber = range.getRow();

    var ss = event.source.getActiveSheet();

    var drugName     = ss.getRange( rowNumber, 1 ).getValue();
    var lastDoseTime = ss.getRange( rowNumber, 2 ).getValue();

    // Validate info in the edited row:
    if( !drugName ) {
        console.warn( "No drug name specified in col 1, row %d.", rowNumber );
        return;
    }

    if( !( lastDoseTime instanceof Date ) ) {
        console.warn("No valid date value in col 2, row %d.", rowNumber );
        return;
    }

    var hoursUntilNextDose = getTimeBetweenDosesInHours( drugName );
    if( !hoursUntilNextDose ) {
        console.warn("No dose time available for the drug \"%s\".", drugName );
        return;
    }

    var timeUntilNextDoseInMilliseconds = hoursUntilNextDose * 60 * 60 * 1000;

    var nextDoseUnix = lastDoseTime.getTime() + timeUntilNextDoseInMilliseconds;
    var nextDoseTime = new Date( nextDoseUnix );

    ss.getRange( rowNumber, 3 ).setValue( nextDoseTime );
}

function getTimeBetweenDosesInHours( drugName ) {

    // toUpperCase() is more robust than toLowerCase(): https://msdn.microsoft.com/en-us/library/bb386042.aspx
    switch( drugName.toUpperCase() ) {
        case "MYCOXOFLOPPIN"  : return 6;
        case "MARYJANEASPLIFF": return 4.20;
        case "GYM"            : return 365 * 24;
        default               : return null;
    }
}

Answer 2

Use a table: Say

Y1: Pill Name    Z1:(Interval(hrs))    
Y2: Dumiliyuop   Z2: 6    
Y3: WhacyHittlir Z3:18

C2:

=B2+VLOOKUP(A2,Y:Z,2,0)/24