Interactively plotting multiple lines with shiny and ggplot2

I'm creating a shiny application that will have a checkboxGroupInput, where each box checked will add another line to a frequency plot. I'm trying to wrap my head around reshape2 and ggplot2 to understand how to make this possible.

data:

  head(testSet)
  date store_id product_id count
1 2015-08-15      3       1     8
2 2015-08-15      3       3     1
3 2015-08-17      3       1     7
4 2015-08-17      3       2     3
5 2015-08-17      3       3     1
6 2015-08-18      3       3     2

class level information:

dput(droplevels(head(testSet, 10)))
structure(list(date = structure(c(16662, 16662, 16664, 
16664, 16664, 16665, 16665, 16665, 16666, 16666), class = "Date"), 
    store_id = c(3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L), product_id = c(1L, 
    3L, 1L, 2L, 3L, 3L, 1L, 2L, 1L, 2L), count = c(8L, 1L, 7L, 
    3L, 1L, 2L, 18L, 1L, 0L, 2L)), .Names = c("date", "store_id", 
"product_id", "count"), row.names = c(NA, 10L), class = "data.frame")

The graph should have an x-axis that corresponds to date, and a y-axis that corresponds to count. I would like to have a checkbox group input where for each box representing a product checked, a line corresponding to product_id will be plotted on the graph. The data is already filtered to store_id.

My first thought was to write a for loop inside of the plot to render a new geom_line() per each returned value of the input$productId vector. -- however after some research it seems that's the wrong way to go about things.

Currently I'm trying to melt() the data down to something useful, and then aes(...group=product_id), but getting errors on whatever I try.

Attempting to melt the data:

meltSet <- melt(testSet, id.vars="product_id", value.name="count", variable.name="date")

head of meltSet

  head(meltSet)
  product_id date count
1       1 date 16662
2       3 date 16662
3       1 date 16664
4       2 date 16664
5       3 date 16664
6       3 date 16665

tail of meltSet

   tail(meltSet)
   product_id date count
76       9      count     5
77       1      count    19
78       2      count     1
79       3      count    39
80       8      count     1
81       9      count     4

Plotting:

ggplot(data=meltSet, aes(x=date, y=count, group = product_id, colour = product_id)) + geom_line()

So my axis and values are all wonky, and not what I'm expecting from setting the plot.